ALBERT

Description: The sensitivity of global climate to the episodicity of fire aerosol emissions Atmospheric Chemistry and Physics Discussions, 13, 23691-23717, 2013 Author(s): S. K. Clark, D. S. Ward, and N. M. Mahowald One of the major ways in which forest and grass fires have an impact on global climate is through the release of aerosols. Most studies focusing on calculating the radiative forcing and other climate impacts of fire aerosols use monthly mean emissions derived from the Global Fire Emissions Database that captures only the seasonal cycle of fire aerosol emissions. Here we present the results of a sensitivity study that investigates the climate response to the episodicity of the fires, based on the standard approach which releases emissions every day, and contrasts that to the response when fires are represented as intense pulses of emissions that occur only over 1–2 days on a monthly, yearly, or five-yearly basis. Overall we find that in the modified cases with increased levels of episodicity, the all sky direct effect radiative forcing increases, the clear sky direct effect radiative forcing remains relatively constant, and the magnitude of the indirect effect radiative forcing decreases by about 1 W m −2 (from −1.6 to −0.6 W m −2 ). In the long term, we find that an increase in aerosol emission episodicity leads to an asymmetric change in indirect radiative forcing in the Northern Hemisphere compared to the Southern Hemisphere contributes to a slight shift in the annual average position of the intertropical convergence zone (ITCZ). This shift is found to have a mixed effect on the overall performance of the model at predicting precipitation rates in the tropics. Given these results we conclude that future studies that look to assess the present day global climate impacts of fire aerosols should consider the need to accurately represent fire episodicity.

Description: A new data set of soil mineralogy for dust-cycle modeling Atmospheric Chemistry and Physics Discussions, 13, 23943-23993, 2013 Author(s): E. Journet, Y. Balkanski, and S. P. Harrison The mineralogy of airborne dust affects the impact of dust particles on direct and indirect radiative forcing, on atmospheric chemistry and on biogeochemical cycling. It is determined partly by the mineralogy of the dust-source regions and partly by size-dependent fractionation during erosion and transport. Here we present a data set that characterizes the clay and silt sized fractions of global soil units in terms of the abundance of 12 minerals that are important for dust-climate interactions: quartz, feldspars, illite, smectite, kaolinite, chlorite, vermiculite, mica, calcite, gypsum, hematite and goethite. The basic mineralogical information is derived from the literature, and is then expanded following explicit rules, in order to characterize as many soil units as possible. We present three alternative realisations of the mineralogical maps that account for the uncertainties in the mineralogical data. We examine the implications of the new database for calculations of the single scattering albedo of airborne dust and thus for dust radiative forcing.

Description: Growth of sulphuric acid nanoparticles under wet and dry conditions Atmospheric Chemistry and Physics Discussions, 13, 24087-24125, 2013 Author(s): L. Škrabalová, D. Brus, T. Anttila, V. Ždímal, and H. Lihavainen New particle formation, which greatly influences the number concentrations and size distributions of an atmospheric aerosol, is often followed by a rapid growth of freshly formed particles. The initial growth of a newly formed aerosol is the crucial process determining the fraction of nucleated particles growing into cloud condensation nuclei sizes, which have a significant influence on climate. In this study, we report the laboratory observations of the growth of nanoparticles produced by nucleation of H 2 SO 4 and water in a laminar flow tube at temperatures of 283, 293 and 303 K, under dry (a relative humidity of 1%) and wet conditions (relative humidity of 30%) and residence times of 30, 45, 60 and 90 s. The initial H 2 SO 4 concentration spans the range from 2 × 10 8 to 1.4 × 10 10 molecule cm −3 and the calculated wall losses of H 2 SO 4 were assumed to be diffusion limited. The detected particle number concentrations, measured by the Ultrafine Condensation Particle Counter (UCPC) and Differential Mobility Particle Sizer (DMPS), were found to depend strongly on the residence time. Hygroscopic particle growth, presented by growth factors, was found to be in good agreement with the previously reported studies. The experimental growth rates ranged from 20 nm h −1 to 890 nm h −1 at RH 1% and from 7 nm h −1 to 980 nm h −1 at RH 30% and were found to increase significantly with the increasing concentration of H 2 SO 4 . Increases in the nucleation temperature had a slight enhancing effect on the growth rates under dry conditions. The influence of relative humidity on growth was not consistent – at lower H 2 SO 4 concentrations, the growth rates were higher under dry conditions while at H 2 SO 4 concentrations greater than 1×10 9 molecule cm −3 the growth rates were higher under wet conditions. The growth rates show only a weak dependence on the residence time. The experimental observations were compared with predictions made using a numerical model, which investigates the growth of particles with three different extents of neutralization by the ammonia NH 3 : (1) pure H 2 SO 4 – H 2 O particles (2) particles formed by ammonium bisulphate, (NH 4 )HSO 4 (3) particles formed by ammonium sulphate, (NH 4 ) 2 SO 4 . The highest growth rates were found for ammonium sulphate particles. Since the model accounting for the initial H 2 SO 4 concentration predicted the experimental growth rates correctly, our results suggest that the commonly presumed diffusional wall losses of H 2 SO 4 are not so significant. We therefore assume that there are not only losses of H 2 SO 4 on the wall but also a flux of H 2 SO 4 molecules from the wall into the flow tube, the effect being more profound under dry conditions and at higher temperatures of the tube wall. Based on a comparison with the atmospheric observations, our results indicate that sulphuric acid alone can not explain the growth rates of particles formed in the atmosphere.

Description: In this work, we present suitable phase accuracy indicators, which are obtained from the first three obtained eigenvalues of the principal component analysis (PCA) demodulation algorithm. These indicators can be used in the measuring process to determine a blind phase goodness assessment, without the need of using any ground truth phase information. Therefore, it is possible to perform further actions if required, as obtaining more interferograms or repeat the measure. Additionally, we present simulated and experimental results that support our mathematical analysis and conclusions. A complete MATLAB software package reproducing any result and figure shown in this work is provided in ( http://goo.gl/fy5EC ).

Description: We propose the use of graded-index few-mode fibers for mode conversion by long-period gratings (LPG) transiently written by ultrashort laser pulses using the optical Kerr effect. The mode interaction is studied by numerically solving the multi-mode coupled nonlinear Schrödinger equations. We present highly efficient conversion of the LP 01 - into the LP 11 -mode preserving the pulse shape in contrast to previous results in step-index fibers. Furthermore, mode conversion using different wavelengths for inducing and probing the LPG is shown. Due to the flat phase-matching curve of the examined modes in the graded-index fiber, mode conversion can be observed for probe center wavelengths of 1,100 nm up to 1,800 nm with a write beam centered around 1,030 nm. Therefore, a complete separation of the probe from the write beam should be possible as well as the application of optically induced guided-mode conversion for all-optical modulation across a broad wavelength range.

Description: Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N 2 , CO 2 , air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2–4 MPa and 473–823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern–Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique.

Description: A core-mode Fabry–Perot (FP) interferometer is constructed by using a dual-core photonic crystal fiber (DCPCF). The FP cavity is formed by a single piece of DCPCF, which can also serve as a direct sensing probe without any additional components. We theoretically and experimentally studied its temperature responses in the range of 40–480 °C. The temperature sensitivity is 13 pm/°C which matches the theoretical results. Since the temperature sensitivity of the proposed sensor is independent on cavity length, precise control of the length of FP cavity or photonic crystal fiber is not required. The sensor size can be as short as 100–200 μm, and its fabrication only involves splicing and cleaving, which make the sensor production very cost-effective. The proposed FP interferometric sensor based on a DCPCF can find applications in high-temperature measurement especially those that need accurate point measurement with high sensitivity.

Description: Impacts of different plant functional types on ambient ozone predictions in the Seoul Metropolitan Areas (SMA), Korea Atmospheric Chemistry and Physics Discussions, 13, 24925-24973, 2013 Author(s): H.-K. Kim, J.-H. Woo, R. S. Park, C. H. Song, J.-H. Kim, S.-J. Ban, and J.-H. Park Plant functional type (PFT) distributions affect the results of biogenic emission modeling as well as O 3 and PM simulations using chemistry-transport models (CTMs). This paper analyzes the variations of both surface biogenic VOC emissions and O 3 concentrations due to changes in the PFT distributions in the Seoul Metropolitan Areas, Korea. Also, this paper attempts to provide important implications for biogenic emissions modeling studies for CTM simulations. MM5-MEGAN-SMOKE-CMAQ model simulations were implemented over the Seoul Metropolitan Areas in Korea to predict surface O 3 concentrations for the period of 1 May to 31 June 2008. Starting from MEGAN biogenic emissions analysis with three different sources of PFT input data, US EPA CMAQ O 3 simulation results were evaluated by surface O 3 monitoring datasets and further considered on the basis of geospatial and statistical analyses. The three PFT datasets considered were "(1)KORPFT", developed with a region specific vegetation database; (2) CDP, adopted from US NCAR; and (3) MODIS, reclassified from the NASA Terra and Aqua combined land cover products. Comparisons of MEGAN biogenic emission results with the three different PFT data showed that broadleaf trees (BT) are the most significant contributor, followed by needleleaf trees (NT), shrub (SB), and herbaceous plants (HB) to the total biogenic volatile organic compounds (BVOCs). In addition, isoprene from BT and terpene from NT were recognized as significant primary and secondary BVOC species in terms of BVOC emissions distributions and O 3 -forming potentials in the study domain. Multiple regression analyses with the different PFT data (δO 3 vs. δPFTs) suggest that KORPFT can provide reasonable information to the framework of MEGAN biogenic emissions modeling and CTM O 3 predictions. Analyses of the CMAQ performance statistics suggest that deviations of BT areas can significantly affect CMAQ isoprene and O 3 predictions. From further evaluations of the isoprene and O 3 prediction results, we explored the PFT area-loss artifact that occurs due to geographical disparity between the PFT and leaf area index distributions, and can cause increased bias in CMAQ O 3 . Thus, the PFT-loss artifact must be a source of limitation in the MEGAN biogenic emission modeling and the CTM O 3 simulation results. Time changes of CMAQ O 3 distributions with the different PFT scenarios suggest that hourly and local impacts from the different PFT distributions on occasional inter-deviations of O 3 are quite noticeable, reaching up to 10 ppb. Exponentially diverging hourly BVOC emissions and O 3 concentrations with increasing ambient temperature suggest that the use of representative PFT distributions becomes more critical for O 3 air quality modeling (or forecasting) in support of air quality decision-making and human health studies.

Description: Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements Atmospheric Chemistry and Physics Discussions, 13, 24975-25012, 2013 Author(s): Z. Ulanowski, P. H. Kaye, E. Hirst, R. S. Greenaway, R. J. Cotton, E. Hesse, and C. T. Collier The knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional light scattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed phase and cirrus clouds. The patterns are analyzed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light scattering properties and also similar causes. Overall, the in situ data is consistent with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic airmasses than in a continental, polluted one. Overall, the roughness and complexity is expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.

Description: Factors controlling pollutant plume length downwind of major roadways in nocturnal surface inversions Atmospheric Chemistry and Physics Discussions, 13, 25253-25290, 2013 Author(s): W. Choi, A. M. Winer, and S. E. Paulson A curve fit method using a Gaussian dispersion model solution was successfully applied to obtain both dispersion coefficients and a particle number emission factor (PNEF) directly from ultrafine particle (UFP) concentration profiles observed downwind of major roadways in California's South Coast Air Basin (SoCAB). The Briggs' formulation for the vertical dispersion parameter σ z was adopted in this study due to its better performance in describing the observed profiles compared to other formulations examined. The two dispersion coefficients in Briggs' formulation, α and β, ranged from 0.02 to 0.07 and from −0.5 × 10 −3 to 2.8 × 10 −3 , respectively, for the four freeway transects studied and are significantly different for freeways passing over vs. under the street on which measurements of the freeway plume were made. These ranges are wider than literature values for α and β under stable conditions. The dispersion coefficients derived from observations showed strong correlations with both surface meteorology (wind speed/direction, temperature, and air stability) and differences in concentrations between the background and plume peak. The relationships were applied to predict freeway plume transport using a multivariate regression, and produced excellent agreement with observed UFP concentration profiles. The mean PNEF for a mixed vehicle fleet on the four freeways was estimated as 1.2 × 10 14 particles mi −1 vehicle −1 , which is about 15% of the value estimated in 2001 for the I-405 freeway, implying significant reductions in UFP emissions over the past decade in the SoCAB.

Description: Summer Sea Ice Albedo in the Arctic in CMIP5 models Atmospheric Chemistry and Physics Discussions, 13, 25219-25251, 2013 Author(s): T. Koenigk, A. Devasthale, and K.-G. Karlsson Spatial and temporal variations of summer sea ice albedo over the Arctic are analyzed using an ensemble of historical CMIP5 model simulations. The results are compared to the CLARA-SAL product that is based on long-term satellite observations. The summer sea ice albedo varies substantially among CMIP5 models and many models show large biases compared to the CLARA-SAL product. Single summer months show an extreme spread of ice albedo among models; July-values vary between 0.3 and 0.7 for individual models. The CMIP5 ensemble mean, however, agrees relatively well in the Central Arctic but shows too high ice albedo near the ice edges and coasts. In most models, the ice albedo is spatially too uniformly distributed. The summer to summer variations seem to be underestimated in many global models and almost no model is able to fully reproduce the temporal evolution of ice albedo throughout the summer. While the satellite observations indicate the lowest ice albedos during August, the models show minimum values in July and substantially higher values in August. Instead, the June values are often lower in the models than in the satellite observations. This is probably due to too high surface temperatures in June, leading to an early start of the melt season and too cold temperatures in August causing an earlier refreezing in the models. The summer sea ice albedo in the CMIP5 models is strongly governed by surface temperature and snow conditions, particularly during the period of melt onset in early summer and refreezing in late summer. The summer surface net solar radiation of the ice covered Arctic areas is highly related to the ice albedo in the CMIP5 models. However, the impact of the ice albedo on the sea ice conditions in the CMIP5 models is not clearly visible. This indicates the importance of other Arctic and large scale processes for the sea ice conditions.

Description: Intercontinental transport and deposition patterns of atmospheric mercury from anthropogenic emissions Atmospheric Chemistry and Physics Discussions, 13, 25185-25218, 2013 Author(s): L. Chen, H.-H. Wang, J.-F. Liu, W. Zhang, D. Hu, C. Chen, and X.-J. Wang Global policies that regulate anthropogenic mercury emissions to the environment require quantitative and comprehensive source–receptor relationships for mercury emissions, transport and deposition among major continental regions. In this study, we use the GEOS-Chem model to establish source–receptor relationships among eleven major continental regions worldwide. Source–receptor relationships for surface mercury concentrations (SMC) show that some regions (e.g. East Asia, the Indian subcontinent and Europe) should be responsible for their local surface Hg(II) and Hg(P) concentrations because of near-field transport and deposition contributions from their local anthropogenic emissions (up to 64% and 71% for Hg(II) and Hg(P), respectively, over East Asia). We define region of primary influence (RPI) and region of secondary influence (RSI) to establish intercontinental influence patterns. Results indicate that East Asia is SMC RPI for almost all other regions, while Europe, Russia and the Indian subcontinent also make some contributions to SMC over some receptor regions because they are dominant RSI source regions. Source–receptor relationships for mercury deposition show that approximately 16% and 17% of dry and wet deposition, respectively, over North America originate from East Asia, indicating that trans-pacific transport of East Asian emissions is the major foreign source of mercury deposition in North America. Europe, Southeast Asia and the Indian subcontinent are also important mercury deposition sources for some receptor regions because they are dominant RSI. We also quantify seasonal variation on mercury deposition contributions over other regions from East Asia. Results show that mercury deposition (including dry and wet) contributions from East Asia over the Northern Hemisphere receptor regions (e.g. North America, Europe, Russia, Middle East and Middle Asia) vary seasonally, with the maximum values in summer and minimum values in winter. The opposite seasonal pattern occurs on mercury dry deposition contributions over Southeast Asia and the Indian subcontinent.

Description: We present measurements of the absorption and emission cross-sections for Yb:YAG , Yb:LuAG and Yb:CaF 2 as a function of temperature between 80 and 340 K. The cross-sections are determined by the combination of the McCumber relation and the Fuchtbauer–Ladenburg (FL) equation to achieve reliable results in spectral regions of high and low absorption. The experimental setup used for the fluorescence measurements minimizes re-absorption effects due to the measurement from small sample volume, providing nearly undisturbed raw data for the FL approach. The retrieved cross-sections together with the spectral characteristics of the tested materials provide important information for the design of energy efficient, high-power laser amplifiers.

Description: An asymmetric chiral metamaterial (CMM) circular polarizer based on bilayer twisted split-ring resonator structure was proposed and investigated. Both numerical simulations and experiments reveal that when a y -polarized wave is incident on this CMM propagating along backward (− z ) direction, the two linear components of the transmitted wave have nearly equal amplitudes and 90°(−90°) phase difference at the resonant frequencies. This means that the right-hand circular polarization and left-hand circular polarization are realized in transmission at 6.4 and 8.1 GHz, respectively. The surface current distributions are studied to illustrate the transformation behavior for both circular polarizations. Further, the influences of the structural parameters of the circular polarizer to the transformation transmissions spectra have been investigated numerically.

Description: A tunable multiwavelength Brillouin-erbium fiber laser (MW-BEFL) using a twin-core fiber (TCF) coupler is proposed and demonstrated. The TCF coupler is formed by splicing a section of TCF between two single-mode fibers. By simply applying bending curvature on the TCF coupler, the peak net gain is shifted close to the Brillouin pump (BP), which has advantage for suppressing self-lasing cavity modes with low-BP-power injection. In this work, the dependency of the Stokes signals tuning range on the free spectral range (FSR) of TCF coupler is studied. It is also found that the tuning range of MW-BEFL can exceed the FSR of TCF coupler by adopting proper BP power and 980-nm pump power. Up to 40 nm tuning range of MW-BEFL in the absence of self-lasing cavity modes is achieved.

Description: The high-precise star sensor calibration method requires high-accurate turntable, collimator, star point plate or other high-precision devices that are very expensive. We present a simple and available method to calibrate the principal point, focal length, radial distortion, tangential distortion and installation error of star sensor in laboratory, and without having high accurate or expensive devices. The calibration model takes the ordinary camera calibration methods and installation error into account. The installation error is modeled by combination of three typical effects: the installation of pan-tilt-zoom (PTZ) initial status, PTZ and charge-coupled device, which result in six parameters. The proposed procedure consists of a closed-form solution, followed by a nonlinear refining based on maximum likelihood criterion. Our calibration method is validated through simulation and real data that shows the superiority with respect to the traditional methods and has the same level as the state-of-the-art methods. The accuracy of our calibration method is 0.015° in the root of mean square distances between testing points and projected ones.

Description: We report on the development of semiconductor double-chirped mirrors with the group delay dispersion of −3,800 ± 100 fs 2 in the wavelength range between 1,058 ÷ 1,064 nm and reflectivity of 99.1 %. The simplified plane-wave reflection transfer method was used to design the mirror multilayer stack. The mirror contains an epitaxial AlAs/GaAs structure topped with a SiNx antireflective layer.

Description: There is significant need for optical diagnostic techniques to measure instantaneous volumetric vector and scalar distributions in fluid flows and combustion processes. This is especially true for investigations where only limited optical access is available, such as in internal combustion engines, furnaces, flow reactors, etc. While techniques such as tomographic PIV for velocity measurement have emerged and reached a good level of maturity, instantaneous 3D measurements of scalar quantities are not available at the same level. Recently, developments in light field technology have progressed to a degree where implementation into scientific 3D imaging becomes feasible. Others have already demonstrated the utility of light field technology toward imaging high-contrast particles for PIV and for imaging flames when treated as single-surface objects. Here, the applicability and shortcomings of current commercially available light field technology toward volumetric imaging of translucent scalar distributions and flames are investigated. Results are presented from imaging canonical chemiluminescent and laser-induced fluorescent systems. While the current light field technology is able to qualitatively determine the position of surfaces by locating high-contrast features, the correlation-based reconstruction algorithm is unable to fully reconstruct the imaged objects for quantitative diagnostics. Current analysis algorithms are based on high-contrast correlation schemes, and new tools, possibly based on tomographic concepts, will have to be implemented to reconstruct the full 3D structure of translucent objects for quantitative analysis.

Description: Balloon-borne match measurements of mid-latitude cirrus clouds Atmospheric Chemistry and Physics Discussions, 13, 25417-25479, 2013 Author(s): A. Cirisan, B. P. Luo, I. Engel, F. G. Wienhold, U. K. Krieger, U. Weers, G. Romanens, G. Levrat, P. Jeannet, D. Ruffieux, R. Philipona, B. Calpini, P. Spichtinger, and T. Peter Observations of persistent high supersaturations with respect to ice inside cirrus clouds are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. Single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information of the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer "SnowWhite" and a particle backscatter detector "COBALD" (Compact Optical Backscatter Aerosol Detector). Extensive trajectory calculations based on regional weather model COSMO forecasts are performed for flight planning and COSMO analyses are used as basis for comprehensive microphysical box modeling (with grid scale 2 km and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2–15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the small-scale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear sky or cloudy sky conditions, highlighting the importance of a proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30% in-cloud supersaturation measured in a massive, 4-km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or – much more likely – by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrometers under the extreme humidity conditions in the upper troposphere.

Description: An explicit study of aerosol mass conversion and its parameterization in warm rain formation of cumulus clouds Atmospheric Chemistry and Physics Discussions, 13, 25481-25536, 2013 Author(s): J. Sun, J. Fen, and R. K. Ungar The life time of atmospheric aerosols is highly affected by in-cloud scavenging processes. Aerosol mass conversion from aerosols embedded in cloud droplets into aerosols embedded in raindrops is a pivotal pathway for wet removal of aerosols in clouds. The aerosol mass conversion rate in the bulk microphysics parameterizations is always assumed to be linearly related to the precipitation production rate, which includes the cloud water autoconversion rate and the cloud water accretion rate. The ratio of the aerosol mass concentration conversion rate to the cloud aerosol mass concentration has typically been considered to be the same as the ratio of the precipitation production rate to the cloud droplet mass concentration. However, the mass of an aerosol embedded in a cloud droplet is not linearly proportional to the mass of the cloud droplet. A simple linear relationship cannot be drawn between the precipitation production rate and the aerosol mass concentration conversion rate. In this paper, we studied the evolution of aerosol mass concentration conversion rates in a warm rain formation process with a 1.5-dimensional non-hydrostatic convective cloud and aerosol interaction model in the bin microphysics. We found that the ratio of the aerosol mass conversion rate to the cloud aerosol mass concentration can be statistically expressed by the ratio of the precipitation production rate to the cloud droplet mass concentration with an exponential function. We further gave some regression equations to determine aerosol conversions in the warm rain formation under different threshold radii of raindrops and different aerosol size distributions.

Description: We describe laser systems for photoionization, Doppler cooling, and quantum state manipulation of beryllium ions. For photoionization of neutral beryllium, we have developed a continuous-wave 235 nm source obtained by two stages of frequency doubling from a diode laser at 940 nm. The system delivers up to 400 mW at 470 nm and 28 mW at 235 nm. For control of the beryllium ion, three laser wavelengths at 313 nm are produced by sum-frequency generation and second-harmonic generation from four infrared fiber lasers. Up to 7.2 W at 626 nm and 1.9 W at 313 nm are obtained using two pump beams at 1051 and 1551 nm. Intensity drifts of around 0.5 % per hour have been measured over 8 h at a 313 nm power of 1 W. These systems have been used to load beryllium ions into a segmented ion trap.

Description: Global and regional impacts of HONO on the chemical composition of clouds and aerosols Atmospheric Chemistry and Physics Discussions, 13, 23599-23638, 2013 Author(s): Y. F. Elshorban, P. J. Crutzen, B. Steil, A. Pozzer, H. Tost, and J. Lelieveld Nitrous acid (HONO) photolysis can significantly increase HO x (OH+HO 2 ) radical formation, enhancing organic and inorganic oxidation products in polluted regions, especially during winter. It has been reported that chemistry-transport models underestimate sulphate concentrations, mostly during winter. Here we show that HONO can significantly enhance aerosol sulphate (S(VI)), mainly due to the increased formation of H 2 SO 4 . Even though in-cloud aqueous phase oxidation of dissolved SO 2 (S(IV)) is the main source of S(VI), it appears that HONO related enhancement of H 2 O 2 does not significantly affect sulphate because of the predominantly S(IV) limited conditions, except over eastern Asia. Nitrate is also increased via enhanced gaseous HNO 3 formation and N 2 O 5 hydrolysis on aerosol particles. Ammonium nitrate is enhanced in ammonia-rich regions but not under ammonia-limited conditions. Furthermore, particle number concentrations are also higher, accompanied by the transfer from hydrophobic to hydrophilic aerosol modes. This implies a significant impact on the particle lifetime and cloud nucleating properties. The HONO induced enhancements of all species studied are relatively strong in winter though negligible in summer. Simulating realistic HONO levels is found to improve the model-measurement agreement of sulphate aerosols, most apparent over the US. Our results underscore the importance of HONO for the atmospheric oxidizing capacity and the central role of cloud chemical processing in aerosol formation.

Description: Injection heights of springtime biomass burning plumes over the Peninsular Southeast Asia and their impacts on pollutant long-range transport Atmospheric Chemistry and Physics Discussions, 13, 23781-23816, 2013 Author(s): Y. Jian and T.-M. Fu We analyzed observations from the Multi-angle Imaging SpectroRadiometer (MISR) to determine the injection heights of biomass burning smoke plumes over the Peninsular Southeast Asia (PSEA) in spring, with the goal of evaluating the impacts on pollutant long-range transport. We retrieved the heights of twenty-two thousand MISR smoke pixels from 607 smoke plumes over the PSEA during February to April of the years 2001–2010. Forty-five percent of the analyzed smoke pixels were above the local mean boundary layer (1 km) at MISR overpass time (10:30 a.m. local time). We used the GEOS-Chem model to simulate the transport of PSEA biomass burning pollutants in March 2001. We found that the direct injection of 40% of the PSEA biomass burning emissions had little impact on the long-range transport of CO to downwind regions, compared to a control simulation where all biomass burning emissions were released in the boundary layer. This was because CO at the surface over the PSEA was efficiently lifted into the free troposphere by deep convection associated with synoptic-scale weather systems. For pollutants with lifetimes shorter than the synoptic timescale, such as black carbon aerosol (BC), their long-range transport was much more sensitive to the initial plume injection height. The direct injection of NO x from PSEA biomass burning into the free troposphere drove increased formation and transport of PAN, which in turn led to significant increases of ozone over downwind southern China and northwestern Pacific. The Pacific subtropical high transported PSEA biomass burning pollutants to the marine boundary layer over the tropical northwestern Pacific. We compared our model results to aircraft measurements over the northwestern Pacific during the TRACE-P campaign (March 2001). The direct injection of 40% of the PSEA biomass burning pollutants in the free troposphere in the model led to a more pronounced BC peak at 3 km over the northwestern Pacific, which was in better agreement with the aircraft observations compared to the control simulation. Our analyses highlighted the point that the injection heights of smoke plumes pose large uncertainty to the interpretation of BC measurements downwind of biomass burning regions.

Description: A novel approach to mass measurements at the 10 −9 level for short-lived nuclides with half-lives well below one second is presented. It is based on the projection of the radial ion motion in a Penning trap onto a position-sensitive detector. Compared with the presently employed time-of-flight ion-cyclotron-resonance technique, the novel approach is 25-times faster and provides a 40-fold gain in resolving power. Moreover, it offers a substantially higher sensitivity since just two ions are sufficient to determine the ion’s cyclotron frequency. Systematic effects specific to the technique that can change the measured cyclotron frequency are considered in detail. It is shown that the main factors that limit the maximal accuracy and resolving power of the technique are collisions of the stored ions with residual gas in the trap, the temporal instability of the trapping voltage, the anharmonicities of the trapping potential and the uncertainty introduced by the conversion of the cyclotron to magnetron motion.

Description: Influence of surface morphology on the immersion mode ice nucleation efficiency of hematite particles Atmospheric Chemistry and Physics Discussions, 13, 23757-23780, 2013 Author(s): N. Hiranuma, N. Hoffmann, A. Kiselev, A. Dreyer, K. Zhang, G. Kulkarni, T. Koop, and O. Möhler In this paper, the effect of the morphological modification of aerosol particles with respect to heterogeneous ice nucleation is comprehensively investigated for laboratory-generated hematite particles as a model substrate for atmospheric dust particles. The surface area-scaled ice nucleation efficiencies of monodisperse cubic hematite particles and milled hematite particles were measured with a series of expansion cooling experiments using the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud simulation chamber. Complementary off-line characterization of physico-chemical properties of both hematite subsets were also carried out with scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, dynamic light scattering (DLS), and an electro-kinetic particle charge detector to further constrain droplet-freezing measurements of hematite particles. Additionally, an empirical parameterization derived from our laboratory measurements was implemented in the single-column version of the Community Atmospheric Model version 5 (CAM5) to investigate the model sensitivity in simulated ice crystal number concentration on different ice nucleation efficiencies. From an experimental perspective, our results show that the immersion mode ice nucleation efficiency of milled hematite particles is almost an order of magnitude higher at −35.2 °C 〈 T 〈 −33.5 °C than that of the cubic hematite particles, indicating a substantial effect of morphological irregularities on immersion mode freezing. Our modeling results similarly show that the increased droplet-freezing rates of milled hematite particles lead to about one order magnitude higher ice crystal number in the upper troposphere than cubic hematite particles. Overall, our results suggest that the surface irregularities and associated active sites lead to greater ice activation through droplet-freezing.

Description: Study of the unknown HONO daytime source at an European suburban site during the MEGAPOLI summer and winter field campaigns Atmospheric Chemistry and Physics Discussions, 13, 23639-23690, 2013 Author(s): V. Michoud, A. Colomb, A. Borbon, K. Miet, M. Beekmann, M. Camredon, B. Aumont, S. Perrier, P. Zapf, G. Siour, W. Ait-Helal, C. Afif, A. Kukui, M. Furger, J. C. Dupont, M. Haeffelin, and J. F. Doussin Nitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NO x , O 3 , photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction), black carbon concentration, total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h −1 and 0.25 ppb h −1 , during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J (NO 2 ) and the product between J (NO 2 ) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring on ground surface and involving water content available at the ground.

Description: Relationship between Amazon biomass burning aerosols and rainfall over La Plata Basin Atmospheric Chemistry and Physics Discussions, 13, 23995-24021, 2013 Author(s): G. Camponogara, M. A. F. Silva Dias, and G. G. Carrió High aerosol loads are discharged into the atmosphere by biomass burning in Amazon and Central Brazil during the dry season. These particles can interact with clouds as cloud condensation nuclei (CCN) changing cloud microphysics and radiative properties and, thereby, affecting the radiative budget of the region. Furthermore, the biomass burning aerosols can be transported by the low level jet (LLJ) to La Plata Basin where many mesoscale convective systems (MCS) are observed during spring and summer. This work proposes to investigate whether the aerosols from biomass burning may affect the MCS in terms of rainfall over La Plata Basin during spring. Since the aerosol effect is very difficult to isolate because convective clouds are very sensitive to small environment disturbances, detailed analyses using different techniques are used. The binplot, 2D histograms and combined empirical orthogonal function (EOF) methods are used to separate certain environment conditions with the possible effects of aerosol loading. Reanalysis 2, TRMM-3B42 and AERONET data are used from 1999 up to 2012 during September-December. The results show that there are two patterns associated to rainfall-aerosol interaction in La Plata Basin: one in which the dynamic conditions are more important than aerosols to generate rain; and a second one where the aerosol particles have a role in rain formation, acting mainly to suppress rainfall over La Plata Basin.

Description: Size-resolved aerosol composition and link to hygroscopicity at a forested site in Colorado Atmospheric Chemistry and Physics Discussions, 13, 23817-23843, 2013 Author(s): E. J. T. Levin, A. J. Prenni, B. Palm, D. Day, P. Campuzano-Jost, P. M. Winkler, S. M. Kreidenweis, P. J. DeMott, J. Jimenez, and J. N. Smith Aerosol hygroscopicity describes the ability of a particle to take up water and form a cloud droplet. Modeling studies have shown sensitivity of precipitation-producing cloud systems to the availability of aerosol particles capable of serving as cloud condensation nuclei (CCN), and hygroscopicity is a key parameter controlling the number of available CCN. Continental aerosol is typically assumed to have a representative hygroscopicity parameter, κ, of 0.3; however, in remote locations this value can be lower due to relatively large mass fractions of organic components. To further our understanding of aerosol properties in remote areas, we measured size-resolved aerosol chemical composition and hygroscopicity in a forested, mountainous site in Colorado during the six-week BEACHON-RoMBAS campaign. This campaign followed a year-long measurement period at this site, and results from the intensive campaign shed light on the previously reported seasonal cycle in aerosol hygroscopicity. New particle formation events were observed routinely at this site and nucleation mode composition measurements indicated that the newly formed particles were predominantly organic. These events likely contribute to the dominance of organic species at smaller sizes, where aerosol organic mass fractions of non-refractory components were between 70–90%. Corresponding aerosol hygroscopicity was observed to range from κ = 0.15–0.22, with hygroscopicity increasing with particle size. Aerosol chemical composition measured by an Aerosol Mass Spectrometer and calculated from hygroscopicity measurements agreed very well during the intensive study with an assumed value of κ org = 0.13 resulting in the best agreement.

Description: Atmospheric parameters in a subtropical cloud regime transition derived by AIRS+MODIS – observed statistical variability compared to ERA-Interim Atmospheric Chemistry and Physics Discussions, 13, 24051-24085, 2013 Author(s): M. M. Schreier, B. H. Kahn, K. Sušelj, J. Karlsson, S. C. Ou, Q. Yue, and S. L. Nasiri Cloud occurrence, microphysical and optical properties and atmospheric profiles within a subtropical cloud regime transition in the northeastern Pacific Ocean are obtained from a synergistic combination of the Atmospheric Infrared Sounder (AIRS) and the MODerate resolution Imaging Spectroradiometer (MODIS). The observed cloud parameters and atmospheric thermodynamic profile retrievals are binned by cloud type and analyzed based on their probability density functions (PDFs). Comparison of the PDFs to data from the European Center for Medium Range Weather Forecasting Re-analysis (ERA-Interim) shows a strong difference in the occurrence of the different cloud types compared to clear sky. An increasing non-Gaussian behavior is observed in cloud optical thickness (τ c ), effective radius ( r e ) and cloud top temperature ( T c ) distributions from Stratocumulus to Trade Cumulus, while decreasing values of lower tropospheric stability are seen. However, variations in the mean, width and shape of the distributions are found. The AIRS potential temperature (θ) and water vapor ( q ) profiles in the presence of varying marine boundary layer (MBL) cloud types show overall similarities to the ERA-Interim in the mean profiles, but differences arise in the higher moments at some altitudes. The differences between the PDFs from AIRS+MODIS and ERA-Interim make it possible to pinpoint systematic errors in both systems and helps to understand joint PDFs of cloud properties and coincident thermodynamic profiles from satellite observations.

Description: The kinetics of signal formation in collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) are discussed, and theoretical equations describing the relation between the concentration of the target molecule and the detected atomic absorption in case of pure and impure samples are derived. The validity of the equation for pure samples is studied experimentally by comparing measured target molecule concentrations to concentrations determined using two other independent techniques. Our study shows that CPFAAS is capable of measuring target molecule concentrations from parts per billion (ppb) to hundreds of parts per million (ppm) in microsecond timescale. Moreover, the possibility to extend the dynamic range to cover eight orders of magnitude with a proper selection of fragmentation light source is discussed. The maximum deviation between the CPFAAS technique and a reference measurement technique is found to be less than 5 %. In this study, potassium chloride vapor and atomic potassium are used as a target molecule and a probed atom, respectively.

Description: The photorefractive (PR) properties of semi-insulating GaAs/AlGaAs multiple quantum wells (MQWs) operating in the Franz–Keldysh geometry are modelled by solving the material equations including the nonlinear transport of hot electrons. This work studies the PR response of MQWs in a two-wave mixing geometry under a moving grating. Calculations were made under the small intensity modulation approximation, and the simulation results are compared with experimental data available in the literature. A reasonable qualitative agreement regarding most experimental characteristics was found. The results can be treated as a test of the correctness of the commonly used band transport model of PR behaviour in MQWs. Analytic solutions for the stationary and transient regimes under negligible diffusion are given. In addition, the conditions for the occurrence of a strong resonance predicted by the model are noted.

Description: Molecular rotational states of nitrogen and oxygen molecules at room temperature and atmospheric pressure are excited by femtosecond double- and multi-pulses with variable temporal pulse distances, and quartz-enhanced photoacoustic spectroscopy is used for their detection. A simple extrapolation of measured double-pulse data is presented, which predicts form and position of Raman-excited spectral features and thus enables us to distinguish between spectral lines caused by Raman-scattering- and collision-induced absorption both appearing when excitation by pulse trains is used.

Description: An improved method that has the potential to improve the retrieval of aerosol optics properties (backscatter/extinction coefficients) from elastic–Raman lidar data is presented. Aerosol backscatter coefficients can be retrieved by choosing the reference height at near-range rather than conventional far-range when the signal-to-noise ratios are low at the far-range or aloft aerosol layers and clouds appear there. Significant retrieval errors in aerosol backscatter coefficients caused by large uncertainties of the aerosol reference value at far-range can be reduced. To avoid the ill-posed retrievals of aerosol extinction from the conventional Raman method, the new method derives the aerosol extinction and lidar ratio with the constrained Fernald inversions by independent aerosol backscatter coefficients from above proposed method. The numerical simulations demonstrated that the proposed method provides good accuracy and resolution of aerosol profile retrievals. And the method is also applied to elastic–Raman lidar measurements at the Hampton University, Hampton, Virginia.

Description: Establishing the contribution of lawn mowing to atmospheric aerosol levels in American suburbs Atmospheric Chemistry and Physics Discussions, 13, 24435-24480, 2013 Author(s): R. M. Harvey, J. Zahardis, and G. A. Petrucci Green leaf volatiles (GLVs) are a class of wound-induced volatile organic compounds emitted by several plant species. Turfgrasses emit a complex profile of GLVs upon mowing, as evidenced by the "freshly cut grass" smell, some of which are readily oxidized in the atmosphere to contribute to secondary organic aerosol (SOA). The contribution of lawn mowing-induced SOA production may be especially impactful at the urban/suburban interface, where urban hubs provide a source of anthropogenic oxidants and SOA while suburban neighborhoods have the potential to emit large quantities of reactive, mow-induced GLVs. This interface provides a unique opportunity to study aerosol formation in a multi-component system and at a regionally relevant scale. Freshly cut grass was collected from a study site in Essex Junction, Vermont and was placed inside a 775 L Teflon experimental chamber. Thermal desorption gas chromatography mass spectrometry (TD-GC/MS) was used to characterize the emitted GLV profile. Ozone was introduced to the experimental chamber and TD-GC/MS was used to monitor the consumption of these GLVs and the subsequent evolution of gas phase products while a scanning mobility particle sizer was used to continuously measure aerosol size distributions and mass loadings as a result of grass clipping ozonolysis. Freshly cut grass found to emit a complex mixture of GLVs, dominated by cis -3-hexenyl acetate and cis -3-hexenol, which were released at an initial rate of 1.8 (±0.5) μg and 0.07 (±0.03) μg per square meter of lawn mowed with each mowing. Chamber studies using pure standards of cis -3-hexenyl acetate (CHA) and cis -3-hexenol (HXL) were found to have aerosol yields of 1.2 (±1.1)% and 3.3 (±3.1)%, respectively. Using these aerosol yields and the emission rate of these CHA and HXL by grass, SOA evolution by ozonolysis of grass clippings was predicted. However, the measured SOA mass produced from the ozonolysis of grass clippings exceeded the predicted amount, by upwards of ~ 150%. The ozonolysis of a mixture of CHA and HXL representative of environmental mixing ratios also failed to accurately model the SOA mass produced by grass clippings. Aerial photographs and geospatial analysis were used to determine the turfgrass coverage in a suburban neighborhood, which was then used along with measured SOA production as a function of grass mowed to determine that lawn mowing has the potential to contribute 47 μg m −2 SOA to the atmosphere per mowing event by ozonolysis, which cannot be modeled solely by the ozonolysis of CHA, HXL or a representative mixture of the two.

Description: Global distributions and trends of atmospheric ammonia (NH 3 ) from IASI satellite observations Atmospheric Chemistry and Physics Discussions, 13, 24301-24342, 2013 Author(s): M. Van Damme, L. Clarisse, C. L. Heald, D. Hurtmans, Y. Ngadi, C. Clerbaux, A. J. Dolman, J. W. Erisman, and P. F. Coheur Ammonia (NH 3 ) emissions in the atmosphere have strongly increased in the past decades, largely because of the intensive livestock production and use of fertilizers. As a short-lived species, NH 3 is highly variable in the atmosphere and its concentration is generally small, except in and close to local source areas. While ground-based measurements are possible, they are challenging and sparse. Advanced infrared sounders in orbit have recently demonstrated their capability to measure NH 3 , offering a new tool to refine global and regional budgets. In this paper we describe an improved retrieval scheme of NH 3 total columns from the measurements of the Infrared Atmospheric Sounding Interferometer (IASI). It exploits the hyperspectral character of this instrument by using an extended spectral range (800–1200 cm −1 ) where NH 3 is optically active. This scheme consists of the calculation of a dimensionless spectral index from the IASI level1C radiances, which is subsequently converted to a total NH 3 column using look-up-tables built from forward radiative transfer model simulations. We show how to retrieve the NH 3 total columns from IASI quasi-globally and twice daily, above both land and sea, without large computational resources and with an improved detection limit. The retrieval also provides error characterization on the retrieved columns. Five years of IASI measurements (1 November 2007 to 31 October 2012) have been processed to acquire the first global and multiple-year dataset of NH 3 total columns, which are evaluated and compared to similar products from other retrieval methods. Spatial distributions from the five years dataset are provided and analyzed at global and regional scales. We show in particular the ability of this method to identify smaller emission sources than those reported previously, as well as transport patterns above sea. The five year time series is further examined in terms of seasonality and inter-annual variability (in particular as a function of fire activity) separately for the Northern and Southern Hemispheres.

Description: Aircraft measurements of polar organic tracer compounds in tropospheric particles (PM 10 ) over Central China Atmospheric Chemistry and Physics Discussions, 13, 24481-24516, 2013 Author(s): P. Q. Fu, K. Kawamura, Y. F. Cheng, S. Hatakeyama, A. Takami, H. Li, and W. Wang Atmospheric aerosol samples were collected by aircraft at low to middle altitudes (0.8–3.5 km a.g.l.) over Central East to West China during summer 2003 and spring 2004. The samples were analyzed for polar organic compounds using a technique of solvent extraction/BSTFA derivatization/gas chromatography-mass spectrometry. Biogenic secondary organic aerosol (SOA) tracers from the oxidation of isoprene were found to be more abundant in summer (3.3–138 ng m −3 , mean 39 ng m −3 ) than in spring (3.2–42 ng m −3 , 15 ng m −3 ), while α/β-pinene and β-caryophyllene SOA tracers showed similar abundance between these two seasons. A strong positive correlation ( R 2 =0.83) between levoglucosan and β-caryophyllinic acid was found in the spring samples versus a weak correlation ( R 2 =0.17) in the summer samples, implying substantial contributions from biomass burning to the β-caryophyllinic acid production in spring. Two organic nitrogen species (oxamic acid and carbamide) were detected in the aircraft aerosol samples and their concentrations were comparable to those of biogenic SOA tracers. Most of the POA and SOA tracers were less abundant at higher altitudes, suggesting they are of ground surface origin, either being directly emitted from anthropogenic/natural sources on the ground surface, or rapidly formed through photooxidation of their precursors emitted from the ground surface and then diluted during uplifting into the troposphere. This study demonstrates that primary biological aerosols, biogenic SOA, and organic nitrogen species are important components of organic aerosols in the troposphere over Central China.

Description: Tunable diode laser absorption spectroscopy based in situ sensors for CO (2.33 μm), CO 2 (2.02 μm), CH 4 (2.29 μm) and H 2 O (1.35 μm) were deployed in a pilot-scale (1 ton/day), high-pressure (up to 18 atm), entrained flow, oxygen-blown, slagging coal gasifier at the University of Utah. Measurements of species mole fraction with 3-s time resolution were taken at the pre- and post-filtration stages of the gasifier synthesis gas (called here syngas) output flow. Although particulate scattering makes pre-filter measurements more difficult, this location avoids the time delay of flow through the filtration devices. With the measured species and known N 2 concentrations, the H 2 content was obtained via balance. The lower heating value and the Wobbe index of the gas mixture were estimated using the measured gas composition. The sensors demonstrated here show promise for monitoring and control of the gasification process.

Description: Black carbon emissions from in-use ships: a California regional assessment Atmospheric Chemistry and Physics Discussions, 13, 24675-24712, 2013 Author(s): G. M. Buffaloe, D. A. Lack, E. J. Williams, D. Coffman, K. L. Hayden, B. M. Lerner, S-M. Li, I. Nuaaman, P. Massoli, T. B. Onasch, P. K. Quinn, and C. D. Cappa Black carbon (BC) mass emission factors (EF BC ; g-BC (kg-fuel) −1 ) from a variety of ocean going vessels have been determined from measurements of BC and carbon dioxide (CO 2 ) concentrations in ship plumes intercepted by the R/V Atlantis during the 2010 California Nexus (CalNex) campaign. The ships encountered were all operating within 24 nautical miles of the California coast and were utilizing relatively low sulphur fuels. Black carbon concentrations within the plumes, from which EF BC values are determined, were measured using four independent instruments: a photoacoustic spectrometer and a particle soot absorption photometer, which measure light absorption, and a single particle soot photometer and soot particle aerosol mass spectrometer, which measure the mass concentration of refractory BC directly. The measured EF BC have been divided into vessel type categories and engine type categories, from which averages have been determined. The geometric average EF BC , determined from over 71 vessels and 135 plumes encountered, was 0.31 g-BC (kg-fuel) −1 . The most frequent engine type encountered was the slow speed diesel (SSD), and the most frequent SSD vessel type was the cargo ship sub-category. Average and median EF BC values from the SSD category are compared with previous observations from the Texas Air Quality Study (TexAQS) in 2006, during which the ships encountered were predominately operating on high sulphur fuels. There is a statistically significant difference between the EF BC values from CalNex and TexAQS for SSD vessels and for the cargo and tanker ship types within this engine category. The CalNex EF BC values are lower than those from TexAQS, suggesting that operation on lower sulphur fuels is associated with smaller EF BC values.

Description: A case study into the measurement of ship emissions from plume intercepts of the NOAA Ship Miller Freeman Atmospheric Chemistry and Physics Discussions, 13, 24635-24674, 2013 Author(s): C. D. Cappa, E. J. Williams, D. A. Lack, G. M. Buffaloe, D. Coffman, K. L. Hayden, S. C. Herndon, B. M. Lerner, S-M. Li, P. Massoli, R. McLaren, I. Nuaaman, T. B. Onasch, and P. K. Quinn Emissions factors (EFs) for gas and sub-micron particle-phase species were measured in intercepted plumes as a function of vessel speed from an underway research vessel, the NOAA Ship Miller Freeman , operating a medium-speed diesel engine on low-sulfur marine gas oil. For many of the particle-phase species, EFs were determined using multiple measurement methodologies, allowing for an assessment of how well EFs from different techniques agree. The total sub-micron PM (PM 1 ) was dominated by particulate black carbon (BC) and particulate organic matter (POM), with an average POM / BC ratio of 1.3. Consideration of the POM / BC ratios observed here with literature studies suggests that laboratory and in-stack measurement methods may over-estimate primary POM EFs relative to those observed in emitted plumes. Comparison of four different methods for black carbon measurement indicates that careful attention must be paid to instrument limitations and biases when assessing EF BC . Particulate sulfate (SO 4 2− ) EFs were extremely small and the particles emitted by Miller Freeman were inefficient as cloud condensation nuclei (CCN), even at high super saturations, consistent with the use of very low sulfur fuel and the overall small emitted particle sizes. All measurement methodologies consistently demonstrate that the measured EFs (fuel mass basis) for PM 1 mass, BC and POM decreased as the ship slowed. Particle number EFs were approximately constant across the speed change, with a shift towards smaller particles being emitted at slower speeds. Emissions factors for gas-phase CO and formaldehyde (HCHO) both increased as the vessel slowed, while EFs for NO x decreased and SO 2 EFs were approximately constant.

Description: Heterogeneous reaction of N 2 O 5 with illite and Arizona Test Dust particles Atmospheric Chemistry and Physics Discussions, 13, 24855-24884, 2013 Author(s): M. J. Tang, G. Schuster, and J. N. Crowley The heterogeneous reaction of N 2 O 5 with airborne illite and Arizona Test Dust particles was investigated at room temperature and at different relative humidities using an atmospheric pressure aerosol flow tube. N 2 O 5 at concentrations in the range 8 to 24×10 12 molecule cm −3 was monitored using thermal-dissociation cavity ring-down spectroscopy at 662 nm. At zero relative humidity a large uptake coefficient of N 2 O 5 to illite was obtained, γ(N 2 O 5 ) = 0.09, which decreased to 0.04 as relative humidity was increased to 67%. In contrast, the uptake coefficient derived for ATD is much lower (~ 0.006) and, within experimental uncertainty, independent of relative humidity (0–67%). Potential explanations are given for the significant differences between the uptake behaviour for ATD and illite and the results are compared with uptake coefficients for N 2 O 5 on other mineral surfaces.

Description: A case study of sea breeze blocking regulated by sea surface temperature along the English south coast Atmospheric Chemistry and Physics Discussions, 13, 24785-24807, 2013 Author(s): J. K. Sweeney, J. M. Chagnon, and S. L. Gray The sensitivity of sea breeze structure to sea surface temperature (SST) and coastal orography is investigated in convection-permitting Met Office Unified Model simulations of a case study along the south coast of England. Changes in SST of 1 K are shown to significantly modify the structure of the sea breeze. On the day of the case study the sea breeze was partially blocked by coastal orography, particularly within Lyme Bay. The extent to which the flow is blocked depends strongly on the static stability of the marine boundary layer. In experiments with colder SST, the marine boundary layer is more stable, and the degree of blocking is more pronounced. The implications of prescribing fixed SST from climatology in numerical weather prediction model forecasts of the sea breeze are discussed.

Description: Using a WRF simulation to examine regions where convection impacts the Asian summer monsoon anticyclone Atmospheric Chemistry and Physics Discussions, 13, 24809-24853, 2013 Author(s): N. K. Heath and H. E. Fuelberg The Asian summer monsoon is a prominent feature of the global circulation that is associated with an upper-level anticyclone (ULAC) that stands out vividly in satellite observations of trace gases. The ULAC also is an important region of troposphere-to-stratosphere transport. We ran the Weather Research and Forecasting (WRF) model at convective-permitting scales (4 km grid spacing) between 10–20 August 2012 to understand the role of convection in transporting boundary layer air into the upper-level anticyclone. Such high-resolution modeling of the Asian ULAC previously has not been documented in the literature. Comparison of our WRF simulation with reanalysis and satellite observations showed that WRF simulated the atmosphere sufficiently well to be used to study convective transport into the ULAC. A back-trajectory analysis based on hourly WRF output showed that 〉 90% of convectively influenced parcels reaching the ULAC came from the Tibetan Plateau (TP) and the southern slope (SS) of the Himalayas. A distinct diurnal cycle is seen in the convective trajectories, with their greatest impact occurring between 1600–2300 local solar time. This finding highlights the role of "everyday" diurnal convection in transporting boundary layer air into the ULAC. WRF output at 15 min intervals was produced for 16 August to examine the convection in greater detail. This high-temporal output revealed that the weakest convection in the study area occurred over the TP. However, because the TP is at 3000–5000 m a.m.s.l., its convection does not have to be as strong to reach the ULAC as in lower altitude regions. In addition, because the TP's elevated heat source is a major cause of the ULAC, we propose that convection over the TP and the neighboring SS is ideally situated geographically to impact the ULAC. The vertical mass flux of water vapor into the ULAC also was calculated. Results show that the TP and SS regions dominate other Asian regions in transporting moisture vertically into the ULAC. Because convection reaching the ULAC is more widespread over the TP than nearby, we propose that the abundant convection partially explains the TP's dominant water vapor fluxes. In addition, greater outgoing longwave radiation reaches the upper levels of the TP due to its elevated terrain. This creates a warmer ambient upper level environment, allowing parcels with greater saturation mixing ratios to enter the ULAC. Lakes in the Tibetan Plateau are shown to provide favorable conditions for deep convection during the night.

Description: Modulation instability can be used to convert a continuous light wave into a train of pulses on a constant background. It is a longstanding discussion whether these pulses can be converted into solitons. We clarify the situation by using a more general mathematical context, invoking the Akhmediev breather, Peregrine soliton and Kuznetsov-Ma soliton solutions of the wave equation, and suggest the use of a Mach–Zehnder interferometer to remove the background. Expressions for the pulse widths and peak powers thus obtained are presented, and their soliton content is determined. It turns out that more than 95 % of each pulse’s energy can be converted to a soliton.

Description: We propose an optodynamical model of interaction of pulsed laser radiation with aggregates of spherical metallic nanoparticles embedded into host media. The model takes into account polydispersity of particles, pair interactions between the particles, dissipation of absorbed energy, heating and melting of the metallic core of particles and of their polymer adsorption layers, and heat exchange between electron and ion components of the particle material as well as heat exchange with the interparticle medium. Temperature dependence of the electron relaxation constant of the particle material and the effect of this dependence on interaction of nanoparticles with laser radiation are first taken into consideration. We study in detail light-induced processes in the simplest resonant domains of multiparticle aggregates consisting of two particles of an arbitrary size in aqueous medium. Optical interparticle forces are realized due to the light-induced dipole interaction. The dipole moment of each particle is calculated by the coupled dipole method (with correction for the effect of higher multipoles). We determined the role of various interrelated factors leading to photomodification of resonant domains and found an essential difference in the photomodification mechanisms between polydisperse and monodisperse nanostructures.

Description: Ferroelectric domains are engineered in lithium niobate crystals by scanning strongly absorbed UV laser light across the crystal surface. Focused UV laser light can not only write, but also erase previously written domains on the non-polar faces of lithium niobate, which allows tailoring of domain patterns. Such domain pattern was generated and afterward investigated by piezoresponse force microscopy and hydrofluoric acid etching. It was found that domains with dimensions down to 2 μm can be engineered, which was ∼30 % of the focus beam diameter (7 μm) used for writing the domains. Additionally, it was found that an unique domain depth profile can be formed, which is inclined to the crystallographic axes and can be described as ‘half-crescent-shaped’.

Description: An assessment of the performance of the Monitor for AeRosols and GAses in ambient air (MARGA): a semi-continuous method for soluble compounds Atmospheric Chemistry and Physics Discussions, 13, 25067-25124, 2013 Author(s): I. C. Rumsey, K. A. Cowen, J. T. Walker, T. J. Kelly, E. A. Hanft, K. Mishoe, C. Rogers, R. Proost, G. M. Beachley, G. Lear, T. Frelink, and R. P. Otjes Ambient air monitoring as part of the US Environmental Protection Agency's (US EPA's) Clean Air Status and Trends Network (CASTNet) currently uses filter packs to measure weekly integrated concentrations. The US EPA is interested in supplementing CASTNet with semi-continuous monitoring systems at select sites to characterize atmospheric chemistry and deposition of nitrogen and sulfur compounds at higher time resolution than the filter pack. The Monitor for AeRosols and GAses in ambient air (MARGA) measures water-soluble gases and aerosols at hourly temporal resolution. The performance of the MARGA was assessed under the US EPA Environmental Technology Verification (ETV) program. The assessment was conducted in Research Triangle Park, North Carolina from 8 September–8 October 2010 and focused on gaseous SO 2 , HNO 3 and NH 3 and aerosol SO 4 − , NO 3 − and NH 4 + . Precision of the MARGA was evaluated by calculating the median absolute relative percent difference (MARPD) between paired hourly results from duplicate MARGA units (MUs), with a performance goal of

Description: Sensitivity of simulated climate to latitudinal distribution of solar insolation reduction in SRM geoengineering methods Atmospheric Chemistry and Physics Discussions, 13, 25387-25415, 2013 Author(s): A. Modak and G. Bala Solar radiation management (SRM) geoengineering has been proposed as a potential option to counteract climate change. We perform a set of idealized geoengineering simulations to understand the global hydrological implications of varying the latitudinal distribution of solar insolation reduction in SRM methods. We find that for a fixed total mass of sulfate aerosols (12.6 Mt of SO 4 ), relative to a uniform distribution which mitigates changes in global mean temperature, global mean radiative forcing is larger when aerosol concentration is maximum at the poles leading to a warmer global mean climate and consequently an intensified hydrological cycle. Opposite changes are simulated when aerosol concentration is maximized in the tropics. We obtain a range of 1 K in global mean temperature and 3% in precipitation changes by varying the distribution pattern: this range is about 50% of the climate change from a doubling of CO 2 . Hence, our study demonstrates that a range of global mean climate states, determined by the global mean radiative forcing, are possible for a fixed total amount of aerosols but with differing latitudinal distribution, highlighting the need for a careful evaluation of SRM proposals.

Description: Source apportionment of PM 10 in a North-Western Europe regional urban background site (Lens, France) using Positive Matrix Factorization and including primary biogenic emissions Atmospheric Chemistry and Physics Discussions, 13, 25325-25385, 2013 Author(s): A. Waked, O. Favez, L. Y. Alleman, C. Piot, J.-E. Petit, T. Delaunay, E. Verlinden, B. Golly, J.-L. Besombes, J.-L. Jaffrezo, and E. Leoz-Garziandia In this work, the source of ambient particulate matter (PM 10 ) collected over a one year period at an urban background site in Lens (France) were determined and investigated using a~Positive Matrix Factorization receptor model (US EPA PMF v3.0). In addition, a Potential Source Contribution Function (PSCF) was performed by means of the Hysplit v4.9 model to assess prevailing geographical origins of the identified sources. A selective iteration process was followed for the qualification of the more robust and meaningful PMF solution. Components measured and used in the PMF include inorganic and organic species: soluble ionic species, trace elements, elemental carbon (EC), sugars alcohols, sugar anhydride, and organic carbon (OC). The mean PM 10 concentration measured from March 2011 to March 2012 was about 21 μg m −3 with typically OM, nitrate and sulfate contributing to most of the mass and accounting respectively for 5.8, 4.5 and 2.3 μg m −3 on a yearly basis. Accordingly, PMF outputs showed that the main emission sources were (in a decreasing order of contribution): secondary inorganic aerosols (28% of the total PM 10 mass), aged marine emissions (19%), with probably predominant contribution of shipping activities, biomass burning (13%), mineral dust (13%), primary biogenic emissions (9%), fresh sea salts (8%), primary traffic emissions (6%) and heavy oil combustion (4%). Significant temporal variations were observed for most of the identified sources. In particular, biomass burning emissions were negligible in summer but responsible for about 25% of total PM 10 and 50% of total OC at wintertime. Conversely, primary biogenic emissions were found to be negligible in winter but to represent about 20% of total PM 10 and 40% of total OC in summer. The latter result calls for more investigations of primary biogenic aerosols using source apportionment studies, which quite usually disregards this type of sources. This study furthermore underlines the major influence of secondary processes during daily threshold exceedances. Finally, apparent discrepancies that could be generally observed between filter-based studies (such as the present one) and Aerosol Mass Spectrometer-based PMF analyses (organic fractions) are also discussed here.

Description: Wind extraction potential from 4D-Var assimilation of O 3 , N 2 O, and H 2 O using a global shallow water model Atmospheric Chemistry and Physics Discussions, 13, 25291-25323, 2013 Author(s): D. R. Allen, K. W. Hoppel, and D. D. Kuhl The wind extraction due to assimilation of trace gas (tracer) data is examined using a 4D-Var data assimilation system based on the shallow water equations coupled to the tracer continuity equation. The procedure is outlined as follows. First, a Nature Run is created, simulating middle stratospheric winter conditions. Second, ozone (O 3 ), nitrous oxide (N 2 O), and water vapor (H 2 O) (treated in this study as passive tracers) are initialized using Microwave Limb Sounder (MLS) mixing ratios at 850 K potential temperature and advected by the Nature Run winds. Third, the initial dynamical conditions are perturbed by using a 6 h offset. Fourth, observations based on the simulated tracer data are then assimilated with a 4D-Var system in which the tracer and winds are coupled via the adjoint of the tracer continuity equation. Finally, the wind extraction potential (WEP) is calculated as the reduction of the Root Mean Square (RMS) vector wind error due to tracer assimilation relative to the total possible reduction from the initial perturbed conditions. For a single 6 h assimilation cycle of "perfect" tracer (unbiased and no imposed random errors), WEP values are 70% for O 3 , 49% for N 2 O and 16% for H 2 O. O 3 and N 2 O provide more wind information than H 2 O due to stronger background gradients relative to the tracer precisions. 10 day multi-cycle simulations with "perfect" tracer result in WEP of 98% for O 3 , 97% for N 2 O, and 90% for H 2 O. There is therefore sufficient information in these fields to nearly completely specify the dynamics, even without assimilation of dynamical information. For assimilation of tracer observations with realistic random noise (based on MLS precision at 10 hPa), the WEP after 10 days decreases to 57% for O 3 , 42% for N 2 O, and 28% for H 2 O. The root-mean-square (RMS) wind errors level out at ~ 1–2 m s −1 for these runs, suggesting a limit to which realistic tracers could constrain the winds, given complete global coverage. With higher observation noise levels, the WEP values decrease further, with negative WEP occurring in cases of very large errors for H 2 O, indicating that assimilation of very noisy observations may worsen the wind fields.

Description: An eigenvalue method is proposed to study the threshold behaviors of plasmonic nano-lasers. The medium gain and dispersion are taken into consideration based on semi-classical laser dynamics, and therefore the lasing threshold, mode pattern, and lasing frequency can be theoretically predicted. The lasing properties of dielectric, plasmonic core, and plasmonic shell nano-lasers are investigated in details. It is found that the lasing thresholds of nano-lasers can be reduced by two orders of magnitude when introducing localized surface plasmon modes.

Description: The simulations of sulfuric acid concentration and new particle formation in an urban atmosphere in China Atmospheric Chemistry and Physics Discussions, 13, 14977-15005, 2013 Author(s): Z. B. Wang, M. Hu, D. Mogensen, D. L. Yue, J. Zheng, R. Y. Zhang, Y. Liu, B. Yuan, X. Li, M. Shao, L. Zhou, Z. J. Wu, A. Wiedensohler, and M. Boy Simulations of sulfuric acid concentration and new particle formation are performed by using the zero-dimensional version of the model MALTE (Model to predict new Aerosol formation in the Lower TropospherE) and measurements from the Campaign of Air Quality Research in Beijing and Surrounding areas (CAREBeijing) in 2008. Chemical reactions from the Master Chemical Mechanism Version 3.2 (MCM v3.2) are used in the model. High correlation (slope = 0.72, R = 0.74) between the modelled and observed sulfuric acid concentrations is found during daytime (06:00–18:00). The aerosol dynamics are simulated by the University of Helsinki Multicomponent Aerosol (UHMA) model including several nucleation mechanisms. The results indicate that the model is able to predict the on- and offset of new particle formation in an urban atmosphere in China. In addition, the number concentrations of newly formed particles in kinetic-type nucleation including homogenous homomolecular ( J=K [H 2 SO 4 ] 2 ) and homogenous heteromolecular nucleation involving organic vapours ( J=K het [H 2 SO 4 ][Org]) are in satisfactory agreement with the observations. However, the specific organic compounds possibly participate in the nucleation process should be investigated in further studies.

Description: We experimentally and theoretically investigate that detection sensitivity in surface plasmon resonance (SPR) biosensors can be significantly enhanced by employing subwavelength dielectric gratings deposited on a gold film. The enhancement originates from an improvement of field-matter interaction: enhanced evanescent field intensity at the binding region and increased surface reaction area. Using a large-area SiO 2 grating array fabricated by nanoimprint lithography, experimental sensor performance measured by parylene film coating shows that the SPR substrates combined with a dielectric grating provide a notable sensitivity improvement compared to a conventional bare gold film. We also demonstrate that plasmon field can be more confined and enhanced at the dielectric gratings with a larger width. The proposed SPR structure could potentially be useful in a variety of plasmonic applications including high-sensitivity biosensors.

Description: Reductions in aircraft particulate emissions due to the use of Fischer–Tropsch fuels Atmospheric Chemistry and Physics Discussions, 13, 15105-15139, 2013 Author(s): A. J. Beyersdorf, M. T. Timko, L. D. Ziemba, D. Bulzan, E. Corporan, S. C. Herndon, R. Howard, R. Miake-Lye, K. L. Thornhill, E. Winstead, C. Wey, Z. Yu, and B. E. Anderson The use of alternative fuels for aviation is likely to increase due to concerns over fuel security, price stability and the sustainability of fuel sources. Concurrent reductions in particulate emissions from these alternative fuels are expected because of changes in fuel composition including reduced sulfur and aromatic content. The NASA Alternative Aviation Fuel Experiment (AAFEX) was conducted in January–February 2009 to investigate the effects of synthetic fuels on gas-phase and particulate emissions. Standard petroleum JP-8 fuel, pure synthetic fuels produced from natural gas and coal feedstocks using the Fischer–Tropsch (FT) process, and 50% blends of both fuels were tested in the CFM-56 engines on a DC-8 aircraft. To examine plume chemistry and particle evolution with time, samples were drawn from inlet probes positioned 1, 30, and 145 m downstream of the aircraft engines. No significant alteration to engine performance was measured when burning the alternative fuels. However, leaks in the aircraft fuel system were detected when operated with the pure FT fuels as a result of the absence of aromatic compounds in the fuel. Dramatic reductions in soot emissions were measured for both the pure FT fuels (reductions of 84% averaged over all powers) and blended fuels (64%) relative to the JP-8 baseline with the largest reductions at idle conditions. The alternative fuels also produced smaller soot (e.g. at 85% power, volume mean diameters were reduced from 78 nm for JP-8 to 51 nm for the FT fuel), which may reduce their ability to act as cloud condensation nuclei (CCN). The reductions in particulate emissions are expected for all alternative fuels with similar reductions in fuel sulfur and aromatic content regardless of the feedstock. As the plume cools downwind of the engine, nucleation-mode aerosols form. For the pure FT fuels, reductions (94% averaged over all powers) in downwind particle number emissions were similar to those measured at the exhaust plane (84%). However, the blended fuels had less of a reduction (reductions of 30–44%) than initially measured (64%). The likely explanation is that the reduced soot emissions in the blended fuel exhaust plume results in promotion of new particle formation microphysics, rather than coating on pre-existing soot particles, which is dominant in the JP-8 exhaust plume. Downwind particle volume emissions were reduced for both the pure (79 and 86% reductions) and blended FT fuels (36 and 46%) due to the large reductions in soot emissions. In addition, the alternative fuels had reduced particulate sulfate production (near-zero for FT fuels) due to decreased fuel sulfur content. To study the formation of volatile aerosols (defined as any aerosol formed as the plume ages) in more detail, tests were performed at varying ambient temperatures (−4 to 20 °C). At idle, particle number and volume emissions were reduced linearly with increasing ambient temperature, with best fit slopes corresponding to −1.2 × 10 6 # (kg fuel) −1 °C −1 for particle number emissions and −9.7 mm 3 (kg fuel) −1 °C −1 for particle volume emissions. The temperature dependence of aerosol formation can have large effects on local air quality surrounding airports in cold regions. Aircraft produced aerosols in these regions will be much larger than levels expected based solely on measurements made directly at the engine exit plane. The majority (90% at idle) of the volatile aerosol mass formed as nucleation-mode aerosols with a smaller fraction as a soot coating. Conversion efficiencies of up to 3.8% were measured for the partitioning of gas-phase precursors (unburned hydrocarbons and SO 2 ) to form volatile aerosols. Highest conversion efficiencies were measured at 45% power.

Description: Undisturbed and disturbed above canopy ponderosa pine emissions: PTR-TOF-MS measurements and MEGAN 2.1 model results Atmospheric Chemistry and Physics Discussions, 13, 15333-15375, 2013 Author(s): L. Kaser, T. Karl, A. Guenther, M. Graus, R. Schnitzhofer, A. Turnipseed, L. Fischer, P. Harley, M. Madronich, D. Gochis, F. N. Keutsch, and A. Hansel We present the first eddy covariance flux measurements of volatile organic compounds (VOCs) using a proton-transfer-reaction time-of-flight mass-spectrometer (PTR-TOF-MS) above a ponderosa pine forest in Colorado, USA. The high mass resolution of the PTR-TOF-MS enabled the identification of chemical sum formulas. During a 30 day measurement period in August and September 2010, 649 different ion mass peaks were detected in the ambient air mass spectrum (including primary ions and mass calibration compounds). Eddy covariance with the vertical wind speed was calculated for all ion mass peaks. On a typical day, 17 ion mass peaks including protonated parent compounds, their fragments and isotopes as well as VOC-H + -water clusters showed a significant flux with daytime average emissions above a reliable flux threshold of 0.1 mg compound m −2 h −1 . These ion mass peaks could be assigned to seven compound classes. The main flux contributions during daytime (10:00–18:00 LT) are attributed to the sum of 2-methyl-3-buten-2-ol (MBO) and isoprene (50%), methanol (12%), the sum of acetic acid and glycolaldehyde (10%) and the sum of monoterpenes (10%). The total MBO + isoprene flux was composed of 10% isoprene and 90% MBO. There was good agreement between the light and temperature dependency of the sum of MBO and isoprene observed for this work and those of earlier studies. The above canopy flux measurements of the sum of MBO and isoprene and the sum of monoterpenes were compared to emissions calculated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN 2.1). The best agreement between MEGAN 2.1 and measurements was reached using emission factors determined from site specific leaf cuvette measurements. While the modelled and measured MBO + isoprene fluxes agree well the emissions of the sum of monoterpenes is underestimated by MEGAN 2.1. This is expected as some factors impacting monoterpene emissions, such as physical damage of needles and branches due to storms, are not included in MEGAN 2.1. After a severe hailstorm event, 22 ion mass peaks (attributed to six compound classes plus some unknown compounds) showed an elevated flux for the two following days. The sum of monoterpene emissions was 4–23 times higher compared to emissions prior to the hailstorm while MBO emissions remained unchanged. If one heavy storm occurs at this site every month we calculate that the monthly monoterpene emissions (in mg compound m −2 ) would be underestimated by 40% if this disturbance source is not considered.

Description: Aerosol variability and atmospheric transport in the Himalayan region from CALIOP 2007–2010 observations Atmospheric Chemistry and Physics Discussions, 13, 15271-15299, 2013 Author(s): S. Bucci, C. Cagnazzo, F. Cairo, L. Di Liberto, and F. Fierli Himalayan Plateau is surrounded by regions with high natural and anthropogenic aerosol emissions that have a strong impact on regional climate. This is particularly critical for the Himalayan glaciers whose equilibrium is also largely influenced by radiative direct and indirect effects induced by aerosol burden. This work focuses on the spatial and vertical distribution of different aerosol types, their seasonal variability and sources. The analysis of the 2007–2010 yr of CALIPSO vertically resolved satellite data allows the identification of spatial patterns of desert dust and carbonaceous particles in different atmospheric layers. Clusters of Lagrangian back-trajectories highlight the transport pathways from source regions during the dusty spring season. The analysis shows a prevalence of dust; at low heights they are distributed mainly north (with a main contribution from the Gobi and Taklamakan deserts) and west of the Tibetan Plateau (originating from the deserts of South-West Asia and advected by the westerlies). Above the Himalayas the dust amount is minor but still not negligible (detectable in around 20% of the measurements), and transport from more distant deserts (Sahara and Arabian Peninsula) is important. Smoke aerosol, produced mainly in North India and East China, is subject to shorter range transport and is indeed observed closer to the sources while there is a limited amount reaching the top of the plateau. Data analysis reveals a clear seasonal variability in the frequencies of occurrence for the main aerosol types; dust is regulated principally by the monsoon dynamics, with maxima of occurrence in spring. The study also highlights relevant interannual differences, showing a larger presence of aerosol in the region during 2007 and 2008 yr.

Description: Quantifying aerosol mixing state with entropy and diversity measures Atmospheric Chemistry and Physics Discussions, 13, 15615-15662, 2013 Author(s): N. Riemer and M. West This paper presents the first quantitative metric for aerosol population mixing state, defined as the distribution of per-particle chemical species composition. This new metric, the mixing state index χ, is an affine ratio of the average per-particle species diversity D α and the bulk population species diversity D γ , both of which are based on information-theoretic entropy measures. The mixing state index χ enables the first rigorous definition of the spectrum of mixing states from so-called external mixture to internal mixture, which is significant for aerosol climate impacts, including aerosol optical properties and cloud condensation nuclei activity. We illustrate the usefulness of this new mixing state framework with model results from the stochastic particle-resolved model PartMC-MOSAIC. These results demonstrate how the mixing state metrics evolve with time for several archetypal cases, each of which isolates a specific process such as coagulation, emission, or condensation. Further, we present an analysis of the mixing state evolution for a complex urban plume case, for which these processes occur simultaneously. We additionally derive theoretical properties of the mixing state index and present a family of generalized mixing state indexes that vary in the importance assigned to low-mass-fraction species.

Description: Long-term observations of positive cluster ion concentration, sources and sinks at the high altitude site of the Puy de Dôme Atmospheric Chemistry and Physics Discussions, 13, 14927-14975, 2013 Author(s): C. Rose, J. Boulon, M. Hervo, H. Holmgren, E. Asmi, M. Ramonet, P. Laj, and K. Sellegri Cluster particles (0.8–1.9 nm) are key entities involved in nucleation and new particle formation processes in the atmosphere. Cluster ions were characterized in clear sky conditions at the Puy de Dôme station (1465 m a.s.l). The studied dataset spread over five years (February 2007–February 2012), which provided a unique chance to catch seasonal variations of cluster ion properties at high altitude. Statistical values of the cluster ion concentration and diameter are reported for both positive and negative polarities. Cluster ions were found to be ubiquitous at the Puy de Dôme and displayed an annual variation with lower concentrations in spring. Positive cluster ions were less numerous than negative ones but were larger in diameters. Negative cluster ion properties seemed insensitive to the occurrence of a new particle formation (NPF) event while positive cluster ions appeared to be significantly more numerous and larger on event days. The parameters of the balance equation for the positive cluster concentration are reported, separately for the different seasons and for the NPF event days and non-event days. The steady state assumption suggests that the ionization rate is balanced with two sinks which are the ion recombination and the attachment on aerosol particles, referred as "aerosol ion sink". The aerosol ion sink was found to be higher during the warm season and dominated the loss of ions. The positive ionization rates derived from the balance equation were well correlated with the ionization rates obtained from radon measurement, and they were on average higher in summer and fall compared to winter and spring. Neither the aerosol ion sink nor the ionization rate were found to be significantly different on event days compared to non-event days, and thus they were not able to explain the different positive cluster concentrations between event and non-event days. Hence, the excess of positive small ions on event days may derive from an additional source of ions coupled with the fact that the steady state was not verified on event days.

Description: Review and uncertainty assessment of size-resolved scavenging coefficient formulations for snow scavenging of atmospheric aerosols Atmospheric Chemistry and Physics Discussions, 13, 14823-14869, 2013 Author(s): L. Zhang, X. Wang, M. D. Moran, and J. Feng Theoretical parameterizations for the size-resolved scavenging coefficient for atmospheric aerosol particles scavenged by snow (Λ snow ) need assumptions regarding (i) snow particle–aerosol particle collection efficiency E , (ii) snow particle size distribution N ( D p ), (iii) snow particle terminal velocity V D , and (iv) snow particle cross-sectional area A . Existing formulas for these parameters are reviewed in the present study and uncertainties in Λ snow caused by various combinations of these parameters are assessed. Different formulations of E can cause uncertainties in Λ snow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. E is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols (Λ rain ) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in Λ snow , and the uncertainties from these parameters are much larger than for Λ rain . Specifically, different N ( D p ) formulations can cause one-order-of-magnitude uncertainties in Λ snow for all aerosol sizes, as is also the case for a combination of uncertainties from both V D and A . In comparison, uncertainties in Λ rain from N ( D p ) are smaller than a factor of 5 and those from V D are smaller than a factor of 2. Λ snow estimated from one empirical formula generated from field measurements falls in the upper range of, or is slightly higher than, theoretically estimated values. The predicted aerosol concentrations obtained using different Λ snow formulas can differ by a factor of two for just a one-centimeter snowfall (liquid water equivalent of approximately 1 mm). It is likely that, for typical rain and snow event the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence.

Description: Atmospheric waves as scaling, turbulent phenomena Atmospheric Chemistry and Physics Discussions, 13, 14797-14822, 2013 Author(s): J. Pinel and S. Lovejoy It is paradoxical that while atmospheric dynamics are highly nonlinear and turbulent that atmospheric waves are commonly modelled by linear or weakly nonlinear theories. We postulate that the laws governing atmospheric waves are on the contrary high Reynold's number ( Re ), emergent laws so that – in common with the emergent high Re turbulent laws – they are also constrained by scaling symmetries. We propose an effective turbulence – wave propagator which corresponds to a fractional and anisotropic extension of the classical wave equation propagator with dispersion relations similar to those of inertial gravity waves (and Kelvin waves) yet with an anomalous (fractional) order H wav /2. Using geostationary IR radiances, we estimate the parameters finding that H wav /2 ≈ 0.17 ± 0.04 (the classical value = 2).

Description: Optimizing Saharan dust CALIPSO retrievals Atmospheric Chemistry and Physics Discussions, 13, 14749-14795, 2013 Author(s): V. Amiridis, U. Wandinger, E. Marinou, E. Giannakaki, A. Tsekeri, S. Basart, S. Kazadzis, A. Gkikas, M. Taylor, J. Baldasano, and A. Ansmann We demonstrate improvements in CALIPSO dust extinction retrievals over North Africa and Europe when corrections are applied regarding the Saharan dust lidar ratio assumption, the separation of dust portion in detected dust mixtures, and the averaging scheme introduced in the Level 3 CALIPSO product. First, a universal, spatially constant lidar ratio of 58 sr instead of 40 sr is applied to individual Level 2 dust-related backscatter products. The resulting aerosol optical depths show an improvement compared with synchronous and co-located AERONET measurements. An absolute bias of the order of −0.03 has been found, improving on the statistically significant biases of the order of −0.10 reported in the literature for the original CALIPSO product. When compared with the MODIS co-located AOD product, the CALIPSO negative bias is even less for the lidar ratio of 58 sr. After introducing the new lidar ratio for the domain studied, we examine potential improvements to the climatological CALIPSO Level 3 extinction product: (1) by introducing a new methodology for the calculation of pure dust extinction from dust mixtures and (2) by applying an averaging scheme that includes zero extinction values for the non-dust aerosol types detected. The scheme is applied at a horizontal spatial resolution of 1° × 1° for ease of comparison with the instantaneous and co-located dust extinction profiles simulated by the BSC-DREAM8b dust model. Comparisons show that the extinction profiles retrieved with the proposed methodology reproduce the well-known model biases per sub-region examined. The very good agreement of the proposed CALIPSO extinction product with respect to AERONET, MODIS and the BSC-DREAM8b dust model, makes this dataset an ideal candidate for the provision of an accurate and robust multi-year dust climatology over North Africa and Europe.

Description: Climatology of pure Tropospheric profiles and column contents of ozone and carbon monoxide using MOZAIC in the mid-northern latitudes (24° N to 50° N) from 1994 to 2009 Atmospheric Chemistry and Physics Discussions, 13, 14695-14747, 2013 Author(s): R. M. Zbinden, V. Thouret, P. Ricaud, F. Carminati, J.-P. Cammas, and P. Nédélec The objective of this paper is to deliver the most accurate ozone (O 3 ) and carbon monoxide (CO) climatology for the pure troposphere only, i.e. exclusively from the ground to the dynamical tropopause on an individual profile basis. The results (profiles and columns) are derived solely from the M easurements of OZ one and water vapour by in-service AI rbus air C raft programme (MOZAIC) over fifteen years (1994–2009). The study, focused on the northern mid-latitudes [24° N–50° N] and [120° W–140° E], includes more than 40 000 profiles over 11 sites to give a quasi-global zonal picture. Considering all the sites, the pure tropospheric column peak-to-peak seasonal cycle ranges are 23.7–43.2 DU for O 3 and 1.7–6.9 × 10 18 mol cm −2 for CO. The maxima of the seasonal cycles are not in phase, occurring in February–April for CO and May–July for O 3 . The phase shift is related to the photochemistry and OH removal efficiencies. The purely tropospheric seasonal profiles are characterized by a typical autumn-winter/spring-summer O 3 dichotomy, (except in Los Angeles, Eastmed – a cluster of Cairo and Tel Aviv – and the regions impacted by the summer monsoon) and a summer-autumn/winter-spring CO dichotomy. We revisit the boundary-layer, mid-tropospheric (MT) and upper-tropospheric (UT) partial columns, using a new monthly-varying MT ceiling. Interestingly, the seasonal cycle maximum of the UT partial columns is shifted from summer to spring for O 3 and to very early spring for CO. Conversely, the MT maximum is shifted from spring to summer and is associated with a summer (winter) MT thickening (thinning). Lastly, the pure tropospheric seasonal cycles derived from our analysis are consistent with the cycles derived from spaceborne measurements, the correlation coefficients being r = 0.6–0.9 for O 3 , and r 〉 0.9 for CO. The cycles observed from space are nevertheless greater than MOZAIC for O 3 (by 9–18 DU) and smaller for CO (up to 1 × 10 18 mol cm −2 ). The larger winter O 3 difference between the two data sets suggests probable stratospheric contamination in satellite data due to the tropopause position. The study underlines the importance of rigorously discriminating between the stratospheric and tropospheric reservoirs and avoiding use of a monthly-averaged tropopause position without this strict discrimination, in order to assess the pure O 3 and CO tropospheric trends.

Description: A climatology of formation conditions for aerodynamic contrails Atmospheric Chemistry and Physics Discussions, 13, 14667-14693, 2013 Author(s): K. Gierens and F. Dilger Aerodynamic contrails are defined in this paper as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data, first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Finally we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally we give an argument for our believe that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

Description: Expansion of global drylands under a warming climate Atmospheric Chemistry and Physics Discussions, 13, 14637-14665, 2013 Author(s): S. Feng and Q. Fu Global drylands encompassing hyper-arid, arid, semiarid, and dry subhumid areas cover about 41% of the earth's terrestrial surface and are home to more than a third of the world's population. By analyzing observations for 1948–2008 and climate model simulations for 1948–2100, we show that global drylands have expanded in last sixty years and will continue to expand in the 21st century. By the end of this century, the world's drylands under a high greenhouse gas emission scenario are projected to be 5.8 × 10 6 km 2 (or 10%) larger than in the 1961–1990 climatology. The major expansion of arid regions will occur over southwest North America, the northern fringe of Africa, southern Africa, and Australia, while major expansions of semiarid regions will occur over the north side of the Mediterranean, southern Africa, and North and South America. The global dryland expansions will increase the population affected by water scarcity and land degradations.

Description: The role of horizontal model resolution in assessing the transport of CO in a middle latitude cyclone using WRF-Chem Atmospheric Chemistry and Physics Discussions, 13, 14871-14925, 2013 Author(s): C. A. Klich and H. E. Fuelberg We use the Weather Research and Forecasting with Chemistry (WRF-Chem) online chemical transport model to simulate a middle latitude cyclone in East Asia at three different horizontal resolutions (45, 15, and 5 km grid spacing). The cyclone contains a typical warm conveyor belt (WCB) with an embedded squall line that passes through an area having large surface concentrations (〉400 ppbv) of carbon monoxide (CO). Model output from WRF-Chem is used to compare differences between the large-scale CO vertical transport by the WCB (the 45 km simulation) with the smaller-scale transport due to its convection (the 5 km simulation). Forward trajectories are calculated from WRF-Chem output using HYSPLIT. At 45 km grid spacing, the WCB exhibits gradual ascent, lofting surface CO to 6–7 km. Upon reaching the warm front, the WCB and associated CO ascend more rapidly and later turn eastward over the Pacific Ocean. Convective transport at 5 km resolution with explicitly resolved convection occurs much more rapidly, with surface CO lofted to altitudes greater than 10 km in 1 h or less. We also compute CO vertical mass fluxes to compare differences in transport due to the different grid spacings. Upward CO flux exceeds 110 000 t h −1 in the domain with explicit convection when the squall line is at peak intensity, while fluxes from the two coarser resolutions are an order of magnitude smaller. Specific areas of interest within the 5 km domain are defined to compare the magnitude of convective transport to that within the entire 5 km region. Although convection encompasses only a small portion of the 5 km domain, it is responsible for ~40% of the upward CO transport. We also examine the vertical transport due to a short wave trough and its associated area of convection, not related to the cyclone, that lofts CO to the upper troposphere. Results indicate that fine-scale resolution with explicitly resolved convection is important when assessing the vertical transport of surface emissions in areas of deep convection.

Description: We show that the spin angular momentum (SAM) flux in a space-variant linearly polarized beam can be separated in the focal plane. Such a beam carries only orbital angular momentum (OAM) and develops a net SAM flux upon focusing. The radial splitting of the SAM flux density is mediated by the phase vortex (or OAM) and can be controlled by the topological charge of the phase vortex. Optical trapping experiments verify the separation of the SAM flux density. The proposed approach enriches the manipulation of the angular momentum of light fields and inspires more designs of focus engineering, which would benefit optical micromanipulation of microscopic particles.

Description: A Lagrangian view of ozone production tendency in North American outflow in summers 2009 and 2010 Atmospheric Chemistry and Physics Discussions, 13, 15141-15190, 2013 Author(s): B. Zhang, R. C. Owen, J. A. Perlinger, A. Kumar, S. Wu, M. Val Martin, L. Kramer, D. Helmig, and R. E. Honrath The Pico Mountain Observatory, located at 2225 m a.s.l. in the Azores Islands, was established in 2001 to observe long-range transport from North America to the central North Atlantic. In previous research conducted at the Observatory, ozone enhancement (〉55 ppbv) in North American outflows was observed, and efficient ozone production in these outflows was postulated. This study is focused on determining the causes for high d [O 3 ]/ d [CO] values (~1 ppbv ppbv −1 ) observed in summers of 2009 and 2010. The folded retroplume technique, developed by Owen and Honrath (2009), was applied to combine upwind FLEXPART transport pathways with GEOS-Chem chemical fields. This folded result provides a semi-Lagrangian view of polluted North American outflow in terms of physical properties and chemical processes, including production/loss rate of ozone and NO x produced by lightning and thermal decomposition of PAN. Two transport events from North America were identified for detailed analysis. High d [O 3 ]/ d [CO] was observed in both events, but due to differing transport mechanisms, ozone production tendency differed between the two. A layer of net ozone production was found at 2 km a.s.l. over the Azores in the first event plume, apparently driven by PAN decomposition during subsidence of air mass in the Azores-Bermuda High. In the second event, net ozone loss occurred during transport in the lower free troposphere, yet observed d [O 3 ]/ d [CO] was high. We estimate that in both events, CO loss through oxidation contributed significantly to d [O 3 ]/ d [CO] enhancement. Thus, CO is not appropriately used as a passive tracer of pollution in these events. In general, use of d [O 3 ]/ d [CO] as an indicator of net ozone production/loss may be invalid for any situation in which oxidants are elevated. Based on our analysis, use of d [O 3 ]/ d [CO] to diagnose ozone enhancement without verifying the assumption of negligible CO loss is not advisable.

Description: Free troposphere ozone and carbon monoxide over the North Atlantic for 2001–2011 Atmospheric Chemistry and Physics Discussions, 13, 15377-15407, 2013 Author(s): A. Kumar, S. Wu, M. F. Weise, R. Honrath, R. C. Owen, D. Helmig, L. Kramer, M. Val Martin, and Q. Li In-situ measurements of carbon monoxide (CO) and ozone (O 3 ) at the Pico Mountain Observatory (PMO) located in the Azores, Portugal are analyzed together with results from atmospheric chemical transport modeling (GEOS-Chem) and satellite remote sensing (AIRS for CO and TES for O 3 ) to examine the evolution of free-troposphere CO and O 3 over the North Atlantic for 2001–2011. GEOS-Chem captured the seasonal cycles for CO and O 3 well but significantly underestimated the mixing ratios of CO, particularly in spring. Statistically significant (using a significance level of 0.05) decreasing trends were found for both CO and O 3 based on harmonic regression analysis of the measurement data. The best estimates of the trend for CO and O 3 measurements are −0.31 ± 0.30 (2-σ) ppbv yr −1 and −0.21 ± 0.11 (2-σ) ppbv yr −1 , respectively. Similar decreasing trends for both species were obtained with GEOS-Chem simulation results. The major factor contributing to the reported decrease in CO and O 3 mixing ratios at PMO over the past decade is the decline in anthropogenic CO and O 3 -precursor emissions in regions such as North America and Europe. The increase in Asian emissions does not seem to outweigh the impact of these declines resulting in overall decreasing trends for both CO and O 3 . For O 3 , however, increase in atmospheric water vapor content associated with climate change also appears to be a contributing factor causing enhanced destruction of the O 3 during transport from source regions. These hypotheses are supported by results from the GEOS-Chem tagged CO and tagged O 3 simulations.

Description: Mesoscale modeling of smoke transport over the Southeast Asian Maritime Continent: coupling of smoke direct radiative feedbacks below and above the low-level clouds Atmospheric Chemistry and Physics Discussions, 13, 15443-15492, 2013 Author(s): C. Ge, J. Wang, and J. S. Reid The online-coupled Weather Research and Forecasting model with Chemistry (WRF-Chem) is used to simulate the direct and semi-direct radiative impacts of smoke particles over the Southeast Asian Marine Continents (MC, 10° S–10° N, 90° E–150° E) during October 2006 when a significant El Nino event caused the highest biomass burning activity since 1997. With the use of OC (Organic Carbon)/BC (Black Carbon) ratio of 10 in the smoke emission inventory, the baseline simulation shows that the low-level clouds amplifying effect on smoke absorption led to a warming effect at the top-of-atmosphere (TOA) with a domain/monthly average forcing value of ~20 W m −2 over the islands of Borneo and Sumatra. The smoke-induced monthly average daytime heating (0.3 K) that is largely confined above the low-level clouds results in the local convergence over the smoke source region. This heating-induced convergence coupled with daytime planetary boundary layer turbulent mixing, transports more smoke particles above the planetary boundary layer height (PBLH), hence rendering a positive feedback. This positive feedback contrasts with the decrease of cloud fraction resulted from the combined effects of smoke heating within the cloud layer and the more stability in the boundary layer; the latter can be considered as a negative feedback in which decrease of cloud fraction weakens the heating by smoke particles above the clouds. During nighttime, the elevated smoke layer (above clouds in daytime) is decoupled from boundary layer, and the reduction of PBLH due to the residual surface cooling from the daytime lead to the accumulation of smoke particles near the surface. Because of smoke radiative extinction, on monthly basis, the amount of the solar input at the surface is reduced as large as 60 W m −2 , which lead to the decrease of sensible heat, latent heat, 2 m air temperature, and PBLH by a maximum of 20 W m −2 , 20 W m −2 , 1 K, 120 m, respectively. The decrease of boundary layer mixing and the generation of convergence above the PBL also results in a reduction of precipitable water 1–2 km above the PBLH and more precipitable water near the surface and in upper part of the middle troposphere with changes around 0.1 mm. Overall, there is less of a change of column water vapor over the land, and an increase of water vapor amount over the Karimata Strait. The cloud changes over continents are mostly occurred over the islands of Sumatra and Borneo during the daytime, where the low-level cloud fraction decreases more than 10%. However, the change of local wind (include sea breeze) induced by the smoke radiative feedback leads to more convergence over Karimata Strait and south coastal area of Kalimantan during both daytime and night time; consequently, cloud fraction is increased there up to 20%. The sensitivities with different OC/BC ratio show the importance of the smoke single scattering albedo for the smoke semi-direct effects. A case study on 31 October 2006 further demonstrated a much larger (more than twice of the monthly average) feedback induced by smoke aerosols. The decreased sea breeze during big events can lead to prominent increase (40%) of low-level cloud over coastal water. Lastly, the direct and semi-direct radiative impact of smoke particles over the Southeast Asian Marine Continents is summarized as a conceptual model.

Description: Global carbon monoxide products from combined AIRS, TES and MLS measurements on A-train satellites Atmospheric Chemistry and Physics Discussions, 13, 15409-15441, 2013 Author(s): J. X. Warner, R. Yang, Z. Wei, F. Carminati, A. Tangborn, Z. Sun, W. Lahoz, J.-L. Attié, L. El Amraoui, and B. Duncan This study tests a novel methodology to add value to satellite datasets. This methodology, data fusion, is similar to data assimilation, except that the background model-based field is replaced by a satellite dataset, in this case AIRS (Atmospheric Infrared Sounder) carbon monoxide (CO) measurements. The observational information comes from CO measurements with lower spatial coverage than AIRS, namely, from TES (Tropospheric Emission Spectrometer) and MLS (Microwave Limb Sounder). We show that combining these datasets with data fusion uses the higher spectral resolution of TES to extend AIRS CO observational sensitivity to the lower troposphere, a region especially important for air quality studies. We also show that combined CO measurements from AIRS and MLS provide enhanced information in the UTLS (upper troposphere/lower stratosphere) region compared to each product individually. The combined AIRS/TES and AIRS/MLS CO products are validated against DACOM (differential absorption mid-IR diode laser spectrometer) in situ CO measurements from the INTEX-B (Intercontinental Chemical Transport Experiment: MILAGRO and Pacific phases) field campaign and in situ data from HIPPO (HIAPER Pole-to-Pole Observations) flights. The data fusion results show improved sensitivities in the lower and upper troposphere (20–30% and above 20%, respectively) as compared with AIRS-only retrievals, and improved coverage compared with TES and MLS CO data.

Description: The mechanism of optical unidirectional (OUD) transmission in parallel subwavelength dual-metal gratings was investigated. It was found that this kind of OUD phenomenon originates from the coupling of the surface plasmon polaritons (SPPs) between the front grating and a layer of metal film which replaces the rear grating. The higher the intensity of the coupled SPPs at the entrances of the rear grating, the higher the transmittance can be achieved. Basing on this property, an effective OUD example was achieved by exploring the intensity difference at the entrances of the rear gratings between the two incidences of opposite directions. In this kind of OUD, the positive transmittance can exceed 80 % and the difference between the transmittances of the two opposite directions can be as large as 63 %. The detailed design process was also presented.

Description: Self-pulsing of continuous-wave Tm:YAlO 3 lasers limits their use for a variety of important applications. We demonstrate for the first time that the pulsing can be suppressed via feedback to the pump diode laser, a technique that is suitable for both external resonator and monolithic lasers. We also show that the optical transfer function of the laser is that of an unstable relaxation oscillator.

Description: An inverse modeling method to assess the source term of the Fukushima nuclear power plant accident using gamma dose rate observations Atmospheric Chemistry and Physics Discussions, 13, 15567-15614, 2013 Author(s): O. Saunier, A. Mathieu, D. Didier, M. Tombette, D. Quélo, V. Winiarek, and M. Bocquet The Chernobyl nuclear accident and more recently the Fukushima accident highlighted that the largest source of error on consequences assessment is the source term including the time evolution of the release rate and its distribution between radioisotopes. Inverse modeling methods, which combine environmental measurements and atmospheric dispersion models, have proven efficient in assessing source term due to an accidental situation (Gudiksen, 1989; Krysta and Bocquet, 2007; Stohl et al., 2012a; Winiarek et al., 2012). Most existing approaches are designed to use air sampling measurements (Winiarek et al., 2012) and some of them also use deposition measurements (Stohl et al., 2012a; Winiarek et al., 2013) but none of them uses dose rate measurements. However, it is the most widespread measurement system, and in the event of a nuclear accident, these data constitute the main source of measurements of the plume and radioactive fallout during releases. This paper proposes a method to use dose rate measurements as part of an inverse modeling approach to assess source terms. The method is proven efficient and reliable when applied to the accident at the Fukushima Daiichi nuclear power plant (FD-NPP). The emissions for the eight main isotopes 133 Xe, 134 Cs, 136 Cs, 137 Cs, 137m Ba, 131 I, 132 I and 132 Te have been assessed. Accordingly, 103 PBq of 131 I, 35.5 PBq of 132 I, 15.5 PBq of 137 Cs and 12 100 PBq of noble gases were released. The events at FD-NPP (such as venting, explosions, etc.) known to have caused atmospheric releases are well identified in the retrieved source term. The estimated source term is validated by comparing simulations of atmospheric dispersion and deposition with environmental observations. The result is that the model-measurement agreement for all of the monitoring locations is correct for 80% of simulated dose rates that are within a factor of 2 of the observed values. Changes in dose rates over time have been overall properly reconstructed, especially in the most contaminated areas to the northwest and south of the FD-NPP. A comparison with observed atmospheric activity concentration and surface deposition shows that the emissions of caesiums and 131 I are realistic but that 132 I and 132 Te are probably underestimated and noble gases are likely overestimated. Finally, an important outcome of this study is that the method proved to be perfectly suited to emergency management and could contribute to improve emergency response in the event of a nuclear accident.

Description: Forcing of stratospheric chemistry and dynamics during the Dalton Minimum Atmospheric Chemistry and Physics Discussions, 13, 15061-15104, 2013 Author(s): J. G. Anet, S. Muthers, E. Rozanov, C. C. Raible, T. Peter, A. Stenke, A. I. Shapiro, J. Beer, F. Steinhilber, S. Brönnimann, F. Arfeuille, Y. Brugnara, and W. Schmutz The response of atmospheric chemistry and climate to volcanic eruptions and a decrease in solar activity during the Dalton Minimum is investigated with the fully coupled atmosphere-ocean-chemistry general circulation model SOCOL-MPIOM covering the time period 1780 to 1840 AD. We carried out several sensitivity ensemble experiments to separate the effects of (i) reduced solar ultra-violet (UV) irradiance, (ii) reduced solar visible and near infrared irradiance, (iii) enhanced galactic cosmic ray intensity as well as less intensive solar energetic proton events and auroral electron precipitation, and (iv) volcanic aerosols. The introduced changes of UV irradiance and volcanic aerosols significantly influence stratospheric climate in the early 19th century, whereas changes in the visible part of the spectrum and energetic particles have smaller effects. A reduction of UV irradiance by 15% causes global ozone decrease below the stratopause reaching 8% in the midlatitudes at 5 hPa and a significant stratospheric cooling of up to 2 °C in the midstratosphere and to 6 °C in the lower mesosphere. Changes in energetic particle precipitation lead only to minor changes in the yearly averaged temperature fields in the stratosphere. Volcanic aerosols heat the tropical lower stratosphere allowing more water vapor to enter the tropical stratosphere, which, via HO x reactions, decreases upper stratospheric and mesospheric ozone by roughly 4%. Conversely, heterogeneous chemistry on aerosols reduces stratospheric NO x leading to a 12% ozone increase in the tropics, whereas a decrease in ozone of up to 5% is found over Antarctica in boreal winter. The linear superposition of the different contributions is not equivalent to the response obtained in a simulation when all forcing factors are applied during the DM – this effect is especially well visible for NO x /NO y . Thus, this study highlights the non-linear behavior of the coupled chemistry-climate system. Finally, we conclude that especially UV and volcanic eruptions dominate the changes in the ozone, temperature and dynamics while the NO x field is dominated by the EPP. Visible radiation changes have only very minor effects on both stratospheric dynamics and chemistry.

Description: Estimation of aerosol water and chemical composition from AERONET at Cabauw, the Netherlands Atmospheric Chemistry and Physics Discussions, 13, 15191-15232, 2013 Author(s): A. J. van Beelen, G. J. H. Roelofs, O. P. Hasekamp, J. S. Henzing, and T. Röckmann Remote sensing of aerosols provides important information on the atmospheric aerosol abundance. However, due to the hygroscopic nature of aerosol particles observed aerosol optical properties are influenced by atmospheric humidity, and the measurements do not unambiguously characterize the aerosol dry mass and composition which complicates the comparison with aerosol models. In this study we derive aerosol water and chemical composition by a modeling approach that combines individual measurements of remotely sensed aerosol properties (e.g. optical thickness, single scattering albedo, refractive index and size distribution) from an AERONET (Aerosol Robotic Network) sun-photometer with radiosonde measurements of relative humidity. The model simulates water uptake by aerosols based on the chemical composition and size distribution. A minimization method is used to calculate aerosol composition and concentration, which are then compared to in situ measurements from the Intensive Measurement Campaign At the Cabauw Tower (IMPACT, May 2008, the Netherlands). Computed concentrations show reasonable agreement with surface observations and follow the day-to-day variability in observations. Total dry mass (33 ± 12 μg m −3 ) and black carbon concentrations (0.7 ± 0.3 μg m −3 ) are generally accurately computed. The uncertainty in the AERONET (real) refractive index (0.025–0.05) introduces larger uncertainty in the modeled aerosol composition (e.g. sulfates, ammonium nitrate or organic matter) and leads to an uncertainty of 0.1–0.25 in aerosol water volume fraction. Water volume fraction is highly variable depending on composition, up to 〉0.5 at 70–80% and

Description: We describe an efficient, low-threshold, continuous-wave (CW) and Q-switched operation of a Ho:YAG laser resonantly, single-pass pumped by a 20 W linearly polarized narrow line width Tm: fiber laser at the wavelength of 1,908 nm. At room temperature for an output coupler of 30 % transmission, a maximum continuous-wave output power of 13.3 W for 18.9 W of absorbed pump power was achieved, corresponding to a slope efficiency of 73 %. In a quasi continuous-wave pumping regime, for several output couplers slope efficiencies of almost 82 % were observed. For a Q-switched operation, a Brewster-cut acousto-optic modulator was used. In a CW pumping regime, the pulse repetition frequency (PRF) was changed from 4 to 15 kHz. Under a Q-switched operation, the maximum output power of 12.25 W in relation to 15 kHz PRF was obtained; however, the maximum peak power of almost 250 kW at the PRF of 4 kHz was demonstrated. In the best case, for 4 kHz PRF, pulse energies of 2.18 mJ with a 8.8 ns FWHM pulse width (one of the shortest pulse durations observed in holmium-doped Q-switched lasers) were achieved. The laser operated at the wavelength of 2,090.23 nm with the FWHM line width of 0.95 nm. The beam quality factor of M 2 was measured to be below 1.42 in both X and Y axis.

Description: Optical, magnetic, and magneto-optical properties have been investigated for the α-Fe 2 O 3 -doped transparent glasses irradiated with an infrared fs laser and subsequently annealed. The values of the saturation magnetization at room temperature for the irradiated glasses were increased compared with the as-prepared samples, which is due to the precipitation of the ferrimagnetic ferrite nanoparticles (NPs). By adding further dopants as precursors of plasmonic metals, Au or Al NPs were space-selectively precipitated together with the ferrite NPs in a confined region after irradiation and thermal annealing. In the case of the glass codoped with Al, magneto-optical Faraday effect was plasmonically enhanced and exhibited a negative distinct peak ascribed to a coupling between the ferrimagnetism of ferrite NPs and the localized surface plasmon resonance of Al NPs, while the glass, in which ferrite and Au NPs were precipitated, showed a positive enhancement of Faraday effect due to a coupling of plasmon resonance with diamagnetism of glass matrix.

Description: Evaluation of various methods to measure particulate bound mercury and associated artifacts Atmospheric Chemistry and Physics Discussions, 13, 8585-8614, 2013 Author(s): S. Wang, T. M. Holsen, J. Huang, and Y.-J. Han This study was performed to determine how sampling artifacts associated with various sampling methods including open faced filter (OFF) pack, micro orifice uniform deposit impactor (MOUDI), and Tekran speciation system (TekSpec) impact particulate bound mercury (PBM) measurements. PBM measured by the MOUDI for 48 h was statistically lower than that measured with the TekSpec every 2 h, indicating that negative artifacts were significant for long sampling durations. Negative artifacts were also identified in lab experiments as the Hg 0 and HgCl 2 concentrations associated with particulate matter on the filter significantly decreased when the filter was exposed to zero air. Positive artifacts were also investigated. The OFF sampling for 48 h, which is likely to be associated with both positive and negative artifacts, measured a significantly lower PBM concentration than the TekSpec while the OFF and MOUDI (48 h sampling – minimal positive artifacts) showed similar results, suggesting that positive artifacts were minor under the rural condition encountered (low atmospheric gaseous oxidized mercury and typical oxidants concentrations). The Hg speciation associated with particles varied with atmospheric temperature, with the contribution of less volatile species including HgO and HgS increasing and more volatile Hg 0 and HgCl 2 decreasing as atmospheric temperature increased. There was significant correlation for PBM larger than 2.5 μm between TekSpec frit and MOUDI in this study, indicating that TekSpec frit is a good alternative sampler for measuring the concentration of coarse PBM.

Description: Aerosol and precipitation chemistry in the southwestern United States: spatiotemporal trends and interrelationships Atmospheric Chemistry and Physics Discussions, 13, 8615-8662, 2013 Author(s): A. Sorooshian, T. Shingler, A. Harpold, C. W. Feagles, T. Meixner, and P. D. Brooks This study characterizes the spatial and temporal patterns of aerosol and precipitation composition at six sites across the United States Southwest between 1995 and 2010. Precipitation accumulation occurs mostly during the wintertime (December–February) and during the monsoon season (July–September). Rain and snow pH levels are usually between 5–6, with crustal-derived species playing a major role in acid neutralization. These species (Ca 2+ , Mg 2+ , K + ,Na + ) exhibit their highest concentrations between March and June in both PM 2.5 and precipitation due mostly to dust. Crustal-derived species concentrations in precipitation exhibit positive relationships with SO 4 2− , NO 3 − , and Cl − , suggesting that acidic gases likely react with and partition to either crustal particles or hydrometeors enriched with crustal constituents. Concentrations of particulate SO 4 2− show a statistically significant correlation with rain SO 4 2− unlike snow SO 4 2− , which may be related to some combination of the vertical distribution of SO 4 2− (and precursors) and the varying degree to which SO 4 2− -enriched particles act as cloud condensation nuclei versus ice nuclei in the region. The coarse : fine aerosol mass ratio was correlated with crustal species concentrations in snow unlike rain, suggestive of a preferential role of coarse particles (mainly dust) as ice nuclei in the region. Precipitation NO 3 − : SO 4 2− ratios exhibit the following features with potential explanations discussed: (i) they are higher in precipitation as compared to PM 2.5 ; (ii) they exhibit the opposite annual cycle compared to particulate NO 3 − : SO 4 2− ratios; and (iii) they are higher in snow relative to rain during the wintertime. Long-term trend analysis for the monsoon season shows that the NO 3 − : SO 4 2− ratio in rain decreased at the majority of sites due mostly to air pollution regulations of SO 4 2− precursors.

Description: Effects of relative humidity on aerosol light scattering: results from different European sites Atmospheric Chemistry and Physics Discussions, 13, 8939-8984, 2013 Author(s): P. Zieger, R. Fierz-Schmidhauser, E. Weingartner, and U. Baltensperger The effect of aerosol water uptake on the aerosol particle light scattering coefficient (σ sp ) is described in this study by comparing measurements from five European sites: the Jungfraujoch, located in the Swiss Alps at 3580 m a.s.l., Ny-Ålesund, located on Spitsbergen in the Arctic, Mace Head, a coastal site in Ireland, Cabauw, a rural site in the Netherlands and Melpitz, a regional background site in Eastern Germany. These sites were selected according to the aerosol type usually encountered at that location. The scattering enhancement factor f (RH,λ) is the key parameter to describe the effect of water uptake on the particle light scattering. It is defined as the σ sp (RH) at a certain relative humidity (RH) and wavelength λ divided by its dry value. f (RH) largely varied at the five sites starting from very low values of f (RH = 85%,λ = 550 nm) around 1.28 for mineral dust to 3.41 for Arctic aerosol. Hysteresis behavior was observed at all sites except at the Jungfraujoch due to the absence of sea salt. Closure studies and Mie simulations showed that both size and chemical composition determine the magnitude of f (RH). Both parameters are also needed to successfully predict f (RH). Finally, the measurement results were compared to the widely used aerosol model OPAC (Hess et al., 1998). Significant discrepancies were seen especially at intermediate RH ranges, which were mainly attributed to inappropriate implemented hygroscopic growth within OPAC. Replacement of the hygroscopic growth with recent literature values showed a clear improvement of the OPAC model.

Description: Spectro-microscopic measurements of carbonaceous aerosol aging in Central California Atmospheric Chemistry and Physics Discussions, 13, 9179-9216, 2013 Author(s): R. C. Moffet, T. C. Rödel, S. T. Kelly, X. Y. Yu, G. T. Carroll, J. Fast, R. A. Zaveri, A. Laskin, and M. K. Gilles Carbonaceous aerosols are responsible for large uncertainties in climate models, degraded visibility, and adverse health effects. The Carbonaceous Aerosols and Radiative Effects Study (CARES) was designed to study carbonaceous aerosols in the natural environment of Central Valley, California, and learn more about their atmospheric formation and aging. This paper presents results from spectro-microscopic measurements of carbonaceous particles collected during CARES at the time of pollution accumulation event (27–29 June 2010), when in situ measurements indicated an increase in the organic carbon content of aerosols as the Sacramento urban plume aged. Computer controlled scanning electron microscopy coupled with an energy dispersive X-ray detector (CCSEM/EDX) and scanning transmission X-ray microscopy coupled with near edge X-ray absorption spectroscopy (STXM/NEXAFS) were used to probe the chemical composition and morphology of individual particles. It was found that the mass of organic carbon on individual particles increased through condensation of secondary organic aerosol. STXM/NEXAFS indicated that the number fraction of homogenous organic particles lacking inorganic inclusions (greater than ~50 nm diameter) increased with plume age as did the organic mass per particle. Comparison of the CARES spectro-microscopic data set with a similar dataset obtained in Mexico City during the MILAGRO campaign showed that individual particles in Mexico City contained twice as much carbon as those sampled during CARES. The number fraction of soot particles at the Mexico City urban site (30%) was larger than at the CARES urban site (10%) and the most aged samples from CARES contained less carbon-carbon double bonds. Differences between carbonaceous particles in Mexico City and California result from different sources, photochemical conditions, gas phase reactants, and secondary organic aerosol precursors. The detailed results provided by these spectro-microscopic measurements will allow for a comprehensive evaluation of aerosol process models used in climate research.

Description: ZnO/MgO core–shell nanorod arrays were synthesized successfully by the hydrothermal growth method. Photoluminescence (PL) emission from the nanorods showed remarkable enhancement after the growth of the MgO layer. The ZnO/MgO core–shell nanorods are type-I heterostructures, the electrons and holes of which are both confined in the core of the nanorods, as a result, leading to the increase of the photoluminescence intensity in this system. In addition, another reason for the enhancement of PL emission was the deposition of MgO shell suppression of surface defects. In addition, the activation energy ( E a ) of 63 meV in the ZnO/MgO core–shell nanorods was obtained from temperature-dependent PL.

Description: Cylindrical vector (CV) partially coherent beam was introduced (Dong et al. Opt Express 19:5979–5992, 2011 ) and generated (Wang et al. Appl Phys Lett 100:051108, 2012 ) recently. In this paper, we derive the realizability conditions for a CV partially coherent beam, and we derive the analytical formula for the cross-spectral density matrix of a CV partially coherent beam propagating in turbulent atmosphere based on the extended Huygens-Fresnel formula. The statistical properties, such as the average intensity, the complex degree of coherence and the degree of polarization of a CV partially coherent beam in turbulent atmosphere are studied in detail and compared with those in free space. It is found that the statistical properties of a CV partially coherent beam in turbulent atmosphere are much different from those in free space, and are affected by the initial beam parameters.

Description: The linewidth of an external cavity quantum cascade laser is studied as a function of injection current and laser scan rate. The laser linewidth is inferred to be ca. 2.5 MHz from Lamb-dip spectra on a low pressure sample of NO and its variation with injection current is well modeled using literature values for the intrinsic material properties of the lasing medium. The laser linewidth measurements are corroborated by polarization spectroscopy studies as well as by analysis of hyperfine structure and cross-over resonances.

Description: Difference frequency generation between broadband visible noncollinear optical parametric amplifier (NOPA) pulses and the fundamental pump laser pulses allows the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase. A simple prism compressor for the visible NOPA pulses is sufficient to generate few-cycle pulses in the infrared and no additional compression is needed. We theoretically investigate the concept, explain the principles, and demonstrate it for high repetition rate, long pulse durations, and various wavelengths by applying it to a Ti:sapphire and an Yb:KYW-based laser systems. For the latter sub-15 fs phase stable pulses around 1.8 μm with an energy of 100 nJ are obtained at 100 kHz repetition rate.

Description: We study the control of quantum resonances in photonic crystals with electromagnetically induced transparency driven by microwave field. In addition to the control laser, the intensity and phase of the maser can alter the transmission and reflection spectra in interesting ways, producing hyperfine resonances through the combined effects of multiple scattering in the superstructure.

Description: In any field theory the interaction of a wave packet with a multilayered potential is of high theoretical and practical relevance. In the present work we show an extension to any number of layers of the classical Fabry–Perot formula that works for any level of absorption, any thickness of the composing layers, any number of layers, any angle of incidence and for evanescent waves as well. More specifically, the ability of dealing with input evanescent waves and complex metal-based structures is of special interest for superlenses analysis and design. Some explicit examples in electromagnetism are also discussed.

Description: We studied the optical scattering noise, measurement artifacts, and their suppression in single-shot measurements of prepulse contrast. The measurement noise due to air scattering and the two kinds of measurement artifacts resulting from multiple reflections of the generated correlation signal and correlation between the pulse under test and the internally reflected sampling pulse were experimentally explored. The scattering noise and measurement artifacts significantly degrade the measurement fidelity. We demonstrate the clean measurement of prepulse contrast in a single-shot cross-correlator by attenuating the main peak of the correlation beam with a dot mirror and designing the correlating process based on a periodically-poled lithium niobate crystal embedded in an unpoled wafer. The standard time-scanning measurements of pulse contrast are also performed to confirm the experimental results of our single-shot measurement.

Description: Anisole is a promising candidate for use as fluorescent tracer for gas-phase imaging diagnostics. Its high-fluorescence quantum yield (FQY) and its large Stokes shift lead to improved signal intensity (up to 100 times stronger) compared with the often used toluene. Fluorescence spectra and effective fluorescence lifetimes of gaseous anisole were investigated after picosecond laser excitation at 266 nm as a function of temperature (296–977 K) and bath gas composition (varying amounts of N 2 and O 2 ) at total pressures in the range of 1–10 bar to provide spectroscopic data and FQY for applications, e.g., in in-cylinder measurements in internal combustion engines. Fluorescence spectra of anisole extend from roughly 270–360 nm with a peak close to 290 nm at 296 K. The spectra show a red-shift with increasing temperature (0.03 nm/K) and O 2 partial pressure (5 nm from N 2 to air). In the investigated temperature range and in pure N 2 at 1 bar total pressure the effective fluorescence lifetime drops with increasing temperature from 13.3 ± 0.5 to 0.05 ± 0.01 ns. Increasing the total pressure of N 2 leads to a small decrease of the lifetime at temperatures above 400 K (e.g., at 525 K from 4.2 ± 0.2 ns at 1 bar to 2.7 ± 0.2 ns at 10 bar). At constant temperature and in the presence of O 2 the lifetimes decrease significantly (e.g., at 296 K from 13.3 ± 0.5 ns in N 2 to 0.40 ± 0.02 ns in air), with this trend diminishing with increasing temperature (e.g., at 675 K from 1.02 ± 0.08 ns in N 2 to 0.25 ± 0.05 ns in air). A phenomenological model that predicts fluorescence lifetimes, i.e., relative quantum yields as a function of temperature, pressure, and O 2 concentration is presented. The photophysics of anisole is discussed in comparison with other aromatics.

Description: The contribution of the propagating and the evanescent waves associated with freely propagating non-paraxial light fields whose transverse component is azimuthally polarized at some plane is investigated. Analytic expressions are derived for describing both the spatial shape and the relative weight of the propagating and the evanescent components integrated over the transverse plane. The analysis is carried out within the framework of the plane-wave angular spectrum approach. These results are used to illustrate the behavior of a kind of donut-like beams with transverse azimuthal polarization at some plane.

Description: A high-efficiency high-power diode-side-pumped quasi-continuous wave (QCW) Nd:YAG ceramic slab laser using zigzag optical path was demonstrated. With an integrating sphere technique, the scattering and absorption coefficient of the ceramic slab were measured to be 0.0024 and 0.0016 cm −1 at 1,064 nm, respectively. Under a pump power of 6.69 kW, an average output power of 2.44 kW at 1,064 nm with a repetition rate of 400 Hz was achieved, corresponding to an optical-to-optical efficiency of 36.5 %. As far as we know, this is the highest conversion efficiency reported for QCW side-pumped single slab Nd:YAG ceramic laser.

Description: We present a carrier–envelope phase (CEP) stabilized sub-two-cycle 5.2 fs pulse source based on soliton-effect self-compression of femtosecond laser pulses in millimetre-long highly nonlinear photonic crystal fibres. We employ a simple and efficient scheme to generate a strong (40–60 dB, configuration dependent) CEP beat signal directly from the pulse source via f- to-2 f interferometry where the second harmonic of the main soliton pulse is mixed with the isolated dispersive blue/green radiation peak that is also generated in the compression process, obviating the need for additional spectral broadening mechanisms.