ALBERT

Beschreibung: Extension of an assessment model of ship traffic exhaust emissions for particulate matter and carbon monoxide Atmospheric Chemistry and Physics, 12, 2641-2659, 2012 Author(s): J.-P. Jalkanen, L. Johansson, J. Kukkonen, A. Brink, J. Kalli, and T. Stipa A method is presented for the evaluation of the exhaust emissions of marine traffic, based on the messages provided by the Automatic Identification System (AIS), which enable the positioning of ship emissions with a high spatial resolution (typically a few tens of metres). The model also takes into account the detailed technical data of each individual vessel. The previously developed model was applicable for evaluating the emissions of NO x , SO x and CO 2 . This paper addresses a substantial extension of the modelling system, to allow also for the mass-based emissions of particulate matter (PM) and carbon monoxide (CO). The presented Ship Traffic Emissions Assessment Model (STEAM2) allows for the influences of accurate travel routes and ship speed, engine load, fuel sulphur content, multiengine setups, abatement methods and waves. We address in particular the modeling of the influence on the emissions of both engine load and the sulphur content of the fuel. The presented methodology can be used to evaluate the total PM emissions, and those of organic carbon, elemental carbon, ash and hydrated sulphate. We have evaluated the performance of the extended model against available experimental data on engine power, fuel consumption and the composition-resolved emissions of PM. We have also compared the annually averaged emission values with those of the corresponding EMEP inventory, As example results, the geographical distributions of the emissions of PM and CO are presented for the marine regions of the Baltic Sea surrounding the Danish Straits.

Beschreibung: Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations Atmospheric Measurement Techniques Discussions, 5, 2221-2271, 2012 Author(s): P. Liebing, K. Bramstedt, S. Noël, V. Rozanov, H. Bovensmann, and J. P. Burrows SCIAMACHY is a passive imaging spectrometer onboard ENVISAT, designed to obtain trace gas abundances from measured radiances and irradiances in the UV to SWIR range in nadir, limb and occultation viewing modes. Its grating spectrometer introduces a substantial sensitivity to the polarization of the incoming light with nonnegligible effects on the radiometric calibration. To be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization Measurement Devices (PMDs). While for the nadir viewing mode the measured atmospheric polarization has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study regarding the limb viewing mode has not yet been performed. This paper aims at an assessment of the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other air- or spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison with radiative transfer simulations by SCIATRAN V3.1(Rozanov et al., 2012) using a wide range of atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable of performing calculations of the multiply scattered radiance in a~spherically symmetric atmosphere. The study shows that the limb polarization data exhibit a large systematic bias which is decreasing with wavelength. The most likely reason for this bias is an instrumental phase shift which changes the relative contributions of different Stokes vector components to the PMD signal as compared to on-ground calibration measurements. It is also shown that it is in principle feasible to recalibrate the polarization sensitivity using the in-flight data and the VRTM simulations, enabling also the monitoring of its degradation. Together with an optimization of the algorithm used to calculate the in-flight polarization data an improved polarization correction can increase the radiometric accuracy of SCIAMACHY limb radiance spectra substantially.

Beschreibung: Analysis of ΔO 2 /ΔCO 2 ratios for the pollution events observed at Hateruma Island, Japan Atmospheric Chemistry and Physics, 12, 2713-2723, 2012 Author(s): C. Minejima, M. Kubo, Y. Tohjima, H. Yamagishi, Y. Koyama, S. Maksyutov, K. Kita, and H. Mukai Pollution events extracted from the in situ observations of atmospheric CO 2 and O 2 mixing ratios at Hateruma Island (HAT, 24° N, 124° E) during the period from October 2006 and December 2008 are examined. The air mass origins for the pollution events are categorized by using back trajectory analysis, and the oxidative ratios (OR = −O 2 :CO 2 molar exchange ratio) for selected pollution events are calculated. We find that there is a significant difference in the average oxidative ratios between events from China (OR = 1.14 ± 0.12, n = 25) and Japan/Korea (OR = 1.37 ± 0.15, n = 16). These values are in a good agreement with the national average oxidative ratios for the emissions from fossil fuel burning and cement production (FFBC) in China (OR FFBC = 1.11 ± 0.03) and Korea/Japan (OR FFBC = 1.36 ± 0.02). Compared with the observation, simulations of the atmospheric O 2 and CO 2 mixing ratios using Lagrangian particle dispersion models do a good job in reconstructing the average oxidative ratio of the pollution events originating in China but tend to underestimate for events originating in Japan/Korea. A sensitivity test suggests that the simulated atmospheric oxidative ratios at HAT are especially sensitive to changes in Chinese fuel mix.

Beschreibung: Carbonaceous aerosols in China: top-down constraints on primary sources and estimation of secondary contribution Atmospheric Chemistry and Physics, 12, 2725-2746, 2012 Author(s): T.-M. Fu, J. J. Cao, X. Y. Zhang, S. C. Lee, Q. Zhang, Y. M. Han, W. J. Qu, Z. Han, R. Zhang, Y. X. Wang, D. Chen, and D. K. Henze We simulated elemental carbon (EC) and organic carbon (OC) aerosols in China and compared model results to surface measurements at Chinese rural and background sites, with the goal of deriving "top-down" emission estimates of EC and OC, as well as better quantifying the secondary sources of OC. We included in the model state-of-the-science Chinese "bottom-up" emission inventories for EC (1.92 TgC yr −1 ) and OC (3.95 TgC yr −1 ), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background sites was 1.1 μgC m −3 , 56% lower than the observed 2.5 μgC m −3 . The average simulated annual mean OC concentration at rural and background sites was 3.4 μgC m −3 , 76% lower than the observed 14 μgC m −3 . Multiple regression to fit surface monthly mean EC observations at rural and background sites yielded the best estimate of Chinese EC source of 3.05 ± 0.78 TgC yr −1 . Based on the top-down EC emission estimate and observed seasonal primary OC/EC ratios, we estimated Chinese OC emissions to be 6.67 ± 1.30 TgC yr −1 . Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites was significantly improved to 1.9 μgC m −3 . However, the model still significantly underestimated observed OC in all seasons (simulated average annual mean OC at rural and background sites was 5.4 μgC m −3 ), with little skill in capturing the spatiotemporal variability. Secondary formation accounts for 21% of Chinese annual mean surface OC in the model, with isoprene being the most important precursor. In summer, as high as 62% of the observed surface OC may be due to secondary formation in eastern China. Our analysis points to four shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is underestimated on a national scale, particularly for OC; (2) the spatiotemporal distributions of emissions are misrepresented; (3) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (4) sources in fall are not well represented, either because the seasonal shifting of emissions and/or secondary formation are poorly captured or because specific fall emission events are missing. In addition, secondary production of OC in China is severely underestimated. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings.

Beschreibung: Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources Atmospheric Chemistry and Physics, 12, 1423-1447, 2012 Author(s): C. Ordóñez, J.-F. Lamarque, S. Tilmes, D. E. Kinnison, E. L. Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, and A. Saiz-Lopez The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr 3 , CH 2 Br 2 , CH 2 BrCl, CHBrCl 2 , CHBr 2 Cl) and three VSL iodocarbons (CH 2 ICl, CH 2 IBr, CH 2 I 2 ) have been parameterised by a biogenic chlorophyll- a (chl- a ) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH 3 I are based on a previous inventory and the longer lived CH 3 Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr −1 for CHBr 3 and 67.3 Gg yr −1 for CH 2 Br 2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH 2 Br 2 in the upper troposphere – lower stratosphere and the underestimation of CH 3 I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH 2 ICl, CH 2 IBr, CH 2 I 2 ), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH 2 I 2 , is key to assess their global source strength.

Beschreibung: Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W) Atmospheric Chemistry and Physics, 12, 1571-1585, 2012 Author(s): K. A. Day, M. J. Taylor, and N. J. Mitchell Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011. The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April−August and to reach monthly-mean velocities of −12 m s −1 . The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s −1 km −1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures. Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength. Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s −1 and 8 K and 20 m s −1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, A T and A W , that passed the Student T-test were found to be related by, A T = 0.34 A W and A T = 0.62 A W for the 16- and 5-day wave, respectively.

Beschreibung: First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change Atmospheric Measurement Techniques Discussions, 5, 1355-1379, 2012 Author(s): F. Forster, R. Sussmann, M. Rettinger, N. M. Deutscher, D. W. T. Griffith, N. Jones, and P. K. Patra We present the intercalibration of dry-air column-averaged mole fractions of methane (XCH 4 ) retrieved from solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC) in the mid-infrared (MIR) versus near-infrared (NIR) soundings from the Total Carbon Column Observing Network (TCCON). The study uses multi-annual quasi-coincident MIR and NIR measurements from the stations Garmisch, Germany (47.48° N, 11.06° E, 743 m a.s.l.) and Wollongong, Australia (34.41° S, 150.88° E, 30 m a.s.l.). Direct comparison of the retrieved MIR and NIR time series shows a phase shift in XCH 4 seasonality, i.e. a significant time-dependent bias leading to a standard deviation (stdv) of the difference time series (NIR-MIR) of 8.4 ppb. After eliminating differences in a prioris by using ACTM-simulated profiles as a common prior, the seasonalities of the (corrected) MIR and NIR time series agree within the noise (stdv = 5.2 ppb for the difference time series). The difference time series (NIR-MIR) do not show a significant trend. Therefore it is possible to use a simple scaling factor for the intercalibration without a time-dependent linear or seasonal component. Using the Garmisch and Wollongong data together, we obtain an overall calibration factor MIR/NIR = 0.9926(18). The individual calibration factors per station are 0.9940(14) for Garmisch and 0.9893(40) for Wollongong. They agree within their error bars with the overall calibration factor which can therefore be used for both stations. Our results suggest that after applying the proposed intercalibration concept to all stations performing both NIR and MIR measurements, it should be possible to obtain one refined overall intercalibration factor for the two networks. This would allow to set up a harmonized NDACC and TCCON XCH 4 data set which can be exploited for joint trend studies, satellite validation, or the inverse modeling of sources and sinks.

Beschreibung: Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat Atmospheric Chemistry and Physics, 12, 1587-1595, 2012 Author(s): S. P. F. Casey, E. J. Fetzer, and B. H. Kahn Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. Three criteria were used in previous studies to identify congestus: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. A majority of congestus convective features satisfy the second and third requirements. However, over 40% of convective features identified had no associated CALIPSO cloud-top height, predominantly due to the extinguishment of the lidar beam above the CloudSat-reported convective cloud. For the remaining cells, approximately 56% of these satisfy all three requirements; when considering the lidar beam-extinction issue, only 31% of congestus convective features are identified using these criteria. This implies that while previous methods used to identify congestus clouds may be accurate in finding vigorous convection (such as transient congestus rising toward the tropopause), these criteria may miss almost 70% of the total observed congestus convective features, suggesting a more general approach should be used to describe congestus and its surrounding environment.

Beschreibung: Characterization and airborne deployment of a new counterflow virtual impactor inlet Atmospheric Measurement Techniques Discussions, 5, 1515-1541, 2012 Author(s): T. Shingler, S. Dey, A. Sorooshian, F. J. Brechtel, Z. Wang, A. Metcalf, M. Coggon, J. Mülmenstädt, L. M. Russell, H. H. Jonsson, and J. H. Seinfeld A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterization tests, and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (~15 l min −1 ) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterized the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7–13.1 μm. The percentage error between cut size measurements and predictions from aerodynamic drag theory are less than 13%. The CVI was deployed on the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California between July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter.

Beschreibung: The isotopic composition of precipitation from a winter storm – a case study with the limited-area model COSMO iso Atmospheric Chemistry and Physics, 12, 1629-1648, 2012 Author(s): S. Pfahl, H. Wernli, and K. Yoshimura Stable water isotopes are valuable tracers of the atmospheric water cycle, and potentially provide useful information also on weather-related processes. In order to further explore this potential, the water isotopes H 2 18 O and HDO are incorporated into the limited-area model COSMO. In a first case study, the new COSMO iso model is used for simulating a winter storm event in January 1986 over the eastern United States associated with intense frontal precipitation. The modelled isotope ratios in precipitation and water vapour are compared to spatially distributed δ 18 O observations. COSMO iso very accurately reproduces the statistical distribution of δ 18 O in precipitation, and also the synoptic-scale spatial pattern and temporal evolution agree well with the measurements. Perpendicular to the front that triggers most of the rainfall during the event, the model simulates a gradient in the isotopic composition of the precipitation, with high δ 18 O values in the warm air and lower values in the cold sector behind the front. This spatial pattern is created through an interplay of large scale air mass advection, removal of heavy isotopes by precipitation at the front and microphysical interactions between rain drops and water vapour beneath the cloud base. This investigation illustrates the usefulness of high resolution, event-based model simulations for understanding the complex processes that cause synoptic-scale variability of the isotopic composition of atmospheric waters. In future research, this will be particularly beneficial in combination with laser spectrometric isotope observations with high temporal resolution.

Beschreibung: Improved cloud screening in MAIAC aerosol retrievals using spectral and spatial analysis Atmospheric Measurement Techniques Discussions, 5, 1575-1595, 2012 Author(s): A. Lyapustin, Y. Wang, I. Laszlo, and S. Korkin An improved cloud/snow screening technique in the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm is described. It is implemented as part of MAIAC aerosol retrievals based on analysis of spectral residuals and spatial variability. Comparisons with AERONET aerosol measurements and a large-scale MODIS data analysis show strong suppression of aerosol optical depth outliers due to unresolved clouds and snow. At the same time, the developed filter does not reduce the aerosol retrieval capability at high 1 km resolution in strongly inhomogeneous environments, such as near centers of the active fires. Despite significant improvement, the optical depth outliers in high spatial resolution data are and will remain the problem to be addressed by the application-dependent specialized filtering techniques.

Beschreibung: Measuring variations of δ 18 O and δ 2 H in atmospheric water vapour using laser spectroscopy: an instrument characterisation study Atmospheric Measurement Techniques Discussions, 5, 1597-1655, 2012 Author(s): F. Aemisegger, P. Sturm, P. Graf, H. Sodemann, S. Pfahl, A. Knohl, and H. Wernli Variations of stable water isotopes in water vapour have become measurable at a measurement frequency of about 1 Hz in recent years using novel laser spectroscopic techniques. This enables us to perform continuous measurements for process-based investigations of the atmospheric water cycle at the time scales relevant for synoptic meteorology. An important prerequisite for the interpretation of data from automated field measurements lasting for several weeks or months is a detailed knowledge about instrument properties and the sources of measurement uncertainty. We present here a comprehensive characterisation and comparison study of two commercial laser spectroscopic systems based on cavity ring-down spectroscopy (Picarro) and off-axis integrated cavity output spectroscopy (Los Gatos Research). The uncertainty components of the measurements were first assessed in laboratory experiments, focussing on the effects of (i) water vapour mixing ratio, (ii) measurement stability, (iii) uncertainties due to calibration and (iv) response times of the isotope measurements due to adsorption-desorption processes on the tubing and measurement cavity walls. Based on the experience from our laboratory experiments we set up a one-week field campaign for comparing measurements of the ambient isotope signals of the two laser spectroscopic systems. The optimal calibration strategy determined for both instruments was applied as well as the correction functions for water vapour mixing ratio effects. The root mean square difference between the isotope signals from the two instruments during the field deployment was 2.3‰ for δ 2 H, 0.5‰ for δ 18 O and 3.1‰ for deuterium excess. These uncertainty estimates from field measurements compare well to those found in the laboratory experiments. The present quality of measurements from laser spectroscopic instruments combined with a calibration system opens new possibilities for investigating the atmospheric water cycle and the land-atmosphere moisture fluxes.

Beschreibung: Consistency between Fourier transform and small-volume few-wave decomposition for spectral and spatial variability of gravity waves above a typhoon Atmospheric Measurement Techniques Discussions, 5, 1763-1793, 2012 Author(s): C. I. Lehmann, Y.-H. Kim, P. Preusse, H.-Y. Chun, M. Ern, and S.-Y. Kim Convective gravity wave (GW) sources are spatially localized and emit at the same time waves with a wide spectrum of phase speeds. Any wave analysis therefore compromises between spectral and spatial resolution. Future satellite borne limb imagers will for a first time provide real 3d volumes of observations. These volumes will be however limited which will impose further constraints on the analysis technique. In this study a three dimensional few-wave appoach fitting sinusoidal waves to limited 3-D volumes is introduced. The method is applied to simulated GWs above typhoon Ewiniar and GW momentum flux is estimated from temperature fluctuations. Phase speed spectra as well as average profiles of positive, negative and net momentum fluxes are compared to momentum flux estimated by Fourier transform as well as spatial averaging of wind fluctuations. The results agree within 10–20%. The few-wave method can also reveal the spatial orientation of the GWs with respect to the source. The relevance of the results for different types of measurements as well as its applicability to model data is discussed.

Beschreibung: Sensitivity studies of dust ice nuclei effect on cirrus clouds with the Community Atmosphere Model CAM5 Atmospheric Chemistry and Physics, 12, 12061-12079, 2012 Author(s): X. Liu, X. Shi, K. Zhang, E. J. Jensen, A. Gettelman, D. Barahona, A. Nenes, and P. Lawson In this study the effect of dust aerosol on upper tropospheric cirrus clouds through heterogeneous ice nucleation is investigated in the Community Atmospheric Model version 5 (CAM5) with two ice nucleation parameterizations. Both parameterizations consider homogeneous and heterogeneous nucleation and the competition between the two mechanisms in cirrus clouds, but differ significantly in the number concentration of heterogeneous ice nuclei (IN) from dust. Heterogeneous nucleation on dust aerosol reduces the occurrence frequency of homogeneous nucleation and thus the ice crystal number concentration in the Northern Hemisphere (NH) cirrus clouds compared to simulations with pure homogeneous nucleation. Global and annual mean shortwave and longwave cloud forcing are reduced by up to 2.0 ± 0.1 W m −2 (1σ uncertainty) and 2.4 ± 0.1 W m −2 , respectively due to the presence of dust IN, with the net cloud forcing change of −0.40 ± 0.20 W m −2 . Comparison of model simulations with in situ aircraft data obtained in NH mid-latitudes suggests that homogeneous ice nucleation may play an important role in the ice nucleation at these regions with temperatures of 205–230 K. However, simulations overestimate observed ice crystal number concentrations in the tropical tropopause regions with temperatures of 190–205 K, and overestimate the frequency of occurrence of high ice crystal number concentration (〉 200 L −1 ) and underestimate the frequency of low ice crystal number concentration ( 〈 30 L −1 ) at NH mid-latitudes. These results highlight the importance of quantifying the number concentrations and properties of heterogeneous IN (including dust aerosol) in the upper troposphere from the global perspective.

Beschreibung: Climate versus emission drivers of methane lifetime against loss by tropospheric OH from 1860–2100 Atmospheric Chemistry and Physics, 12, 12021-12036, 2012 Author(s): J. G. John, A. M. Fiore, V. Naik, L. W. Horowitz, and J. P. Dunne With a more-than-doubling in the atmospheric abundance of the potent greenhouse gas methane (CH 4 ) since preindustrial times, and indications of renewed growth following a leveling off in recent years, questions arise as to future trends and resulting climate and public health impacts from continued growth without mitigation. Changes in atmospheric methane lifetime are determined by factors which regulate the abundance of OH, the primary methane removal mechanism, including changes in CH 4 itself. We investigate the role of emissions of short-lived species and climate in determining the evolution of methane lifetime against loss by tropospheric OH, (τ CH4_OH ), in a suite of historical (1860–2005) and future Representative Concentration Pathway (RCP) simulations (2006–2100), conducted with the Geophysical Fluid Dynamics Laboratory (GFDL) fully coupled chemistry-climate model (CM3). From preindustrial to present, CM3 simulates an overall 5% increase in τ CH4_OH due to a doubling of the methane burden which offsets coincident increases in nitrogen oxide (NO x emissions. Over the last two decades, however, the τ CH4_OH declines steadily, coinciding with the most rapid climate warming and observed slow-down in CH 4 growth rates, reflecting a possible negative feedback through the CH 4 sink. Sensitivity simulations with CM3 suggest that the aerosol indirect effect (aerosol-cloud interactions) plays a significant role in cooling the CM3 climate. The projected decline in aerosols under all RCPs contributes to climate warming over the 21st century, which influences the future evolution of OH concentration and τ CH4_OH . Projected changes in τ CH4_OH from 2006 to 2100 range from −13% to +4%. The only projected increase occurs in the most extreme warming case (RCP8.5) due to the near-doubling of the CH 4 abundance, reflecting a positive feedback on the climate system. The largest decrease occurs in the RCP4.5 scenario due to changes in short-lived climate forcing agents which reinforce climate warming and enhance OH. This decrease is more-than-halved in a sensitivity simulation in which only well-mixed greenhouse gas radiative forcing changes along the RCP4.5 scenario (5% vs. 13%).

Beschreibung: Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results Atmospheric Chemistry and Physics, 12, 12037-12059, 2012 Author(s): V.-M. Kerminen, M. Paramonov, T. Anttila, I. Riipinen, C. Fountoukis, H. Korhonen, E. Asmi, L. Laakso, H. Lihavainen, E. Swietlicki, B. Svenningsson, A. Asmi, S. N. Pandis, M. Kulmala, and T. Petäjä This paper synthesizes the available scientific information connecting atmospheric nucleation with subsequent cloud condensation nuclei (CCN) formation. We review both observations and model studies related to this topic, and discuss the potential climatic implications. We conclude that CCN production associated with atmospheric nucleation is both frequent and widespread phenomenon in many types of continental boundary layers, and probably also over a large fraction of the free troposphere. The contribution of nucleation to the global CCN budget spans a relatively large uncertainty range, which, together with our poor understanding of aerosol-cloud interactions, results in major uncertainties in the radiative forcing by atmospheric aerosols. In order to better quantify the role of atmospheric nucleation in CCN formation and Earth System behavior, more information is needed on (i) the factors controlling atmospheric CCN production and (ii) the properties of both primary and secondary CCN and their interconnections. In future investigations, more emphasis should be put on combining field measurements with regional and large-scale model studies.

Beschreibung: Effect of sampling variation on error of rainfall variables measured by optical disdrometer Atmospheric Measurement Techniques Discussions, 5, 8895-8924, 2012 Author(s): X. C. Liu, T. C. Gao, and L. Liu During the sampling process of precipitation particles by optical disdrometers, the randomness of particles and sampling variability has great impact on the accuracy of precipitation variables. Based on a marked point model of raindrop size distribution, the effect of sampling variation on drop size distribution and velocity distribution measurement using optical disdrometers are analyzed by Monte Carlo simulation. The results show that the samples number, rain rate, drop size distribution, and sampling size have different influences on the accuracy of rainfall variables. The relative errors of rainfall variables caused by sampling variation in a descending order as: water concentration, mean diameter, mass weighed mean diameter, mean volume diameter, radar reflectivity factor, and number density, which are independent with samples number basically; the relative error of rain variables are positively correlated with the margin probability, which is also positively correlated with the rain rate and the mean diameter of raindrops; the sampling size is one of the main factors that influence the margin probability, with the decreasing of sampling area, especially the decreasing of short side of sample size, the probability of margin raindrops is getting greater, hence the error of rain variables are getting greater, and the variables of median size raindrops have the maximum error. To ensure the relative error of rainfall variables measured by optical disdrometer less than 1%, the width of light beam should be at least 40 mm.

Beschreibung: Amino acids in Arctic aerosols Atmospheric Chemistry and Physics, 12, 10453-10463, 2012 Author(s): E. Scalabrin, R. Zangrando, E. Barbaro, N. M. Kehrwald, J. Gabrieli, C. Barbante, and A. Gambaro Amino acids are significant components of atmospheric aerosols, affecting organic nitrogen input to marine ecosystems, atmospheric radiation balance, and the global water cycle. The wide range of amino acid reactivities suggest that amino acids may serve as markers of atmospheric transport and deposition of particles. Despite this potential, few measurements have been conducted in remote areas to assess amino acid concentrations and potential sources. Polar regions offer a unique opportunity to investigate atmospheric processes and to conduct source apportionment studies of such compounds. In order to better understand the importance of amino acid compounds in the global atmosphere, we determined free amino acids (FAAs) in seventeen size-segregated aerosol samples collected in a polar station in the Svalbard Islands from 19 April until 14 September 2010. We used an HPLC coupled with a tandem mass spectrometer (ESI-MS/MS) to analyze 20 amino acids and quantify compounds at fmol m −3 levels. Mean total FAA concentration was 1070 fmol m −3 where serine and glycine were the most abundant compounds in almost all samples and accounted for 45–60% of the total amino acid relative abundance. The other eighteen compounds had average concentrations between 0.3 and 98 fmol m −3 . The higher amino acid concentrations were present in the ultrafine aerosol fraction ( 〈 0.49 μm) and accounted for the majority of the total amino acid content. Local marine sources dominate the boreal summer amino acid concentrations, with the exception of the regional input from Icelandic volcanic emissions.

Beschreibung: A multi-model study of impacts of climate change on surface ozone in Europe Atmospheric Chemistry and Physics, 12, 10423-10440, 2012 Author(s): J. Langner, M. Engardt, A. Baklanov, J. H. Christensen, M. Gauss, C. Geels, G. B. Hedegaard, R. Nuterman, D. Simpson, J. Soares, M. Sofiev, P. Wind, and A. Zakey The impact of climate change on surface ozone over Europe was studied using four offline regional chemistry transport models (CTMs) and one online regional integrated climate-chemistry model (CCM), driven by the same global projection of future climate under the SRES A1B scenario. Anthropogenic emissions of ozone precursors from RCP4.5 for year 2000 were used for simulations of both present and future periods in order to isolate the impact of climate change and to assess the robustness of the results across the different models. The sensitivity of the simulated surface ozone to changes in climate between the periods 2000–2009 and 2040–2049 differs by a factor of two between the models, but the general pattern of change with an increase in southern Europe is similar across different models. Emissions of isoprene differ substantially between different CTMs ranging from 1.6 to 8.0 Tg yr −1 for the current climate, partly due to differences in horizontal resolution of meteorological input data. Also the simulated change in total isoprene emissions varies substantially across models explaining part of the different climate response on surface ozone. Ensemble mean changes in summer mean ozone and mean of daily maximum ozone are close to 1 ppb(v) in parts of the land area in southern Europe. Corresponding changes of 95-percentiles of hourly ozone are close to 2 ppb(v) in the same region. In northern Europe ensemble mean for mean and daily maximum show negative changes while there are no negative changes for the higher percentiles indicating that climate impacts on O 3 could be especially important in connection with extreme summer events.

Beschreibung: Tropospheric column ozone: matching individual profiles from Aura OMI and TES with a chemistry-transport model Atmospheric Chemistry and Physics, 12, 10441-10452, 2012 Author(s): Q. Tang and M. J. Prather Of all satellite measurements of ozone, only two instruments have coincident, spatially overlapping measurements to allow direct comparison of tropospheric column ozone (TCO): the Ozone Monitoring Instrument (OMI) and the Tropospheric Emission Spectrometer (TES) on the NASA Aura spacecraft. For two years (2005–2006), we collect all observations between 60° S and 60° N from nadir (~65 000 from OMI and TES) and cross-track swaths (~30 000 000 from OMI) and compare with a chemistry-transport model (CTM) simulating each observation with corresponding spatial and temporal coincidence. High-frequency TCO variations are indicative of stratospheric intrusions of ozone-rich air, and the individual, level 2 data provide access to these short-lived phenomena. Although we can identify some seasonal and large-scale biases in the model, the CTM as a transfer standard identifies weaknesses in the observations and further helps quantify the measurement noise of individual profiles. The relatively noise-free CTM bridges these two satellite measurements and improves their cross-validation to better precision than a simple direct comparison. Previous validation studies of TES TCO versus ozonesondes found a bias of about +4 Dobson Units (DU) for large regions. The three-way comparison and the CTM transfer method that use a far greater number of coincidences, indicate that monthly zonal mean OMI-TES TCO biases fall within 5–10%, and thus quantifies the zonal mean OMI TCO bias at a few DU. For small regions (i.e., 5 × 5°), however, the monthly mean OMI-TES differences can exceed ±10 DU at many places (e.g., tropics for the direct OMI-TES comparison) due to different tropospheric sensitivities of the two instruments at these locations. Partly removing the influence of different sensitivities by applying the CTM as the transfer standard, the OMI-TES differences generally decrease, especially over the tropics. In addition, the CTM-TES comparison split into day versus night observations shows no apparent bias in TES at very low levels, ±1 DU. These OMI-TES-CTM comparisons highlight the importance of the a priori ozone profiles that went into each satellite retrieval, including a false agreement due to CTM-a priori similarity, and the importance of including the vertical information (i.e., averaging kernel) in the retrieval products. This study also highlights the advantages of overlapping measurements in terms of cross-validation and the application of a model as the transfer standard.

Beschreibung: On the effect of moisture on the detection of tropospheric turbulence from in situ measurements Atmospheric Measurement Techniques Discussions, 5, 8223-8240, 2012 Author(s): R. Wilson, H. Luce, H. Hashiguchi, M. Shiotani, and F. Dalaudier The present note addresses the detection of turbulence based on the Thorpe (1977) method applied to an atmosphere where saturation of water vapor occurs. The detection method proposed by Thorpe relies on the reordering in ascending order of a measured profile of a variable conserved through adiabatic processes (e.g. potential temperature). For saturated air, the reordering should be applied to a moist-conservative potential temperature, θ m , which is analogous to potential temperature for a dry (subsaturated) atmosphere. Here, θ m is estimated from the Brunt-Väisälä frequency derived by Lalas and Einaudi (1974) in a saturated atmosphere. The application to balloon data shows that the effective turbulent fraction of the troposphere can dramatically increase when saturation is taken into account. Preliminary results of comparisons with data simultaneously collected from the VHF Middle and Upper atmosphere radar (MUR, Japan) seem to give credence to the proposed approach.

Beschreibung: Spectral absorption of biomass burning aerosol determined from retrieved single scattering albedo during ARCTAS Atmospheric Chemistry and Physics, 12, 10505-10518, 2012 Author(s): C. A. Corr, S. R. Hall, K. Ullmann, B. E. Anderson, A. J. Beyersdorf, K. L. Thornhill, M. J. Cubison, J. L. Jimenez, A. Wisthaler, and J. E. Dibb Actinic flux, as well as aerosol chemical and optical properties, were measured aboard the NASA DC-8 aircraft during the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) mission in Spring and Summer 2008. These measurements were used in a radiative transfer code to retrieve spectral (350–550 nm) aerosol single scattering albedo (SSA) for biomass burning plumes encountered on 17 April and 29 June. Retrieved SSA values were subsequently used to calculate the absorption Angstrom exponent (AAE) over the 350–500 nm range. Both plumes exhibited enhanced spectral absorption with AAE values that exceeded 1 (6.78 ± 0.38 for 17 April and 3.34 ± 0.11 for 29 June). This enhanced absorption was primarily due to organic aerosol (OA) which contributed significantly to total absorption at all wavelengths for both 17 April (57.7%) and 29 June (56.2%). OA contributions to absorption were greater at UV wavelengths than at visible wavelengths for both cases. Differences in AAE values between the two cases were attributed to differences in plume age and thus to differences in the ratio of OA and black carbon (BC) concentrations. However, notable differences between AAE values calculated for the OA (AAE OA ) for 17 April (11.15 ± 0.59) and 29 June (4.94 ± 0.19) suggested differences in the plume AAE values might also be due to differences in organic aerosol composition. The 17 April OA was much more oxidized than the 29 June OA as denoted by a higher oxidation state value for 17 April (+0.16 vs. −0.32). Differences in the AAE OA , as well as the overall AAE, were thus also possibly due to oxidation of biomass burning primary organic aerosol in the 17 April plume that resulted in the formation of OA with a greater spectral-dependence of absorption.

Beschreibung: A Tropospheric Emission Spectrometer HDO/H 2 O retrieval simulator for climate models Atmospheric Chemistry and Physics, 12, 10485-10504, 2012 Author(s): R. D. Field, C. Risi, G. A. Schmidt, J. Worden, A. Voulgarakis, A. N. LeGrande, A. H. Sobel, and R. J. Healy Retrievals of the isotopic composition of water vapor from the Aura Tropospheric Emission Spectrometer (TES) have unique value in constraining moist processes in climate models. Accurate comparison between simulated and retrieved values requires that model profiles that would be poorly retrieved are excluded, and that an instrument operator be applied to the remaining profiles. Typically, this is done by sampling model output at satellite measurement points and using the quality flags and averaging kernels from individual retrievals at specific places and times. This approach is not reliable when the model meteorological conditions influencing retrieval sensitivity are different from those observed by the instrument at short time scales, which will be the case for free-running climate simulations. In this study, we describe an alternative, "categorical" approach to applying the instrument operator, implemented within the NASA GISS ModelE general circulation model. Retrieval quality and averaging kernel structure are predicted empirically from model conditions, rather than obtained from collocated satellite observations. This approach can be used for arbitrary model configurations, and requires no agreement between satellite-retrieved and model meteorology at short time scales. To test this approach, nudged simulations were conducted using both the retrieval-based and categorical operators. Cloud cover, surface temperature and free-tropospheric moisture content were the most important predictors of retrieval quality and averaging kernel structure. There was good agreement between the δD fields after applying the retrieval-based and more detailed categorical operators, with increases of up to 30‰ over the ocean and decreases of up to 40‰ over land relative to the raw model fields. The categorical operator performed better over the ocean than over land, and requires further refinement for use outside of the tropics. After applying the TES operator, ModelE had δD biases of −8‰ over ocean and −34‰ over land compared to TES δD, which were less than the biases using raw model δD fields.

Beschreibung: Calibration and validation of the advanced E-Region Wind Interferometer Atmospheric Measurement Techniques Discussions, 5, 8271-8311, 2012 Author(s): S. K. Kristoffersen, W. E. Ward, S. Brown, and J. R. Drummond The advanced E-Region Wind Interferometer (ERWIN II) combines the imaging capabilities of a CCD detector with the wide field associated with field widened Michelson interferometry. This instrument is capable of simultaneous multi-directional wind observations for three different airglow emissions (oxygen green line (O( 1 S)), the P Q(7) and P P(7) emission lines in the O 2 (0–1) atmospheric band and P 1 (3) emission line in the (6,2) hydroxyl Meinel band) on a three minute cadence. In each direction, for 45 s measurements for typical airglow brightness the instrument is capable of line-of-sight wind precisions of ~ 1 m s −1 for hydroxyl and O( 1 S) and ~ 4 m s −1 for O 2 . This precision is achieved using a new data analysis algorithm which takes advantage of the imaging capabilities of the CCD detector along with knowledge of the instrument phase variation as a function of pixel location across the detector. This instrument is currently located in Eureka, Nunavut as part of the Polar Environment Atmospheric Research Laboratory (PEARL). The details of the physical configuration, the data analysis algorithm, the measurement calibration and validation of the observations are described. Field measurements which demonstrate the capabilities of this instrument are presented. To our knowledge, the wind determinations with this instrument are the most accurate and have the highest observational cadence for airglow wind observations of this region of the atmosphere and match the capabilities of other wind measuring techniques.

Beschreibung: Corrigendum to "Discrimination of biomass burning smoke and clouds in MAIAC algorithm" published in Atmos. Chem. Phys., 12, 9679–9686, 2012 Atmospheric Chemistry and Physics, 12, 10631-10631, 2012 Author(s): A. Lyapustin, S. Korkin, Y. Wang, B. Quayle, and I. Laszlo No abstract available.

Beschreibung: Experimental and modeled UV erythemal irradiance under overcast conditions: the role of cloud optical depth Atmospheric Chemistry and Physics, 12, 11723-11732, 2012 Author(s): M. Antón, L. Alados-Arboledas, J. L. Guerrero-Rascado, M. J. Costa, J. C Chiu, and F. J. Olmo This paper evaluates the relationship between the cloud modification factor (CMF) in the ultraviolet erythemal range and the cloud optical depth (COD) retrieved from the Aerosol Robotic Network (AERONET) "cloud mode" algorithm under overcast cloudy conditions (confirmed with sky images) at Granada, Spain, mainly for non-precipitating, overcast and relatively homogenous water clouds. Empirical CMF showed a clear exponential dependence on experimental COD values, decreasing approximately from 0.7 for COD = 10 to 0.25 for COD = 50. In addition, these COD measurements were used as input in the LibRadtran radiative transfer code allowing the simulation of CMF values for the selected overcast cases. The modeled CMF exhibited a dependence on COD similar to the empirical CMF, but modeled values present a strong underestimation with respect to the empirical factors (mean bias of 22%). To explain this high bias, an exhaustive comparison between modeled and experimental UV erythemal irradiance (UVER) data was performed. The comparison revealed that the radiative transfer simulations were 8% higher than the observations for clear-sky conditions. The rest of the bias (~14%) may be attributed to the substantial underestimation of modeled UVER with respect to experimental UVER under overcast conditions, although the correlation between both dataset was high ( R 2 ~ 0.93). A sensitive test showed that the main reason responsible for that underestimation is the experimental AERONET COD used as input in the simulations, which has been retrieved from zenith radiances in the visible range. In this sense, effective COD in the erythemal interval were derived from an iteration procedure based on searching the best match between modeled and experimental UVER values for each selected overcast case. These effective COD values were smaller than AERONET COD data in about 80% of the overcast cases with a mean relative difference of 22%.

Beschreibung: Vertical profiles of aerosol optical properties over central Illinois and comparison with surface and satellite measurements Atmospheric Chemistry and Physics, 12, 11695-11721, 2012 Author(s): P. J. Sheridan, E. Andrews, J. A. Ogren, J. L. Tackett, and D. M. Winker Between June 2006 and September 2009, an instrumented light aircraft measured over 400 vertical profiles of aerosol and trace gas properties over eastern and central Illinois. The primary objectives of this program were to (1) measure the in situ aerosol properties and determine their vertical and temporal variability and (2) relate these aircraft measurements to concurrent surface and satellite measurements. The primary profile location was within 15 km of the NOAA/ESRL surface aerosol monitoring station near Bondville, Illinois. Identical instruments at the surface and on the aircraft ensured that the data from both platforms would be directly comparable and permitted a determination of how representative surface aerosol properties were of the lower column. Aircraft profiles were also conducted occasionally at two other nearby locations to increase the frequency of A-Train satellite underflights for the purpose of comparing in situ and satellite-retrieved aerosol data. Measurements of aerosol properties conducted at low relative humidity over the Bondville site compare well with the analogous surface aerosol data and do not indicate any major sampling issues or that the aerosol is radically different at the surface compared with the lowest flyby altitude of ~ 240 m above ground level. Statistical analyses of the in situ vertical profile data indicate that aerosol light scattering and absorption (related to aerosol amount) decreases substantially with increasing altitude. Parameters related to the nature of the aerosol (e.g., single-scattering albedo, Ångström exponent, etc.), however, are relatively constant throughout the mixed layer, and do not vary as much as the aerosol amount throughout the profile. While individual profiles often showed more variability, the median in situ single-scattering albedo was 0.93–0.95 for all sampled altitudes. Several parameters (e.g., submicrometer scattering fraction, hemispheric backscattering fraction, and scattering Ångström exponent) suggest that the fraction of smaller particles in the aerosol is larger near the surface than at high altitudes. The observed dependence of scattering on size, wavelength, angular integration range, and relative humidity, together with the spectral dependence of absorption, show that the aerosol at higher altitudes is larger, less hygroscopic, and more strongly absorbing at shorter wavelengths, suggesting an increased contribution from dust or organic aerosols. The aerosol profiles show significant differences among seasons. The largest amounts of aerosol (as determined by median light extinction profile measurements) throughout most of the sampled column were observed during summer, with the lowest amounts in the winter and intermediate values in the spring and fall. The highest three profile levels (3.1, 3.7, 4.6 km), however, showed larger median extinction values in the spring, which could reflect long-range transport of dust or smoke aerosols. The aerosols in the mixed layer were darkest (i.e., lowest single-scattering albedo) in the fall, in agreement with surface measurements at Bondville and other continental sites in the US. In situ profiles of aerosol radiative forcing efficiency showed little seasonal or vertical variability. Underflights of the CALIPSO satellite show reasonable agreement in a majority of retrieved profiles between aircraft-measured extinction at 532 nm (adjusted to ambient relative humidity) and CALIPSO-retrieved extinction, and suggest that routine aircraft profiling programs can be used to better understand and validate satellite retrieval algorithms. CALIPSO tended to overestimate the aerosol extinction at this location in some boundary layer flight segments when scattered or broken clouds were present, which could be related to problems with CALIPSO cloud screening methods. The in situ aircraft-collected aerosol data suggest extinction thresholds for the likelihood of aerosol layers being detected by the CALIOP lidar. In this study, aerosol layers with light extinction (532 nm) values 〉 50 Mm −1 were detected by CALIPSO ~ 95% of the time, while aerosol layers with extinction values lower than 10 Mm −1 had a detection efficiency of 〈 2%. For all collocated comparison cases, a 50% probability of detection falls at an in situ extinction level of 20–25 Mm −1 . These statistical data offer guidance as to the likelihood of CALIPSO's ability to retrieve aerosol extinction at various locations around the globe.

Beschreibung: Rate coefficients for the reaction of O( 1 D) with the atmospherically long-lived greenhouse gases NF 3 , SF 5 CF 3 , CHF 3 , C 2 F 6 , c-C 4 F 8 , n -C 5 F 12 , and n -C 6 F 14 Atmospheric Chemistry and Physics, 12, 11753-11764, 2012 Author(s): M. Baasandorj, B. D. Hall, and J. B. Burkholder The contribution of atmospherically persistent (long-lived) greenhouse gases to the radiative forcing of Earth has increased over the past several decades. The impact of highly fluorinated, saturated compounds, in particular perfluorinated compounds, on climate change is a concern because of their long atmospheric lifetimes, which are primarily determined by stratospheric loss processes, as well as their strong absorption in the infrared "window" region. A potentially key stratospheric loss process for these compounds is their gas-phase reaction with electronically excited oxygen atoms, O( 1 D). Therefore, accurate reaction rate coefficient data is desired for input to climate change models. In this work, rate coefficients, k , were measured for the reaction of O( 1 D) with several key long-lived greenhouse gases, namely NF 3 , SF 5 CF 3 , CHF 3 (HFC-23), C 2 F 6 , c-C 4 F 8 , n -C 5 F 12 , and n -C 6 F 14 . Room temperature rate coefficients for the total reaction, k Tot , corresponding to loss of O( 1 D), and reactive channel, k R , corresponding to the loss of the reactant compound, were measured for NF 3 and SF 5 CF 3 using competitive reaction and relative rate methods, respectively. k R was measured for the CHF 3 reaction and improved upper-limits were determined for the perfluorinated compounds included in this study. For NF 3 , k Tot was determined to be (2.55 ± 0.38) × 10 −11 cm 3 molecule −1 s −1 and k R , which was measured using CF 3 Cl, N 2 O, CF 2 ClCF 2 Cl (CFC-114), and CF 3 CFCl 2 (CFC-114a) as reference compounds, was determined to be (2.21 ± 0.33) × 10 −11 cm 3 molecule −1 s −1 . For SF 5 CF 3 , k Tot = (3.24 ± 0.50) × 10 −13 cm 3 molecule −1 s −1 and k R 〈 5.8 × 10 ×14 cm 3 molecule −1 s −1 were measured, where k R is a factor of three lower than the current recommendation of k Tot for use in atmospheric modeling. For CHF 3 k R was determined to be (2.35 ± 0.35) × 10 −12 cm 3 molecule −1 s −1 , which corresponds to a reactive channel yield of 0.26 ± 0.04, and resolves a large discrepancy among previously reported values. The quoted uncertainties are 2σ and include estimated systematic errors. Upper-limits for k R for the C 2 F 6 , c-C 4 F 8 , n -C 5 F 12 , and n -C 6 F 14 reactions were determined to be 3.0, 3.5, 5.0, and 16 (in units of 10 −14 cm 3 molecule −1 s −1 ), respectively. The results from this work are compared with results from previous studies. As part of this work, infrared absorption band strengths for NF 3 and SF 5 CF 3 were measured and found to be in good agreement with recently reported values.

Beschreibung: On the diurnal cycle of urban aerosols, black carbon and the occurrence of new particle formation events in springtime São Paulo, Brazil Atmospheric Chemistry and Physics, 12, 11733-11751, 2012 Author(s): J. Backman, L. V. Rizzo, J. Hakala, T. Nieminen, H. E. Manninen, F. Morais, P. P. Aalto, E. Siivola, S. Carbone, R. Hillamo, P. Artaxo, A. Virkkula, T. Petäjä, and M. Kulmala Large conurbations are a significant source of the anthropogenic pollution and demographic differences between cities that result in a different pollution burden. The metropolitan area of São Paulo (MASP, population 20 million) accounts for one fifth of the Brazilian vehicular fleet. A feature of MASP is the amount of ethanol used by the vehicular fleet, known to exacerbate air quality. The study describes the diurnal behaviour of the submicron aerosol and relies on total particle number concentration, particle number size distribution, light scattering and light absorption measurements. Modelled planetary boundary layer (PBL) depth and air mass movement data were used to aid the interpretation. During morning rush-hour, stagnant air and a shallow PBL height favour the accumulation of aerosol pollution. During clear-sky conditions, there was a wind shift towards the edge of the city indicating a heat island effect with implications on particulate pollution levels at the site. The median total particle number concentration for the submicron aerosol typically varied in the range 1.6 × 10 4 –3.2 × 10 4 cm −3 frequently exceeding 4 × 10 4 cm −3 during the day. During weekdays, nucleation-mode particles are responsible for most of the particles by numbers. The highest concentrations of total particle number concentrations and black carbon (BC) were observed on Fridays. Median diurnal values for light absorption and light scattering (at 637 nm wavelength) varied in the range 12–33 Mm −1 and 21–64 Mm −1 , respectively. The former one is equal to 1.8–5.0 μg m −3 of BC. The growth of the PBL, from the morning rush-hour until noon, is consistent with the diurnal cycle of BC mass concentrations. Weekday hourly median single-scattering albedo (ω 0 ) varied in the range 0.59–0.76. Overall, this suggests a top of atmosphere (TOA) warming effect. However, considering the low surface reflectance of urban areas, for the given range of ω 0 , the TOA radiative forcing can be either positive or negative for the sources within the MASP. On the average, weekend ω 0 values were 0.074 higher than during weekdays. During 11% of the days, new particle formation (NPF) events occurred. The analysed events growth rates ranged between 9 and 25 nm h −1 . Sulphuric acid proxy concentrations calculated for the site were less than 5% of the concentration needed to explain the observed growth. Thus, other vapours are likely contributors to the observed growth.

Beschreibung: Selected topics on the interaction between cirrus clouds and embedded contrails Atmospheric Chemistry and Physics, 12, 11943-11949, 2012 Author(s): K. Gierens Persistent contrails and natural cirrus clouds often coexist in the upper troposphere and contrails can be embedded within cirrus clouds. The present paper deals with some questions regarding the interaction of cirrus clouds and embedded contrails. I have selected only questions that can be answered by analytical means. I find that (1) the emission index for water vapour is only slightly changed when an aircraft crosses a cirrus cloud, (2) that contrail formation is not affected by an ambient cirrus, (3) that cirrus ice crystals entrained into the trailing wing tip vortex do not efficiently retard the sublimation of contrail ice crystals, and (4) that cirrus can start to dissolve an embedded contrail after a couple of hours by aggregation.

Beschreibung: Characterisation of GOME-2 formaldehyde retrieval sensitivity Atmospheric Measurement Techniques Discussions, 5, 7095-7139, 2012 Author(s): W. Hewson, H. Bösch, M. P. Barkley, and I. De Smedt Formaldehyde (HCHO) is an important tracer of tropospheric photochemistry, whose slant column abundance can be retrieved from satellite measurements of solar backscattered UV radiation, using differential absorption retrieval techniques. In this work a spectral fitting sensitivity analysis is conducted on HCHO slant columns retrieved from the Global Ozone Monitoring Experiment 2 (GOME-2) instrument. Despite quite different spectral fitting approaches, the retrieved HCHO slant columns have geographic distributions that generally match expected HCHO sources, though the slant column magnitudes and corresponding uncertainties are particularly sensitive to the retrieval set-up. The choice of spectral fitting window, polynomial order, I 0 correction, and inclusion of minor absorbers tend to have the largest impact on the fit residuals. However, application of a reference sector correction using observations over the remote Pacific Ocean, is shown to largely homogenise the resulting HCHO vertical columns, thereby largely reducing any systematic erroneous spectral fitting.

Beschreibung: Feasibility study of using a "travelling" CO 2 and CH 4 instrument to validate continuous in-situ measurement stations Atmospheric Measurement Techniques Discussions, 5, 7141-7185, 2012 Author(s): S. Hammer, G. Konrad, A. T. Vermeulen, O. Laurent, M. Delmotte, A. Jordan, L. Hazan, S. Conil, and I. Levin In the course of the ICOS (Integrated Carbon Observation System)Demo Experiment a feasibility study on the usefulness of a Travelling Comparison Instrument (TCI) was conducted in order to evaluate continuous atmospheric CO 2 and CH 4 measurements at two European stations. The aim of the TCI is to independently measure ambient air in parallel to the standard station instrumentation, thus providing a comprehensive comparison that includes the sample intake system, the instrument itself as well as its calibration and data evaluation. Observed differences between the TCI and the Heidelberg gas chromatographic system, which acted as a reference for the TCI, were −0.02 ± 0.08 μmol mol −1 for CO 2 and −0.3 ± 2.3 nmol mol −1 for CH 4 . Over a period of two weeks each, the continuous CO 2 and CH 4 measurements at two ICOS field stations, Cabauw and OPE, were compared to co-located TCI measurements. At Cabauw mean differences of 0.21 ± 0.06 μmol mol −1 for CO 2 and 0.41 ± 0.50 nmol mol −1 for CH 4 were found. For OPE the mean differences were 0.13 ± 0.07 μmol mol −1 for CO 2 and 0.44 ± 0.36 nmol mol −1 for CH 4 . Potential causes of these observed differences are leakages or contaminations in the intake lines and/or there flushing pumps. At Cabauw station an additional error contribution originates from insufficient flushing of standard gases. Offsets arising from differences in the working standard calibrations or leakages/contaminations in the drying systems are too small to explain the observed differences. Finally a comprehensive quality management strategy for atmospheric monitoring networks is proposed.

Beschreibung: Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures Atmospheric Chemistry and Physics, 12, 8611-8632, 2012 Author(s): T. W. Wilson, B. J. Murray, R. Wagner, O. Möhler, H. Saathoff, M. Schnaiter, J. Skrotzki, H. C. Price, T. L. Malkin, S. Dobbie, and S. M. R. K. Al-Jumur Atmospheric secondary organic aerosol (SOA) is likely to exist in a semi-solid or glassy state, particularly at low temperatures and humidities. Previously, it has been shown that glassy aqueous citric acid aerosol is able to nucleate ice heterogeneously under conditions relevant to cirrus in the tropical tropopause layer (TTL). In this study we test if glassy aerosol distributions with a range of chemical compositions heterogeneously nucleate ice under cirrus conditions. Three single component aqueous solution aerosols (raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA) and levoglucosan) and one multi component aqueous solution aerosol (raffinose mixed with five dicarboxylic acids and ammonium sulphate) were studied in both the liquid and glassy states at a large cloud simulation chamber. The investigated organic compounds have similar functionality to oxidised organic material found in atmospheric aerosol and have estimated temperature/humidity induced glass transition thresholds that fall within the range predicted for atmospheric SOA. A small fraction of aerosol particles of all compositions were found to nucleate ice heterogeneously in the deposition mode at temperatures relevant to the TTL (

Beschreibung: Calibration of column-averaged CH 4 over European TCCON FTS sites with airborne in-situ measurements Atmospheric Chemistry and Physics, 12, 8763-8775, 2012 Author(s): M. C. Geibel, J. Messerschmidt, C. Gerbig, T. Blumenstock, H. Chen, F. Hase, O. Kolle, J. V. Lavrič, J. Notholt, M. Palm, M. Rettinger, M. Schmidt, R. Sussmann, T. Warneke, and D. G. Feist In September/October 2009, six European ground-based Fourier Transform Spectrometers (FTS) of the Total Carbon Column Observation Network (TCCON) were calibrated for the first time using aircraft measurements. The campaign was part of the Infrastructure for Measurement of the European Carbon Cycle (IMECC) project. During this campaign, altitude profiles of several trace gases and meteorological parameters were taken close to the FTS sites (typically within 1–2 km distance for flight altitudes below 5000 m). Profiles of CO 2 , CH 4 , CO and H 2 O were measured continuously. N 2 O, H 2 , and SF 6 were later derived from flask measurements. The aircraft data had a vertical coverage ranging from approximately 300 to 13 000 m, corresponding to ~80% of the total atmospheric column seen by the FTS. This study summarizes the calibration results for CH 4 . The resulting calibration factor of 0.978 ± 0.002 (±1 σ) from the IMECC campaign agreed very well with the results that Wunch et al. (2010) had derived for TCCON instruments in North America, Australia, New Zealand, and Japan using similar methods. By combining our results with the data of Wunch et al. (2010), the uncertainty of the calibration factor could be reduced by a factor of three (compared to using only IMECC or only Wunch et al. (2010) data). A careful analysis of the calibration method used by Wunch et al. (2010) revealed that the incomplete vertical coverage of the aircraft profiles can lead to a bias in the calibration factor. This bias can be compensated with a new iterative approach that we developed. Using this improved method, we derived a significantly lower calibration factor of 0.974 ± 0.002 (±1 σ). This corresponds to a correction of all TCCON CH 4 measurements by roughly −7 ppb.

Beschreibung: Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem Atmospheric Chemistry and Physics, 12, 8777-8796, 2012 Author(s): Q. Yang, W. I. Gustafson Jr., J. D. Fast, H. Wang, R. C. Easter, M. Wang, S. J. Ghan, L. K. Berg, L. R. Leung, and H. Morrison Cloud-system resolving simulations with the chemistry version of the Weather Research and Forecasting (WRF-Chem) model are used to quantify the relative impacts of regional anthropogenic and oceanic emissions on changes in aerosol properties, cloud macro- and microphysics, and cloud radiative forcing over the Southeast Pacific (SEP) during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) (15 October–16 November 2008). Two distinct regions are identified. The near-coast polluted region is characterized by low surface precipitation rates, the strong suppression of non-sea-salt particle activation due to sea-salt particles, a predominant albedo effect in aerosol indirect effects, and limited impact of aerosols associated with anthropogenic emissions on clouds. Opposite sensitivities to natural marine and anthropogenic aerosol perturbations are seen in cloud properties (e.g., cloud optical depth and cloud-top and cloud-base heights), precipitation, and the top-of-atmosphere and surface shortwave fluxes over this region. The relatively clean remote region is characterized by large contributions of aerosols from non-regional sources (lateral boundaries) and much stronger drizzle at the surface. Under a scenario of five-fold increase in regional anthropogenic emissions, this relatively clean region shows large cloud responses, for example, a 13% increase in cloud-top height and a 9% increase in albedo in response to a moderate increase (25% of the reference case) in cloud condensation nuclei (CCN) concentration. The reduction of precipitation due to this increase in anthropogenic aerosols more than doubles the aerosol lifetime in the clean marine boundary layer. Therefore, the aerosol impacts on precipitation are amplified by the positive feedback of precipitation on aerosol, which ultimately alters the cloud micro- and macro-physical properties, leading to strong aerosol-cloud-precipitation interactions. The high sensitivity is also related to an increase in cloud-top entrainment rate (by 16% at night) due to the increased anthropogenic aerosols. The simulated aerosol-cloud-precipitation interactions due to the increased anthropogenic aerosols have a stronger diurnal cycle over the clean region compared to the near-coast region with stronger interactions at night. During the day, solar heating results in more frequent decoupling of the cloud and sub-cloud layers, thinner clouds, reduced precipitation, and reduced sensitivity to the increase in anthropogenic emissions. This study shows the importance of natural aerosols in accurately quantifying anthropogenic forcing within a regional modeling framework. The results of this study also imply that the energy balance perturbations from increased anthropogenic emissions are larger in the more susceptible clean environment than in already polluted environment and are larger than possible from the first indirect effect alone.

Beschreibung: Note on the application of planar-fit rotation for non-omnidirectional sonic anemometers Atmospheric Measurement Techniques Discussions, 5, 7323-7340, 2012 Author(s): M. Li, W. Babel, K. Tanaka, and T. Foken For non-omnidirectional sonic anenometers like the Kaijo-Denki DAT 600 TR61A probe, it is shown that separate planar fit rotations must be used for the undisturbed (open part of the sonic anemometer) and the disturbed sector. This increases the friction velocity while no effect on the scalar fluxes was found. In the disturbed sector, irregular values of − u ′ w ′ 〈 0 were detected for low wind velocities. This study was done for data sets from the Naqu-BJ site on the Tibetan Plateau.

Beschreibung: Some effects of ice crystals on the FSSP measurements in mixed phase clouds Atmospheric Chemistry and Physics, 12, 8963-8977, 2012 Author(s): G. Febvre, J.-F. Gayet, V. Shcherbakov, C. Gourbeyre, and O. Jourdan In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD). The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s −1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the FSSP) and the concentration of (natural) ice particles (CPI data). In mixed cloud, a simple estimation of the number of ice crystals impacting the FSSP inlet shows that the ice crystal shattering effect is the main factor in observed ice production.

Beschreibung: Estimation of mercury emissions from forest fires, lakes, regional and local sources using measurements in Milwaukee and an inverse method Atmospheric Chemistry and Physics, 12, 8993-9011, 2012 Author(s): B. de Foy, C. Wiedinmyer, and J. J. Schauer Gaseous elemental mercury is a global pollutant that can lead to serious health concerns via deposition to the biosphere and bio-accumulation in the food chain. Hourly measurements between June 2004 and May 2005 in an urban site (Milwaukee, WI) show elevated levels of mercury in the atmosphere with numerous short-lived peaks as well as longer-lived episodes. The measurements are analyzed with an inverse model to obtain information about mercury emissions. The model is based on high resolution meteorological simulations (WRF), hourly back-trajectories (WRF-FLEXPART) and a chemical transport model (CAMx). The hybrid formulation combining back-trajectories and Eulerian simulations is used to identify potential source regions as well as the impacts of forest fires and lake surface emissions. Uncertainty bounds are estimated using a bootstrap method on the inversions. Comparison with the US Environmental Protection Agency's National Emission Inventory (NEI) and Toxic Release Inventory (TRI) shows that emissions from coal-fired power plants are properly characterized, but emissions from local urban sources, waste incineration and metal processing could be significantly under-estimated. Emissions from the lake surface and from forest fires were found to have significant impacts on mercury levels in Milwaukee, and to be underestimated by a factor of two or more.

Beschreibung: Aerosol absorption retrieval at ultraviolet wavelengths in a complex environment Atmospheric Measurement Techniques Discussions, 5, 6991-7023, 2012 Author(s): S. Kazadzis, N. Kouremeti, V. Amiridis, A. Arola, and E. Gerasopoulos We have combined sun and sky radiance measurements from a CIMEL sun-photometer and total and diffuse UV irradiance measurements with a multi-filter rotating shadow-band radiometer (UVMFR), in order to calculate aerosol absorption properties (single scattering albedo) in the UV range, for a 10 month period in Athens, Greece. The aerosol extinction optical thickness measured by the CIMEL instrument has been used for the inter-calibration of the UVMFR. The measurements from both instruments were used as input to a radiative transfer model and the single scattering albedo (SSA) for 368 nm and 332 nm has been calculated. The SSA values at these wavelengths, together with synchronous SSA, CIMEL-derived, retrievals at 440 nm, show a mean of 0.88, 0.86 and 0.80, with lowest values (higher absorption) towards lower wavelengths. In addition, noticeable diurnal variations of the SSA in all wavelengths are revealed, with amplitudes in the order of 0.05. Higher SSA wavelength dependence is found for cases of lower Ångström exponents and also an SSA decrease with decreasing extinction optical depth, suggesting an effect of the different aerosol composition.

Beschreibung: Development of a new JMA flask sampling and trace gas measuring system for observation on a cargo aircraft C-130H Atmospheric Measurement Techniques Discussions, 5, 7067-7094, 2012 Author(s): K. Tsuboi, H. Matsueda, Y. Sawa, Y. Niwa, M. Nakamura, D. Kuboike, K. Saito, H. Ohmori, S. Iwatsubo, H. Nishi, Y. Hanamiya, K. Tsuji, and Y. Baba We developed and evaluated a flask air sampling system for atmospheric trace gas observation on a cargo C-130H aircraft, as well as an automated analysis system for the flask samples, as part of a new operational monitoring program of the Japan Meteorological Agency (JMA). Air samples were collected during each flight, between Kanagawa Prefecture (near Tokyo) and Minamitorishima (an island located nearly 2000 km southeast of Tokyo), from the air-conditioning system on the aircraft. The quality assurance test of the flask sampling air was made by specially coordinated flights at a low altitude of 1000 ft over Minamitorishima and comparing the flask values with those obtained at the surface. Based on our storage tests, the flask samples remained stable until analyses. The concentration measuring system for the flask samples has, in addition to the conventional sensors, two laser-based analyzers using wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) and off-axis integrated cavity output spectroscopy (ICOS). Laboratory tests of the measuring system indicated relatively high reproducibility with overall precisions of less than 0.06 ppm for CO 2 , 0.68 ppb for CH 4 , 0.36 ppb for CO, and 0.03 ppb for N 2 O. Inter-comparison experiments for ambient air measurements showed excellent agreements between the laser-based measurement techniques and the conventional methods currently in use. We also found that there are no significant influences of isotope effects for the laser-based analyzers.

Beschreibung: A statistical approach to quantify uncertainty in carbon monoxide measurements at the Izaña global GAW station: 2008–2011 Atmospheric Measurement Techniques Discussions, 5, 6949-6989, 2012 Author(s): A. J. Gomez-Pelaez, R. Ramos, V. Gomez-Trueba, P. C. Novelli, and R. Campo-Hernandez Atmospheric CO in-situ measurements are carried out at the Izaña (Tenerife) global GAW mountain station using a RGA (Reduction Gas Analyser). In-situ measurements at Izaña are representative of the subtropical North-East Atlantic free troposphere, specially during the night period. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Izaña's 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Izaña station which could be applied to other GAW stations. We determine the combined standard uncertainty from four components of the measurement: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the response function parameters uncertainties (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol −1 to 1.66 nmol mol −1 , due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute exactly the mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In-situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty in the differences is determined and whether these are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between −2.39 and 2.5 nmol mol −1 . Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol −1 compatibility goal of GAW.

Beschreibung: Model evaluation of marine primary organic aerosol emission schemes Atmospheric Chemistry and Physics, 12, 8553-8566, 2012 Author(s): B. Gantt, M. S. Johnson, N. Meskhidze, J. Sciare, J. Ovadnevaite, D. Ceburnis, and C. D. O'Dowd In this study, several marine primary organic aerosol (POA) emission schemes have been evaluated using the GEOS-Chem chemical transport model in order to provide guidance for their implementation in air quality and climate models. These emission schemes, based on varying dependencies of chlorophyll a concentration ([chl a ]) and 10 m wind speed ( U 10 ), have large differences in their magnitude, spatial distribution, and seasonality. Model comparison with weekly and monthly mean values of the organic aerosol mass concentration at two coastal sites shows that the source function exclusively related to [chl a ] does a better job replicating surface observations. Sensitivity simulations in which the negative U 10 and positive [chl a ] dependence of the organic mass fraction of sea spray aerosol are enhanced show improved prediction of the seasonality of the marine POA concentrations. A top-down estimate of submicron marine POA emissions based on the parameterization that compares best to the observed weekly and monthly mean values of marine organic aerosol surface concentrations has a global average emission rate of 6.3 Tg yr −1 . Evaluation of existing marine POA source functions against a case study during which marine POA contributed the major fraction of submicron aerosol mass shows that none of the existing parameterizations are able to reproduce the hourly-averaged observations. Our calculations suggest that in order to capture episodic events and short-term variability in submicron marine POA concentration over the ocean, new source functions need to be developed that are grounded in the physical processes unique to the organic fraction of sea spray aerosol.

Beschreibung: Factor analysis of combined organic and inorganic aerosol mass spectra from high resolution aerosol mass spectrometer measurements Atmospheric Chemistry and Physics, 12, 8537-8551, 2012 Author(s): Y. L. Sun, Q. Zhang, J. J. Schwab, T. Yang, N. L. Ng, and K. L. Demerjian Positive matrix factorization (PMF) was applied to the merged high resolution mass spectra of organic and inorganic aerosols from aerosol mass spectrometer (AMS) measurements to investigate the sources and evolution processes of submicron aerosols in New York City in summer 2009. This new approach is able to study the distribution of organic and inorganic species in different types of aerosols, the acidity of organic aerosol (OA) factors, and the fragment ion patterns related to photochemical processing. In this study, PMF analysis of the unified AMS spectral matrix resolved 8 factors. The hydrocarbon-like OA (HOA) and cooking OA (COA) factors contain negligible amounts of inorganic species. The two factors that are primarily ammonium sulfate (SO 4 -OA) and ammonium nitrate (NO 3 -OA), respectively, are overall neutralized. Among all OA factors the organic fraction of SO 4 -OA shows the highest degree of oxidation (O/C = 0.69). Two semi-volatile oxygenated OA (OOA) factors, i.e., a less oxidized (LO-OOA) and a more oxidized (MO-OOA), were also identified. MO-OOA represents local photochemical products with a diurnal profile exhibiting a pronounced noon peak, consistent with those of formaldehyde (HCHO) and O x (= O 3 + NO 2 ). The NO + /NO 2 + ion ratio in MO-OOA is much higher than that in NO 3 -OA and in pure ammonium nitrate, indicating the formation of organic nitrates. The nitrogen-enriched OA (NOA) factor contains ~25% of acidic inorganic salts, suggesting the formation of secondary OA via acid-base reactions of amines. The size distributions of OA factors derived from the size-resolved mass spectra show distinct diurnal evolving behaviors but overall a progressing evolution from smaller to larger particle mode as the oxidation degree of OA increases. Our results demonstrate that PMF analysis of the unified aerosol mass spectral matrix which contains both inorganic and organic aerosol signals may enable the deconvolution of more OA factors and gain more insights into the sources, processes, and chemical characteristics of OA in the atmosphere.

Beschreibung: Technical Note: Synthesis of isoprene atmospheric oxidation products: isomeric epoxydiols and the rearrangement products cis - and trans -3-methyl-3,4-dihydroxytetrahydrofuran Atmospheric Chemistry and Physics, 12, 8529-8535, 2012 Author(s): Z. Zhang, Y.-H. Lin, H. Zhang, J. D. Surratt, L. M. Ball, and A. Gold Isoprene epoxydiol (IEPOX) isomers are key gas-phase intermediates of isoprene atmospheric oxidation. Secondary organic aerosols derived from such intermediates have important impacts on air quality and health. We report here convergent and unambiguous pathways developed for the synthesis of isomeric IEPOX species and the rearrangement products cis - and trans -3-methyl-3,4-dihydroxytetrahydrofuran in good yield. The availability of such compounds is necessary to expedite research on isoprene atmospheric oxidation mechanisms and subsequent aerosol formation as well as the toxicological properties of the aerosols.

Beschreibung: Modelling of organic aerosols over Europe (2002–2007) using a volatility basis set (VBS) framework: application of different assumptions regarding the formation of secondary organic aerosol Atmospheric Chemistry and Physics, 12, 8499-8527, 2012 Author(s): R. Bergström, H. A. C. Denier van der Gon, A. S. H. Prévôt, K. E. Yttri, and D. Simpson A new organic aerosol module has been implemented into the EMEP chemical transport model. Four different volatility basis set (VBS) schemes have been tested in long-term simulations for Europe, covering the six years 2002–2007. Different assumptions regarding partitioning of primary organic aerosol and aging of primary semi-volatile and intermediate volatility organic carbon (S/IVOC) species and secondary organic aerosol (SOA) have been explored. Model results are compared to filter measurements, aerosol mass spectrometry (AMS) data and source apportionment studies, as well as to other model studies. The present study indicates that many different sources contribute significantly to organic aerosol in Europe. Biogenic and anthropogenic SOA, residential wood combustion and vegetation fire emissions may all contribute more than 10% each over substantial parts of Europe. This study shows smaller contributions from biogenic SOA to organic aerosol in Europe than earlier work, but relatively greater anthropogenic SOA. Simple VBS based organic aerosol models can give reasonably good results for summer conditions but more observational studies are needed to constrain the VBS parameterisations and to help improve emission inventories. The volatility distribution of primary emissions is one important issue for further work. Emissions of volatile organic compounds from biogenic sources are also highly uncertain and need further validation. We can not reproduce winter levels of organic aerosol in Europe, and there are many indications that the present emission inventories substantially underestimate emissions from residential wood combustion in large parts of Europe.

Beschreibung: Systematic variations of cloud top temperature and precipitation rate with aerosols over the global tropics Atmospheric Chemistry and Physics, 12, 8491-8498, 2012 Author(s): Feng Niu and Zhanqing Li Aerosols may modify cloud properties and precipitation via a variety of mechanisms with varying and contradicting consequences. Using a large ensemble of satellite data acquired by the Moderate Resolution Imaging Spectroradiometer onboard the Earth Observing System's Aqua platform, the CloudSat cloud profiling radar and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite over the tropical oceans, we identified two distinct correlations of clouds and precipitation with aerosol loading. Cloud-top temperatures are significantly negatively correlated with increasing aerosol index (AI) over oceans and aerosol optical depth (AOT) over land for deep mixed-phase clouds with liquid droplets near the warm bases and ice crystals near the cold tops; no significant changes were found for uniformly liquid clouds. Precipitation rates are positively correlated with the AI for mixed-phase clouds, but negatively correlated for liquid clouds. These distinct correlations might be a manifestation of two potential mechanisms: the invigoration effect (which enhances convection and precipitation) and the microphysical effect (which suppresses precipitation). We note that the highly limited information garnered from satellite products cannot unequivocally support the causal relationships between cloud-top temperature/precipitation rate and aerosol loading. But if aerosols are indeed the causes for the observed relationships, they may change the overall distribution of precipitation, leading to a more extreme and unfavorable rainfall pattern of suppressing light rains and fostering heavy rains.

Beschreibung: Potential of the future thermal infrared space-borne sensor IASI-NG to monitor lower tropospheric ozone Atmospheric Measurement Techniques Discussions, 5, 7025-7065, 2012 Author(s): P. Sellitto, G. Dufour, M. Eremenko, J. Cuesta, P. Dauphin, G. Forêt, B. Gaubert, M. Beekmann, V.-H. Peuch, and J.-M. Flaud The lower tropospheric (LT) ozone concentration is a key factor for air quality (AQ). Observing efficiently LT ozone from space is crucial to monitor and better understand pollution phenomena occurring from inter-continental to local scales, and that have a proven noxious effect on the human health and the biosphere. The Infrared Atmospheric Sounder Interferometer (IASI) flies on MetOp-A spacecraft and is planned to be launched in the next future as part of the other MetOp modules, i.e. MetOp-B and C. IASI has demonstrated to have the capability to single out the LT ozone signal only at favourable conditions, i.e. in presence of high thermal contrast scenarios. New generation satellite instruments are being designed to address several pressing geophysical issues, including a better observation capability of LT ozone. IASI-NG (New Generation), now having reached the accomplishment of design phase-A for launch in the 2020 timeframe as part of the EPS-SG (EUMETSAT Polar System-Second Generation, formerly post-EPS) mission, may render feasible a better observation of AQ in terms of LT ozone. To evaluate the added-value brought by IASI-NG in this context, we developed a pseudo-observation simulator, including a direct simulator of thermal infrared spectra and a full inversion scheme to retrieve ozone concentration profiles. We produced one month (August 2009) of tropospheric ozone pseudo-observations based on both IASI and IASI-NG instrumental configurations. We compared the pseudo-observations and we found a clear improvement of LT ozone (up to 6 km altitude) pseudo-observations quality for IASI-NG. The estimated total error is expected to be more than 35% smaller at 5 km, and 20% smaller for the LT ozone column. The total error on the LT ozone column is, on average, lower than 10% for IASI-NG. IASI-NG is expected to have a significantly better vertical sensitivity (monthly average degrees of freedom surface-6 km of 0.70) and to be sensitive at lower altitudes (more than 0.5 km lower than IASI, reaching values of nearly 3.0 km). Vertical ozone layers of 4 to 5 km thickness are expected to be resolved by IASI-NG, while IASI has a vertical resolution of 6–8 km. According to our analyses, IASI-NG is expected to have the possibility of effectively separate lower from upper tropospheric ozone information even for low sensitivity scenarios. In addition, IASI-NG is expected to be able to better monitor LT ozone patterns at local spatial scale and to monitor abrupt temporal evolutions occurring at time-scales of a few days, thus bringing an expected added-value with respect to IASI for the monitoring of AQ.

Beschreibung: How relevant is the deposition of mercury onto snowpacks? – Part 1: A statistical study on~the~impact of environmental factors Atmospheric Chemistry and Physics, 12, 9221-9249, 2012 Author(s): D. A. Durnford, A. P. Dastoor, A. O. Steen, T. Berg, A. Ryzhkov, D. Figueras-Nieto, L. R. Hole, K. A. Pfaffhuber, and H. Hung A portion of the highly toxic methylmercury that bioaccumulates in aquatic life is created from mercury entering bodies of water with snowpack meltwater. To determine the importance of meltwater as a source of aquatic mercury, it is necessary to understand the environmental processes that govern the behavior of snowpack-related mercury. In this study we investigate relationships among 5 types of snowpack-related mercury observations and 20 model environmental variables. The observation types are the 24-h fractional loss of mercury from surface snow, and the concentrations of mercury in surface snow, seasonal snowpacks, the snowpack meltwater's ionic pulse, and long-term snowpack-related records. The model environmental variables include those related to atmospheric mercury, insolation, wind, atmospheric stability, snowpack physical characteristics, atmospheric pressure, and solid precipitation. Bivariate and multiple linear regressions were performed twice for each mercury observation type: once with all observations, and once excluding observations from locations where the snowpack's burden of oxidizing and stabilizing halogens is known or presumed to affect snowpack mercury. Since no observations from long-term snowpack-related records were considered affected by halogens, this group of observations was included with the sets of uninfluenced observations and was not discussed with the complete, original sets of observations. When all observations are included, only 37% of their variability can be explained, on average, with significance confidence levels averaging 81%; a separate regression model predicts each mercury observation type. Without the influence of halogens, the regression models are able to explain an average of 79% of the observations' variability with significance confidence levels averaging 97%. The snowpack-related mercury observations are most strongly controlled by the dry and wet depositions of oxidized mercury, and by precipitation. Mercury deposited through wet processes is more strongly retained by snowpacks than mercury deposited through dry processes. Revolatilization of mercury deposited through wet processes may be inhibited through burial by fresh snowfalls and/or by its more central location, compared to that of mercury deposited through dry deposition, within snowpack snow grains. The two depositions of oxidized mercury together explain 84% of the variability in observed concentrations of mercury in surface snow, 52% of the variability of observed concentrations of mercury in seasonal snowpacks and their meltwater's ionic pulse, and only 20% of the variability of observed concentrations of mercury in long-term snowpack-related records; other environmental controls seemingly gain in relevance as time passes. The concentration of mercury in long-term records is apparently primarily affected by latitude; both the primary sources of anthropogenic mercury and the strong upper-level zonal winds are located in the midlatitudes.

Beschreibung: Simulating ultrafine particle formation in Europe using a regional CTM: contribution of primary emissions versus secondary formation to aerosol number concentrations Atmospheric Chemistry and Physics, 12, 8663-8677, 2012 Author(s): C. Fountoukis, I. Riipinen, H. A. C. Denier van der Gon, P. E. Charalampidis, C. Pilinis, A. Wiedensohler, C. O'Dowd, J. P. Putaud, M. Moerman, and S. N. Pandis A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm ( N 10 ) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N 50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.

Beschreibung: Influence of a Carrington-like event on the atmospheric chemistry, temperature and dynamics Atmospheric Chemistry and Physics, 12, 8679-8686, 2012 Author(s): M. Calisto, P. T. Verronen, E. Rozanov, and T. Peter We have modeled the atmospheric impact of a major solar energetic particle event similar in intensity to what is thought of the Carrington Event of 1–2 September 1859. Ionization rates for the August 1972 solar proton event, which had an energy spectrum comparable to the Carrington Event, were scaled up in proportion to the fluence estimated for both events. We have assumed such an event to take place in the year 2020 in order to investigate the impact on the modern, near future atmosphere. Effects on atmospheric chemistry, temperature and dynamics were investigated using the 3-D Chemistry Climate Model SOCOL v2.0. We find significant responses of NO x , HO x , ozone, temperature and zonal wind. Ozone and NO x have in common an unusually strong and long-lived response to this solar proton event. The model suggests a 3-fold increase of NO x generated in the upper stratosphere lasting until the end of November, and an up to 10-fold increase in upper mesospheric HO x . Due to the NO x and HO x enhancements, ozone reduces by up to 60–80% in the mesosphere during the days after the event, and by up to 20–40% in the middle stratosphere lasting for several months after the event. Total ozone is reduced by up to 20 DU in the Northern Hemisphere and up to 10 DU in the Southern Hemisphere. Free tropospheric and surface air temperatures show a significant cooling of more than 3 K and zonal winds change significantly by 3–5 m s −1 in the UTLS region. In conclusion, a solar proton event, if it took place in the near future with an intensity similar to that ascribed to of the Carrington Event of 1859, must be expected to have a major impact on atmospheric composition throughout the middle atmosphere, resulting in significant and persistent decrease in total ozone.

Beschreibung: Atmospheric CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 measurements at Jungfraujoch, Switzerland: results from a flask sampling intercomparison program Atmospheric Measurement Techniques Discussions, 5, 7293-7322, 2012 Author(s): I. T. van der Laan-Luijkx, S. van der Laan, C. Uglietti, M. F. Schibig, R. E. M. Neubert, H. A. J. Meijer, W. A. Brand, A. Jordan, J. M. Richter, M. Rothe, and M. C. Leuenberger We present results from an intercomparison program of CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 measurements from atmospheric flask samples. Flask samples are collected on a bi-weekly basis at the High Altitude Research Station Jungfraujoch in Switzerland for three European laboratories: the University of Bern, Switzerland, the University of Groningen, the Netherlands and the Max Planck Institute for Biogeochemistry in Jena, Germany. Almost 4 yr of measurements of CO 2 , δ(O 2 /N 2 ) and δ 13 CO 2 are compared in this paper to assess the measurement compatibility of the three laboratories. While the average difference for the CO 2 measurements between the laboratories in Bern and Jena meets the required compatibility goal as defined by the World Meteorological Organisation, the standard deviation of the average differences between all laboratories is not within the required goal. However, the obtained annual trend and seasonalities are the same within their estimated uncertainties. For δ(O 2 /N 2 ) significant differences are observed between the three laboratories. The comparison for δ 13 CO 2 yields the least compatible results and the required goals are not met between the three laboratories. Our study shows the importance of regular intercomparison exercises to identify potential biases between laboratories and the need to improve the quality of atmospheric measurements.

Beschreibung: Analysis of stratospheric NO 2 trends above Jungfraujoch using ground-based UV-visible, FTIR, and satellite nadir observations Atmospheric Chemistry and Physics, 12, 8851-8864, 2012 Author(s): F. Hendrick, E. Mahieu, G. E. Bodeker, K. F. Boersma, M. P. Chipperfield, M. De Mazière, I. De Smedt, P. Demoulin, C. Fayt, C. Hermans, K. Kreher, B. Lejeune, G. Pinardi, C. Servais, R. Stübi, R. van der A, J.-P. Vernier, and M. Van Roozendael The trend in stratospheric NO 2 column at the NDACC (Network for the Detection of Atmospheric Composition Change) station of Jungfraujoch (46.5° N, 8.0° E) is assessed using ground-based FTIR and zenith-scattered visible sunlight SAOZ measurements over the period 1990 to 2009 as well as a composite satellite nadir data set constructed from ERS-2/GOME, ENVISAT/SCIAMACHY, and METOP-A/GOME-2 observations over the 1996–2009 period. To calculate the trends, a linear least squares regression model including explanatory variables for a linear trend, the mean annual cycle, the quasi-biennial oscillation (QBO), solar activity, and stratospheric aerosol loading is used. For the 1990–2009 period, statistically indistinguishable trends of −3.7 ± 1.1% decade −1 and −3.6 ± 0.9% decade −1 are derived for the SAOZ and FTIR NO 2 column time series, respectively. SAOZ, FTIR, and satellite nadir data sets show a similar decrease over the 1996–2009 period, with trends of −2.4 ± 1.1% decade −1 , −4.3 ± 1.4% decade −1 , and −3.6 ± 2.2% decade −1 , respectively. The fact that these declines are opposite in sign to the globally observed +2.5% decade −1 trend in N 2 O, suggests that factors other than N 2 O are driving the evolution of stratospheric NO 2 at northern mid-latitudes. Possible causes of the decrease in stratospheric NO 2 columns have been investigated. The most likely cause is a change in the NO 2 /NO partitioning in favor of NO, due to a possible stratospheric cooling and a decrease in stratospheric chlorine content, the latter being further confirmed by the negative trend in the ClONO 2 column derived from FTIR observations at Jungfraujoch. Decreasing ClO concentrations slows the NO + ClO → NO 2 + Cl reaction and a stratospheric cooling slows the NO + O 3 → NO 2 + O 2 reaction, leaving more NO x in the form of NO. The slightly positive trends in ozone estimated from ground- and satellite-based data sets are also consistent with the decrease of NO 2 through the NO 2 + O 3 → NO 3 + O 2 reaction. Finally, we cannot rule out the possibility that a strengthening of the Dobson-Brewer circulation, which reduces the time available for N 2 O photolysis in the stratosphere, could also contribute to the observed decline in stratospheric NO 2 above Jungfraujoch.

Beschreibung: Model investigation of NO 3 secondary organic aerosol (SOA) source and heterogeneous organic aerosol (OA) sink in the western United States Atmospheric Chemistry and Physics, 12, 8797-8811, 2012 Author(s): J. L. Fry and K. Sackinger The relative importance of NO 3 -initiated source and heterogeneous sink of organic aerosol in the western United States is investigated using the WRF/Chem regional weather and chemistry model. The model is run for the four individual months, representing the four seasons, of January, May, August, and October, to produce hourly spatial maps of surface concentrations of NO 3 , organic aerosol (OA), and reactive organic gases (ROG, a sum of alkene species tracked in the lumped chemical mechanism employed). These "baseline" simulations are used in conjunction with literature data on secondary organic aerosol (SOA) mass yields, average organic aerosol composition, and reactive uptake coefficients for NO 3 on organic surfaces to predict SOA source and OA heterogeneous loss rates due to reactions initiated by NO 3 . We find both source and sink rates maximized downwind of urban centers, therefore with a varying location that depends on wind direction. Both source and sink terms are maximum in summer, and SOA source dominates over OA loss by approximately three orders of magnitude, with large day-to-day variability. The NO 3 source of SOA (peak production rates of 0.4–3.0 μg kg −1 h −1 ) is found to be significantly larger than the heterogeneous sink of OA via NO 3 surface reactions (peak loss rates of 0.5–8 × 10 −4 μg kg −1 h −1 ).

Beschreibung: Long-term greenhouse gas measurements from aircraft Atmospheric Measurement Techniques Discussions, 5, 7341-7382, 2012 Author(s): A. Karion, C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. Andrews, J. Kofler, D. Neff, and P. Tans In March 2009 the NOAA/ESRL/GMD Carbon Cycle and Greenhouse Gases Group collaborated with the US Coast Guard (USCG) to establish the Alaska Coast Guard (ACG) sampling site, a unique addition to NOAA's atmospheric monitoring network. This collaboration takes advantage of USCG bi-weekly Arctic Domain Awareness (ADA) flights, conducted with Hercules C-130 aircraft from March to November each year. NOAA has installed window-replacement inlet plates on two USCG C-130 aircraft and deploys a pallet with NOAA instrumentation on each ADA flight. Flights typically last 8 h and cover a very large area, traveling from Kodiak, AK in the south up to Barrow, AK in the north, and making altitude profiles near the coast as well as in the interior. NOAA instrumentation on each flight includes: a flask sampling system, a continuous CO 2 /CH 4 /CO/H 2 O analyzer, a continuous ozone analyzer, and an ambient temperature and humidity sensor. GPS time and location from the aircraft's navigation system are also collected. Air samples collected in flight are analyzed at NOAA/ESRL for the major greenhouse gases and a variety of halocarbons and hydrocarbons that influence climate, stratospheric ozone, and air quality. Instruments on this aircraft are designed and deployed to be able to collect air samples and data autonomously, so that NOAA personnel visit the site only for installation at the beginning of each season. We present an assessment of the cavity ring-down spectroscopy (CRDS) CO 2 /CH 4 /CO/H 2 O analyzer performance operating on an aircraft over a three-year period. We describe the overall system for making accurate greenhouse gas measurements using a CRDS analyzer on an aircraft with minimal operator interaction. Short and long-term stability of the CRDS analyzer over a seven-month deployment period is better than 0.15 ppm, 2 ppb, and 5 ppb for CO 2 , CH 4 , CO respectively, considering differences of on-board reference tank measurements from a laboratory calibration performed prior to deployment. This stability is not affected by variation in pressure or temperature during flight. Biases and standard deviations of comparisons with flask samples suggest that atmospheric variability, flask-to-flask variability, and possible flask sampling biases may be driving biases in the comparison between flasks and in-situ CRDS measurements.

Beschreibung: Comparing Lagrangian and Eulerian models for CO 2 transport – a step towards Bayesian inverse modeling using WRF/STILT-VPRM Atmospheric Chemistry and Physics, 12, 8979-8991, 2012 Author(s): D. Pillai, C. Gerbig, R. Kretschmer, V. Beck, U. Karstens, B. Neininger, and M. Heimann We present simulations of atmospheric CO 2 concentrations provided by two modeling systems, run at high spatial resolution: the Eulerian-based Weather Research Forecasting (WRF) model and the Lagrangian-based Stochastic Time-Inverted Lagrangian Transport (STILT) model, both of which are coupled to a diagnostic biospheric model, the Vegetation Photosynthesis and Respiration Model (VPRM). The consistency of the simulations is assessed with special attention paid to the details of horizontal as well as vertical transport and mixing of CO 2 concentrations in the atmosphere. The dependence of model mismatch (Eulerian vs. Lagrangian) on models' spatial resolution is further investigated. A case study using airborne measurements during which two models showed large deviations from each other is analyzed in detail as an extreme case. Using aircraft observations and pulse release simulations, we identified differences in the representation of details in the interaction between turbulent mixing and advection through wind shear as the main cause of discrepancies between WRF and STILT transport at a spatial resolution such as 2 and 6 km. Based on observations and inter-model comparisons of atmospheric CO 2 concentrations, we show that a refinement of the parameterization of turbulent velocity variance and Lagrangian time-scale in STILT is needed to achieve a better match between the Eulerian and the Lagrangian transport at such a high spatial resolution (e.g. 2 and 6 km). Nevertheless, the inter-model differences in simulated CO 2 time series for a tall tower observatory at Ochsenkopf in Germany are about a factor of two smaller than the model-data mismatch and about a factor of three smaller than the mismatch between the current global model simulations and the data.

Beschreibung: Radiative impacts of cloud heterogeneity and overlap in an atmospheric General Circulation Model Atmospheric Chemistry and Physics, 12, 9097-9111, 2012 Author(s): L. Oreopoulos, D. Lee, Y. C. Sud, and M. J. Suarez The radiative impacts of horizontal heterogeneity of layer cloud condensate, and vertical overlap of both condensate and cloud fraction are examined with the aid of a new radiation package operating in the GEOS-5 Atmospheric General Circulation Model. The impacts are examined in terms of diagnostic top-of-the atmosphere shortwave (SW) and longwave (LW) cloud radiative effect (CRE) calculations for a range of assumptions and overlap parameter specifications. The investigation is conducted for two distinct cloud schemes, one that comes with the standard GEOS-5 distribution, and another used experimentally for its enhanced cloud microphysical capabilities. Both schemes are coupled to a cloud generator allowing arbitrary cloud overlap specification. Results show that cloud overlap radiative impacts are significantly stronger in the operational cloud scheme where a change of cloud fraction overlap from maximum-random to generalized results in global changes of SW and LW CRE of ~4 Wm −2 , and zonal changes of up to ~10 Wm −2 . This is an outcome of fewer occurrences (compared to the other scheme) of large layer cloud fractions and fewer multi-layer situations where large numbers of atmospheric layers are simultaneously cloudy, both conditions that make overlap details more important. The impact of the specifics of condensate distribution overlap on CRE is much weaker. Once generalized overlap is adopted, both cloud schemes are only modestly sensitive to the exact values of the overlap parameters. When one of the CRE components is overestimated and the other underestimated, both cannot be driven simoultaneously towards observed values by adjustments to cloud condensate heterogeneity and overlap specifications alone.

Beschreibung: Interpretation of FRESCO cloud retrievals in case of absorbing aerosol events Atmospheric Chemistry and Physics, 12, 9057-9077, 2012 Author(s): P. Wang, O. N. E. Tuinder, L. G. Tilstra, M. de Graaf, and P. Stammes Cloud and aerosol information is needed in trace gas retrievals from satellite measurements. The Fast REtrieval Scheme for Clouds from the Oxygen A band (FRESCO) cloud algorithm employs reflectance spectra of the O 2 A band around 760 nm to derive cloud pressure and effective cloud fraction. In general, clouds contribute more to the O 2 A band reflectance than aerosols. Therefore, the FRESCO algorithm does not correct for aerosol effects in the retrievals and attributes the retrieved cloud information entirely to the presence of clouds, and not to aerosols. For events with high aerosol loading, aerosols may have a dominant effect, especially for almost cloud free scenes. We have analysed FRESCO cloud data and Absorbing Aerosol Index (AAI) data from the Global Ozone Monitoring Experiment (GOME-2) instrument on the Metop-A satellite for events with typical absorbing aerosol types, such as volcanic ash, desert dust and smoke. We find that the FRESCO effective cloud fractions are correlated with the AAI data for these absorbing aerosol events and that the FRESCO cloud pressure contains information on aerosol layer pressure. For cloud free scenes, the derived FRESCO cloud pressure is close to the aerosol layer pressure, especially for optically thick aerosol layers. For cloudy scenes, if the strongly absorbing aerosols are located above the clouds, then the retrieved FRESCO cloud pressure may represent the height of the aerosol layer rather than the height of the clouds. Combining FRESCO and AAI data, an estimate for the aerosol layer pressure can be given.

Beschreibung: On the formation of sulphuric acid – amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation Atmospheric Chemistry and Physics, 12, 9113-9133, 2012 Author(s): P. Paasonen, T. Olenius, O. Kupiainen, T. Kurtén, T. Petäjä, W. Birmili, A. Hamed, M. Hu, L. G. Huey, C. Plass-Duelmer, J. N. Smith, A. Wiedensohler, V. Loukonen, M. J. McGrath, I. K. Ortega, A. Laaksonen, H. Vehkamäki, V.-M. Kerminen, and M. Kulmala Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules ( J A2B2 ) at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H 2 SO 4 ]), dimethylamine ([DMA]) and trimethylamine ([TMA]), temperature and relative humidity (RH). We also tested how the model results change if we assume that the clusters with two sulphuric acid and two amine molecules would act as seeds for heterogeneous nucleation of organic vapours (other than amines) with higher atmospheric concentrations than sulphuric acid. The modelled formation rates J A2B2 were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients K A2B2 connecting the cluster formation rate and sulphuric acid concentrations as J A2B2 = K A2B2 [H 2 SO 4 ] 2 turned out to depend also on amine concentrations, temperature and relative humidity. We compared the modelled coefficients K A2B2 with the corresponding coefficients calculated from the atmospheric observations ( K obs ) from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of J A2B2 as a function of [H 2 SO 4 ], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the traditional semi-empirical formulae based on sulphuric acid concentration only. The formation rates of clusters with two sulphuric acid and two amine molecules with different amine compositions (DMA or TMA or one of both) had different responses to varying meteorological conditions and concentrations of vapours participating in particle formation. The observed inverse proportionality of the coefficient K obs with RH and temperature agreed best with the modelled coefficient K A2B2 related to formation of a cluster with two H 2 SO 4 and one or two TMA molecules, assuming that these clusters can grow in collisions with abundant organic vapour molecules. In case this assumption is valid, our results suggest that the formation rate of clusters with at least two of both sulphuric acid and amine molecules might be the rate-limiting step for atmospheric particle formation. More generally, our analysis elucidates the sensitivity of the atmospheric particle formation rate to meteorological variables and concentrations of vapours participating in particle formation (also other than H 2 SO 4 ).

Beschreibung: Effects of business-as-usual anthropogenic emissions on air quality Atmospheric Chemistry and Physics, 12, 6915-6937, 2012 Author(s): A. Pozzer, P. Zimmermann, U.M. Doering, J. van Aardenne, H. Tost, F. Dentener, G. Janssens-Maenhout, and J. Lelieveld The atmospheric chemistry general circulation model EMAC has been used to estimate the impact of anthropogenic emission changes on global and regional air quality in recent and future years (2005, 2010, 2025 and 2050). The emission scenario assumes that population and economic growth largely determine energy and food consumption and consequent pollution sources with the current technologies ("business as usual"). This scenario is chosen to show the effects of not implementing legislation to prevent additional climate change and growing air pollution, other than what is in place for the base year 2005, representing a pessimistic (but plausible) future. By comparing with recent observations, it is shown that the model reproduces the main features of regional air pollution distributions though with some imprecisions inherent to the coarse horizontal resolution (~100 km) and simplified bottom-up emission input. To identify possible future hot spots of poor air quality, a multi pollutant index (MPI), suited for global model output, has been applied. It appears that East and South Asia and the Middle East represent such hotspots due to very high pollutant concentrations, while a general increase of MPIs is observed in all populated regions in the Northern Hemisphere. In East Asia a range of pollutant gases and fine particulate matter (PM 2.5 ) is projected to reach very high levels from 2005 onward, while in South Asia air pollution, including ozone, will grow rapidly towards the middle of the century. Around the Persian Gulf, where natural PM 2.5 concentrations are already high (desert dust), ozone levels are expected to increase strongly. The population weighted MPI (PW-MPI), which combines demographic and pollutant concentration projections, shows that a rapidly increasing number of people worldwide will experience reduced air quality during the first half of the 21st century. Following this business as usual scenario, it is projected that air quality for the global average citizen in 2050 would be almost comparable to that for the average citizen in East Asia in the year 2005, which underscores the need to pursue emission reductions.

Beschreibung: The formaldehyde budget as seen by a global-scale multi-constraint and multi-species inversion system Atmospheric Chemistry and Physics, 12, 6699-6721, 2012 Author(s): A. Fortems-Cheiney, F. Chevallier, I. Pison, P. Bousquet, M. Saunois, S. Szopa, C. Cressot, T. P. Kurosu, K. Chance, and A. Fried For the first time, carbon monoxide (CO) and formaldehyde (HCHO) satellite retrievals are used together with methane (CH 4 ) and methyl choloroform (CH 3 CCl 3 or MCF) surface measurements in an advanced inversion system. The CO and HCHO are respectively from the MOPITT and OMI instruments. The multi-species and multi-satellite dataset inversion is done for the 2005–2010 period. The robustness of our results is evaluated by comparing our posterior-modeled concentrations with several sets of independent measurements of atmospheric mixing ratios. The inversion leads to significant changes from the prior to the posterior, in terms of magnitude and seasonality of the CO and CH 4 surface fluxes and of the HCHO production by non-methane volatile organic compounds (NMVOC). The latter is significantly decreased, indicating an overestimation of the biogenic NMVOC emissions, such as isoprene, in the GEIA inventory. CO and CH 4 surface emissions are increased by the inversion, from 1037 to 1394 TgCO and from 489 to 529 TgCH 4 on average for the 2005–2010 period. CH 4 emissions present significant interannual variability and a joint CO-CH 4 fluxes analysis reveals that tropical biomass burning probably played a role in the recent increase of atmospheric methane.

Beschreibung: Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA evolution Atmospheric Chemistry and Physics, 12, 6827-6843, 2012 Author(s): R. H. H. Janssen, J. Vilà-Guerau de Arellano, L. N. Ganzeveld, P. Kabat, J. L. Jimenez, D. K. Farmer, C. C. van Heerwaarden, and I. Mammarella We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to satisfactorily reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentrations show that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically investigate the role of the land surface, which governs both the surface energy balance partitioning and terpene emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore, it influences the relationship between organic aerosol and terpene concentrations. Our findings indicate that the diurnal evolution of secondary organic aerosols (SOA) in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

Beschreibung: Can a global model reproduce observed trends in summertime surface ozone levels? Atmospheric Chemistry and Physics, 12, 6983-6998, 2012 Author(s): S. Koumoutsaris and I. Bey Quantifying trends in surface ozone concentrations is critical for assessing pollution control strategies. Here we use observations and results from a global chemical transport model to examine the trends (1991–2005) in daily maximum 8-h average concentrations in summertime surface ozone at rural sites in Europe and the United States (US). We find a decrease in observed ozone concentrations at the high end of the probability distribution at many of the sites in both regions. The model attributes these trends to a decrease in local anthropogenic ozone precursors, although simulated decreasing trends are overestimated in comparison with observed ones. The low end of observed distribution show small upward trends over Europe and the western US and downward trends in Eastern US. The model cannot reproduce these observed trends, especially over Europe and the western US. In particular, simulated changes between the low and high end of the distributions in these two regions are not significant. Sensitivity simulations indicate that emissions from far away source regions do not affect significantly summer ozone trends at both ends of the distribution in both Europe and US. Possible reasons for discrepancies between observed and simulated trends are discussed.

Beschreibung: Optical property retrievals of subvisual cirrus clouds from OSIRIS limb-scatter measurements Atmospheric Measurement Techniques Discussions, 5, 5313-5355, 2012 Author(s): J. T. Wiensz, D. A. Degenstein, N. D. Lloyd, and A. E. Bourassa We present a technique for retrieving the optical properties of subvisual cirrus clouds detected by OSIRIS, a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Optical properties from an in-situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is demonstrated that the retrieved extinction profile models accurately the measured in-cloud radiances from OSIRIS. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.

Beschreibung: Aerosol hygroscopicity at a regional background site (Ispra) in Northern Italy Atmospheric Chemistry and Physics, 12, 5703-5717, 2012 Author(s): M. Adam, J. P. Putaud, S. Martins dos Santos, A. Dell'Acqua, and C. Gruening This study focuses on the aerosol hygroscopic properties as determined from ground-based measurements and Mie theory. Usually, aerosol ground-based measurements are taken in dry conditions in order to have a consistency within networks. The dependence of the various aerosol optical characteristics (e.g. aerosol absorption, scattering, backscattering or extinction coefficients) on relative humidity has therefore to be established in order to determine their values in the atmosphere, where relative humidity can reach high values. We calculated mean monthly diurnal values of the aerosol hygroscopic growth factor at 90% relative humidity GF(90) based on measurements performed at the atmospheric research station in Ispra (Italy) with a Hygroscopicity Tandem Differential Mobility Analyzer over eight months in 2008 and 2009. Particle hygroscopicity increases with particle dry diameter ranging from 35 to 165 nm for all seasons. We observed a clear seasonal variation in GF(90) for particles larger than 75 nm, and a diurnal cycle in spring and winter for all sizes. For 165 nm particles, GF(90) averages 1.32 ± 0.06. The effect of the particle hygroscopic growth on the aerosol optical properties (scattering, extinction, absorption and backscatter coefficients, asymmetry parameter and backscatter faction) was computed using the Mie theory, based on data obtained from a series of instruments running at our station. We found median enhancement factors (defined as ratios between the values of optical variables at 90% and 0% relative humidity) equal to 1.1, 2.1, 1.7, and 1.8, for the aerosol absorption, scattering, backscattering, and extinction coefficients, respectively. All except the absorption enhancement factors show a strong correlation with the hygroscopic growth factor. The enhancement factors observed at our site are among the lowest observed across the world for the aerosol scattering coefficient, and among the highest for the aerosol backscatter fraction.

Beschreibung: Effect of bacterial ice nuclei on the frequency and intensity of lightning activity inferred by the BRAMS model Atmospheric Chemistry and Physics, 12, 5677-5689, 2012 Author(s): F. L. T. Gonçalves, J. A. Martins, R. I. Albrecht, C. A. Morales, M. A. Silva Dias, and C. E. Morris Many studies from the last decades have shown that airborne microorganisms can be intrinsically linked to atmospheric processes. Certain bacteria may constitute the most active ice nuclei found in the atmosphere and might have some influence on the formation of ice crystals in clouds. This study deals with the ice nucleation activity of Pseudomonas syringae inside of thunderstorms through numerical simulations using BRAMS ( Brazilian Regional Atmospheric Model System ). The numerical simulations were developed in order to investigate the effect on the total amount of rainwater as a function of ice nuclei (IN) P. syringae concentrations with different scenarios (classified as S2 to S4 scenarios) corresponding to a maximum of 10 2 to 10 4 IN bacteria per liter of cloud water plus the BRAMS default (classified as S5 scenario). Additionally, two other scenarios were included without any IN (S1) and the sum of RAMS default and S4 scenario (classified as S6). The chosen radiosonde data is for 3 March 2003, typical summertime in São Paulo City which presents a strong convective cell. The objective of the simulations was to analyze the effect of the IN concentrations on the BRAMS modeled cloud properties and precipitation. The simulated electrification of the cloud permitted analysis of the total flashes estimated from precipitable and non-precipitable ice mass fluxes in two different lightning frequencies. Among all scenarios, only S4 and S6 presented a tendency to decrease the total cloud water, and all bacteria scenarios presented a tendency to decrease the total amount of rain (−8%), corroborating other reports in the literature. All bacteria scenarios also present higher precipitable ice concentrations compared to S5 scenario, the RAMS default. The main results present the total flash number per simulation as well. From the results, the total flash numbers, from both lightning frequencies, in S4 and S6 scenarios, are from 3.1 to 3.7 higher than the BRAMS default. Even the lower bacterial concentrations (scenarios S2 and S3) produced 3 time higher number of flashes, compared to S5 scenario. This result is a function of the hydrometeors in each simulation. In conclusion, IN bacteria could affect directly the thunderstorm structure and lightning formation with many other microphysical implications.

Beschreibung: Understanding and forecasting polar stratospheric variability with statistical models Atmospheric Chemistry and Physics, 12, 5691-5701, 2012 Author(s): C. Blume and K. Matthes The variability of the north-polar stratospheric vortex is a prominent aspect of the middle atmosphere. This work investigates a wide class of statistical models with respect to their ability to model geopotential and temperature anomalies, representing variability in the polar stratosphere. Four partly nonstationary, nonlinear models are assessed: linear discriminant analysis (LDA); a cluster method based on finite elements (FEM-VARX); a neural network, namely the multi-layer perceptron (MLP); and support vector regression (SVR). These methods model time series by incorporating all significant external factors simultaneously, including ENSO, QBO, the solar cycle, volcanoes, to then quantify their statistical importance. We show that variability in reanalysis data from 1980 to 2005 is successfully modeled. The period from 2005 to 2011 can be hindcasted to a certain extent, where MLP performs significantly better than the remaining models. However, variability remains that cannot be statistically hindcasted within the current framework, such as the unexpected major warming in January 2009. Finally, the statistical model with the best generalization performance is used to predict a winter 2011/12 with warm and weak vortex conditions. A vortex breakdown is predicted for late January, early February 2012.

Beschreibung: A method for cloud detection and opacity classification based on ground based sky imagery Atmospheric Measurement Techniques Discussions, 5, 4535-4569, 2012 Author(s): M. S. Ghonima, B. Urquhart, C. W. Chow, J. E. Shields, A. Cazorla, and J. Kleissl Digital images of the sky obtained using a total sky imager (TSI) are classified pixel by pixel into clear sky, optically thin and optically thick clouds. A new classification algorithm was developed that compares the pixel red-blue ratio (RBR) to the RBR of a clear sky library (CSL) generated from images captured on clear days. The difference, rather than the ratio, between pixel RBR and CSL RBR resulted in more accurate cloud classification. High correlation between TSI image RBR and aerosol optical depth (AOD) measured by an AERONET photometer was observed and motivated the addition of a haze correction factor (HCF) to the classification model to account for variations in AOD. Thresholds for clear and thick clouds were chosen based on a training image set and validated with set of manually annotated images. Misclassifications of clear and thick clouds into the opposite category were less than 1%. Thin clouds were classified with an accuracy of 60%. Accurate cloud detection and opacity classification techniques will improve the accuracy of short-term solar power forecasting.

Beschreibung: Global stratospheric aerosol extinction profile retrievals from SCIAMACHY limb-scatter observations Atmospheric Measurement Techniques Discussions, 5, 5993-6035, 2012 Author(s): F. Ernst, C. von Savigny, A. Rozanov, V. Rozanov, K.-U. Eichmann, L. A. Brinkhoff, H. Bovensmann, and J. P. Burrows Stratospheric aerosol extinction profiles are retrieved from SCIAMACHY/Envisat limb-scatter observations in the visible spectral range. The retrieval algorithm is based on a colour-index approach using the normalized limb-radiance profiles at 470 nm and 750 nm wavelength. The optimal estimation approach in combination with the radiative transfer model SCIATRAN is employed for the retrievals. This study presents a detailed description of the retrieval algorithm, and a sensitivity analysis investigating the impact of the most important parameters that affect the aerosol extinction profile retrieval accuracy. It is found that the parameter with the largest impact is surface albedo, particularly for SCIAMACHY observations in the Southern Hemisphere where the error in stratospheric aerosol extinction can be up to 50% if the surface albedo is not well known. The effect of errors in the assumed ozone and neutral density profiles on the aerosol profile retrievals is with generally less than 6% relatively small. The aerosol extinction profiles retrieved from SCIAMACHY are compared with co-located SAGE II solar occultation measurements of stratospheric aerosol extinction during the period 2003–2005. The mean aerosol extinction profiles averaged over all co-locations agree to within 20% between 15 and 35 km altitude. However, larger differences are observed at specific latitudes.

Beschreibung: Long-term continuous atmospheric CO 2 measurements at Baring Head, New Zealand Atmospheric Measurement Techniques Discussions, 5, 5889-5912, 2012 Author(s): G. W. Brailsford, B. B. Stephens, A. J. Gomez, K. Riedel, S. E. Mikaloff Fletcher, S. E. Nichol, and M. R. Manning We present a 39-yr record of continuous atmospheric carbon dioxide (CO 2 ) observations made at Baring Head, New Zealand using a succession of infrared analyser instruments. We include descriptions of the in situ instrumentation, calibration procedures, intercomparison efforts, and data-filtering methods. Located on the southern coast of the North Island, Baring Head is exposed to extended periods of strong air flow from the south with minimal terrestrial influence resulting in low CO 2 variability. The site is therefore well suited for sampling air masses that are representative of the Southern Ocean region. Instrumental precision is better than 0.015 ppm (1-σ) on 1-Hz values and comparisons to over 600 co-located flask samples, as well as laboratory based flask and cylinder comparison exercises, suggests that over recent decades compatibility with respect to the Scripps Institute of Oceanography (SIO) and World Meteorological Organisation (WMO) CO 2 scales has been 0.3 ppm or better.

Beschreibung: Solar Backscatter UV (SBUV) total ozone and profile algorithm Atmospheric Measurement Techniques Discussions, 5, 5913-5951, 2012 Author(s): P. K. Bhartia, R. D. McPeters, L. E. Flynn, S. Taylor, N. A. Kramrova, S. Frith, B. Fisher, and M. DeLand We describe the algorithm that has been applied to develop a 41 yr time series of total ozone and ozone profiles from eight solar-backscatter UV (sbuv) instruments launched on NASA and NOAA satellites since April 1970. Although the basic algorithm is similar to the V8 algorithm that was released about a decade ago and has been in use since then at NOAA, the details of the V8 algorithm have never been published. The current version (V8.6) incorporates several changes including the use of new ozone absorption cross-sections and new ozone and cloud height climatologies. A particular emphasis in this paper is on characterizing the sources of errors that are relevant for deriving trends from monthly mean anomalies and for estimating biases between different types of ozone sensors. We show that variations in the local time of the measurement due to drifting NOAA satellite orbits can complicate the analysis of trends in the upper stratosphere. Such variations not only increase instrumental and algorithmic uncertainties but also require correction for true local time variations of ozone in the upper stratosphere and lower mesosphere for trend analysis. We find that the monthly zonal anomalies derived from the SBUV data have high precision, sufficient to track year-to-year changes in ozone over a broad range of altitudes. However, because of poor vertical resolution the data are less well suited to track short-term variability of ozone at lower altitudes.

Beschreibung: High accuracy measurements of dry mole fractions of carbon dioxide and methane in humid air Atmospheric Measurement Techniques Discussions, 5, 5823-5888, 2012 Author(s): C. W. Rella, H. Chen, A. E. Andrews, A. Filges, C. Gerbig, J. Hatakka, A. Karion, N. L. Miles, S. J. Richardson, M. Steinbacher, C. Sweeney, B. Wastine, and C. Zellweger Traditional techniques for measuring the mole fractions of greenhouse gas in the well-mixed atmosphere have required extremely dry sample gas streams (dew point 〈 −25 °C) to achieve the inter-laboratory compatibility goals set forth by the Global Atmospheric Watch program of the World Meteorological Organization (WMO/GAW) for carbon dioxide (±0.1 ppm) and methane (±2 ppb). Drying the sample gas to low levels of water vapor can be expensive, time-consuming, and/or problematic, especially at remote sites where access is difficult. Recent advances in optical measurement techniques, in particular Cavity Ring Down Spectroscopy (CRDS), have led to the development of highly stable and precise greenhouse gas analyzers capable of highly accurate measurements of carbon dioxide, methane, and water vapor. Unlike many older technologies, which can suffer from significant uncorrected interference from water vapor, these instruments permit for the first time accurate and precise greenhouse gas measurements that can meet the WMO/GAW inter-laboratory compatibility goals without drying the sample gas. In this paper, we present laboratory methodology for empirically deriving the water vapor correction factors, and we summarize a series of in-situ validation experiments comparing the measurements in humid gas streams to well-characterized dry-gas measurements. By using the manufacturer-supplied correction factors, the dry-mole fraction measurements have been demonstrated to be well within the GAW compatibility goals up to at least 1% water vapor. By determining the correction factors for individual instruments once at the start of life, this range can be extended to at least 2% over the life of the instrument, and if the correction factors are determined periodically over time, the evidence suggests that this range can be extended above 4%.

Beschreibung: Summer ammonia measurements in a densely populated Mediterranean city Atmospheric Chemistry and Physics, 12, 7557-7575, 2012 Author(s): M. Pandolfi, F. Amato, C. Reche, A. Alastuey, R. P. Otjes, M. J. Blom, and X. Querol Real-time measurements of ambient concentrations of gas-phase ammonia (NH 3 ) were performed in Barcelona (NE Spain) in summer between May and September 2011. Two measurement sites were selected: one in an urban background traffic-influenced area (UB) and the other in the historical city centre (CC). Levels of NH 3 were higher at CC (5.6 ± 2.1 μg m −3 or 7.5 ± 2.8 ppbv) compared with UB (2.2 ± 1.0 μg m −3 or 2.9 ± 1.3 ppbv). This difference is attributed to the contribution from non-traffic sources such as waste containers, sewage systems, humans and open markets more dense in the densely populated historical city centre. Under high temperatures in summer these sources had the potential to increase the ambient levels of NH 3 well above the urban-background-traffic-influenced UB measurement station. Measurements were used to assess major local emissions, sinks and diurnal evolution of NH 3 . The measured levels of NH 3 , especially high in the old city, may contribute to the high mean annual concentrations of secondary sulfate and nitrate measured in Barcelona compared with other cities in Spain affected by high traffic intensity. Ancillary measurements, including PM 10 , PM 2.5 , PM 1 levels (Particulate Matter with aerodynamic diameter smaller than 10 μm, 2.5 μm, and 1 μm), gases and black carbon concentrations and meteorological data, were performed during the measurement campaign. The analysis of specific periods (3 special cases) during the campaign revealed that road traffic was a significant source of NH 3 . However, its effect was more evident at UB compared with CC where it was masked given the high levels of NH 3 from non-traffic sources measured in the old city. The relationship between SO 4 2− daily concentrations and gas-fraction ammonia (NH 3 /(NH 3 + NH 4 + )) revealed that the gas-to-particle phase partitioning (volatilization or ammonium salts formation) also played an important role in the evolution of NH 3 concentration in summer in Barcelona.

Beschreibung: Cirrus crystal fall velocity estimates using the Match method with ground-based lidars: a first case study Atmospheric Measurement Techniques Discussions, 5, 5787-5822, 2012 Author(s): D. Dionisi, P. Kekchut, C. Hoareau, N. Montoux, and F. Congeduti Cirrus ice particle sedimentation velocity ( v r ) is one of the critical variables for the parameterization of cirrus properties in a global climate model (GCM). In this study a methodology to estimate cirrus properties, such as crystal mean fall speed, through successive lidar measurements is evaluated. This "Match" technique has been applied on cirrus cloud observations and then tested with measurements from two ground-based lidars located in the Mediterranean Area. These systems have similar instrumental characteristics, and are operated manually respectively at the Observatory of Haute Provence (OHP, 43.9° N, 5.7° E) in France and at Rome Tor Vergata (RTV, 41.8° N, 12.6° E) in Italy at a distance of approximately 600 km providing systematic measurements since several years. The both sites are along a typical direction of an air path and a test case of an upper tropospheric cirrus, observed over both sites during the night between 13 and 14 of March 2008, has been identified and investigated. The analysis through lidar primarily parameters (cloud shape and vertical location) reveals a case of a thin sub-visible cirrus (SVC) located around the tropopause. The feasibility to estimate crystal fall velocity has been tested and values of 1.4–1.9 cm s −1 , consistent with simple-shaped small crystals, have been retrieved. Despite several uncertainties that affect the single-wavelength lidar measurements, sedimentation could be a partial reason for the cirrus property changes (e.g. geometrical thickness and back-scattering profile distribution) observed from one site to the other. The backward trajectory analysis suggests a type of cirrus formed by large-scale transport processes (adiabatic cooling of moist air masses coming from the subtropical area around Mexico gulf), which is characterized by a long atmospheric lifetime and horizontal extension of several hundreds of km. This study shows that such approach can be improved in using closer locations, ancillary data (e.g. temperature, water vapour, etc.), particle distribution utilizing multi-wavelengths space-borne lidar measurements or balloon size particle and cirrus microphysical-resolved models.

Beschreibung: Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments Atmospheric Measurement Techniques Discussions, 5, 5753-5785, 2012 Author(s): T. Clauss, A. Kiselev, S. Hartmann, S. Augustin, S. Pfeifer, D. Niedermeier, H. Wex, and F. Stratmann We report on the development and test results of the new optical particle counter TOPS-Ice (Thermostabilized Optical Particle Spectrometer for the detection of Ice particles). The instrument uses measurements of the depolarized component of light scattered by single particles into the near-forward direction (42.5° ± 12.7°) to distinguish between spherical and non-spherical particles. This approach allows the differentiation between liquid water droplets (spherical) and ice particles (non-spherical) having similar volume equivalent sizes and therefore can be used to determine the fraction of frozen droplets in a typical immersion freezing experiment. We show that the numerical simulation of the light scattering on non-spherical particles (ellipsoids in random orientation) with account for the actual scattering geometry used in the instrument supports the validity of the approach, even though the cross polarized component of the light scattered by spherical droplets is not vanishing in this scattering angle. For the separation of the ice particle mode from the liquid droplet mode, we use the width of the pulse detected in the depolarization channel instead of the pulse height. Exploiting the intrinsic relationship between pulse height and pulse width for Gaussian pulses allows us to calculate the fraction of frozen droplets even if the liquid droplet mode dominates the particle ensemble. We present test results obtained with TOPS-Ice in the immersion freezing experiments at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator) and demonstrate the excellent agreement with the data obtained in the same experiment with a different optical instrument. Finally, the advantages of using the cross-polarized light measurements for the differentiation of liquid and frozen droplets in the realistic immersion freezing experiments are discussed.

Beschreibung: On the interpretation of an unusual in-situ measured ice crystal scattering phase function Atmospheric Chemistry and Physics, 12, 9355-9364, 2012 Author(s): A. J. Baran, J.-F. Gayet, and V. Shcherbakov In-situ Polar Nephelometer (PN) measurements of unusual ice crystal scattering phase functions, obtained near the cloud-top of a mid-latitude anvil cloud, at a temperature of about −58 °C, were recently reported by Gayet et al. (2012). The ice crystal habits that produced the phase functions consisted of aggregates of ice crystals and aggregates of quasi-spherical ice particles. The diameters of the individual quasi-spherical ice particles were estimated to be between about 15 μm and 20 μm. The measured-averaged scattering phase functions were featureless, at scattering angles less than about 100°, but an ice bow-like feature was noted between the scattering angles of about 120° to 160°. The estimated asymmetry parameter was 0.78 ± 0.04. In this paper, the averaged scattering phase function is interpreted in terms of a weighted habit mixture model. The model that provides the best overall fit to the measured scattering phase function comprises of highly distorted ten-element hexagonal ice aggregates and quasi-spherical ice particles. The smaller quasi-spherical ice crystals are represented by Chebyshev ice particles of order 3, and were assumed to have equivalent spherical diameters of 24 μm. The asymmetry parameter of the best overall model was found to be 0.79. It is argued that the Chebyshev-like ice particles are responsible for the ice bow-like feature and mostly dominate the scattered intensity measured by the PN. The results from this paper have important implications for climate modelling (energy balance of anvils), cloud physics and the remote sensing of cirrus properties.

Beschreibung: On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble \newline transition metals Atmospheric Chemistry and Physics, 12, 9321-9333, 2012 Author(s): J. G. Charrier and C. Anastasio The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM 2.5 samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM 2.5 samples approximately 80% of DTT loss is from transition metals (especially copper and manganese), while quinones account for approximately 20%. We find a similar result for DTT loss measured in a small set of PM 2.5 samples from the San Joaquin Valley of California. Because of the important contribution from metals, we also tested how the DTT assay is affected by EDTA, a chelator that is sometimes used in the assay. EDTA significantly suppresses the response from both metals and quinones; we therefore recommend that EDTA should not be included in the DTT assay.

Beschreibung: The detection of nocturnal N 2 O 5 as HNO 3 by alkali- and aqueous-denuder techniques Atmospheric Measurement Techniques Discussions, 5, 7489-7505, 2012 Author(s): G. J. Phillips, U. Makkonen, G. Schuster, N. Sobanski, H. Hakola, and J. Crowley The almost total anthropogenic control of the nitrogen cycle has led to wide ranging trans-national and national efforts to quantify the effects of reactive nitrogen on the environment. A number of monitoring techniques have been developed for the measurement of nitric acid and subsequent estimation of nitrogen deposition within large networks and for process studies on shorter measurement campaigns. We discuss the likelihood that many of these techniques are sensitive to another important gas-phase component of oxidized nitrogen; dinitrogen pentoxide (N 2 O 5 ). We present measurements using a MARGA wet annular denuder device alongside measurements of N 2 O 5 with a discussion of evidence from the laboratory and the field which suggests that alkali- and aqueous-denuder measurements are sensitive to the sum of HNO 3 + N 2 O 5 . Nocturnal data from these denuder devices should be treated with care before using HNO 3 concentrations derived from these data. This is a systematic error which is highly dependent on ambient conditions and is likely to cause systematic misinterpretation of datasets in periods where N 2 O 5 is significant proportion of NO y . It is also likely that deposition estimates of HNO 3 via data obtained with these methods is compromised to greater or lesser extents depending on the season and environment of the sampling location.

Beschreibung: Measurements of hydrogen cyanide (HCN) and acetylene (C 2 H 2 ) from the Infrared Atmospheric Sounding Interferometer (IASI) Atmospheric Measurement Techniques Discussions, 5, 7567-7586, 2012 Author(s): V. Duflot, D. Hurtmans, L. Clarisse, Y. R'honi, C. Vigouroux, M. De Mazière, E. Mahieu, C. Servais, C. Clerbaux, and P.-F. Coheur Hydrogen cyanide (HCN) and acetylene (C 2 H 2 ) are ubiquitous atmospheric trace gases with medium lifetime, which are frequently used as indicators of combustion sources and as tracers for atmospheric transport and chemistry. Because of their weak infrared absorption, overlapped by the CO 2 Q -branch near 720 cm −1 , nadir sounders have up to now failed to measure these gases routinely. Taking into account CO 2 line mixing we provide for the first time extensive measurements of HCN and C 2 H 2 total columns at Reunion Island (21° S; 55° E) and Jungfraujoch (46° N; 8° E) in 2009–2010 using observations from the Infrared Atmospheric Sounding Interferometer (IASI). These are compared with local ground-based Fourier Transform InfraRed (FTIR) measurements and we demonstrate that the seasonality is well captured, except for HCN at Jungfraujoch. We also examine a nonspecific biomass burning plume over austral Africa and show that the emission ratios with respect to CO agree with previously reported values.

Beschreibung: Climatology of aerosol optical properties in Northern Norway and Svalbard Atmospheric Measurement Techniques Discussions, 5, 7619-7640, 2012 Author(s): Y.-C. Chen, B. Hamre, Ø Frette, and J. J. Stamnes We present comparisons between estimates of the aerosol optical thickness and the Ångström exponent in Northern Norway and Svalbard based on data from AERONET stations at Andenes (69° N, 16° E, 379 m altitude) and Hornsund (77° N, 15° E, 10 m altitude) for the period 2008–2010. The three-year annual mean values for the aerosol optical thickness at 500 nm τ (500) at Andenes and Hornsund were 0.11 and 0.10, respectively. At Hornsund, there was less variation of the monthly mean value of τ (500) than at Andenes. The annual mean values of the Ångström exponent α at Andenes and Hornsund were 1.18 and 1.37, respectively. At Andenes and Hornsund α was found to be larger than 1.0 in 68% and 93% of the observations, respectively, indicating that fine-mode particles were dominating at both sites. Both sites had a similar seasonal variation of the aerosol size distribution although one site is in an Arctic area while the other site is in a sub-arctic area.

Beschreibung: Deliquescence, efflorescence, and phase miscibility of mixed particles of ammonium sulfate and isoprene-derived secondary organic material Atmospheric Chemistry and Physics, 12, 9613-9628, 2012 Author(s): M. L. Smith, A. K. Bertram, and S. T. Martin The hygroscopic phase transitions of ammonium sulfate mixed with isoprene-derived secondary organic material were investigated in aerosol experiments. The organic material was produced by isoprene photo-oxidation at 40% and 60% relative humidity. The low volatility fraction of the photo-oxidation products condensed onto ammonium sulfate particles. The particle-phase organic material had oxygen-to-carbon ratios of 0.67 to 0.74 (±0.2) for mass concentrations of 20 to 30 μg m −3 . The deliquescence, efflorescence, and phase miscibility of the mixed particles were investigated using a dual arm tandem differential mobility analyzer. The isoprene photo-oxidation products induced deviations in behavior relative to pure ammonium sulfate. Compared to an efflorescence relative humidity (ERH) of 30 to 35% for pure ammonium sulfate, efflorescence was eliminated for aqueous particles having organic volume fractions ϵ of 0.6 and greater. Compared to a deliquescence relative humidity (DRH) of 80% for pure ammonium sulfate, the DRH steadily decreased with increasing ϵ , approaching a DRH of 40% for ϵ of 0.9. Parameterizations of the DRH( ϵ ) and ERH( ϵ ) curves were as follows: DRH( ϵ )= ∑ i c i,d ϵ i valid for 0 ≤ ϵ ≤0.86 and ERH( ϵ )= ∑ i c i,e ϵ i valid for 0 ≤ ϵ ≤ 0.55 for the coefficients c 0, d = 80.67, c 0, e = 28.35, c 1, d = −11.45, c 1, e = −13.66, c 2, d = 0, c 2, e = 0, c 3, d = 57.99, c 3, e = -83.80, c 4, d = −106.80, and c 4, e = 0. The molecular description that is thermodynamically implied by these strongly sloped DRH( ϵ ) and ERH( ϵ ) curves is that the organic isoprene photo-oxidation products, the inorganic ammonium sulfate, and water form a miscible liquid phase even at low relative humidity. This phase miscibility is in contrast to the liquid-liquid separation that occurs for some other types of secondary organic material. These differences in liquid-liquid separation are consistent with a prediction recently presented in the literature that the bifurcation between liquid-liquid phase separation versus mixing depends on the oxygen-to-carbon ratio of the organic material. The conclusions are that the influence of secondary organic material on the hygroscopic properties of ammonium sulfate varies with organic composition and that the degree of oxygenation of the organic material, which is a measurable characteristic of complex organic materials, is an important variable influencing the hygroscopic properties of mixed organic-inorganic particles.

Beschreibung: Characterization of wind power resource in the United States Atmospheric Chemistry and Physics, 12, 9687-9702, 2012 Author(s): U. B. Gunturu and C. A. Schlosser Wind resource in the continental and offshore United States has been reconstructed and characterized using metrics that describe, apart from abundance, its availability, persistence and intermittency. The Modern Era Retrospective-Analysis for Research and Applications (MERRA) boundary layer flux data has been used to construct wind profile at 50 m, 80 m, 100 m, 120 m turbine hub heights. The wind power density (WPD) estimates at 50 m are qualitatively similar to those in the US wind atlas developed by the National Renewable Energy Laboratory (NREL), but quantitatively a class less in some regions, but are within the limits of uncertainty. The wind speeds at 80 m were quantitatively and qualitatively close to the NREL wind map. The possible reasons for overestimation by NREL have been discussed. For long tailed distributions like those of the WPD, the mean is an overestimation and median is suggested for summary representation of the wind resource. The impact of raising the wind turbine hub height on metrics of abundance, persistence, variability and intermittency is analyzed. There is a general increase in availability and abundance of wind resource but there is an increase in intermittency in terms of level crossing rate in low resource regions.

Beschreibung: Organics in environmental ices: sources, chemistry, and impacts Atmospheric Chemistry and Physics, 12, 9653-9678, 2012 Author(s): V. F. McNeill, A. M. Grannas, J. P. D. Abbatt, M. Ammann, P. Ariya, T. Bartels-Rausch, F. Domine, D. J. Donaldson, M. I. Guzman, D. Heger, T. F. Kahan, P. Klán, S. Masclin, C. Toubin, and D. Voisin The physical, chemical, and biological processes involving organics in ice in the environment impact a number of atmospheric and biogeochemical cycles. Organic material in snow or ice may be biological in origin, deposited from aerosols or atmospheric gases, or formed chemically in situ. In this manuscript, we review the current state of knowledge regarding the sources, properties, and chemistry of organic materials in environmental ices. Several outstanding questions remain to be resolved and fundamental data gathered before an accurate model of transformations and transport of organic species in the cryosphere will be possible. For example, more information is needed regarding the quantitative impacts of chemical and biological processes, ice morphology, and snow formation on the fate of organic material in cold regions. Interdisciplinary work at the interfaces of chemistry, physics and biology is needed in order to fully characterize the nature and evolution of organics in the cryosphere and predict the effects of climate change on the Earth's carbon cycle.

Beschreibung: Critical evaluation of the MODIS Deep Blue aerosol optical depth product for data assimilation over North Africa Atmospheric Measurement Techniques Discussions, 5, 7815-7865, 2012 Author(s): Y. Shi, J. Zhang, J. S. Reid, E. J. Hyer, and N. C. Hsu A total of eight years of Terra (2000–2007) and Aqua (2002–2009) Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue (DB) collection 5.1 (c5.1) data were examined for their potential usage in aerosol assimilation. Uncertainties in the DB Aerosol Optical Depth (AOD) were identified and studied. Empirical corrections and quality assurance procedures were developed for North Africa and the Arabian Peninsula. After applying quality assurance and quality check procedures, the Root-Mean-Square-Error (RMSE) in the MODIS Terra and Aqua AOD are reduced by 18.1 and 18.2% to 0.16 and 0.17, respectively, with respect to AERONET data. These procedures were also applied to two months of DB collection 6 (c6) AOD data and reductions in RMSE were found, indicating that the algorithms developed for c5.1 data are applicable to c6 data to some extent. A new quality-assured DB level 3 AOD product was developed for future implementations in both aerosol data assimilation and climate related applications.

Beschreibung: Evidence for heavy fuel oil combustion aerosols from chemical analyses at the island of Lampedusa: a possible large role of ships emissions in the Mediterranean Atmospheric Chemistry and Physics, 12, 3479-3492, 2012 Author(s): S. Becagli, D. M. Sferlazzo, G. Pace, A. di Sarra, C. Bommarito, G. Calzolai, C. Ghedini, F. Lucarelli, D. Meloni, F. Monteleone, M. Severi, R. Traversi, and R. Udisti Measurements of aerosol chemical composition made on the island of Lampedusa, south of the Sicily channel, during years 2004–2008, are used to identify the influence of heavy fuel oil (HFO) combustion emissions on aerosol particles in the Central Mediterranean. Aerosol samples influenced by HFO are characterized by elevated Ni and V soluble fraction (about 80% for aerosol from HFO combustion, versus about 40% for crustal particles), high V and Ni to Si ratios, and values of V sol 〉6 ng m −3 . Evidence of HFO combustion influence is found in 17% of the daily samples. Back trajectories analysis on the selected events show that air masses prevalently come from the Sicily channel region, where an intense ship traffic occurs. This behavior suggests that single fixed sources like refineries are not the main responsible for the elevated V and Ni events, which are probably mainly due to ships emissions. V sol , Ni sol , and non-sea salt SO 4 2− (nssSO 4 2− ) show a marked seasonal behaviour, with an evident summer maximum. Such a pattern can be explained by several processes: (i) increased photochemical activity in summer, leading to a faster production of secondary aerosols, mainly nssSO 4 2− , from the oxidation of SO 2 (ii) stronger marine boundary layer (MBL) stability in summer, leading to higher concentration of emitted compounds in the lowest atmospheric layers. A very intense event in spring 2008 was studied in detail, also using size segregated chemical measurements. These data show that elements arising from heavy oil combustion (V, Ni, Al, Fe) are distributed in the sub-micrometric fraction of the aerosol, and the metals are present as free metals, carbonates, oxides hydrates or labile complex with organic ligands, so that they are dissolved in mild condition (HNO 3 , pH1.5). Data suggest a characteristic nssSO 4 2− /V ratio in the range 200–400 for HFO combustion aerosols in summer at Lampedusa. By using the value of 200 a lower limit for the HFO contribution to total sulphates is estimated. HFO combustion emissions account, as a summer average, at least for 1.2 μg m −3 , representing about 30% of the total nssSO 4 2− , 3.9% of PM 10 , 8% of PM 2.5 , and 11% of PM 1 . Within the used dataset, sulphate from HFO combustion emissions reached the peak value of 6.1 μg m −3 on 26 June 2008, when it contributed by 47% to nssSO 4 2− , and by 15% to PM 10 .

Beschreibung: Differences between downscaling with spectral and grid nudging using WRF Atmospheric Chemistry and Physics, 12, 3601-3610, 2012 Author(s): P. Liu, A. P. Tsimpidi, Y. Hu, B. Stone, A. G. Russell, and A. Nenes Dynamical downscaling has been extensively used to study regional climate forced by large-scale global climate models. During the downscaling process, however, the simulation of regional climate models (RCMs) tends to drift away from the driving fields. Developing a solution that addresses this issue, by retaining the large scale features (from the large-scale fields) and the small-scale features (from the RCMs) has led to the development of "nudging" techniques. Here, we examine the performance of two nudging techniques, grid and spectral nudging, in the downscaling of NCEP/NCAR data with the Weather Research and Forecasting (WRF) Model. The simulations are compared against the results with North America Regional Reanalysis (NARR) data set at different scales of interest using the concept of similarity. We show that with the appropriate choice of wave numbers, spectral nudging outperforms grid nudging in the capacity of balancing the performance of simulation at the large and small scales.

Beschreibung: Amine substitution into sulfuric acid – ammonia clusters Atmospheric Chemistry and Physics, 12, 3591-3599, 2012 Author(s): O. Kupiainen, I. K. Ortega, T. Kurtén, and H. Vehkamäki The substitution of ammonia by dimethylamine in sulfuric acid – ammonia – dimethylamine clusters was studied using a collision and evaporation dynamics model. Quantum chemical formation free energies were computed using B3LYP/CBSB7 for geometries and frequencies and RI-CC2/aug-cc-pV(T+d)Z for electronic energies. We first demonstrate the good performance of our method by a comparison with an experimental study investigating base substitution in positively charged clusters, and then continue by simulating base exchange in neutral clusters, which cannot be measured directly. Collisions of a dimethylamine molecule with an ammonia containing positively charged cluster result in the instantaneous evaporation of an ammonia molecule, while the dimethylamine molecule remains in the cluster. According to our simulations, a similar base exchange can take place in neutral clusters, although the overall process is more complicated. Neutral sulfuric acid – ammonia clusters are significantly less stable than their positively charged counterparts, resulting in a competition between cluster evaporation and base exchange.

Beschreibung: Aerosol information content analysis of multi-angle high spectral resolution measurements and its benefit for high accuracy greenhouse gas retrievals Atmospheric Measurement Techniques Discussions, 5, 2857-2885, 2012 Author(s): C. Frankenberg, O. Hasekamp, C. O'Dell, S. Sanghavi, A. Butz, and J. Worden New generations of space-borne spectrometers for the retrieval of atmospheric abundances of greenhouse gases require unprecedented accuracies as atmospheric variability of long-lived gases is very low. These instruments, such as GOSAT and OCO-2, typically use a high spectral resolution oxygen channel (O 2 A-band) in addition to CO 2 and CH 4 channels to discriminate changes in the photon path-length distribution from actual trace gas amount changes. Inaccurate knowledge of the photon path-length distribution, determined by scatterers in the atmosphere, is the prime source of systematic biases in the retrieval. In this paper, we investigate the combined aerosol and greenhouse gas retrieval using multiple satellite viewing angles simultaneously. We find that this method, hitherto only applied in multi-angle imagery such as from MISR, greatly enhances the ability to retrieve aerosol properties by 2–3 degrees of freedom. We find that the improved capability to retrieve aerosol parameters significantly reduces interference errors introduced into retrieved CO 2 and CH 4 total column averages. Instead of focussing solely on improvements in spectral and spatial resolution, signal-to-noise ratios or sampling frequency, multiple angles reduce uncertainty in space based greenhouse gas retrievals more effectively and provide a new potential for dedicated aerosols retrievals.

Beschreibung: Evaluation of continuous water vapor δD and δ 18 O measurements by off-axis integrated cavity output spectroscopy Atmospheric Measurement Techniques Discussions, 5, 2821-2855, 2012 Author(s): N. Kurita, B. D. Newman, L. J. Araguas-Araguas, and P. Aggarwal Recent commercially available laser spectroscopy systems enabled us to continuously and reliably measure the δD and δ 18 O of atmospheric water vapor. The use of this new technology is becoming popular because of its advantages over the conventional approach based on cold trap collection. These advantages include much higher temporal resolution/continuous monitoring and the ability to make direct measurements of both isotopes in the field. Here, we evaluate the accuracy and precision of the laser based water vapor isotope instrument through a comparison of measurements with those found using the conventional cold trap method. A commercially available water vapor isotope analyzer (WVIA) with the vaporization system of a liquid water standard (Water Vapor Isotope Standard Source, WVISS) from Los Gatos Research (LGR) Inc. was used for this study. We found that the WVIA instrument can provide accurate results if: (1) correction is applied for time-dependent isotope drift, (2) normalization to the VSMOW/SLAP scale is implemented, and (3) the water vapor concentration dependence of the isotopic ratio is also corrected. In addition, since the isotopic value of water vapor generated by the WVISS is also dependent on the concentration of water vapor, this effect must be considered to determine the true water vapor concentration effect on the resulting isotope measurement. To test our calibration procedure, continuous water vapor isotope measurements using both a laser instrument and a cold trap system were carried out at the IAEA Isotope Hydrology Laboratory in Vienna from August to December 2011. The calibrated isotopic values measured using the WVIA agree well with those obtained via the cold trap method. The standard deviation of the isotopic difference between both methods is about 1.4‰ for δD and 0.28‰ for δ 18 O. This precision allowed us to obtain reliable values for d -excess. The day-to-day variation of d -excess measured by WVIA also agrees well with that found using the cold trap method. These results demonstrate that a coupled system, using commercially available WVIA and WVISS instruments can provide continuous and accurate isotope data, with results achieved similar to those obtained using the conventional method, but with drastically improved temporal resolution.

Beschreibung: CO at 40–80 km above Kiruna observed by the ground-based microwave radiometer KIMRA and simulated by the Whole Atmosphere Community Climate Model Atmospheric Chemistry and Physics, 12, 3261-3271, 2012 Author(s): C. G. Hoffmann, D. E. Kinnison, R. R. Garcia, M. Palm, J. Notholt, U. Raffalski, and G. Hochschild This study compares CO in the Arctic stratosphere and mesosphere measured by ground-based microwave radiometry with simulations made with the Whole Atmosphere Community Climate Model driven with specified dynamical fields (SD-WACCM4) for the Arctic winters 2008/2009 and 2009/2010. CO is a tracer for polar winter middle atmosphere dynamics, hence the representation of polar dynamics in the model is examined indirectly. Measurements were taken with the KIruna Microwave RAdiometer (KIMRA). The instrument, which is located in Kiruna, Northern Sweden (67.8° N, 20.4° E), provides CO profiles between 40 and 80 km altitude. The present comparison, which is one of the first between SD-WACCM4 and measurements, is performed on the smallest space and time scales currently simulated by the model; the global model is evaluated daily at the particular model grid-point closest to Kiruna. As a guide to what can generally be expected from such a comparison, the same analysis is repeated for observations of CO from the Microwave Limb Sounder (MLS), a microwave radiometer onboard NASA's Aura satellite, which has global coverage. First, time-mean profiles of CO are compared, revealing that the profile shape of KIMRA deviates from SD-WACCM4 and MLS, especially in the upper mesosphere. SD-WACCM4 and MLS are mostly consistent throughout the range of altitude considered; however, SD-WACCM4 shows slightly lower values in the upper mesosphere. Second, the time evolution is compared for the complete time series, as well as for the slowly and rapidly evolving parts alone. Overall, the agreement among the datasets is very good and the model is almost as consistent with the measurements as the measurements are with each other. Mutual correlation coefficients of the slowly varying part of the CO time series are ≥0.9 over a wide altitude range. This demonstrates that the polar winter middle atmosphere dynamics is very well represented in SD-WACCM4 and that the relaxation to analyzed meteorological fields below 50 km constrains the behavior of the simulation sufficiently, even at higher altitudes, such that the simulation above 50 km is close to the measurements. However, above 50 km, the model-measurement correlation for the rapidly varying part of the CO time series is lower (0.3) than the measurement-measurement correlation (0.6). This is attributed to the fact that the gravity wave parametrization in WACCM is based on a generic gravity wave spectrum and cannot be expected to capture the instantaneous behavior of the actual gravity wave field present in the atmosphere.

Beschreibung: A disjunct eddy accumulation system for the measurement of BVOC fluxes: instrument characterizations and field deployment Atmospheric Measurement Techniques Discussions, 5, 2703-2746, 2012 Author(s): G. D. Edwards, D. K. Martins, T. Starn, K. Pratt, and P. B. Shepson Biological volatile organic compounds (BVOCs), such as isoprene and monoterpenes, are emitted in large amounts from forests. Quantification of the flux of BVOCs is critical in the evaluation of the impact of these compounds on the concentrations of atmospheric oxidants and on the production of secondary organic aerosol. A disjunct eddy accumulation (DEA) sampler system was constructed for the measurement of speciated BVOC fluxes. Unlike traditional eddy covariance (EC), the relatively new technique of disjunct sampling differs by taking short, discrete samples that allows for slower sampling frequencies. Disjunct sample airflow is directed into cartridges containing sorbent materials at sampling rates proportional to the magnitude of the vertical wind. Compounds accumulated on the cartridges are then quantified by thermal desorption and gas chromatography. Herein, we describe our initial tests to evaluate the disjunct sampler including the application of using vertical wind measurements to create optimized sampling thresholds. Measurements of BVOC fluxes obtained from DEA during its deployment above a mixed hardwood forest at the University of Michigan Biological Station (Pellston, MI) during the 2009 CABINEX field campaign are reported. Daytime (09:00 a.m. to 05:00 p.m.) isoprene fluxes, when averaged over the footprint of the tower were 1.31 mg m −2 h −1 which is comparable to previous flux measurements at this location. Speciated monoterpene fluxes are some of the first to be reported from this site. Daytime averages were 26.7 μg m −2 h −1 for α-pinene and 10.6 μg m −2 h −1 for β-pinene. These measured concentrations and fluxes were compared to the output of an atmospheric chemistry model, and were found to be consistent with our knowledge of the variables that control BVOCs fluxes at this site.

Beschreibung: Tight coupling of particle size, number and composition in atmospheric cloud droplet activation Atmospheric Chemistry and Physics, 12, 3253-3260, 2012 Author(s): D. O. Topping and G. McFiggans The substantial uncertainty in the indirect effect of aerosol particles on radiative forcing in large part arises from the influences of atmospheric aerosol particles on (i) the brightness of clouds, exerting significant shortwave cooling with no appreciable compensation in the long wave, and on (ii) their ability to precipitate, with implications for cloud cover and lifetime. Predicting the ambient conditions at which aerosol particles may become cloud droplets is largely reliant on an equilibrium relationship derived by Köhler (1936). However, the theoretical basis of the relationship restricts its application to particles solely comprising involatile compounds and water, whereas a substantial fraction of particles in the real atmosphere will contain potentially thousands of semi-volatile organic compounds in addition to containing semi-volatile inorganic components such as ammonium nitrate. We show that equilibration of atmospherically reasonable concentrations of organic compounds with a growing particle as the ambient humidity increases has potentially larger implications on cloud droplet formation than any other equilibrium compositional dependence, owing to inextricable linkage between the aerosol composition, a particles size and concentration under ambient conditions. Whilst previous attempts to account for co-condensation of gases other than water vapour have been restricted to one inorganic condensate, our method demonstrates that accounting for the co-condensation of any number of organic compounds substantially decreases the saturation ratio of water vapour required for droplet activation. This effect is far greater than any other compositional dependence; more so even than the unphysical effect of surface tension reduction in aqueous organic mixtures, ignoring differences in bulk and surface surfactant concentrations.

Beschreibung: Primary and secondary sources of formaldehyde in urban atmospheres: Houston Texas region Atmospheric Chemistry and Physics, 12, 3273-3288, 2012 Author(s): D. D. Parrish, T. B. Ryerson, J. Mellqvist, J. Johansson, A. Fried, D. Richter, J. G. Walega, R. A. Washenfelder, J. A. de Gouw, J. Peischl, K. C. Aikin, S. A. McKeen, G. J. Frost, F. C. Fehsenfeld, and S. C. Herndon We evaluate the rates of secondary production and primary emission of formaldehyde (CH 2 O) from petrochemical industrial facilities and on-road vehicles in the Houston Texas region. This evaluation is based upon ambient measurements collected during field studies in 2000, 2006 and 2009. The predominant CH 2 O source (92 ± 4% of total) is secondary production formed during the atmospheric oxidation of highly reactive volatile organic compounds (HRVOCs) emitted from the petrochemical facilities. Smaller contributions are primary emissions from these facilities (4 ± 2%), and secondary production (~3%) and primary emissions (~1%) from vehicles. The primary emissions from both sectors are well quantified by current emission inventories. Since secondary production dominates, control efforts directed at primary CH 2 O emissions cannot address the large majority of CH 2 O sources in the Houston area, although there may still be a role for such efforts. Ongoing efforts to control alkene emissions from the petrochemical facilities, as well as volatile organic compound emissions from the motor vehicle fleet, will effectively reduce the CH 2 O concentrations in the Houston region. We do not address other emission sectors, such as off-road mobile sources or secondary formation from biogenic hydrocarbons. Previous analyses based on correlations between ambient concentrations of CH 2 O and various marker species have suggested much larger primary emissions of CH 2 O, but those results neglect confounding effects of dilution and loss processes, and do not demonstrate the causes of the observed correlations. Similar problems must be suspected in any source apportionment analysis of secondary species based upon correlations of ambient concentrations of pollutants.

Beschreibung: Carbon monoxide measurements onboard the CARIBIC passenger aircraft using UV resonance fluorescence Atmospheric Measurement Techniques Discussions, 5, 2681-2702, 2012 Author(s): D. Scharffe, F. Slemr, C. A. M. Brenninkmejer, and A. Zahn Goal of the project CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container) is to carry out regular and detailed observations of atmospheric composition (particles and gases) at cruising altitudes of passenger aircraft, i.e., at 9–12 km. Continuous, fast measurement of CO is indispensable for the chemical characterization of encountered air masses, for the detection of plumes of polluted air and for studying troposphere-stratosphere transport. CO is measured by a commercial resonance fluorescence UV instrument modified for the use onboard passenger aircraft. Modifications were necessary to optimize the instrument reliability allowing unattended operation for several days. The instrument has a precision of 1–2 ppbv at an integration time of 1 s. The response time to reach 66.6% signal strength is 2 s. We describe the modifications of the instrument, the experiences made during its operation since December 2004, the quality control of CO measurements onboard CARIBIC, and suggest a regular service routine that guarantees long-term high-quality data.

Beschreibung: Influence of aerosols and thin cirrus clouds on the GOSAT-observed CO 2 : a case study over Tsukuba Atmospheric Chemistry and Physics, 12, 3393-3404, 2012 Author(s): O. Uchino, N. Kikuchi, T. Sakai, I. Morino, Y. Yoshida, T. Nagai, A. Shimizu, T. Shibata, A. Yamazaki, A. Uchiyama, N. Kikuchi, S. Oshchepkov, A. Bril, and T. Yokota Lidar observations of vertical profiles of aerosols and thin cirrus clouds were made at Tsukuba (36.05° N, 140.12° E), Japan, to investigate the influence of aerosols and thin cirrus clouds on the column-averaged dry-air mole fraction of carbon dioxide (XCO 2 ) retrieved from observation data of the Thermal And Near-infrared Sensor for carbon Observation Fourier Transform Spectrometer, measured in the Short-Wavelength InfraRed band (TANSO-FTS SWIR), onboard the Greenhouse gases Observing SATellite (GOSAT). The lidar system measured the backscattering ratio, depolarization ratio, and/or the wavelength exponent of atmospheric particles. The lidar observations and ground-based high-resolution FTS measurements at the Tsukuba Total Carbon Column Observing Network (Tsukuba TCCON) site were recorded simultaneously during passages of GOSAT over Tsukuba. GOSAT SWIR XCO 2 data (Version 01.xx) released in August 2010 were compared with the lidar and Tsukuba TCCON data. High-altitude aerosols and thin cirrus clouds had a large impact on the GOSAT SWIR XCO 2 results. By taking into account the observed aerosol/cirrus vertical profiles and using a more adequate solar irradiance database in the GOSAT SWIR retrieval, the difference between the GOSAT SWIR XCO 2 data and the Tsukuba TCCON data was reduced. The 3-band retrieval approach where the aerosol and cirrus profiles were retrieved gave us the best results and the retrieved XCO 2 data followed the seasonal cycle of ~8 ppm observed at Tsukuba TCCON site.

Beschreibung: Climatic effects of 1950–2050 changes in US anthropogenic aerosols – Part 2: Climate response Atmospheric Chemistry and Physics, 12, 3349-3362, 2012 Author(s): E. M. Leibensperger, L. J. Mickley, D. J. Jacob, W.-T. Chen, J. H. Seinfeld, A. Nenes, P. J. Adams, D. G. Streets, N. Kumar, and D. Rind We investigate the climate response to changing US anthropogenic aerosol sources over the 1950–2050 period by using the NASA GISS general circulation model (GCM) and comparing to observed US temperature trends. Time-dependent aerosol distributions are generated from the GEOS-Chem chemical transport model applied to historical emission inventories and future projections. Radiative forcing from US anthropogenic aerosols peaked in 1970–1990 and has strongly declined since due to air quality regulations. We find that the regional radiative forcing from US anthropogenic aerosols elicits a strong regional climate response, cooling the central and eastern US by 0.5–1.0 °C on average during 1970–1990, with the strongest effects on maximum daytime temperatures in summer and autumn. Aerosol cooling reflects comparable contributions from direct and indirect (cloud-mediated) radiative effects. Absorbing aerosol (mainly black carbon) has negligible warming effect. Aerosol cooling reduces surface evaporation and thus decreases precipitation along the US east coast, but also increases the southerly flow of moisture from the Gulf of Mexico resulting in increased cloud cover and precipitation in the central US. Observations over the eastern US show a lack of warming in 1960–1980 followed by very rapid warming since, which we reproduce in the GCM and attribute to trends in US anthropogenic aerosol sources. Present US aerosol concentrations are sufficiently low that future air quality improvements are projected to cause little further warming in the US (0.1 °C over 2010–2050). We find that most of the warming from aerosol source controls in the US has already been realized over the 1980–2010 period.

Beschreibung: Modelling atmospheric structure, cloud and their response to CCN in the central Arctic: ASCOS case studies Atmospheric Chemistry and Physics, 12, 3419-3435, 2012 Author(s): C. E. Birch, I. M. Brooks, M. Tjernström, M. D. Shupe, T. Mauritsen, J. Sedlar, A. P. Lock, P. Earnshaw, P. O. G. Persson, S. F. Milton, and C. Leck Observations made during late summer in the central Arctic Ocean, as part of the Arctic Summer Cloud Ocean Study (ASCOS), are used to evaluate cloud and vertical temperature structure in the Met Office Unified Model (MetUM). The observation period can be split into 5 regimes; the first two regimes had a large number of frontal systems, which were associated with deep cloud. During the remainder of the campaign a layer of low-level cloud occurred, typical of central Arctic summer conditions, along with two periods of greatly reduced cloud cover. The short-range operational NWP forecasts could not accurately reproduce the observed variations in near-surface temperature. A major source of this error was found to be the temperature-dependant surface albedo parameterisation scheme. The model reproduced the low-level cloud layer, though it was too thin, too shallow, and in a boundary-layer that was too frequently well-mixed. The model was also unable to reproduce the observed periods of reduced cloud cover, which were associated with very low cloud condensation nuclei (CCN) concentrations (

Beschreibung: Implications of satellite swath width on global aerosol optical thickness statistics Atmospheric Measurement Techniques Discussions, 5, 2795-2820, 2012 Author(s): P. R. Colarco, L. A. Remer, R. A. Kahn, R. C. Levy, and E. J. Welton We assess the impact of swath width on the statistics of aerosol optical thickness (AOT) retrieved by satellite, as inferred from observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS). Using collocated AERONET sun photometer observations we develop a correction to the MODIS data to account for calibration and algorithmic view angle dependency in the retrieved AOT. We sub-sample and correct the AOT data from the MODIS Aqua instrument along several candidate swaths of various widths for the years 2003–2011. We find that over ocean the global, annual mean AOT is within ± 0.01 of the full swath AOT for all of our sub-samples. Over land, however, most of our sub-samples are outside of this criterion range in the global, annual mean. Moreover, at smaller spatial and temporal scales we find wide deviation in the sub-sample AOT relative to the full swath over both land and ocean. In all, the sub-sample AOT is within ± 0.01 of the full swath value less than 25% of the time over land, and less than 50% of the time over ocean (less than 35% for all but the widest of our sub-sample swaths). These results suggest that future aerosol satellite missions having only narrow swath views may not sample the true AOT distribution sufficiently to reduce significantly the uncertainty in aerosol direct forcing of climate.

Beschreibung: Molecular characterization of water soluble organic nitrogen in marine rainwater by ultra-high resolution electrospray ionization mass spectrometry Atmospheric Chemistry and Physics, 12, 3557-3571, 2012 Author(s): K. E. Altieri, M. G. Hastings, A. J. Peters, and D. M. Sigman Atmospheric water soluble organic nitrogen (WSON) is a subset of the complex organic matter in aerosols and rainwater, which impacts cloud condensation processes and aerosol chemical and optical properties and may play a significant role in the biogeochemical cycle of N. However, its sources, composition, connections to inorganic N, and variability are largely unknown. Rainwater samples were collected on the island of Bermuda (32.27° N, 64.87° W), which experiences both anthropogenic and marine influenced air masses. Samples were analyzed by ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to chemically characterize the WSON. Elemental compositions of 2281 N containing compounds were determined over the mass range m / z + 50 to 500. The five compound classes with the largest number of elemental formulas identified, in order from the highest number of formulas to the lowest, contained carbon, hydrogen, oxygen, and nitrogen (CHON+), CHON compounds that contained sulfur (CHONS+), CHON compounds that contained phosphorus (CHONP+), CHON compounds that contained both sulfur and phosphorus (CHONSP+), and compounds that contained only carbon, hydrogen, and nitrogen (CHN+). Compared to rainwater collected in the continental USA, average O:C ratios of all N containing compound classes were lower in the marine samples whereas double bond equivalent values were higher, suggesting a reduced role of secondary formation mechanisms. Despite their prevalence in continental rainwater, no organonitrates or nitrooxy-organosulfates were detected, but there was an increased presence of organic S and organic P containing compounds in the marine rainwater. Cluster analysis showed a clear chemical distinction between samples collected during the cold season (October to March) which have anthropogenic air mass origins and samples collected during the warm season (April to September) with remote marine air mass origins. This, in conjunction with patterns identified in van Krevelen diagrams, suggests that the cold season WSON is a mixture of organic matter with both marine and anthropogenic sources while in the warm season the WSON appears to be dominated by marine sources. These findings indicate that, although the concentrations and percent contribution of WSON to total N is fairly consistent across diverse geographic regions, the chemical composition of WSON varies strongly as a function of source region and atmospheric environment.

Beschreibung: Climatic effects of 1950–2050 changes in US anthropogenic aerosols – Part 1: Aerosol trends and radiative forcing Atmospheric Chemistry and Physics, 12, 3333-3348, 2012 Author(s): E. M. Leibensperger, L. J. Mickley, D. J. Jacob, W.-T. Chen, J. H. Seinfeld, A. Nenes, P. J. Adams, D. G. Streets, N. Kumar, and D. Rind We calculate decadal aerosol direct and indirect (warm cloud) radiative forcings from US anthropogenic sources over the 1950–2050 period. Past and future aerosol distributions are constructed using GEOS-Chem and historical emission inventories and future projections from the IPCC A1B scenario. Aerosol simulations are evaluated with observed spatial distributions and 1980–2010 trends of aerosol concentrations and wet deposition in the contiguous US. Direct and indirect radiative forcing is calculated using the GISS general circulation model and monthly mean aerosol distributions from GEOS-Chem. The radiative forcing from US anthropogenic aerosols is strongly localized over the eastern US. We find that its magnitude peaked in 1970–1990, with values over the eastern US (east of 100° W) of −2.0 W m −2 for direct forcing including contributions from sulfate (−2.0 W m −2 ), nitrate (−0.2 W m −2 ), organic carbon (−0.2 W m −2 ), and black carbon (+0.4 W m −2 ). The uncertainties in radiative forcing due to aerosol radiative properties are estimated to be about 50%. The aerosol indirect effect is estimated to be of comparable magnitude to the direct forcing. We find that the magnitude of the forcing declined sharply from 1990 to 2010 (by 0.8 W m −2 direct and 1.0 W m −2 indirect), mainly reflecting decreases in SO 2 emissions, and project that it will continue declining post-2010 but at a much slower rate since US SO 2 emissions have already declined by almost 60% from their peak. This suggests that much of the warming effect of reducing US anthropogenic aerosol sources has already been realized. The small positive radiative forcing from US BC emissions (+0.3 W m −2 over the eastern US in 2010; 5% of the global forcing from anthropogenic BC emissions worldwide) suggests that a US emission control strategy focused on BC would have only limited climate benefit.

Beschreibung: Observed and simulated time evolution of HCl, ClONO 2 , and HF total column abundances Atmospheric Chemistry and Physics, 12, 3527-3556, 2012 Author(s): R. Kohlhepp, R. Ruhnke, M. P. Chipperfield, M. De Mazière, J. Notholt, S. Barthlott, R. L. Batchelor, R. D. Blatherwick, Th. Blumenstock, M. T. Coffey, P. Demoulin, H. Fast, W. Feng, A. Goldman, D. W. T. Griffith, K. Hamann, J. W. Hannigan, F. Hase, N. B. Jones, A. Kagawa, I. Kaiser, Y. Kasai, O. Kirner, W. Kouker, R. Lindenmaier, E. Mahieu, R. L. Mittermeier, B. Monge-Sanz, I. Morino, I. Murata, H. Nakajima, M. Palm, C. Paton-Walsh, U. Raffalski, Th. Reddmann, M. Rettinger, C. P. Rinsland, E. Rozanov, M. Schneider, C. Senten, C. Servais, B.-M. Sinnhuber, D. Smale, K. Strong, R. Sussmann, J. R. Taylor, G. Vanhaelewyn, T. Warneke, C. Whaley, M. Wiehle, and S. W. Wood Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO 2 ), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO 2 , the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO 2 , and HF are calculated from both measurement and model time series data, with a focus on the time range 2000–2009. This period is chosen because from most of the measurement sites taking part in this study, data are available during these years. The precision of the trends is estimated with the bootstrap resampling method. The sensitivity of the trend results with respect to the fitting function, the time of year chosen and time series length is investigated, as well as a bias due to the irregular sampling of the measurements. The measurements and model results investigated here agree qualitatively on a decrease of the chlorine species by around 1% yr −1 . The models simulate an increase of HF of around 1% yr −1 . This also agrees well with most of the measurements, but some of the FTIR series in the Northern Hemisphere show a stabilisation or even a decrease in the last few years. In general, for all three gases, the measured trends vary more strongly with latitude and hemisphere than the modelled trends. Relative to the FTIR measurements, the models tend to underestimate the decreasing chlorine trends and to overestimate the fluorine increase in the Northern Hemisphere. At most sites, the models simulate a stronger decrease of ClONO 2 than of HCl. In the FTIR measurements, this difference between the trends of HCl and ClONO 2 depends strongly on latitude, especially in the Northern Hemisphere.