ALBERT

Description: Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates Biogeosciences Discussions, 10, 14861-14885, 2013 Author(s): K. Schmidt, C. L. De La Rocha, M. Gallinari, and G. Cortese Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d −1 , became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

Description: Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles Atmospheric Chemistry and Physics, 13, 9097-9118, 2013 Author(s): Z. A. Kanji, A. Welti, C. Chou, O. Stetzer, and U. Lohmann Ice nucleation in the atmosphere is central to the understanding the microphysical properties of mixed-phase and cirrus clouds. Ambient conditions such as temperature ( T ) and relative humidity (RH), as well as aerosol properties such as chemical composition and mixing state play an important role in predicting ice formation in the troposphere. Previous field studies have reported the absence of sulfate and organic compounds on mineral dust ice crystal residuals sampled at mountain top stations or aircraft based measurements despite the long-range transport mineral dust is subjected to. We present laboratory studies of ice nucleation for immersion and deposition mode on ozone aged mineral dust particles for 233 〈 T 〈 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka) and Arizona Test Dust (ATD) particles is compared to corresponding aged particles that are subjected to ozone concentrations of 0.4–4.3 ppmv in a stainless steel aerosol tank. The portable ice nucleation counter (PINC) and immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode measurements, respectively. Ice active fractions as well as ice active surface site densities ( n s ) are reported and observed to increase as a function of decreasing temperature. We present first results that demonstrate enhancement of the ice nucleation ability of aged mineral dust particles in both the deposition and immersion mode due to ageing. We also present the first results to show a suppression of heterogeneous ice nucleation activity without the condensation of a coating of (in)organic material. In immersion mode, low ozone exposed Ka particles showed enhanced ice activity requiring a median freezing temperature of 1.5 K warmer than that of untreated Ka, whereas high ozone exposed ATD particles showed suppressed ice nucleation requiring a median freezing temperature of 3 K colder than that of untreated ATD. In deposition mode, low exposure Ka had ice active fractions of an order of magnitude higher than untreated Ka, whereas high ozone exposed ATD had ice active fractions up to a factor of 4 lower than untreated ATD. From our results, we derive and present parameterizations in terms of n s ( T ) that can be used in models to predict ice nuclei concentrations based on available aerosol surface area.

Description: Phenology as a strategy for carbon optimality: a global model Biogeosciences Discussions, 10, 15107-15152, 2013 Author(s): S. Caldararu, D. W. Purves, and P. I. Palmer Phenology is essential to our understanding of biogeochemical cycles and the climate system. We develop a global mechanistic model of leaf phenology based on the hypothesis that phenology is a strategy for optimal carbon gain at the canopy level so that trees adjust leaf gains and losses in response to environmental factors such as light, temperature and soil moisture, to achieve maximum carbon assimilation. We fit this model to five years of satellite observations of leaf area index (LAI) using a Bayesian fitting algorithm. We show that our model is able to reproduce phenological patterns for all vegetation types and use it to explore variations in growing season length and the climate factors that limit leaf growth for different biomes. Phenology in wet tropical areas is limited by leaf age physiological constraints while at higher latitude leaf seasonality is limited by low temperature and light availability. Leaf growth in grassland regions is limited by water availability but often in combination with other factors. This model will advance the current understanding of phenology for ecosystem carbon models and our ability to predict future phenological behaviour.

Description: A plume-in-grid approach to characterize air quality impacts of aircraft emissions at the Hartsfield–Jackson Atlanta International Airport Atmospheric Chemistry and Physics, 13, 9285-9302, 2013 Author(s): J. Rissman, S. Arunachalam, M. Woody, J. J. West, T. BenDor, and F. S. Binkowski This study examined the impacts of aircraft emissions during the landing and takeoff cycle on PM 2.5 concentrations during the months of June and July 2002 at the Hartsfield–Jackson Atlanta International Airport. Primary and secondary pollutants were modeled using the Advanced Modeling System for Transport, Emissions, Reactions, and Deposition of Atmospheric Matter (AMSTERDAM). AMSTERDAM is a modified version of the Community Multiscale Air Quality (CMAQ) model that incorporates a plume-in-grid process to simulate emissions sources of interest at a finer scale than can be achieved using CMAQ's model grid. Three fundamental issues were investigated: the effects of aircraft on PM 2.5 concentrations throughout northern Georgia, the differences resulting from use of AMSTERDAM's plume-in-grid process rather than a traditional CMAQ simulation, and the concentrations observed in aircraft plumes at subgrid scales. Comparison of model results with an air quality monitor located in the vicinity of the airport found that normalized mean bias ranges from −77.5% to 6.2% and normalized mean error ranges from 40.4% to 77.5%, varying by species. Aircraft influence average PM 2.5 concentrations by up to 0.232 μg m −3 near the airport and by 0.001–0.007 μg m −3 throughout the Atlanta metro area. The plume-in-grid process increases concentrations of secondary PM pollutants by 0.005–0.020 μg m −3 (compared to the traditional grid-based treatment) but reduces the concentration of non-reactive primary PM pollutants by up to 0.010 μg m −3 , with changes concentrated near the airport. Examination of subgrid-scale results indicates that median aircraft contribution to grid cells is higher than median puff concentration in the airport's grid cell and outside of a 20 km × 20 km square area centered on the airport, while in a 12 km × 12 km square ring centered on the airport, puffs have median concentrations over an order of magnitude higher than aircraft contribution to the grid cells. Maximum puff impacts are seen within the 12 km × 12 km ring, not in the airport's own grid cell, while maximum grid cell impacts occur within the airport's grid cell. Twenty-one (21)% of all aircraft-related puffs from the Atlanta airport have at least 0.1 μg m −3 PM 2.5 concentrations. Near the airport, median daily puff concentrations vary between 0.017 and 0.134 μg m −3 (0.05 and 0.35 μg m −3 at ground level), while maximum daily puff concentrations vary between 6.1 and 42.1 μg m −3 (7.5 and 42.1 μg m −3 at ground level) during the 2-month period. In contrast, median daily aircraft contribution to grid concentrations varies between 0.015 and 0.091 μg m −3 (0.09 and 0.40 μg m −3 at ground level), while the maximum varies between 0.75 and 2.55 μg m −3 (0.75 and 2.0 μg m −3 at ground level). Future researchers may consider using a plume-in-grid process, such as the one used here, to understand the impacts of aircraft emissions at other airports, for proposed future airports, for airport expansion projects under various future scenarios, and for other national-scale studies specifically when the maximum impacts at fine scales are of interest.

Description: Corrigendum to "Atmospheric column-averaged mole fractions of carbon dioxide at 53 aircraft measurement sites" published in Atmos. Chem. Phys. 13, 5265–5275, 2013 Atmospheric Chemistry and Physics, 13, 9213-9216, 2013 Author(s): Y. Miyamoto, M. Inoue, I. Morino, O. Uchino, T. Yokota, T. Machida, Y. Sawa, H. Matsueda, C. Sweeney, P. P. Tans, A. E. Andrews, S. C. Biraud, and P. K. Patra No abstract available.

Description: Timing of sea ice retreat can alter phytoplankton community structure in the western Arctic Ocean Biogeosciences Discussions, 10, 15153-15180, 2013 Author(s): given_name prefix surname suffix, A. Fujiwara, T. Hirawake, K. Suzuki, I. Imai, and S.-I. Saitoh This study assesses the response of phytoplankton assemblages to recent climate change, especially with regard to the shrinking of sea ice in the northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of phytoplankton groups in the late summers of 2008–2010 were analyzed based on HPLC pigment signatures and, the following four major algal groups were inferred via multiple regression and cluster analyses: prasinophytes, diatoms, haptophytes and dinoflagellates. A remarkable interannual difference in the distribution pattern of the groups was found in the northern basin area. Haptophytes dominated and dispersed widely in warm surface waters in 2008, whereas prasinophytes dominated in cold water in 2009 and 2010. A difference in the onset date of sea ice retreat was evident among years – the sea ice retreat in 2008 was 1–2 months earlier than in 2009 and 2010. The spatial distribution of early sea ice retreat matched the areas in which a shift in algal community composition was observed. Steel-Dwass's multiple comparison tests were used to assess the physical, chemical and biological parameters of the four clusters. We found a statistically significant difference in temperature between the haptophyte-dominated cluster and the other clusters, suggesting that the change in the phytoplankton communities was related to the earlier sea ice retreat in 2008 and the corollary increase in sea surface temperatures. Longer periods of open water during the summer, which are expected in the future, may affect food webs and biogeochemical cycles in the western Arctic due to shifts in phytoplankton community structure.

Description: Regional CO 2 flux estimates for 2009–2010 based on GOSAT and ground-based CO 2 observations Atmospheric Chemistry and Physics, 13, 9351-9373, 2013 Author(s): S. Maksyutov, H. Takagi, V. K. Valsala, M. Saito, T. Oda, T. Saeki, D. A. Belikov, R. Saito, A. Ito, Y. Yoshida, I. Morino, O. Uchino, R. J. Andres, and T. Yokota We present the application of a global carbon cycle modeling system to the estimation of monthly regional CO 2 fluxes from the column-averaged mole fractions of CO 2 ( X CO 2 ) retrieved from spectral observations made by the Greenhouse gases Observing SATellite (GOSAT). The regional flux estimates are to be publicly disseminated as the GOSAT Level 4 data product. The forward modeling components of the system include an atmospheric tracer transport model, an anthropogenic emissions inventory, a terrestrial biosphere exchange model, and an oceanic flux model. The atmospheric tracer transport was simulated using isentropic coordinates in the stratosphere and was tuned to reproduce the age of air. We used a fossil fuel emission inventory based on large point source data and observations of nighttime lights. The terrestrial biospheric model was optimized by fitting model parameters to observed atmospheric CO 2 seasonal cycle, net primary production data, and a biomass distribution map. The oceanic surface p CO 2 distribution was estimated with a 4-D variational data assimilation system based on reanalyzed ocean currents. Monthly CO 2 fluxes of 64 sub-continental regions, between June 2009 and May 2010, were estimated from GOSAT FTS SWIR Level 2 X CO 2 retrievals (ver. 02.00) gridded to 5° × 5° cells and averaged on a monthly basis and monthly-mean GLOBALVIEW-CO 2 data. Our result indicated that adding the GOSAT X CO 2 retrievals to the GLOBALVIEW data in the flux estimation brings changes to fluxes of tropics and other remote regions where the surface-based data are sparse. The uncertainties of these remote fluxes were reduced by as much as 60% through such addition. Optimized fluxes estimated for many of these regions, were brought closer to the prior fluxes by the addition of the GOSAT retrievals. In most of the regions and seasons considered here, the estimated fluxes fell within the range of natural flux variabilities estimated with the component models.

Description: Global ozone–CO correlations from OMI and AIRS: constraints on tropospheric ozone sources Atmospheric Chemistry and Physics, 13, 9321-9335, 2013 Author(s): P. S. Kim, D. J. Jacob, X. Liu, J. X. Warner, K. Yang, K. Chance, V. Thouret, and P. Nedelec We present a global data set of free tropospheric ozone–CO correlations with 2° × 2.5° spatial resolution from the Ozone Monitoring Instrument (OMI) and Atmospheric Infrared Sounder (AIRS) satellite instruments for each season of 2008. OMI and AIRS have near-daily global coverage of ozone and CO respectively and observe coincident scenes with similar vertical sensitivities. The resulting ozone–CO correlations are highly statistically significant (positive or negative) in most regions of the world, and are less noisy than previous satellite-based studies that used sparser data. Comparison with ozone–CO correlations and regression slopes ( d O 3 / d CO) from MOZAIC (Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) aircraft profiles shows good general agreement. We interpret the observed ozone–CO correlations with the GEOS (Goddard Earth Observing System)-Chem chemical transport model to infer constraints on ozone sources. Driving GEOS-Chem with different meteorological fields generally shows consistent ozone–CO correlation patterns, except in some tropical regions where the correlations are strongly sensitive to model transport error associated with deep convection. GEOS-Chem reproduces the general structure of the observed ozone–CO correlations and regression slopes, although there are some large regional discrepancies. We examine the model sensitivity of d O 3 / d CO to different ozone sources (combustion, biosphere, stratosphere, and lightning NO x ) by correlating the ozone change from that source to CO from the standard simulation. The model reproduces the observed positive d O 3 / d CO in the extratropical Northern Hemisphere in spring–summer, driven by combustion sources. Stratospheric influence there is also associated with a positive d O 3 / d CO because of the interweaving of stratospheric downwelling with continental outflow. The well-known ozone maximum over the tropical South Atlantic is associated with negative d O 3 / d CO in the observations; this feature is reproduced in GEOS-Chem and supports a dominant contribution from lightning to the ozone maximum. A major model discrepancy is found over the northeastern Pacific in summer–fall where d O 3 / d CO is positive in the observations but negative in the model, for all ozone sources. We suggest that this reflects a model overestimate of lightning at northern midlatitudes combined with an underestimate of the East Asian CO source.

Description: Uptake of phytodetritus by benthic foraminifera under oxygen depletion at the Indian Margin (Arabian Sea) Biogeosciences Discussions, 10, 15305-15335, 2013 Author(s): A. J. Enge, U. Witte, M. Kucera, and P. Heinz Benthic foraminifera in sediments on the Indian margin of the Arabian Sea where the oxygen minimum zone (OMZ) impinges on the continental slope are exposed to particularly severe levels of oxygen depletion. Food supply for the benthic community is high but delivered in distinct pulses during upwelling and water mixing events associated with summer and winter monsoon periods. In order to investigate the response by benthic foraminifera to such pulsed food delivery under oxygen concentrations of less than 0.1 mL L −1 (4.5 μmol L −1 ), an in situ isotope labeling experiment ( 13 C, 15 N) was performed at the western continental slope of India at 540 m water depth (OMZ core region). The assemblage of living foraminifera (〉125 μm) in the uppermost centimeter at this depth is characterized by an unexpectedly high population density of 3982 ind. 10 cm −2 and a strong dominance by few calcareous species. For the experiment, we concentrated on the nine most abundant taxa, which constitute 93% of the entire foraminifera population at 0–1 cm sediment depth. Increased concentrations of 13 C and 15 N in the cytoplasm indicate that all investigated taxa took up the labeled phytodetritus during the 4 day experimental phase. In total, these nine species had assimilated 113.8 mg C m −2 (17.5% of the total added carbon). The uptake of nitrogen by the three most abundant taxa ( Bolivina aff. B. dilatata , Cassidulina sp., Bulimina gibba ) was 2.7 mg N m −2 (2% of the total added nitrogen) and showed the successful application of 15 N as tracer in foraminiferal studies. The short-term response to the offered phytodetritus varied largely among foraminiferal species with Uvigerina schwageri being by far the most important species in short-term processing whereas the most abundant taxa Bolivina aff. B. dilatata and Cassidulina sp. showed comparably low uptake of the offered food. We suggest that the observed species-specific differences are related to individual biomass of species and to specific feeding preferences. The high numbers of living foraminifera and their rapid response to deposited fresh phytodetritus demonstrate the importance of foraminifera in short-term carbon cycling under oxygen-depleted conditions. We propose that foraminifera at the studied site benefit from unique adaptations in their metabolisms to nearly anoxic conditions as well as from the exclusion of macrofauna and the resulting relaxation of competition for food and low predation pressure.

Description: Emission ratio and isotopic signatures of molecular hydrogen emissions from tropical biomass burning Atmospheric Chemistry and Physics, 13, 9401-9413, 2013 Author(s): F. A. Haumann, A. M. Batenburg, G. Pieterse, C. Gerbig, M. C. Krol, and T. Röckmann In this study, we identify a biomass-burning signal in molecular hydrogen (H 2 ) over the Amazonian tropical rainforest. To quantify this signal, we measure the mixing ratios of H 2 and several other species as well as the H 2 isotopic composition in air samples that were collected in the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) aircraft campaign during the dry season. We derive a relative H 2 emission ratio with respect to carbon monoxide (CO) of 0.31 ± 0.04 ppb ppb −1 and an isotopic source signature of −280 ± 41‰ in the air masses influenced by tropical biomass burning. In order to retrieve a clear source signal that is not influenced by the soil uptake of H 2 , we exclude samples from the atmospheric boundary layer. This procedure is supported by data from a global chemistry transport model. The ΔH 2 / ΔCO emission ratio is significantly lower than some earlier estimates for the tropical rainforest. In addition, our results confirm the lower values of the previously conflicting estimates of the H 2 isotopic source signature from biomass burning. These values for the emission ratio and isotopic source signatures of H 2 from tropical biomass burning can be used in future bottom-up and top-down approaches aiming to constrain the strength of the biomass-burning source for H 2 . Hitherto, these two quantities relied only on combustion experiments or on statistical relations, since no direct signal had been obtained from in-situ observations.

Description: Cloud and boundary layer interactions over the Arctic sea ice in late summer Atmospheric Chemistry and Physics, 13, 9379-9399, 2013 Author(s): M. D. Shupe, P. O. G. Persson, I. M. Brooks, M. Tjernström, J. Sedlar, T. Mauritsen, S. Sjogren, and C. Leck Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the central Arctic sea-ice pack in late summer 2008, provide a detailed view of cloud–atmosphere–surface interactions and vertical mixing processes over the sea-ice environment. Measurements from a suite of ground-based remote sensors, near-surface meteorological and aerosol instruments, and profiles from radiosondes and a helicopter are combined to characterize a week-long period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed case studies and statistical analyses are used to develop a conceptual model for the cloud and atmosphere structure and their interactions in this environment. Clouds were persistent during the period of study, having qualities that suggest they were sustained through a combination of advective influences and in-cloud processes, with little contribution from the surface. Radiative cooling near cloud top produced buoyancy-driven, turbulent eddies that contributed to cloud formation and created a cloud-driven mixed layer. The depth of this mixed layer was related to the amount of turbulence and condensed cloud water. Coupling of this cloud-driven mixed layer to the surface boundary layer was primarily determined by proximity. For 75% of the period of study, the primary stratocumulus cloud-driven mixed layer was decoupled from the surface and typically at a warmer potential temperature. Since the near-surface temperature was constrained by the ocean–ice mixture, warm temperatures aloft suggest that these air masses had not significantly interacted with the sea-ice surface. Instead, back-trajectory analyses suggest that these warm air masses advected into the central Arctic Basin from lower latitudes. Moisture and aerosol particles likely accompanied these air masses, providing necessary support for cloud formation. On the occasions when cloud–surface coupling did occur, back trajectories indicated that these air masses advected at low levels, while mixing processes kept the mixed layer in equilibrium with the near-surface environment. Rather than contributing buoyancy forcing for the mixed-layer dynamics, the surface instead simply appeared to respond to the mixed-layer processes aloft. Clouds in these cases often contained slightly higher condensed water amounts, potentially due to additional moisture sources from below.

Description: Multiannual changes of CO 2 emissions in China: indirect estimates derived from satellite measurements of tropospheric NO 2 columns Atmospheric Chemistry and Physics, 13, 9415-9438, 2013 Author(s): E. V. Berezin, I. B. Konovalov, P. Ciais, A. Richter, S. Tao, G. Janssens-Maenhout, M. Beekmann, and E.-D. Schulze Multiannual satellite measurements of tropospheric NO 2 columns are used for evaluation of CO 2 emission changes in China in the period from 1996 to 2008. Indirect top-down annual estimates of CO 2 emissions are derived from the satellite NO 2 column measurements by means of a simple inverse modeling procedure involving simulations performed with the CHIMERE mesoscale chemistry–transport model and the CO 2 -to-NO x emission ratios from the Emission Database for Global Atmospheric Research (EDGAR) global anthropogenic emission inventory and Regional Emission Inventory in Asia (REAS). Exponential trends in the normalized time series of annual emissions are evaluated separately for the periods from 1996 to 2001 and from 2001 to 2008. The results indicate that the both periods manifest strong positive trends in the CO 2 emissions, and that the trend in the second period was significantly larger than the trend in the first period. Specifically, the trends in the first and second periods are best estimated to be in the range from 3.7 to 8.3 and from 11.0 to 13.2% per year, respectively, taking into account statistical uncertainties and differences between the CO 2 -to-NO x emission ratios from the EDGAR and REAS inventories. Comparison of our indirect top-down estimates of the CO 2 emission changes with the corresponding bottom-up estimates provided by the EDGAR (version 4.2) and Global Carbon Project (GCP) glomal emission inventories reveals that while acceleration of the CO 2 emission growth in the considered period is a common feature of both kinds of estimates, nonlinearity in the CO 2 emission changes may be strongly exaggerated in the global emission inventories. Specifically, the atmospheric NO 2 observations do not confirm the existence of a sharp bend in the emission inventory data time series in the period from 2000 to 2002. A significant quantitative difference is revealed between the bottom-up and indirect top-down estimates of the CO 2 emission trend in the period from 1996 to 2001 (specifically, the trend was not positive according to the global emission inventories, but is strongly positive in our estimates). These results confirm the findings of earlier studies that indicated probable large uncertainties in the energy production and other activity data for China from international energy statistics used as the input information in the global emission inventories. For the period from 2001 to 2008, some quantitative differences between the different kinds of estimates are found to be in the range of possible systematic uncertainties associated with our estimation method. In general, satellite measurements of tropospheric NO 2 are shown to be a useful source of information on CO 2 sources collocated with sources of nitrogen oxides; the corresponding potential of these measurements should be exploited further in future studies.

Description: Summertime canopy albedo is sensitive to forest thinning Biogeosciences Discussions, 10, 15373-15414, 2013 Author(s): J. Otto, D. Berveiller, F.-M. Bréon, N. Delpierre, G. Geppert, A. Granier, W. Jans, A. Knohl, A. Kuusk, B. Longdoz, E. Moors, M. Mund, B. Pinty, M.-J. Schelhaas, and S. Luyssaert Despite an emerging body of literature linking canopy albedo to forest management, understanding of the process is still fragmented. We combined a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning, that is removing trees at a certain time during the forest rotation, on summertime canopy albedo. The effects of different forest species (pine, beech, oak) and four thinning strategies (light to intense thinning regimes) were examined. During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning on summertime canopy albedo. These trends continue until the end of the rotation where thinning explains up to 50% of the variance in near-infrared canopy albedo and up to 70% of the variance in visible canopy albedo. More intense thinning lowers the summertime shortwave albedo in the canopy by as much as 0.02 compared to unthinned forest. The structural changes associated with forest thinning can be described by the change in LAI in combination with crown volume. However, forests with identical canopy structure can have different summertime albedo values due to their location: the further north a forest is situated, the more the solar zenith angle increases and thus the higher is the summertime canopy albedo, independent of the wavelength. Despite the increase of absolute summertime canopy albedo values with latitude, the difference in canopy albedo between managed and unmanaged forest decreases with increasing latitude. Forest management thus strongly altered summertime forest albedo.

Description: Air quality over Europe: modelling gaseous and particulate pollutants Atmospheric Chemistry and Physics, 13, 9661-9673, 2013 Author(s): E. Tagaris, R. E. P. Sotiropoulou, N. Gounaris, S. Andronopoulos, and D. Vlachogiannis Air quality over Europe using Models-3 (i.e., CMAQ, MM5, SMOKE) modelling system is performed for winter (i.e., January 2006) and summer (i.e., July 2006) months with the 2006 TNO gridded anthropogenic emissions database. Higher ozone mixing ratios are predicted in southern Europe while higher NO 2 levels are simulated over western Europe. Elevated SO 2 values are simulated over eastern Europe and higher PM 2.5 concentrations over eastern and western Europe. Regional average results suggest that NO 2 and PM 2.5 are underpredicted, SO 2 is overpredicted, while Max8hrO 3 is overpredicted for low mixing ratios and is underpredicted for the higher mixing ratios. However, in a number of countries observed and predicted values are in good agreement for the pollutants examined here. Speciated PM 2.5 components suggest that NO 3 is dominant during winter over western Europe and in a few eastern countries due to the high NO 2 mixing ratios. During summer NO 3 is dominant only in regions with elevated NH 3 emissions. For the rest of the domain SO 4 is dominant. Low OC concentrations are simulated mainly due to the uncertain representation of SOA formation.

Description: On the uses of a new linear scheme for stratospheric methane in global models: water source, transport tracer and radiative forcing Atmospheric Chemistry and Physics, 13, 9641-9660, 2013 Author(s): B. M. Monge-Sanz, M. P. Chipperfield, A. Untch, J.-J. Morcrette, A. Rap, and A. J. Simmons This study evaluates effects and applications of a new linear parameterisation for stratospheric methane and water vapour. The new scheme (CoMeCAT) is derived from a 3-D full-chemistry-transport model (CTM). It is suitable for any global model, and is shown here to produce realistic profiles in the TOMCAT/SLIMCAT 3-D CTM and the ECMWF (European Centre for Medium-Range Weather Forecasts) general circulation model (GCM). Results from the new scheme are in good agreement with the full-chemistry CTM CH 4 field and with observations from the Halogen Occultation Experiment (HALOE). The scheme is also used to derive stratospheric water increments, which in the CTM produce vertical and latitudinal H 2 O variations in fair agreement with satellite observations. Stratospheric H 2 O distributions in the ECMWF GCM show realistic overall features, although concentrations are smaller than in the CTM run (up to 0.5 ppmv smaller above 10 hPa). The potential of the new CoMeCAT tracer for evaluating stratospheric transport is exploited to assess the impacts of nudging the free-running GCM to ERA-40 and ERA-Interim reanalyses. The nudged GCM shows similar transport patterns to the offline CTM forced by the corresponding reanalysis data. The new scheme also impacts radiation and temperature in the model. Compared to the default CH 4 climatology and H 2 O used by the ECMWF radiation scheme, the main effect on ECMWF temperatures when considering both CH 4 and H 2 O from CoMeCAT is a decrease of up to 1.0 K over the tropical mid/low stratosphere. The effect of using the CoMeCAT scheme for radiative forcing (RF) calculations is investigated using the offline Edwards–Slingo radiative transfer model. Compared to the default model option of a tropospheric global 3-D CH 4 value, the CoMeCAT distribution produces an overall change in the annual mean net RF of up to −30 mW m −2 .

Description: A global historical ozone data set and prominent features of stratospheric variability prior to 1979 Atmospheric Chemistry and Physics, 13, 9623-9639, 2013 Author(s): S. Brönnimann, J. Bhend, J. Franke, S. Flückiger, A. M. Fischer, R. Bleisch, G. Bodeker, B. Hassler, E. Rozanov, and M. Schraner We present a vertically resolved zonal mean monthly mean global ozone data set spanning the period 1901 to 2007, called HISTOZ.1.0. It is based on a new approach that combines information from an ensemble of chemistry climate model (CCM) simulations with historical total column ozone information. The CCM simulations incorporate important external drivers of stratospheric chemistry and dynamics (in particular solar and volcanic effects, greenhouse gases and ozone depleting substances, sea surface temperatures, and the quasi-biennial oscillation). The historical total column ozone observations include ground-based measurements from the 1920s onward and satellite observations from 1970 to 1976. An off-line data assimilation approach is used to combine model simulations, observations, and information on the observation error. The period starting in 1979 was used for validation with existing ozone data sets and therefore only ground-based measurements were assimilated. Results demonstrate considerable skill from the CCM simulations alone. Assimilating observations provides additional skill for total column ozone. With respect to the vertical ozone distribution, assimilating observations increases on average the correlation with a reference data set, but does not decrease the mean squared error. Analyses of HISTOZ.1.0 with respect to the effects of El Niño–Southern Oscillation (ENSO) and of the 11 yr solar cycle on stratospheric ozone from 1934 to 1979 qualitatively confirm previous studies that focussed on the post-1979 period. The ENSO signature exhibits a much clearer imprint of a change in strength of the Brewer–Dobson circulation compared to the post-1979 period. The imprint of the 11 yr solar cycle is slightly weaker in the earlier period. Furthermore, the total column ozone increase from the 1950s to around 1970 at northern mid-latitudes is briefly discussed. Indications for contributions of a tropospheric ozone increase, greenhouse gases, and changes in atmospheric circulation are found. Finally, the paper points at several possible future improvements of HISTOZ.1.0.

Description: Oxygen minimum zone of the open Arabian Sea: variability of oxygen and nitrite from daily to decadal time scales Biogeosciences Discussions, 10, 15455-15517, 2013 Author(s): K. Banse, S. W. A. Naqvi, P. V. Narvekar, J. R. Postel, and D. A. Jayakumar The oxygen minimum zone (OMZ) of the Arabian Sea is the thickest of the three oceanic OMZs, which is of global biogeochemical significance because of denitrification in the upper part leading to N 2 and N 2 O production. The residence time of the OMZ water is believed to be less than a decade. The upper few hundred meters of this zone are nearly anoxic but non-sulfidic and still support animal (metazoan) pelagic life, possibly as a result of episodic injections of O 2 by physical processes. The very low O 2 values obtained with the new STOX sensor in the eastern tropical South Pacific probably also characterize the Arabian Sea OMZ, but there is no apparent reason as to why the temporal trends of the historic data should not hold. We report on discrete measurements of dissolved O 2 and NO 2 - , besides temperature and salinity, made between 1959 and 2004 well below the tops of the sharp pycno- and oxyclines near 150, 200, 300, 400, and 500 m depth. We assemble nearly all O 2 determinations (originally, 849 values, 695 in the OMZ) by the visual endpoint detection of the iodometric Winkler procedure, which in our data base yields about 0.04 mL L −1 (∼2 μM) O 2 above the endpoint from modern automated titration methods. We find 632 values acceptable (480 from 150 stations in the OMZ). The data are grouped in zonally-paired boxes of 1° lat. and 2° long. centered at 8°, 10°, 12°, 15°, 18°, 20°, and 21° N along 65° E and 67° E. The latitudes of 8–12° N, outside the OMZ, are only treated in passing. The principal results are as follows: (1) an O 2 climatology for the upper OMZ reveals a marked seasonality at 200 to 500 m depth with O 2 levels during the northeast monsoon and spring intermonsoon season elevated over those during the southwest monsoon season (median difference, 0.08 mL L −1 [3.5 μM]). The medians of the slopes of the seasonal regressions of O 2 on year for the NE and SW monsoon seasons are −0.0043 and −0.0019 mL L −1 a −1 , respectively (−0.19 and −0.08 μM a −1 ; n = 10 and 12, differing at p = 0.01); (2) four decades of statistically significant decreases of O 2 between 15° and 20° N but a trend to a similar increase near 21° N are observed. The balance of the mechanisms that more or less annually maintain the O 2 levels are still uncertain. At least between 300 and 500 m the annual reconstitution of the decrease is inferred to be due to lateral, isopycnal re-supply of O 2 , while at 200 (250?) m it is diapycnal, most likely by eddies. Similarly, recent models show large vertical advection of O 2 well below the pycno- cum -oxycline. The spatial (within drift stations) and temporal (daily) variability in hydrography and chemistry is large also below the principal pycnocline. The seasonal change of hydrography is considerable even at 500 m. There is no trend in the redox environment for a quarter of a century at a GEOSECS station near 20° N. In the entire OMZ the slopes on year within seasons for the quite variable NO 2 - (taken as an indicator of active denitrification) do not show a clear pattern. Also, future O 2 or nutrient budgets for the OMZ should not be based on single cruises or sections obtained during one season only. Steady state cannot be assumed any longer for the intermediate layers of the central Arabian Sea.

Description: Naphthalene SOA: redox activity and naphthoquinone gas–particle partitioning Atmospheric Chemistry and Physics, 13, 9731-9744, 2013 Author(s): R. D. McWhinney, S. Zhou, and J. P. D. Abbatt Chamber secondary organic aerosol (SOA) from low-NO x photooxidation of naphthalene by hydroxyl radical was examined with respect to its redox cycling behaviour using the dithiothreitol (DTT) assay. Naphthalene SOA was highly redox-active, consuming DTT at an average rate of 118 ± 14 pmol per minute per μg of SOA material. Measured particle-phase masses of the major previously identified redox active products, 1,2- and 1,4-naphthoquinone, accounted for only 21 ± 3% of the observed redox cycling activity. The redox-active 5-hydroxy-1,4-naphthoquinone was identified as a new minor product of naphthalene oxidation, and including this species in redox activity predictions increased the predicted DTT reactivity to 30 ± 5% of observations. These results suggest that there are substantial unidentified redox-active SOA constituents beyond the small quinones that may be important toxic components of these particles. A gas-to-SOA particle partitioning coefficient was calculated to be (7.0 ± 2.5) × 10 −4 m 3 μg −1 for 1,4-naphthoquinone at 25 °C. This value suggests that under typical warm conditions, 1,4-naphthoquinone is unlikely to contribute strongly to redox behaviour of ambient particles, although further work is needed to determine the potential impact under conditions such as low temperatures where partitioning to the particle is more favourable. Also, higher order oxidation products that likely account for a substantial fraction of the redox cycling capability of the naphthalene SOA are likely to partition much more strongly to the particle phase.

Description: Satellite observation of lowermost tropospheric ozone by multispectral synergism of IASI thermal infrared and GOME-2 ultraviolet measurements over Europe Atmospheric Chemistry and Physics, 13, 9675-9693, 2013 Author(s): J. Cuesta, M. Eremenko, X. Liu, G. Dufour, Z. Cai, M. Höpfner, T. von Clarmann, P. Sellitto, G. Foret, B. Gaubert, M. Beekmann, J. Orphal, K. Chance, R. Spurr, and J.-M. Flaud We present a new multispectral approach for observing lowermost tropospheric ozone from space by synergism of atmospheric radiances in the thermal infrared (TIR) observed by IASI (Infrared Atmospheric Sounding Interferometer) and earth reflectances in the ultraviolet (UV) measured by GOME-2 (Global Ozone Monitoring Experiment-2). Both instruments are onboard the series of MetOp satellites (in orbit since 2006 and expected until 2022) and their scanning capabilities offer global coverage every day, with a relatively fine ground pixel resolution (12 km-diameter pixels spaced by 25 km for IASI at nadir). Our technique uses altitude-dependent Tikhonov–Phillips-type constraints, which optimize sensitivity to lower tropospheric ozone. It integrates the VLIDORT (Vector Linearized Discrete Ordinate Radiative Transfer) and KOPRA (Karlsruhe Optimized and Precise Radiative transfer Algorithm) radiative transfer codes for simulating UV reflectance and TIR radiance, respectively. We have used our method to analyse real observations over Europe during an ozone pollution episode in the summer of 2009. The results show that the multispectral synergism of IASI (TIR) and GOME-2 (UV) enables the observation of the spatial distribution of ozone plumes in the lowermost troposphere (LMT, from the surface up to 3 km a.s.l., above sea level), in good agreement with the CHIMERE regional chemistry-transport model. In this case study, when high ozone concentrations extend vertically above 3 km a.s.l., they are similarly observed over land by both the multispectral and IASI retrievals. On the other hand, ozone plumes located below 3 km a.s.l. are only clearly depicted by the multispectral retrieval (both over land and over ocean). This is achieved by a clear enhancement of sensitivity to ozone in the lowest atmospheric layers. The multispectral sensitivity in the LMT peaks at 2 to 2.5 km a.s.l. over land, while sensitivity for IASI or GOME-2 only peaks at 3 to 4 km a.s.l. at lowest (above the LMT). The degrees of freedom for the multispectral retrieval increase by 0.1 (40% in relative terms) with respect to IASI only retrievals for the LMT. Validations with ozonesondes (over Europe during summer 2009) show that our synergetic approach for combining IASI (TIR) and GOME-2 (UV) measurements retrieves lowermost tropospheric ozone with a mean bias of 1% and a precision of 16%, when smoothing by the retrieval vertical sensitivity (1% mean bias and 21% precision for direct comparisons).

Description: Tethered balloon-borne aerosol measurements: seasonal and vertical variations of aerosol constituents over Syowa Station, Antarctica Atmospheric Chemistry and Physics, 13, 9119-9139, 2013 Author(s): K. Hara, K. Osada, and T. Yamanouchi Tethered balloon-borne aerosol measurements were conducted at Syowa Station, Antarctica, during the 46th Japanese Antarctic expedition (2005–2006). Direct aerosol sampling was operated from near the surface to the lower free troposphere (approximately 2500 m) using a balloon-borne aerosol impactor. Individual aerosol particles were analyzed using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Seasonal and vertical features of aerosol constituents and their mixing states were investigated. Results show that sulfate particles were predominant in the boundary layer and lower free troposphere in summer, whereas sea-salt particles were predominant during winter through spring. Minerals, MgSO 4 , and sulfate containing K were identified as minor aerosol constituents in both boundary layer and free troposphere over Syowa Station. Although sea-salt particles were predominant during winter through spring, the relative abundance of sulfate particles increased in the boundary layer when air masses fell from the free troposphere over the Antarctic coast and continent. Sea-salt particles were modified considerably through heterogeneous reactions with SO 4 2− CH 3 SO 3 − and their precursors during summer, and were modified slightly through heterogeneous reactions with NO 3 − and its precursors. During winter through spring, sea-salt modification was insignificant, particularly in the cases of high relative abundance of sea-salt particles and higher number concentrations. In August, NO 3 − and its precursors contributed greatly to sea-salt modification over Syowa Station. Because of the occurrence of sea-salt fractionation on sea ice, Mg-rich sea-salt particles were identified during the months of April through November. In contrast, Mg-free sea-salt particles and slightly Mg-rich sea-salt particles coexisted in the lower troposphere during summer. Thereby, Mg separation can proceed by sea-salt fractionation during summer in Antarctic regions.

Description: Regional inversion of CO 2 ecosystem fluxes from atmospheric measurements: reliability of the uncertainty estimates Atmospheric Chemistry and Physics, 13, 9039-9056, 2013 Author(s): G. Broquet, F. Chevallier, F.-M. Bréon, N. Kadygrov, M. Alemanno, F. Apadula, S. Hammer, L. Haszpra, F. Meinhardt, J. A. Morguí, J. Necki, S. Piacentino, M. Ramonet, M. Schmidt, R. L. Thompson, A. T. Vermeulen, C. Yver, and P. Ciais The Bayesian framework of CO 2 flux inversions permits estimates of the retrieved flux uncertainties. Here, the reliability of these theoretical estimates is studied through a comparison against the misfits between the inverted fluxes and independent measurements of the CO 2 Net Ecosystem Exchange (NEE) made by the eddy covariance technique at local (few hectares) scale. Regional inversions at 0.5° resolution are applied for the western European domain where ~ 50 eddy covariance sites are operated. These inversions are conducted for the period 2002–2007. They use a mesoscale atmospheric transport model, a prior estimate of the NEE from a terrestrial ecosystem model and rely on the variational assimilation of in situ continuous measurements of CO 2 atmospheric mole fractions. Averaged over monthly periods and over the whole domain, the misfits are in good agreement with the theoretical uncertainties for prior and inverted NEE, and pass the chi-square test for the variance at the 30% and 5% significance levels respectively, despite the scale mismatch and the independence between the prior (respectively inverted) NEE and the flux measurements. The theoretical uncertainty reduction for the monthly NEE at the measurement sites is 53% while the inversion decreases the standard deviation of the misfits by 38%. These results build confidence in the NEE estimates at the European/monthly scales and in their theoretical uncertainty from the regional inverse modelling system. However, the uncertainties at the monthly (respectively annual) scale remain larger than the amplitude of the inter-annual variability of monthly (respectively annual) fluxes, so that this study does not engender confidence in the inter-annual variations. The uncertainties at the monthly scale are significantly smaller than the seasonal variations. The seasonal cycle of the inverted fluxes is thus reliable. In particular, the CO 2 sink period over the European continent likely ends later than represented by the prior ecosystem model.

Description: Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions Annales Geophysicae, 31, 1559-1567, 2013 Author(s): E. K. J. Kilpua, H. Hietala, H. E. J. Koskinen, D. Fontaine, and L. Turc Compressed sheath regions form ahead of interplanetary coronal mass ejections (ICMEs) that are sufficiently faster than the preceding solar wind. The turbulent sheath regions are important drivers of magnetospheric activity, but due to their complex internal structure, relatively little is known on the distribution of the magnetic field and plasma variations in them. In this paper we investigate ultra low frequency (ULF) fluctuations in the interplanetary magnetic field (IMF) and in dynamic pressure ( P dyn ) using a superposed epoch analysis of 41 sheath regions observed during solar cycle 23. We find strongest fluctuation power near the shock and in the vicinity of the ICME leading edge. The IMF and P dyn ULF power have different profiles within the sheath; the former is enhanced in the leading part of the sheath, while the latter is increased in the trailing part of the sheath. We also find that the ICME properties affect the level and distribution of the ULF power in sheath regions. For example, sheath regions associated with strong or fast ICMEs, or those that are crossed at intermediate distances from the center, have strongest ULF power and large variation in the power throughout the sheath region. The weaker or slower ICMEs, or those that are crossed centrally, have in general considerably weaker ULF power with relatively smooth profiles. The strong and abrupt decrease of the IMF ULF power at the ICME leading edge could be used to distinguish the ICME from the preceding sheath plasma.

Description: Key chemical NO x sink uncertainties and how they influence top-down emissions of nitrogen oxides Atmospheric Chemistry and Physics, 13, 9057-9082, 2013 Author(s): T. Stavrakou, J.-F. Müller, K. F. Boersma, R. J. van der A, J. Kurokawa, T. Ohara, and Q. Zhang Triggered by recent developments from laboratory and field studies regarding major NO x sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NO x sinks for global NO x distributions calculated by the IMAGESv2 chemistry-transport model, and quantifies their significance for top-down NO x emission estimates. Our study focuses on five key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO 2 with OH radicals, the newly identified HNO 3 -forming channel in the reaction of NO with HO 2 , the reactive uptake of N 2 O 5 and HO 2 by aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO 2 +OH reaction is the largest NO x sink globally accounting for ca. 60% of the total sink, the reactions contributing the most to the overall uncertainty are the formation of HNO 3 in NO+HO 2 , leading to NO x column changes exceeding a factor of two over tropical regions, and the uptake of HO 2 by aqueous aerosols, in particular over East and South Asia. Emission inversion experiments are carried out using model settings which either minimise (MINLOSS) or maximise (MAXLOSS) the total NO x sink, both constrained by one year of OMI NO 2 column data from the DOMINO v2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 75% higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (1.8). The global anthropogenic source is better constrained (factor of 1.57) than the natural sources, except over South Asia where the combined uncertainty primarily associated to the NO+HO 2 reaction in summer and HO 2 uptake by aerosol in winter lead to top-down emission differences exceeding a factor of 2. Evaluation of the emission optimisation is performed against independent satellite observations from the SCIAMACHY sensor, with airborne NO 2 measurements of the INTEX-A and INTEX-B campaigns, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO 2 profile measurements, consistent with the results of a previous analysis (Henderson et al., 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NO x loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source.

Description: Stable isotopes dissect food webs from top to the bottom Biogeosciences Discussions, 10, 14923-14952, 2013 Author(s): J. J. Middelburg Stable isotopes have been used extensively to study food web functioning, i.e. the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of carbon and nitrogen isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows then measurement of entire food webs, i.e. from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotope to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

Description: Cluster observation of few-hour-scale evolution of structured plasma in the inner magnetosphere Annales Geophysicae, 31, 1569-1578, 2013 Author(s): M. Yamauchi, I. Dandouras, H. Rème, R. Lundin, and L. M. Kistler Using Cluster Ion Spectrometry (CIS) data from the spacecraft-4 perigee traversals during the 2001–2006 period (nearly 500 traversals after removing those that are highly contaminated by radiation belt particles), we statistically examined the local time distribution of structured trapped ions at sub- to few-keV range as well as inbound–outbound differences of these ion signatures in intensities and energy–latitude dispersion directions. Since the Cluster orbit during this period was almost constant and approximately north–south symmetric at nearly constant local time near the perigee, inbound–outbound differences are attributed to temporal developments in a 1–2 h timescale. Three types of structured ions at sub- to few keV range that are commonly found in the inner magnetosphere are examined: – Energy–latitude dispersed structured ions at less than a few keV, – Short-lived dispersionless ion stripes at wide energy range extending 0.1–10 keV, – Short-lived low-energy ion bursts at less than a few hundred eV. The statistics revealed that the wedge-like dispersed ions are most often observed in the dawn sector (60% of traversals), and a large portion of them show significant enhancement during the traversals at all local times. The short-lived ion stripes are predominantly found near midnight, where most stripes are significantly enhanced during the traversals and are associated with substorm activities with geomagnetic AL 〈 −300 nT. The low-energy bursts are observed at all local times and under all geomagnetic conditions, with moderate peak of the occurrence rate in the afternoon sector. A large portion of them again show significant enhancement or decay during the traversals.

Description: Responses of carbon dioxide flux and plant biomass to drought in a treed peatland in northern Alberta: a climate change perspective Biogeosciences Discussions, 10, 14999-15031, 2013 Author(s): T. M. Munir, B. Xu, M. Perkins, and M. Strack Northern peatland ecosystems represent large carbon stocks that are susceptible to changes such as accelerated mineralization due to water table lowering expected under a climate change scenario. During the growing seasons of 2011 and 2012 we monitored CO 2 fluxes and plant biomass along a microtopographic gradient (hummocks-hollows) in an undisturbed dry continental boreal treed bog (control) and a nearby site that was drained (drained) in 2001. Ten years of drainage in the bog significantly increased coverage of shrubs at hummocks and lichens at hollows. Considering measured hummock coverage and including tree incremental growth, we estimate that the control site was a larger sink in 2011 of −40 than that of −13 g C m −2 in 2012 while the drained site was a source of 144 and 140 g C m −2 over the same years. We infer that, drainage induced changes in vegetation growth led to increased biomass to counteract a portion of soil carbon losses. These results suggest that spatial variability (microtopography) and changes in vegetation community in boreal peatlands will affect how these ecosystems respond to lowered water table potentially induced by climate change.

Description: The coccolithophores Emiliania huxleyi and Coccolithus pelagicus : extant populations from the Norwegian-Iceland Sea and Fram Strait Biogeosciences Discussions, 10, 15077-15106, 2013 Author(s): C. V. Dylmer, J. Giraudeau, V. Hanquiez, and K. Husum Extant coccolithophores and their relation to the governing oceanographic features in the northern North Atlantic were investigated along two zonal transects of surface water sampling, both conducted during summer 2011 and fall 2007. The northern transects crossed Fram Strait and its two opposing boundary currents (West Spitsbergen Current and East Greenland Current), while the southern transects sampled the Norwegian and Iceland Seas (passing the island Jan Mayen) from the Lofoten Islands to the continental margin off Eastern Greenland. The distribution of the dominant coccolithophore species Emiliania huxleyi and Coccolithus pelagicus is discussed in view of both the surface hydrology at the time of sampling and the structure of the surface mixed layer. Remote-sensing images as well as CTD and ARGO profiles are used to constrain the physico-chemical state of the surface water at the time of sampling. Both transects were characterized by strong seasonal differences in bulk coccolithophore standing stocks with maximum values of 53 × 10 3 cells L −1 for the northern transect and 72 × 10 3 cells L −1 for the southern transect in fall and summer, respectively. The highest recorded bulk cell densities are essentially explained by E. huxleyi . This species shows a zonal shift in peak abundance in the Norwegian-Iceland Seas from a summer maximum in the Lofoten gyre to peak cell densities around the island Jan Mayen in fall. Vertical mixing of Atlantic waters west of Lofoten Island, a phenomenom related to pervasive summer large scale atmospheric changes in the eastern Nordic Seas, on one hand, and strengthened influence of melt-water and related surface water stratification around the island Jan Mayen during fall, on the other hand, explains the observed seasonal migration of the E. huxleyi peak production area, as well as the seasonal change in dominating species within the Iceland Sea. In addition our datasets are indicative of a well-defined maximum boundary temperature of 6 °C for the production of C. pelagicus in the northern North Atlantic. The Fram Strait transects provides, to our knowledge, a first view of the zonal distribution of extant coccolithophores in this remote setting during summer and fall. Our datasets are indicative of a seasonal change in the species community from an E. huxleyi -dominated assemblage during summer to a C. pelagicus -rich population during fall. Here, higher irradiance and increased Atlantic water influence during summer favored the production of the opportunistic species E. huxleyi close to the Arctic Front, whereas the peak production area during fall, with high concentrations of C. pelagicus , lays in true Arctic/Polar waters.

Description: Airborne hydrogen cyanide measurements using a chemical ionisation mass spectrometer for the plume identification of biomass burning forest fires Atmospheric Chemistry and Physics, 13, 9217-9232, 2013 Author(s): M. Le Breton, A. Bacak, J. B. A. Muller, S. J. O'Shea, P. Xiao, M. N. R. Ashfold, M. C. Cooke, R. Batt, D. E. Shallcross, D. E. Oram, G. Forster, S. J.-B. Bauguitte, and C. J. Percival A chemical ionisation mass spectrometer (CIMS) was developed for measuring hydrogen cyanide (HCN) from biomass burning events in Canada using I − reagent ions on board the FAAM BAe-146 research aircraft during the BORTAS campaign in 2011. The ionisation scheme enabled highly sensitive measurements at 1 Hz frequency through biomass burning plumes in the troposphere. A strong correlation between the HCN, carbon monoxide (CO) and acetonitrile (CH 3 CN) was observed, indicating the potential of HCN as a biomass burning (BB) marker. A plume was defined as being 6 standard deviations above background for the flights. This method was compared with a number of alternative plume-defining techniques employing CO and CH 3 CN measurements. The 6-sigma technique produced the highest R 2 values for correlations with CO. A normalised excess mixing ratio (NEMR) of 3.68 ± 0.149 pptv ppbv −1 was calculated, which is within the range quoted in previous research (Hornbrook et al., 2011). The global tropospheric model STOCHEM-CRI incorporated both the observed ratio and extreme ratios derived from other studies to generate global emission totals of HCN via biomass burning. Using the ratio derived from this work, the emission total for HCN from BB was 0.92 Tg (N) yr −1 .

Description: Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry Atmospheric Chemistry and Physics, 13, 9159-9168, 2013 Author(s): S. Palit, T. Basak, S. K. Mondal, S. Pal, and S. K. Chakrabarti X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

Description: Absorption properties of Mediterranean aerosols obtained from multi-year ground-based remote sensing observations Atmospheric Chemistry and Physics, 13, 9195-9210, 2013 Author(s): M. Mallet, O. Dubovik, P. Nabat, F. Dulac, R. Kahn, J. Sciare, D. Paronis, and J. F. Léon Aerosol absorption properties are of high importance to assess aerosol impact on regional climate. This study presents an analysis of aerosol absorption products obtained over the Mediterranean basin or land stations in the region from multi-year ground-based AERONET observations with a focus on the Absorbing Aerosol Optical Depth (AAOD), Single Scattering Albedo (SSA) and their spectral dependence. The AAOD and Absorption Angström Exponent (AAE) dataset is composed of daily averaged AERONET level 2 data from a total of 22 Mediterranean stations having long time series, mainly under the influence of urban-industrial aerosols and/or soil dust. This dataset covers the 17-yr period 1996–2012 with most data being from 2003–2011 (~89% of level-2 AAOD data). Since AERONET level-2 absorption products require a high aerosol load (AOD at 440 nm 〉 0.4), which is most often related to the presence of desert dust, we also consider level-1.5 SSA data, despite their higher uncertainty, and filter out data with an Angström exponent 〈 1.0 in order to study absorption by carbonaceous aerosols. The SSA dataset includes AERONET level-2 products. Sun-photometer observations show that values of AAOD at 440 nm vary between 0.024 ± 0.01 (resp. 0.040 ± 0.01) and 0.050 ± 0.01 (0.055 ± 0.01) for urban (dusty) sites. Analysis shows that the Mediterranean urban-industrial aerosols appear "moderately" absorbing with values of SSA close to ~0.94–0.95 ± 0.04 (at 440 nm) in most cases except over the large cities of Rome and Athens, where aerosol appears more absorbing (SSA ~0.89–0.90 ± 0.04). The aerosol Absorption Angström Exponent (AAE, estimated using 440 and 870 nm) is found to be larger than 1 for most sites over the Mediterranean, a manifestation of mineral dust (iron) and/or brown carbon producing the observed absorption. AERONET level-2 sun-photometer data indicate a possible East-West gradient, with higher values over the eastern basin (AAE East = 1.39/AAE West = 1.33). The North-South AAE gradient is more pronounced, especially over the western basin. Our additional analysis of AERONET level-1.5 data also shows that organic absorbing aerosols significantly affect some Mediterranean sites. These results indicate that current climate models treating organics as nonabsorbing over the Mediterranean certainly underestimate the warming effect due to carbonaceous aerosols.

Description: Anthropogenic and natural methane fluxes in Switzerland synthesized within a spatially-explicit inventory Biogeosciences Discussions, 10, 15181-15224, 2013 Author(s): R. V. Hiller, D. Bretscher, T. DelSontro, T. Diem, W. Eugster, R. Henneberger, S. Hobi, E. Hodson, D. Imer, M. Kreuzer, T. Künzle, L. Merbold, P. A. Niklaus, B. Rihm, A. Schellenberger, M. H. Schroth, C. J. Schubert, H. Siegrist, J. Stieger, N. Buchmann, and D. Brunner We present the first high-resolution (500 m × 500 m) gridded methane (CH 4 ) emission inventory for Switzerland, which integrates the national emission totals reported to the United Nations Framework Convention on Climate Change (UNFCCC) and recent CH 4 flux studies conducted by research groups across Switzerland. In addition to anthropogenic emissions, we also include natural and semi-natural CH 4 fluxes, i.e., emissions from lakes and reservoirs, wetlands, wild animals as well as uptake by forest soils. National CH 4 emissions were disaggregated using detailed geostatistical information on source locations and their spatial extent and process- or area-specific emission factors. In Switzerland, the highest CH 4 emissions in 2011 originated from the agricultural sector (150 Gg CH 4 yr −1 ), mainly produced by ruminants and manure management, followed by emissions from waste management (15 Gg CH 4 yr −1 ) mainly from landfills and the energy sector (12 Gg CH 4 yr −1 ), which was dominated by emissions from natural gas distribution. Compared to the anthropogenic sources, emissions from natural and semi-natural sources were relatively small (6 Gg CH 4 yr −1 ), making up only 3 % of the total emissions in Switzerland. CH 4 fluxes from agricultural soils were estimated to be not significantly different from zero (between −1.5 and 0 Gg CH 4 yr −1 ), while forest soils are a CH 4 sink (approx. −2.8 Gg CH 4 yr −1 ), partially offsetting other natural emissions. Estimates of uncertainties are provided for the different sources, including an estimate of spatial disaggregation errors deduced from a comparison with a global (EDGAR v4.2) and a European CH 4 inventory (TNO/MACC). This new spatially-explicit emission inventory for Switzerland will provide valuable input for regional scale atmospheric modeling and inverse source estimation.

Description: Seasonal trends of dry and bulk concentration of nitrogen compounds over a rain forest in Ghana Biogeosciences Discussions, 10, 15225-15255, 2013 Author(s): F. Fattore, T. Bertolini, S. Materia, S. Gualdi, A. Thongo M'Bou, G. Nicolini, R. Valentini, A. De Grandcourt, D. Tedesco, and S. Castaldi African tropical forests of the equatorial belt might receive significant input of extra nitrogen derived from biomass burning occurring in the north savanna belt and transported equator wards by NE winds. In order to test this hypothesis an experiment was set up in a tropical rain forest in the National park of Ankasa (Ghana) aiming at: quantifying magnitude and seasonal variability of concentrations of N compounds, present as gas and aerosol (dry nitrogen) or in the rainfall (bulk nitrogen), over the studied forest; relating their seasonal variability to trends of local and regional winds and rainfall and to variations of fire events in the region. Three Delta systems, implemented for monthly measurements of NO 2 , were mounted over a tower at 45 m height, 20 m above forest canopy to sample gas (NH 3 , NO 2 , HNO 3 , HCl, SO 2 ) and aerosol (NH 4 + , NO 3 − , and several ions), together with three tanks for bulk rainfall collection (to analyze NH 4 + , NO 3 − and ion concentration). The tower was provided with a sonic anemometer to estimate local wind data. The experiment started in October 2011 and data up to October 2012 are presented. To interpret the observed seasonal trends of measured compounds, local and regional meteo data and regional satellite fire data were analyzed. The concentration of N compounds significantly increased from December to April, during the drier period, peaking in December-February when North Eastern winds (Harmattan) were moving dry air masses over the West central African region and the inter tropical convergence zone (ITCZ) was at its minimum latitude over the equator. This period also coincided with peaks of fire in the whole region. On the contrary, N concentration in gas, aerosol and rain decreased from May to October when prevalent winds arrived from the sea (South-East), during the Monsoon period. Both ionic compositions of rain and analysis of local wind direction showed a significant and continuous presence of see-breeze at site. The ionic composition of rain water resulted much closer to see water and poorer in N compounds from May to October.

Description: Optical, microphysical, mass and geometrical properties of aged volcanic particles observed over Athens, Greece, during the Eyjafjallajökull eruption in April 2010 through synergy of Raman lidar and sunphotometer measurements Atmospheric Chemistry and Physics, 13, 9303-9320, 2013 Author(s): P. Kokkalis, A. Papayannis, V. Amiridis, R. E. Mamouri, I. Veselovskii, A. Kolgotin, G. Tsaknakis, N. I. Kristiansen, A. Stohl, and L. Mona Vertical profiles of the optical (extinction and backscatter coefficients, lidar ratio and Ångström exponent), microphysical (mean effective radius, mean refractive index, mean number concentration) and geometrical properties as well as the mass concentration of volcanic particles from the Eyjafjallajökull eruption were retrieved at selected heights over Athens, Greece, using multi-wavelength Raman lidar measurements performed during the period 21–24 April 2010. Aerosol Robotic Network (AERONET) particulate columnar measurements along with inversion schemes were initialized together with lidar observations to deliver the aforementioned products. The well-known FLEXPART (FLEXible PARTicle dispersion model) model used for volcanic dispersion simulations is initiated as well in order to estimate the horizontal and vertical distribution of volcanic particles. Compared with the lidar measurements within the planetary boundary layer over Athens, FLEXPART proved to be a useful tool for determining the state of mixing of ash with other, locally emitted aerosol types. The major findings presented in our work concern the identification of volcanic particles layers in the form of filaments after 7-day transport from the volcanic source (approximately 4000 km away from our site) from the surface and up to 10 km according to the lidar measurements. Mean hourly averaged lidar signals indicated that the layer thickness of volcanic particles ranged between 1.5 and 2.2 km. The corresponding aerosol optical depth was found to vary from 0.01 to 0.18 at 355 nm and from 0.02 up to 0.17 at 532 nm. Furthermore, the corresponding lidar ratios ( S ) ranged between 60 and 80 sr at 355 nm and 44 and 88 sr at 532 nm. The mean effective radius of the volcanic particles estimated by applying inversion scheme to the lidar data found to vary within the range 0.13–0.38 μm and the refractive index ranged from 1.39+0.009 i to 1.48+0.006 i . This high variability is most probably attributed to the mixing of aged volcanic particles with other aerosol types of local origin. Finally, the LIRIC (LIdar/Radiometer Inversion Code) lidar/sunphotometric combined inversion algorithm has been applied in order to retrieve particle concentrations. These have been compared with FLEXPART simulations of the vertical distribution of ash showing good agreement concerning not only the geometrical properties of the volcanic particles layers but also the particles mass concentration.

Description: Corrigendum to "The magnitude and causes of uncertainty in global model simulations of cloud condensation nuclei" published in Atmos. Chem. Phys., 13, 8879–8914, 2013 Atmospheric Chemistry and Physics, 13, 9375-9377, 2013 Author(s): L. A. Lee, K. J. Pringle, C. L. Reddington, G. W. Mann, P. Stier, D. V. Spracklen, J. R. Pierce, and K. S. Carslaw No abstract available.

Description: Inferences from CO 2 and CH 4 concentration profiles at the Zotino Tall Tower Observatory (ZOTTO) on local summer-time ecosystem fluxes Biogeosciences Discussions, 10, 15337-15372, 2013 Author(s): J. Winderlich, C. Gerbig, O. Kolle, and M. Heimann The Siberian region is still sparsely covered by ecosystem observatories, which motivates to exploit existing datasets to gain spatially and temporally better-resolved carbon fluxes. The Zotino Tall Tower Observatory (ZOTTO, 60°48' N, 89°21' E) observations of CO 2 and CH 4 mole fractions as well as meteorological parameters from six different heights up to 301 m allow for an additional estimate of surface-atmosphere fluxes of CO 2 and CH 4 for the Middle-Siberian region since 2009. The total carbon flux is calculated from the storage and the turbulent flux component. The gradients between the different tower levels determine the storage flux component, which dominates the local fluxes, especially during night. As a correction term, the turbulent flux component was estimated by the modified Bowen ratio method based on the sensible heat flux measurements at the top of the tower. The gained average night time fluxes (23:00 to 04:00 local time) are 2.7 ± 1.1 μmol (m 2 s) −1 for CO 2 and 5.6 ± 4.5 nmol (m 2 s) −1 for CH 4 during the summer months June-September in 2009 and 2011. During day, the method is limited due to numeric instabilities from vanishing vertical gradients; however, the derived CO 2 fluxes exhibit reasonable diurnal shape and magnitude compared to the eddy covariance technique, which become available at the site in 2012. Therefore, the tall tower data facilitates the extension of the new eddy covariance flux dataset back in time. The diurnal signal of the CH 4 flux is predominantly characterized by a strong morning transition, which is explained by local topographic effects.

Description: Live foraminiferal faunas (Rose Bengal stained) from the northern Arabian Sea: links with bottom-water oxygenation Biogeosciences Discussions, 10, 15257-15304, 2013 Author(s): C. Caulle, K. A. Koho, M. Mojtahid, G. J. Reichart, and F. J. Jorissen Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea Oxygen Minimum Zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom-water oxygenation (BWO), pore-water chemistry and organic matter (organic carbon and phytopigment) distribution. A series of multicores were recovered from a ten-station oxygen (BWO: 2–78 μM) and bathymetric (885–3010 m depth) transect during the winter monsoon in January 2009. Foraminifera were investigated from three different size fractions (63–125 μm, 125–150 μm and 〉 150 μm). The larger foraminifera (〉 125 μm) were strongly dominated by agglutinated species (e.g. Reophax spp.). In contrast, in the 63–125 μm fraction, calcareous taxa were more abundant, especially in the core of the OMZ, suggesting an opportunistic behaviour. On the basis of a Principal Component Analysis, three foraminiferal groups were identified, reflecting the environmental parameters along the study transect. The faunas from the shallowest stations, in the core of the OMZ (BWO: 2 μM), were composed of "low oxygen" species, typical of the Arabian Sea OMZ (e.g., Rotaliatinopsis semiinvoluta , Praeglobobulimina spp. , Bulimina exilis, Uvigerina peregrina type parva ). These taxa are adapted to the very low BWO conditions and to high phytodetritus supplies. The transitional group, typical for the lower part of the OMZ (BWO: 5–16 μM), is composed of more cosmopolitan taxa tolerant to low-oxygen concentrations ( Globocassidulina subglobosa , Ehrenbergina trigona ). Below the OMZ (BWO: 26–78 μM), where food availability is more limited and becomes increasingly restricted to surficial sediments, more cosmopolitan calcareous taxa were present, such as Bulimina aculeata, Melonis barleeanus, Uvigerina peregrina and Epistominella exigua . Miliolids were uniquely observed in this last group, reflecting the higher BWO. At these deeper sites, the faunas exhibit a clear depth succession of superficial, intermediate and deep-infaunal microhabitats, because of the deeper oxygen and nitrate penetration into the sediment.

Description: Introduction to special issue: the TransBrom Sonne expedition in the tropical West Pacific Atmospheric Chemistry and Physics, 13, 9439-9446, 2013 Author(s): K. Krüger and B. Quack This special section of Atmospheric Chemistry and Physics gives an overview of scientific results, collected during a West Pacific ship expedition in October 2009 with the Research Vessel (R/V) Sonne . The cruise focussed on chemical interactions between the ocean surface and the atmosphere above the tropical West Pacific and was planned within the national research project TransBrom ( www.geomar.de/~transbrom ). TransBrom aimed to particularly investigate very short lived bromine compounds in the ocean and their transport to and relevance for the stratosphere. For this purpose, chemical and biological parameters were analysed in the ocean and in the atmosphere, accompanied by a high frequency of meteorological measurements, to derive new insights into the multidisciplinary research field. This introduction paper presents the scientific goals and the meteorological and oceanographic background. The main research findings of the TransBrom Sonne expedition are highlighted.

Description: Quantitative determination of carbonaceous particle mixing state in Paris using single-particle mass spectrometer and aerosol mass spectrometer measurements Atmospheric Chemistry and Physics, 13, 9479-9496, 2013 Author(s): R. M. Healy, J. Sciare, L. Poulain, M. Crippa, A. Wiedensohler, A. S. H. Prévôt, U. Baltensperger, R. Sarda-Estève, M. L. McGuire, C.-H. Jeong, E. McGillicuddy, I. P. O'Connor, J. R. Sodeau, G. J. Evans, and J. C. Wenger Single-particle mixing state information can be a powerful tool for assessing the relative impact of local and regional sources of ambient particulate matter in urban environments. However, quantitative mixing state data are challenging to obtain using single-particle mass spectrometers. In this study, the quantitative chemical composition of carbonaceous single particles has been determined using an aerosol time-of-flight mass spectrometer (ATOFMS) as part of the MEGAPOLI 2010 winter campaign in Paris, France. Relative peak areas of marker ions for elemental carbon (EC), organic aerosol (OA), ammonium, nitrate, sulfate and potassium were compared with concurrent measurements from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a thermal–optical OCEC analyser and a particle into liquid sampler coupled with ion chromatography (PILS-IC). ATOFMS-derived estimated mass concentrations reproduced the variability of these species well ( R 2 = 0.67–0.78), and 10 discrete mixing states for carbonaceous particles were identified and quantified. The chemical mixing state of HR-ToF-AMS organic aerosol factors, resolved using positive matrix factorisation, was also investigated through comparison with the ATOFMS dataset. The results indicate that hydrocarbon-like OA (HOA) detected in Paris is associated with two EC-rich mixing states which differ in their relative sulfate content, while fresh biomass burning OA (BBOA) is associated with two mixing states which differ significantly in their OA / EC ratios. Aged biomass burning OA (OOA 2 -BBOA) was found to be significantly internally mixed with nitrate, while secondary, oxidised OA (OOA) was associated with five particle mixing states, each exhibiting different relative secondary inorganic ion content. Externally mixed secondary organic aerosol was not observed. These findings demonstrate the range of primary and secondary organic aerosol mixing states in Paris. Examination of the temporal behaviour and chemical composition of the ATOFMS classes also enabled estimation of the relative contribution of transported emissions of each chemical species and total particle mass in the size range investigated. Only 22% of the total ATOFMS-derived particle mass was apportioned to fresh, local emissions, with 78% apportioned to regional/continental-scale emissions.

Description: Landscape-scale changes in forest structure and functional traits along an Andes-to-Amazon elevation gradient Biogeosciences Discussions, 10, 15415-15454, 2013 Author(s): G. P. Asner, C. Anderson, R. E. Martin, D. E. Knapp, R. Tupayachi, T. Kennedy-Bowdoin, F. Sinca, and Y. Malhi Elevation gradients provide opportunities to explore environmental controls on forest structure and functioning, but plot-based studies have proven highly variable due to limited geographic scope. We used airborne imaging spectroscopy and LiDAR (light detection and ranging) to quantify changes in three-dimensional forest structure and canopy functional traits in a series of 25 ha landscapes distributed along a 3300 m elevation gradient from lowland Amazonia to treeline in the Peruvian Andes. Canopy greenness, photosynthetic fractional cover and exposed non-photosynthetic vegetation varied as much across lowland forests (100–200 m) as they did from the lowlands to the Andean treeline (3400 m). Elevation was positively correlated with canopy gap density and understory vegetation cover, and negatively related to canopy height and vertical profile. Increases in gap density were tightly linked to increases in understory plant cover, and larger gaps (20–200 m 2 produced 25–30 times the response in understory cover than did smaller gaps ( 〈 5 m 2 . Scaling of gap size to gap frequency was, however, relatively constant along the elevation gradient, which when combined with other canopy structural information, indicates equilibrium turnover patterns from the lowlands to treeline. Our results provide a first landscape-scale quantification of forest structure and canopy functional traits with changing elevation, thereby improving our understanding of disturbance, demography and ecosystem processes in the Andes-to-Amazon corridor.

Description: Springtime phytoplankton dynamics in the Arctic Krossfjorden and Kongsfjorden (Spitsbergen) as a function of glacier proximity Biogeosciences Discussions, 10, 15519-15557, 2013 Author(s): A. M.-T. Piquet, W. H. van de Poll, R. J. W. Visser, C. Wiencke, H. Bolhuis, and A. G. J. Buma The hydrographic properties of the Kongsfjorden – Krossfjorden system (79° N, Spitsbergen) are affected by Atlantic water incursions as well as glacier meltwater runoff. This results in strong physical gradients (temperature, salinity and irradiance) within the fjords. Here, we tested the hypothesis that glaciers affect phytoplankton dynamics as early as the productive spring bloom period. During two campaigns in 2007 (late spring) and 2008 (early spring) we studied hydrographic characteristics and phytoplankton variability along 2 transects in both fjords, using HPLC-CHEMTAX pigment fingerprinting, molecular fingerprinting (DGGE) and sequencing of 18S rRNA genes. The sheltered inner fjord locations remained colder during spring as opposed to the outer locations. Vertical light attenuation coefficients increased from early spring onwards, at all locations, but in particular at the inner locations. During the end of spring, meltwater input had stratified surface waters throughout the fjords. The inner fjord locations were characterized by overall lower phytoplankton biomass. Furthermore HPLC-CHEMTAX data revealed that diatoms and Phaeocystis sp. were replaced by small nano- and picophytoplankton during late spring, coinciding with low nutrient availability. The innermost stations showed higher relative abundances of nano- and picophytoplankton throughout, notably of cyanophytes and cryptophytes. Molecular fingerprinting revealed a high similarity between inner fjord samples from early spring and late spring samples from all locations, while outer samples from early spring clustered separately. We conclude that glacier influence, mediated by early meltwater input, modifies phytoplankton biomass and composition already during the spring bloom period, in favor of low biomass and small cell size communities. This may affect higher trophic levels especially when regional warming further increases the period and volume of meltwater.

Description: Simulating microbial degradation of organic matter in a simple porous system using the 3-D diffusion based model MOSAIC Biogeosciences Discussions, 10, 15613-15640, 2013 Author(s): O. Monga, P. Garnier, V. Pot, E. Coucheney, N. Nunan, W. Otten, and C. Chenu This paper deals with the simulation of microbial degradation in soil within pore space at microscopic scale. Pore space was described using sphere network coming from a geometrical modeling algorithm. The biological model was improved regarding previous work in order to include transformation of dissolved organic compounds and diffusion processes. Our model was tested using experimental results of a simple substrate decomposition (Fructose) within a simple media (the sand). Diverse microbial communities were inoculated. Separated incubations in microcosms were carried out using 5 different bacterial communities at 2 different water potentials of −10 cm and −100 cm of water. We calibrated the biological parameters by means of experimental data obtained at high water content and we tested the model without any parameters change at low water content. Same as for experimental data, our simulation results showed the decrease in water content involved the decrease of mineralisation. The model was able to simulate the decrease of connectivity between substrate and microorganism due the decrease of water content.

Description: Influence of temperature and CO 2 on the strontium and magnesium composition of coccolithophore calcite Biogeosciences Discussions, 10, 15559-15586, 2013 Author(s): M. N. Müller, M. Lebrato, U. Riebesell, J. Barcelos e Ramos, K. G. Schulz, S. Blanco-Ameijeiras, S. Sett, A. Eisenhauer, and H. M. Stoll Marine calcareous sediments provide a fundamental basis for paleoceanographic studies aiming to reconstruct past oceanic conditions and understand key biogeochemical element cycles. Calcifying unicellular phytoplankton (coccolithophores) are a major contributor to both carbon and calcium cycling by photosynthesis and the production of calcite (coccoliths) in the euphotic zone and the subsequent long-term deposition and burial into marine sediments. Here we present data from controlled laboratory experiments on four coccolithophore species and elucidate the relation between the divalent cation (Sr, Mg and Ca) partitioning in coccoliths and cellular physiology (growth, calcification and photosynthesis). Coccolithophores were cultured under different seawater temperature and carbonate chemistry conditions. The partition coefficient of strontium ( D Sr ) was positively correlated with both carbon dioxide ( p CO 2 ) and temperature but displayed no coherent relation to particulate organic and inorganic carbon production rates. Furthermore, D Sr correlated positively with cellular growth rates when driven by temperature but no correlation was present when changes in growth rates were p CO 2 -induced. The results demonstrate the complex interaction between environmental forcing and physiological control on the strontium partitioning in coccolithophore calcite. The partition coefficient of magnesium ( D Mg ) displayed species-specific differences and elevated values under nutrient limitation. No conclusive correlation between coccolith D Mg and temperature was observed but p CO 2 induced a rising trend in coccolith D Mg . Interestingly, the best correlation was found between coccolith D Mg and chlorophyll a production suggesting that chlorophyll a and calcite associated Mg originate from the same intracellular pool. These results give an extended insight into the driving factors that lead to variations in the coccolith Mg / Ca ratio and can be used for Sr / Ca and Mg / Ca paleoproxy calibration.

Description: Forest NEP is significantly driven by previous year's weather Biogeosciences Discussions, 10, 15587-15611, 2013 Author(s): S. Zielis, S. Etzold, R. Zweifel, W. Eugster, M. Haeni, and N. Buchmann Understanding the response of forest net ecosystem productivity (NEP) to environmental drivers under climate change is highly relevant for predictions of annual forest carbon (C) flux budgets. Modeling annual forest NEP with soil–vegetation–atmosphere transfer models (SVATs), however, remains challenging due to unknown responses of forests to weather of the previous year. In this study, we addressed the influence of previous year's weather on the inter-annual variability of NEP for a subalpine spruce forest in Switzerland. Analysis of long-term (1997–2011) eddy covariance measurements showed that the Norway spruce forest Davos Seehornwald was a consistent sink for atmospheric CO 2 , sequestering 210 ± 88 g C m −2 per year on average. Previous year's weather strongly affected inter-annual variability of NEP, increasing the explained variance in linear models to 53% compared to 20% without previous year's weather. Thus, our results highlight the need to consider previous year's weather in modeling annual C budgets of forests. Furthermore, soil temperature in the current year's spring played a major role controlling annual NEP, mainly by influencing gross primary productivity early in the year, with spring NEP accounting for 56% of annual NEP. Consequently, we expect an increase in net CO 2 uptake with future climate warming, as long as no other resources become limiting.

Description: Influence of the terrestrial magnetic field geometry on the cutoff rigidity of cosmic ray particles Annales Geophysicae, 31, 1637-1643, 2013 Author(s): K. Herbst, A. Kopp, and B. Heber Studies of the propagation of charged energetic particles in the Earth's magnetic field go back to Carl Størmer. In the end, his investigations finally lead to the definition of the so-called cutoff rigidity R C ; that is, the minimum momentum per charge a particle must have in order to reach a certain geographical location. Employing Monte Carlo simulations with the PLANETOCOSMICS code we investigate the correlation between the geomagnetic field structure and the cutoff rigidity. We show that the geometry of the magnetic field has a considerable influence on the resulting cutoff rigidity distribution. Furthermore, we will present a simple geometry-based parameter, δ B , which is able to reflect the location-dependent cutoff rigidity. We show that this correlation is also visible in the temporal evolution of the Earth's magnetic field, at least over the last 100 yr. Using latitude scans with neutron monitors, changes of the relative counting rates at different positions are calculated, showing small variations for, e.g., Kiel and Moscow, while large ones occur at Mexico City as well as on the British Virgin Islands.

Description: Electron acceleration at Jupiter: input from cyclotron-resonant interaction with whistler-mode chorus waves Annales Geophysicae, 31, 1619-1630, 2013 Author(s): E. E. Woodfield, R. B. Horne, S. A. Glauert, J. D. Menietti, and Y. Y. Shprits Jupiter has the most intense radiation belts of all the outer planets. It is not yet known how electrons can be accelerated to energies of 10 MeV or more. It has been suggested that cyclotron-resonant wave-particle interactions by chorus waves could accelerate electrons to a few MeV near the orbit of Io. Here we use the chorus wave intensities observed by the Galileo spacecraft to calculate the changes in electron flux as a result of pitch angle and energy diffusion. We show that, when the bandwidth of the waves and its variation with L are taken into account, pitch angle and energy diffusion due to chorus waves is a factor of 8 larger at L -shells greater than 10 than previously shown. We have used the latitudinal wave intensity profile from Galileo data to model the time evolution of the electron flux using the British Antarctic Survey Radiation Belt (BAS) model. This profile confines intense chorus waves near the magnetic equator with a peak intensity at ∼5° latitude. Electron fluxes in the BAS model increase by an order of magnitude for energies around 3 MeV. Extending our results to L = 14 shows that cyclotron-resonant interactions with chorus waves are equally important for electron acceleration beyond L = 10. These results suggest that there is significant electron acceleration by cyclotron-resonant interactions at Jupiter contributing to the creation of Jupiter's radiation belts and also increasing the range of L -shells over which this mechanism should be considered.

Description: The coupling between the solar wind and proton fluxes at GEO Annales Geophysicae, 31, 1631-1636, 2013 Author(s): R. J. Boynton, S. A. Billings, O. A. Amariutei, and I. Moiseenko The relationship between the solar wind and the proton flux at geosynchronous Earth orbit (GEO) is investigated using the error reduction ratio (ERR) analysis. The ERR analysis is able to search for the most appropriate inputs that control the evolution of the system. This approach is a black box method and is able to derive a mathematical model of a system from input-output data. This method is used to analyse eight energy ranges of the proton flux at GEO from 80 keV to 14.5 MeV. The inputs to the algorithm were solar wind velocity, density and pressure; the Dst index; the solar energetic proton (SEP) flux; and a function of the interplanetary magnetic field (IMF) tangential magnitude and clock angle. The results show that for lowest five energy channels (80 to 800 keV) the GEO proton fluxes are controlled by the solar wind velocity with a lag of two to three days. However, above 350 keV, the SEP fluxes, accounts for a significant portion of the GEO proton flux variance. For the highest three energy channels (0.74 to 14.5 MeV), the SEPs account for the majority of the ERR. The results also show an anisotropy of protons with gyrocenters inside GEO and outside GEO, where the protons inside GEO are controlled partly by the Dst index and also an IMF-clock angle function.

Description: Contact freezing: a review of experimental studies Atmospheric Chemistry and Physics, 13, 9745-9769, 2013 Author(s): L. A. Ladino Moreno, O. Stetzer, and U. Lohmann This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

Description: Validation of XCO 2 derived from SWIR spectra of GOSAT TANSO-FTS with aircraft measurement data Atmospheric Chemistry and Physics, 13, 9771-9788, 2013 Author(s): M. Inoue, I. Morino, O. Uchino, Y. Miyamoto, Y. Yoshida, T. Yokota, T. Machida, Y. Sawa, H. Matsueda, C. Sweeney, P. P. Tans, A. E. Andrews, S. C. Biraud, T. Tanaka, S. Kawakami, and P. K. Patra Column-averaged dry air mole fractions of carbon dioxide (XCO 2 ) retrieved from Greenhouse gases Observing SATellite (GOSAT) Short-Wavelength InfraRed (SWIR) observations were validated with aircraft measurements by the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project, the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. To calculate XCO 2 based on aircraft measurements (aircraft-based XCO 2 ), tower measurements and model outputs were used for additional information near the surface and above the tropopause, respectively. Before validation, we investigated the impacts of GOSAT SWIR column averaging kernels (CAKs) and the shape of a priori profiles on the aircraft-based XCO 2 calculation. The differences between aircraft-based XCO 2 with and without the application of GOSAT CAK were evaluated to be less than ±0.4 ppm at most, and less than ±0.1 ppm on average. Therefore, we concluded that the GOSAT CAK produces only a minor effect on the aircraft-based XCO 2 calculation in terms of the overall uncertainty of GOSAT XCO 2 . We compared GOSAT data retrieved within ±2 or ±5° latitude/longitude boxes centered at each aircraft measurement site to aircraft-based data measured on a GOSAT overpass day. The results indicated that GOSAT XCO 2 over land regions agreed with aircraft-based XCO 2 , except that the former is biased by −0.68 ppm (−0.99 ppm) with a standard deviation of 2.56 ppm (2.51 ppm), whereas the averages of the differences between the GOSAT XCO 2 over ocean and the aircraft-based XCO 2 were −1.82 ppm (−2.27 ppm) with a standard deviation of 1.04 ppm (1.79 ppm) for ±2° (±5°) boxes.

Description: A comparison of atmospheric composition using the Carbon Bond and Regional Atmospheric Chemistry Mechanisms Atmospheric Chemistry and Physics, 13, 9695-9712, 2013 Author(s): G. Sarwar, J. Godowitch, B. H. Henderson, K. Fahey, G. Pouliot, W. T. Hutzell, R. Mathur, D. Kang, W. S. Goliff, and W. R. Stockwell We incorporate the recently developed Regional Atmospheric Chemistry Mechanism (version 2, RACM2) into the Community Multiscale Air Quality modeling system for comparison with the existing 2005 Carbon Bond mechanism with updated toluene chemistry (CB05TU). Compared to CB05TU, RACM2 enhances the domain-wide monthly mean hydroxyl radical concentrations by 46% and nitric acid by 26%. However, it reduces hydrogen peroxide by 2%, peroxyacetic acid by 94%, methyl hydrogen peroxide by 19%, peroxyacetyl nitrate by 40%, and organic nitrate by 41%. RACM2 enhances ozone compared to CB05TU at all ambient levels. Although it exhibited greater overestimates at lower observed concentrations, it displayed an improved performance at higher observed concentrations. The RACM2 ozone predictions are also supported by increased ozone production efficiency that agrees better with observations. Compared to CB05TU, RACM2 enhances the domain-wide monthly mean sulfate by 10%, nitrate by 6%, ammonium by 10%, anthropogenic secondary organic aerosols by 42%, biogenic secondary organic aerosols by 5%, and in-cloud secondary organic aerosols by 7%. Increased inorganic and organic aerosols with RACM2 agree better with observed data. Any air pollution control strategies developed using the two mechanisms do not differ appreciably.

Description: Climate and chemistry effects of a regional scale nuclear conflict Atmospheric Chemistry and Physics, 13, 9713-9729, 2013 Author(s): A. Stenke, C. R. Hoyle, B. Luo, E. Rozanov, J. Gröbner, L. Maag, S. Brönnimann, and T. Peter Previous studies have highlighted the severity of detrimental effects for life on earth after an assumed regionally limited nuclear war. These effects are caused by climatic, chemical and radiative changes persisting for up to one decade. However, so far only a very limited number of climate model simulations have been performed, giving rise to the question how realistic previous computations have been. This study uses the coupled chemistry climate model (CCM) SOCOL, which belongs to a different family of CCMs than previously used, to investigate the consequences of such a hypothetical nuclear conflict. In accordance with previous studies, the present work assumes a scenario of a nuclear conflict between India and Pakistan, each applying 50 warheads with an individual blasting power of 15 kt ("Hiroshima size") against the major population centers, resulting in the emission of tiny soot particles, which are generated in the firestorms expected in the aftermath of the detonations. Substantial uncertainties related to the calculation of likely soot emissions, particularly concerning assumptions of target fuel loading and targeting of weapons, have been addressed by simulating several scenarios, with soot emissions ranging from 1 to 12 Tg. Their high absorptivity with respect to solar radiation leads to a rapid self-lofting of the soot particles into the strato- and mesosphere within a few days after emission, where they remain for several years. Consequently, the model suggests earth's surface temperatures to drop by several degrees Celsius due to the shielding of solar irradiance by the soot, indicating a major global cooling. In addition, there is a substantial reduction of precipitation lasting 5 to 10 yr after the conflict, depending on the magnitude of the initial soot release. Extreme cold spells associated with an increase in sea ice formation are found during Northern Hemisphere winter, which expose the continental land masses of North America and Eurasia to a cooling of several degrees. In the stratosphere, the strong heating leads to an acceleration of catalytic ozone loss and, consequently, to enhancements of UV radiation at the ground. In contrast to surface temperature and precipitation changes, which show a linear dependence to the soot burden, there is a saturation effect with respect to stratospheric ozone chemistry. Soot emissions of 5 Tg lead to an ozone column reduction of almost 50% in northern high latitudes, while emitting 12 Tg only increases ozone loss by a further 10%. In summary, this study, though using a different chemistry climate model, corroborates the previous investigations with respect to the atmospheric impacts. In addition to these persistent effects, the present study draws attention to episodically cold phases, which would likely add to the severity of human harm worldwide. The best insurance against such a catastrophic development would be the delegitimization of nuclear weapons.

Description: Synoptic evaluation of carbon cycling in Beaufort Sea during summer: contrasting river inputs, ecosystem metabolism and air–sea CO 2 fluxes Biogeosciences Discussions, 10, 15641-15710, 2013 Author(s): A. Forest, P. Coupel, B. Else, S. Nahavandian, B. Lansard, P. Raimbault, T. Papakyriakou, Y. Gratton, L. Fortier, J.-É. Tremblay, and M. Babin The accelerated decline in Arctic sea ice combined with an ongoing trend toward a more dynamic atmosphere is modifying carbon cycling in the Arctic Ocean. A critical issue is to understand how net community production (NCP; the balance between gross primary production and community respiration) responds to changes and modulates air–sea CO 2 fluxes. Using data collected as part of the ArcticNet-Malina 2009 expedition in southeastern Beaufort Sea (Arctic Ocean), we synthesize information on sea ice, wind, river, water column properties, metabolism of the planktonic food web, organic carbon fluxes and pools, as well as air–sea CO 2 exchange, with the aim of identifying indices of ecosystem response to environmental changes. Data were analyzed to develop a non-steady-state carbon budget and an assessment of NCP against air–sea CO 2 fluxes. The mean atmospheric forcing was a mild upwelling-favorable wind (~5 km h −1 ) blowing from the N-E and a decaying ice cover ( 600 mg C m −2 d −1 ) over the shelf prior to our survey, (2) freshwater dilution by river runoff and ice melt, and (3) the presence of cold surface waters offshore. Only the Mackenzie River delta and localized shelf areas directly affected by upwelling were identified as substantial sources of CO 2 to the atmosphere (〉10mmol C m −2 d −1 ). Although generally

Description: Observations of peroxyacetyl nitrate (PAN) in the upper troposphere by the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) Atmospheric Chemistry and Physics, 13, 5601-5613, 2013 Author(s): K. A. Tereszchuk, D. P. Moore, J. J. Harrison, C. D. Boone, M. Park, J. J. Remedios, W. J. Randel, and P. F. Bernath Peroxyacetyl nitrate (CH 3 CO·O 2 NO 2 , abbreviated as PAN) is a trace molecular species present in the troposphere and lower stratosphere due primarily to pollution from fuel combustion and the pyrogenic outflows from biomass burning. In the lower troposphere, PAN has a relatively short lifetime and is principally destroyed within a few hours through thermolysis, but it can act as a reservoir and carrier of NO x in the colder temperatures of the upper troposphere, where UV photolysis becomes the dominant loss mechanism. Pyroconvective updrafts from large biomass burning events can inject PAN into the upper troposphere and lower stratosphere (UTLS), providing a means for the long-range transport of NO x . Given the extended lifetimes at these higher altitudes, PAN is readily detectable via satellite remote sensing. A new PAN data product is now available for the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) version 3.0 data set. We report observations of PAN in boreal biomass burning plumes recorded during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) campaign (12 July to 3 August 2011). The retrieval method employed by incorporating laboratory-recorded absorption cross sections into version 3.0 of the ACE-FTS forward model and retrieval software is described in full detail. The estimated detection limit for ACE-FTS PAN is 5 pptv, and the total systematic error contribution to the ACE-FTS PAN retrieval is ~ 16%. The retrieved volume mixing ratio (VMR) profiles are compared to coincident measurements made by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument on the European Space Agency (ESA) Environmental Satellite (ENVISAT). The MIPAS measurements demonstrated good agreement with the ACE-FTS VMR profiles for PAN, where the measured VMR values are well within the associated measurement errors for both instruments and comparative measurements differ no more than 70 pptv. The ACE-FTS PAN data set is used to obtain zonal mean distributions of seasonal averages from ~ 5–20 km. A strong seasonality is clearly observed for PAN concentrations in the global UTLS. Since the principal source of PAN in the UTLS is due to lofted biomass burning emissions from the pyroconvective updrafts created by large fires, the observed seasonality in enhanced PAN coincides with fire activity in different geographical regions throughout the year.

Description: Multiple daytime nucleation events in semi-clean savannah and industrial environments in South Africa: analysis based on observations Atmospheric Chemistry and Physics, 13, 5523-5532, 2013 Author(s): A. Hirsikko, V. Vakkari, P. Tiitta, J. Hatakka, V.-M. Kerminen, A.-M. Sundström, J. P. Beukes, H. E. Manninen, M. Kulmala, and L. Laakso Recent studies have shown very high frequencies of atmospheric new particle formation in different environments in South Africa. Our aim here was to investigate the causes for two or three consecutive daytime nucleation events, followed by subsequent particle growth during the same day. We analysed 108 and 31 such days observed in a polluted industrial and moderately polluted rural environments, respectively, in South Africa. The analysis was based on two years of measurements at each site. After rejecting the days having notable changes in the air mass origin or local wind direction, i.e. two major reasons for observed multiple nucleation events, we were able to investigate other factors causing this phenomenon. Clouds were present during, or in between most of the analysed multiple particle formation events. Therefore, some of these events may have been single events, interrupted somehow by the presence of clouds. From further analysis, we propose that the first nucleation and growth event of the day was often associated with the mixing of a residual air layer rich in SO 2 (oxidized to sulphuric acid) into the shallow surface-coupled layer. The second nucleation and growth event of the day usually started before midday and was sometimes associated with renewed SO 2 emissions from industrial origin. However, it was also evident that vapours other than sulphuric acid were required for the particle growth during both events. This was especially the case when two simultaneously growing particle modes were observed. Based on our analysis, we conclude that the relative contributions of estimated H 2 SO 4 and other vapours on the first and second nucleation and growth events of the day varied from day to day, depending on anthropogenic and natural emissions, as well as atmospheric conditions.

Description: Evolution of particle composition in CLOUD nucleation experiments Atmospheric Chemistry and Physics, 13, 5587-5600, 2013 Author(s): H. Keskinen, A. Virtanen, J. Joutsensaari, G. Tsagkogeorgas, J. Duplissy, S. Schobesberger, M. Gysel, F. Riccobono, J. G. Slowik, F. Bianchi, T. Yli-Juuti, K. Lehtipalo, L. Rondo, M. Breitenlechner, A. Kupc, J. Almeida, A. Amorim, E. M. Dunne, A. J. Downard, S. Ehrhart, A. Franchin, M.K. Kajos, J. Kirkby, A. Kürten, T. Nieminen, V. Makhmutov, S. Mathot, P. Miettinen, A. Onnela, T. Petäjä, A. Praplan, F. D. Santos, S. Schallhart, M. Sipilä, Y. Stozhkov, A. Tomé, P. Vaattovaara, D. Wimmer, A. Prevot, J. Dommen, N. M. Donahue, R.C. Flagan, E. Weingartner, Y. Viisanen, I. Riipinen, A. Hansel, J. Curtius, M. Kulmala, D. R. Worsnop, U. Baltensperger, H. Wex, F. Stratmann, and A. Laaksonen Sulphuric acid, ammonia, amines, and oxidised organics play a crucial role in nanoparticle formation in the atmosphere. In this study, we investigate the composition of nucleated nanoparticles formed from these compounds in the CLOUD (Cosmics Leaving Outdoor Droplets) chamber experiments at CERN (Centre européen pour la recherche nucléaire). The investigation was carried out via analysis of the particle hygroscopicity, ethanol affinity, oxidation state, and ion composition. Hygroscopicity was studied by a hygroscopic tandem differential mobility analyser and a cloud condensation nuclei counter, ethanol affinity by an organic differential mobility analyser and particle oxidation level by a high-resolution time-of-flight aerosol mass spectrometer. The ion composition was studied by an atmospheric pressure interface time-of-flight mass spectrometer. The volume fraction of the organics in the particles during their growth from sizes of a few nanometers to tens of nanometers was derived from measured hygroscopicity assuming the Zdanovskii–Stokes–Robinson relationship, and compared to values gained from the spectrometers. The ZSR-relationship was also applied to obtain the measured ethanol affinities during the particle growth, which were used to derive the volume fractions of sulphuric acid and the other inorganics (e.g. ammonium salts). In the presence of sulphuric acid and ammonia, particles with a mobility diameter of 150 nm were chemically neutralised to ammonium sulphate. In the presence of oxidation products of pinanediol, the organic volume fraction of freshly nucleated particles increased from 0.4 to ~0.9, with an increase in diameter from 2 to 63 nm. Conversely, the sulphuric acid volume fraction decreased from 0.6 to 0.1 when the particle diameter increased from 2 to 50 nm. The results provide information on the composition of nucleated aerosol particles during their growth in the presence of various combinations of sulphuric acid, ammonia, dimethylamine and organic oxidation products.

Description: Comparison of three vertically resolved ozone data sets: climatology, trends and radiative forcings Atmospheric Chemistry and Physics, 13, 5533-5550, 2013 Author(s): B. Hassler, P. J. Young, R. W. Portmann, G. E. Bodeker, J. S. Daniel, K. H. Rosenlof, and S. Solomon Climate models that do not simulate changes in stratospheric ozone concentrations require the prescription of ozone fields to accurately calculate UV fluxes and stratospheric heating rates. In this study, three different global ozone time series that are available for this purpose are compared: the data set of Randel and Wu (2007) (RW07), Cionni et al. (2011) (SPARC), and Bodeker et al. (2013) (BDBP). All three data sets represent multiple-linear regression fits to vertically resolved ozone observations, resulting in a spatially and temporally continuous stratospheric ozone field covering at least the period from 1979 to 2005. The main differences among the data sets result from regression models, which use different observations and include different basis functions. The data sets are compared against ozonesonde and satellite observations to assess how the data sets represent concentrations, trends and interannual variability. In the Southern Hemisphere polar region, RW07 and SPARC underestimate the ozone depletion in spring ozonesonde measurements. A piecewise linear trend regression is performed to estimate the 1979–1996 ozone decrease globally, covering a period of extreme depletion in most regions. BDBP overestimates Arctic and tropical ozone depletion over this period relative to the available measurements, whereas the depletion is underestimated in RW07 and SPARC. While the three data sets yield ozone concentrations that are within a range of different observations, there is a large spread in their respective ozone trends. One consequence of this is differences of almost a factor of four in the calculated stratospheric ozone radiative forcing between the data sets (RW07: −0.038 Wm −2 , SPARC: −0.033 Wm −2 , BDBP: −0.119 Wm −2 ), important in assessing the contribution of stratospheric ozone depletion to the total anthropogenic radiative forcing.

Description: Foraminiferal survival after long term experimentally induced anoxia Biogeosciences Discussions, 10, 9243-9284, 2013 Author(s): D. Langlet, E. Geslin, C. Baal, E. Metzger, F. Lejzerowicz, B. Riedel, M. Zuschin, J. Pawlowski, M. Stachowitsch, and F. J. Jorissen Anoxia has been successfully induced in four benthic chambers installed on the Northern Adriatic seafloor from 1 week to 10 months. To accurately determine whether benthic foraminifera can survive experimentally induced prolonged anoxia, the CellTrackerGreen method has been applied. Numerous individuals have been found living at all sampling times and at all sampling depths, showing that benthic foraminifera can survive up to 10 months of anoxia with co-occurring hydrogen sulphides. However, foraminiferal standing stocks decrease with sampling time in an irregular way. A large difference in standing stock between two cores samples in initial conditions indicates the presence of a large spatial heterogeneity of the foraminiferal faunas. An unexpected increase in standing stocks after 1 month is tentatively interpreted as a reaction to increased food availability due to the massive mortality of infaunal macrofaunal organisms. After this, standing stocks decrease again in a core sampled after 2 months of anoxia, to attain a minimum in the cores sampled after 10 months. We speculate that the trend of overall decrease of standing stocks is not due to the adverse effects of anoxia and hydrogen sulphides, but rather due to a continuous diminution of labile organic matter.

Description: Environmental controls on the Emiliania huxleyi calcite mass Biogeosciences Discussions, 10, 9285-9313, 2013 Author(s): M. T. Horigome, P. Ziveri, M. Grelaud, K.-H. Baumann, G. Marino, and P. G. Mortyn Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO 3 2− ], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO 3 2− ]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi , the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO 2 world and improve interpretation of paleorecords.

Description: A statistical study on O + flux in the dayside magnetosheath Annales Geophysicae, 31, 1005-1010, 2013 Author(s): R. Slapak, H. Nilsson, and L. G. Westerberg Studies on terrestrial oxygen ion (O + ) escape into the interplanetary space have considered a number of different escape paths. Recent observations however suggest a yet insufficiently investigated additional escape route for hot O + : along open magnetic field lines in the high altitude cusp and mantle. Here we present a statistical study on O + flux in the high-latitude dayside magnetosheath. The O + is generally seen relatively close to the magnetopause, consistent with observations of O + flowing primarily tangentially to the magnetopause. We estimate the total escape flux in this region to be ~ 7 × 10 24 s −1 , implying this escape route to significantly contribute to the overall total O + loss into interplanetary space.

Description: Newly observed peroxides and the water effect on the formation and removal of hydroxyalkyl hydroperoxides in the ozonolysis of isoprene Atmospheric Chemistry and Physics, 13, 5671-5683, 2013 Author(s): D. Huang, Z. M. Chen, Y. Zhao, and H. Liang The ozonolysis of alkenes is considered to be an important source of atmospheric peroxides, which serve as oxidants, reservoirs of HO x radicals, and components of secondary organic aerosols (SOAs). Recent laboratory investigations of this reaction identified hydrogen peroxide (H 2 O 2 ) and hydroxymethyl hydroperoxide (HMHP) in ozonolysis of isoprene. Although larger hydroxyalkyl hydroperoxides (HAHPs) were also expected, their presence is not currently supported by experimental evidence. In the present study, we investigated the formation of peroxides in the gas phase ozonolysis of isoprene at various relative humidities on a time scale of tens of seconds, using a quartz flow tube reactor coupled with the online detection of peroxides. We detected a variety of conventional peroxides, including H 2 O 2 , HMHP, methyl hydroperoxide, bis-hydroxymethyl hydroperoxide, and ethyl hydroperoxide, and interestingly found three unknown peroxides. The molar yields of the conventional peroxides fell within the range of values provided in the literature. The three unknown peroxides had a combined molar yield of ~ 30% at 5% relative humidity (RH), which was comparable with that of the conventional peroxides. Unlike H 2 O 2 and HMHP, the molar yields of these three unknown peroxides were inversely related to the RH. On the basis of experimental kinetic and box model analysis, we tentatively assigned these unknown peroxides to C2−C4 HAHPs, which are produced by the reactions of different Criegee intermediates with water. Our study provides experimental evidence for the formation of large HAHPs in the ozonolysis of isoprene (one of the alkenes). These large HAHPs have a sufficiently long lifetime, estimated as tens of minutes, which allows them to become involved in atmospheric chemical processes, e.g., SOA formation and radical recycling.

Description: UV-induced carbon monoxide emission from living vegetation Biogeosciences Discussions, 10, 9373-9388, 2013 Author(s): D. Bruhn, K. R. Albert, T. N. Mikkelsen, and P. Ambus The global burden of carbon monoxide (CO) is rather uncertain. In this paper we address the potential for UV-induced CO emission by living terrestrial vegetation surfaces. Real-time measurements of CO concentrations were made with a cavity enhanced laser spectrometer connected in closed loop to either an ecosystem chamber or a plant-leaf scale chamber. Leaves of all examined plant species exhibited emission of CO in response to artificial UV-radiation as well as the UV-component of natural solar radiation. The UV-induced rate of CO emission exhibited a rather low dependence on temperature, indicating an abiotic process. The emission of CO in response to the UV-component of natural solar radiation was also evident at the ecosystem scale.

Description: Simulation of the influence of historical land cover changes on the global climate Annales Geophysicae, 31, 995-1004, 2013 Author(s): Y. Wang, X. Yan, and Z. Wang In order to estimate biogeophysical effects of historical land cover change on climate during last three centuries, a set of experiments with a climate system model of intermediate complexity (MPM-2) is performed. In response to historical deforestation, the model simulates a decrease in annual mean global temperature in the range of 0.07–0.14 °C based on different grassland albedos. The effect of land cover changes is most pronounced in the middle northern latitudes with maximum cooling reaching approximately 0.6 °C during northern summer. The cooling reaches 0.57 °C during northern spring owing to the large effects of land surface albedo. These results suggest that land cover forcing is important for study on historical climate change and that more research is necessary in the assessment of land management options for climate change mitigation.

Description: Nutrient dynamics in tropical rivers, estuarine-lagoons, and coastal ecosystems along the eastern Hainan Island Biogeosciences Discussions, 10, 9091-9147, 2013 Author(s): R. H. Li, S. M. Liu, Y. W. Li, G. L. Zhang, J. L. Ren, and J. Zhang Nutrient dynamics were studied along the eastern Hainan Island based on field observations during 2006–2009, to understand nutrient biogeochemical processes and to have an overview of human perturbations on coastal ecosystems in this tropical region. The concentrations of nutrients in the rivers had seasonal variations enriched with dissolved inorganic nitrogen (DIN). High riverine concentrations of nitrate were mainly originated from agricultural fertilizer input. The ratios of DIN : PO 4 3− ranged from 37 to 1063, suggesting preferential PO 4 3− relative to nitrogen in the rivers. The areal yields of dissolved silicate (DSi) varied from 76 to 448 × 10 3 mol km −2 yr −1 due to erosion over the drainage area, inducing high levels of DSi among worldwide tropical systems. Aquaculture ponds contained high concentrations of NH 4 + (up to 157 μM) and DON (up to 130 μM). Particulate phosphorus concentrations (0.5 ∼1.4 μM) were in lower level comparied with estuaries around the world. Particulate silicate levels in rivers and lagoons were lower than global average level. Nutrient biogeochemistry in coastal areas were affected by human activities (e.g. aquaculture, agriculture), as well as natural events such as typhoon. Nutrient concentrations were low because open sea water dispersed land-derived nutrients. Nutrient budgets were built based on a steady-state box model, which showed that riverine fluxes would be magnified by estuarine processes (e.g. regeneration, desorption) in the Wenchanghe/Wenjiaohe Estuary, Wanquan River estuary, and the Laoyehai Lagoon except in the Xiaohai Lagoon. Riverine and groundwater input were the major sources of nutrients to the Xiaohai Lagoon and the Laiyehai Lagoon, respectively. Riverine input and aquaculture effluent were the major sources of nutrients to the eastern coastal of Hainan Island. Nutrient inputs to the coastal ecosystem can be increased by typhoon-induced runoff of rainwater, and phytoplankton bloom in the sea would be caused.

Description: Megacity impacts on regional ozone formation: observations and WRF-Chem modeling for the MIRAGE-Shanghai field campaign Atmospheric Chemistry and Physics, 13, 5655-5669, 2013 Author(s): X. Tie, F. Geng, A. Guenther, J. Cao, J. Greenberg, R. Zhang, E. Apel, G. Li, A. Weinheimer, J. Chen, and C. Cai The MIRAGE-Shanghai experiment was designed to characterize the factors controlling regional air pollution near a Chinese megacity (Shanghai) and was conducted during September 2009. This paper provides information on the measurements conducted for this study. In order to have some deep analysis of the measurements, a regional chemical/dynamical model (version 3 of Weather Research and Forecasting Chemical model – WRF-Chemv3) is applied for this study. The model results are intensively compared with the measurements to evaluate the model capability for calculating air pollutants in the Shanghai region, especially the chemical species related to ozone formation. The results show that the model is able to calculate the general distributions (the level and the variability) of air pollutants in the Shanghai region, and the differences between the model calculation and the measurement are mostly smaller than 30%, except the calculations of HONO (nitrous acid) at PD (Pudong) and CO (carbon monoxide) at DT (Dongtan). The main scientific focus is the study of ozone chemical formation not only in the urban area, but also on a regional scale of the surrounding area of Shanghai. The results show that during the experiment period, the ozone photochemical formation was strongly under the VOC (volatile organic compound)-limited condition in the urban area of Shanghai. Moreover, the VOC-limited condition occurred not only in the city, but also in the larger regional area. There was a continuous enhancement of ozone concentrations in the downwind of the megacity of Shanghai, resulting in a significant enhancement of ozone concentrations in a very large regional area in the surrounding region of Shanghai. The sensitivity study of the model suggests that there is a threshold value for switching from VOC-limited condition to NO x (nitric oxide and nitrogen dioxide)-limited condition. The threshold value is strongly dependent on the emission ratio of NO x / VOCs. When the ratio is about 0.4, the Shanghai region is under a strong VOC-limited condition over the regional scale. In contrast, when the ratio is reduced to about 0.1, the Shanghai region is under a strong NO x -limited condition. The estimated threshold value (on the regional scale) for switching from VOC-limited to NO x -limited condition ranges from 0.1 to 0.2. This result has important implications for ozone production in this region and will facilitate the development of effective O 3 control strategies in the Shanghai region.

Description: Estimate of surface direct radiative forcing of desert dust from atmospheric modulation of the aerosol optical depth Atmospheric Chemistry and Physics, 13, 5647-5654, 2013 Author(s): A. di Sarra, D. Fuà, and D. Meloni Measurements carried out on the island of Lampedusa, in the central Mediterranean, on 7 September 2005, show the occurrence of a quasi-periodic oscillation of aerosol optical depth, column water vapour, and surface irradiance in different spectral bands. The oscillation has a period of about 13 min and is attributed to the propagation of a gravity wave able to modify the vertical structure of the planetary boundary layer, as also confirmed by satellite images. The wave occurred during a Saharan dust event. The oscillation amplitude is about 0.1 for the aerosol optical depth, and about 0.4 cm for the column water vapour. The modulation of the downward surface irradiances is in opposition of phase with respect to aerosol optical depth and water vapour column variations. The perturbation of the downward irradiance produced by the aerosols is determined by comparing the measured irradiances with estimated irradiances at a fixed value of the aerosol optical depth, and by correcting for the effect of the water vapour in the shortwave spectral range. The direct radiative forcing efficiency, i.e., the radiative perturbation of the net surface irradiance produced by a unit of optical depth aerosol layer, is determined at different solar zenith angles as the slope of the irradiance perturbation versus the aerosol optical depth. The estimated direct surface forcing efficiency at about 60° solar zenith angle is −(181 ± 17) W m −2 in the shortwave, and −(83 ± 7) W m −2 in the photosynthetic spectral range. The estimated daily average forcing efficiencies are of about −79 and −46 W m −2 for the shortwave and photosynthetic spectral range, respectively.

Description: Southern Hemisphere imprint for Indo–Asian summer monsoons during the last glacial period as revealed by Arabian Sea productivity records Biogeosciences Discussions, 10, 9315-9343, 2013 Author(s): T. Caley, S. Zaragosi, J. Bourget, P. Martinez, B. Malaizé, F. Eynaud, L. Rossignol, T. Garlan, and N. Ellouz-Zimmermann The monsoon is one of the most important climatic phenomena: it promotes inter-hemispheric exchange of energy and affects the economical prosperity of several countries exposed to its seasonal seesaw. Previous studies in both the Indian and Asian monsoon systems have suggested a dominant north hemispheric (NH) control on summer monsoon dynamics at the scale of suborbital-millennial climatic changes, while the forcing/response of Indian and Asian monsoons at the orbital scale remains a matter of debate. Here nine marine sediment cores distributed across the whole Arabian Sea are used to build a regional surface marine productivity signal. The productivity signal is driven by the intensity of Indian summer monsoon winds. Results demonstrate the existence of an imprint of suborbital Southern Hemisphere (SH) temperature changes (i.e., Antarctica) on the Indian summer monsoon during the last glacial period, challenging the traditional and exclusive NH forcing hypothesis. Meanwhile, during the last deglaciation, the NH plays a more significant role. The δ 18 O signal recorded in the Asian monsoon speleothem records could be exported by winds from the Indian summer monsoon region, as recently proposed in modelling exercise, explaining the SH signature observed in Asian cave speleothems. Contrary to the view of a passive response of Indian and Asian monsoons to NH anomalies, the present results strongly suggest that the Indo–Asian summer monsoon plays an active role in amplifying millennial inter-hemispheric asymmetric patterns. Additionally, this study helps to decipher the observed differences between Indian and Asian-speleothem monsoonal records at the orbital-precession scale.

Description: IMF effect on the polar cap contraction and expansion during a period of substorms Annales Geophysicae, 31, 1021-1034, 2013 Author(s): A. T. Aikio, T. Pitkänen, I. Honkonen, M. Palmroth, and O. Amm The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase. In addition, we suggest that the IMF B z component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

Description: Heterogeneity of impacts of high CO 2 on the North Western European Shelf Biogeosciences Discussions, 10, 9389-9413, 2013 Author(s): Y. Artioli, J. C. Blackford, G. Nondal, R. G. J. Bellerby, S. L. Wakelin, J.T. Holt, M. Butenschön, and J. I. Allen The increase in atmospheric CO 2 is a dual threat to the marine environment: from one side it drives climate change leading to changes in water temperature, circulation patterns and stratification intensity; on the other side it causes a decrease in pH (Ocean Acidification or OA) due to the increase in dissolved CO 2 . Assessing the combined impact of climate change and OA on marine ecosystems is a challenging task: the response of the ecosystem to a single driver is highly variable and still uncertain, as well as the interaction between these that could be either synergistic or antagonistic. In this work we use the coupled oceanographic-ecosystem model POLCOMS-ERSEM driven by climate forcing to study the interaction between climate change and OA. We focus in particular on primary production and nitrogen speciation. The model has been run in three different configurations in order to separate the impacts of ocean acidification from those due to climate change. The model shows significant interaction among the drivers and high variability in the spatial response of the ecosystem. Impacts of climate change and of OA on primary production have similar magnitude, compensating in some area and exacerbating in others. On the contrary, the direct impact of OA on nitrification is much lower than the one imposed by climate change.

Description: On the "well-mixed" assumption and numerical 2-D tracing of atmospheric moisture Atmospheric Chemistry and Physics, 13, 5567-5585, 2013 Author(s): H. F. Goessling and C. H. Reick Atmospheric water vapour tracers (WVTs) are an elegant tool to determine source–sink relations of moisture "online" in atmospheric general circulation models (AGCMs). However, it is sometimes desirable to establish such relations "offline" based on already existing atmospheric data (e.g. reanalysis data). One simple and frequently applied offline method is 2-D moisture tracing. It makes use of the "well-mixed" assumption, which allows for treating the vertical dimension integratively. Here we scrutinise the "well-mixed" assumption and 2-D moisture tracing by means of analytical considerations in combination with AGCM-WVT simulations. We find that vertically well-mixed conditions are seldom met. Due to the presence of vertical inhomogeneities, 2-D moisture tracing (i) neglects a significant degree of fast-recycling, and (ii) results in erroneous advection where the direction of the horizontal winds varies vertically. The latter is not so much the case in the extratropics, but in the tropics this can lead to large errors. For example, computed by 2-D moisture tracing, the fraction of precipitation in the western Sahel that originates from beyond the Sahara is ~40%, whereas the fraction that originates from the tropical and Southern Atlantic is only ~4%. According to full (i.e. 3-D) moisture tracing, however, both regions contribute roughly equally, showing that the errors introduced by the 2-D approximation can be substantial.

Description: Southern hemispheric halon trends and global halon emissions, 1978–2011 Atmospheric Chemistry and Physics, 13, 5551-5565, 2013 Author(s): M. J. Newland, C. E. Reeves, D. E. Oram, J. C. Laube, W. T. Sturges, C. Hogan, P. Begley, and P. J. Fraser The atmospheric records of four halons, H-1211 (CBrClF 2 ), H-1301 (CBrF 3 ), H-2402 (CBrF 2 CBrF 2 ) and H-1202 (CBr 2 F 2 ), measured from air collected at Cape Grim, Tasmania, between 1978 and 2011, are reported. Mixing ratios of H-1211, H-2402 and H-1202 began to decline in the early to mid-2000s, but those of H-1301 continue to increase up to mid-2011. These trends are compared to those reported by NOAA (National Oceanic and Atmospheric Administration) and AGAGE (Advanced Global Atmospheric Experiment). The observations suggest that the contribution of the halons to total tropospheric bromine at Cape Grim has begun to decline from a peak in 2008 of about 8.1 ppt. An extrapolation of halon mixing ratios to 2060, based on reported banks and predicted release factors, shows this decline becoming more rapid in the coming decades, with a contribution to total tropospheric bromine of about 3 ppt in 2060. Top-down global annual emissions of the halons were derived using a two-dimensional atmospheric model. The emissions of all four have decreased since peaking in the late 1980s–mid-1990s, but this decline has slowed recently, particularly for H-1301 and H-2402 which have shown no decrease in emissions over the past five years. The UEA (University of East Anglia) top-down model-derived emissions are compared to those reported using a top-down approach by NOAA and AGAGE and the bottom-up estimates of HTOC (Halons Technical Options Committee). The implications of an alternative set of steady-state atmospheric lifetimes are discussed. Using a lifetime of 14 yr or less for H-1211 to calculate top-down emissions estimates would lead to small, or even negative, estimated banks given reported production data. Finally emissions of H-1202, a product of over-bromination during the production process of H-1211, have continued despite reported production of H-1211 ceasing in 2010. This raises questions as to the source of these H-1202 emissions.

Description: Impacts of aircraft emissions on the air quality near the ground Atmospheric Chemistry and Physics, 13, 5505-5522, 2013 Author(s): H. Lee, S. C. Olsen, D. J. Wuebbles, and D. Youn The continuing increase in demand for commercial aviation transport raises questions about the effects of resulting emissions on the environment. The purpose of this study is to investigate, using a global chemistry transport model, to what extent aviation emissions outside the boundary layer influence air quality in the boundary layer. The large-scale effects of current levels of aircraft emissions were studied through comparison of multiple simulations allowing for the separated effects of aviation emissions occurring in the low, middle and upper troposphere. We show that emissions near cruise altitudes (9–11 km in altitude) rather than emissions during landing and take-off are responsible for most of the total odd-nitrogen (NO y ), ozone (O 3 ) and aerosol perturbations near the ground with a noticeable seasonal difference. Overall, the perturbations of these species are smaller than 1 ppb even in winter when the perturbations are greater than in summer. Based on the widely used air quality standards and uncertainty of state-of-the-art models, we conclude that aviation-induced perturbations have a negligible effect on air quality even in areas with heavy air traffic. Aviation emissions lead to a less than 1% aerosol enhancement in the boundary layer due to a slight increase in ammonium nitrate (NH 4 NO 3 ) during cold seasons and a statistically insignificant aerosol perturbation in summer. In addition, statistical analysis using probability density functions, Hellinger distance, and p value indicate that aviation emissions outside the boundary layer do not affect the occurrence of extremely high aerosol concentrations in the boundary layer. An additional sensitivity simulation assuming the doubling of surface ammonia emissions demonstrates that the aviation induced aerosol increase near the ground is highly dependent on background ammonia concentrations whose current range of uncertainty is large.

Description: Corrigendum to "Tropospheric NO 2 vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008–2011) and satellite validation" published in Atmos. Chem. Phys., 13, 1547–1567, 2013 Atmospheric Chemistry and Physics, 13, 5629-5629, 2013 Author(s): J. Z. Ma, S. Beirle, J. L. Jin, R. Shaiganfar, P. Yan, and T. Wagner No abstract available.

Description: Large-eddy simulation of organized precipitating trade wind cumulus clouds Atmospheric Chemistry and Physics, 13, 5631-5645, 2013 Author(s): A. Seifert and T. Heus Trade wind cumulus clouds often organize in along-wind cloud streets and across-wind mesoscale arcs. We present a benchmark large-eddy simulation which resolves the individual clouds as well as the mesoscale organization on scales of O(10 km). Different methods to quantify organization of cloud fields are applied and discussed. Using perturbed physics large-eddy simulation experiments, the processes leading to the formation of cloud clusters and the mesoscale arcs are revealed. We find that both cold pools as well as the sub-cloud layer moisture field are crucial to understand the organization of precipitating shallow convection. Further sensitivity studies show that microphysical assumptions can have a pronounced impact on the onset of cloud organization.

Description: On the role of mesoscale eddies for the biological productivity and biogeochemistry in the eastern tropical Pacific Ocean off Peru Biogeosciences Discussions, 10, 9179-9211, 2013 Author(s): L. Stramma, H. W. Bange, R. Czeschel, A. Lorenzo, and M. Frank Mesoscale eddies seem to play an important role for both the hydrography and biogeochemistry of the eastern tropical Pacific Ocean (ETSP) off Peru. However, detailed surveys of these eddies are not available, which has so far hampered an in depth understanding of their implications for nutrient distribution and biological productivity. In this study three eddies along a section at 16°45' S have been surveyed intensively during R/V Meteor cruise M90 in November 2012. A coastal mode water eddy, an open ocean mode water eddy and an open ocean cyclonic eddy have been identified and sampled in order to determine both their hydrographic properties and their influence on the biogeochemical setting of the ETSP. In the thermocline the temperature of the coastal anticyclonic eddy was up to 2 °C warmer, 0.2 more saline and the swirl velocity was up to 35 cm s –1 . The observed temperature and salinity anomalies, as well as swirl velocities of both types of eddies were about twice as large as had been described for the mean eddies in the ETSP and the observed heat and salt anomalies (AHA, ASA) show a much larger variability than the mean AHA and ASA. We found that the eddies contributed significantly to productivity by maintaining pronounced subsurface maxima of chlorophyll. Based on a comparison of the coastal (young) mode water eddy and the open ocean (old) mode water eddy we conclude that the aging of eddies when they detach from the coast and move westward to the open ocean considerably influences the eddies' properties: chlorophyll maxima are weaker and nutrients are subducted. The coastal mode water eddy was found to be a hotspot of nitrogen loss in the OMZ, whereas, the open ocean cyclonic eddy was of negligible importance for nitrogen loss. Our results show that the important role the eddies play in the ETSP can only be fully deciphered and understood through dedicated high spatial and temporal resolution oceanographic/biogeochemical surveys.

Description: Soil moisture modifies the response of soil respiration to temperature in a desert shrub ecosystem Biogeosciences Discussions, 10, 9213-9242, 2013 Author(s): B. Wang, T. S. Zha, X. Jia, B. Wu, Y. Q. Zhang, and S. G. Qin The response of soil respiration (Rs) to soil temperature and moisture have been well documented in forests, but data and information from desert shrub ecosystems are limited. Soil CO 2 efflux from a desert shrub ecosystem was measured continuously with automated chambers in Ningxia, northwest China, from June to October 2012. The responses of Rs to Ts was strongly affected diurnally by soil moisture, with the diel variation in Rs being strongly related to 10 cm soil temperature (Ts) at moderate and high soil volumetric water content (VWC), but less related to Ts at low VWC. Ts typically lagged Rs by 3–4 h, however, the lag time varied in relation to VWC, with increased lag times at low VWC. Over the seasonal cycle, daily mean Rs was positively correlated with Ts when VWC exceeded 0.08 m 3 m −3 , but became decoupled from Ts when VWC dropped below this threshold. The annual temperature sensitivity of Rs ( Q 10 ) was 1.5. The short-term sensitivity of Rs to Ts, computed using three-day windows, varied significantly over the seasonal cycle; the short-term Q 10 was negatively correlated with Ts and positively correlated with VWC. These results suggest the potential for a negative feedback to climate warming in desert ecosystems, related to the impact of low soil moisture on Rs. The results highlight the biological causes of diel hysteresis between Rs and Ts and the need for carbon cycle models to account for the interacting effects of Ts and VWC as joint determinants of Rs in desert ecosystem.

Description: Do successive climate extremes weaken the resistance of plant communities? An experimental study using plant assemblages Biogeosciences Discussions, 10, 9149-9177, 2013 Author(s): F. E. Dreesen, H. J. De Boeck, I. A. Janssens, and I. Nijs The probability that plant communities undergo successive climate extremes increases under climate change. Exposure to an extreme event might elicit acclimatory responses and thereby greater resistance to a subsequent event, but might also reduce resistance if the recovery period is too short or resilience too low. Using experimental plant assemblages, we compared the effects of two successive extremes (either two drought extremes, two heat extremes or two drought + heat extremes) to those of assemblages being exposed only to the second extreme. Additionally, the recovery period between the successive extremes was varied (2, 3.5 or 6 weeks). Among the different types of climate extremes, combined drought + heat extremes induced substantial leaf and plant mortality, while the effects of drought and heat extremes were smaller. Preceding drought + heat extremes lowered the resistance in terms of leaf survival to a subsequent drought + heat extreme if the recovery period was 2 weeks, even though the leaves had completely recovered during that interval. No reduced resistance to subsequent extremes was recorded with longer recovery times or with drought or heat extremes. Despite mortality on the short term, the drought + heat and the heat extremes increased the end-of-season aboveground biomass, independent of the number of events or the recovery period. These results show that the effect of a preceding extreme event disappears quite quickly, but that recurrent climate extremes with short time intervals can weaken the resistance of herbaceous plant assemblages. This can however be compensated afterwards through rapid recovery and secondary, positive effects in the longer term.

Description: A comparison of bow shock models with Cluster observations during low Alfvén Mach number magnetic clouds Annales Geophysicae, 31, 1011-1019, 2013 Author(s): L. Turc, D. Fontaine, P. Savoini, H. Hietala, and E. K. J. Kilpua Magnetic clouds (MCs) are very geoeffective solar wind structures. Their properties in the interplanetary medium have been extensively studied, yet little is known about their characteristics in the Earth's magnetosheath. The Cluster spacecraft offer the opportunity to observe MCs in the magnetosheath, but before MCs reach the magnetosphere, their structure is altered when they interact with the terrestrial bow shock (BS). The physics taking place at the BS strongly depends on Θ Bn , the angle between the shock normal and the interplanetary magnetic field. However, in situ observations of the BS during an MC's crossing are seldom available. In order to relate magnetosheath observations to solar wind conditions, we need to rely on a model to determine the shock's position and normal direction. Yet during MCs, the models tend to be less accurate, because the Alfvén Mach number ( M A ) is often significantly lower than in regular solar wind. On the contrary, the models are generally optimised for high M A conditions. In this study, we compare the predictions of four widely used models available in the literature (Wu et al., 2000; Chapman and Cairns, 2003; Jeřáb et al., 2005; Měrka et al., 2005b) to Cluster's dayside BS crossings observed during five MC events. Our analysis shows that the Θ Bn angle is well predicted by all four models. On the other hand, the Jeřáb et al. (2005) model yields the best estimates of the BS position during low M A MCs. The other models locate the BS either too far from or too close to Earth. The results of this paper can be directly used to estimate the BS parameters in all studies of MC interaction with Earth's magnetosphere.

Description: Investigation of gaseous and particulate emissions from various marine vessel types measured on the banks of the Elbe in Northern Germany Atmospheric Chemistry and Physics, 13, 3603-3618, 2013 Author(s): J.-M. Diesch, F. Drewnick, T. Klimach, and S. Borrmann Measurements of the ambient aerosol, various trace gases and meteorological quantities using a mobile laboratory (MoLa) were performed on the banks of the Lower Elbe in an emission control area (ECA) which is passed by numerous private and commercial marine vessels reaching and leaving the port of Hamburg, Germany. From 25–29 April 2011 a total of 178 vessels were probed at a distance of about 0.8–1.2 km with high temporal resolution. 139 ship emission plumes were of sufficient quality to be analyzed further and to determine emission factors (EFs). Concentrations of aerosol number and mass as well as polycyclic aromatic hydrocarbons (PAH) and black carbon were measured in PM 1 and size distribution instruments covered the diameter range from 6 nm up to 32 μm. The chemical composition of the non-refractory submicron aerosol was measured by means of an Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS). Gas phase species analyzers monitored various trace gases (O 3 , SO 2 , NO, NO 2 , CO 2 ) in the air and a weather station provided wind, precipitation, solar radiation data and other quantities. Together with ship information for each vessel obtained from Automatic Identification System (AIS) broadcasts a detailed characterization of the individual ship types and of features affecting gas and particulate emissions is provided. Particle number EFs (average 2.6 e +16 # kg −1 ) and PM 1 mass EFs (average 2.4 g kg −1 ) tend to increase with the fuel sulfur content. Observed PM 1 composition of the vessel emissions was dominated by organic matter (72%), sulfate (22%) and black carbon (6%) while PAHs only account for 0.2% of the submicron aerosol mass. Measurements of gaseous components showed an increase of SO 2 (average EF: 7.7 g kg −1 ) and NO x (average EF: 53 g kg −1 ) while O 3 decreased when a ship plume reached the sampling site. The particle number size distributions of the vessels are generally characterized by a bimodal size distribution, with the nucleation mode in the 10–20 nm diameter range and a combustion aerosol mode centered at about 35 nm while particles \textgreater 1 μm were not found. "High particle number emitters" are characterized by a dominant nucleation mode. By contrast, increased particle concentrations around 150 nm primarily occurred for "high black carbon emitters". Classifying the vessels according to their gross tonnage shows a decrease of the number, black carbon and PAH EFs while EFs of SO 2 , NO, NO 2 , NO x , AMS species (particulate organics, sulfate) and PM 1 mass concentration increase with increasing gross tonnages.

Description: Modeling of daytime HONO vertical gradients during SHARP 2009 Atmospheric Chemistry and Physics, 13, 3587-3601, 2013 Author(s): K. W. Wong, C. Tsai, B. Lefer, N. Grossberg, and J. Stutz Nitrous acid (HONO) acts as a major precursor of the hydroxyl radical (OH) in the urban atmospheric boundary layer in the morning and throughout the day. Despite its importance, HONO formation mechanisms are not yet completely understood. It is generally accepted that conversion of NO 2 on surfaces in the presence of water is responsible for the formation of HONO in the nocturnal boundary layer, although the type of surface on which the mechanism occurs is still under debate. Recent observations of higher than expected daytime HONO concentrations in both urban and rural areas indicate the presence of unknown daytime HONO source(s). Various formation pathways in the gas phase, and on aerosol and ground surfaces have been proposed to explain the presence of daytime HONO. However, it is unclear which mechanism dominates and, in the cases of heterogeneous mechanisms, on which surfaces they occur. Vertical concentration profiles of HONO and its precursors can help in identifying the dominant HONO formation pathways. In this study, daytime HONO and NO 2 vertical profiles, measured in three different height intervals (20–70, 70–130, and 130–300 m) in Houston, TX, during the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) are analyzed using a one-dimensional (1-D) chemistry and transport model. Model results with various HONO formation pathways suggested in the literature are compared to the the daytime HONO and HONO/NO 2 ratios observed during SHARP. The best agreement of HONO and HONO/NO 2 ratios between model and observations is achieved by including both a photolytic source of HONO at the ground and on the aerosol. Model sensitivity studies show that the observed diurnal variations of the HONO/NO 2 ratio are not reproduced by the model if there is only a photolytic HONO source on aerosol or in the gas phase from NO 2 * + H 2 O. Further analysis of the formation and loss pathways of HONO shows a vertical dependence of HONO chemistry during the day. Photolytic HONO formation at the ground is the major formation pathway in the lowest 20 m, while a combination of gas-phase, photolytic formation on aerosol, and vertical transport is responsible for daytime HONO between 200–300 m a.g.l. HONO removal is dominated by vertical transport below 20 m and photolysis between 200–300 m a.g.l.

Description: Antarctic new particle formation from continental biogenic precursors Atmospheric Chemistry and Physics, 13, 3527-3546, 2013 Author(s): E.-M. Kyrö, V.-M. Kerminen, A. Virkkula, M. Dal Maso, J. Parshintsev, J. Ruíz-Jimenez, L. Forsström, H. E. Manninen, M.-L. Riekkola, P. Heinonen, and M. Kulmala Over Antarctica, aerosol particles originate almost entirely from marine areas, with minor contribution from long-range transported dust or anthropogenic material. The Antarctic continent itself, unlike all other continental areas, has been thought to be practically free of aerosol sources. Here we present evidence of local aerosol production associated with melt-water ponds in continental Antarctica. We show that in air masses passing such ponds, new aerosol particles are efficiently formed and these particles grow up to sizes where they may act as cloud condensation nuclei (CCN). The precursor vapours responsible for aerosol formation and growth originate very likely from highly abundant cyanobacteria Nostoc commune (Vaucher) communities of local ponds. This is the first time freshwater vegetation has been identified as an aerosol precursor source. The influence of the new source on clouds and climate may increase in future Antarctica, and possibly elsewhere undergoing accelerating summer melting of semi-permanent snow cover.

Description: The influence of snow grain size and impurities on the vertical profiles of actinic flux and associated NO x emissions on the Antarctic and Greenland ice sheets Atmospheric Chemistry and Physics, 13, 3547-3567, 2013 Author(s): M. C. Zatko, T. C. Grenfell, B. Alexander, S. J. Doherty, J. L. Thomas, and X. Yang We use observations of the absorption properties of black carbon and non-black carbon impurities in near-surface snow collected near the research stations at South Pole and Dome C, Antarctica, and Summit, Greenland, combined with a snowpack actinic flux parameterization to estimate the vertical profile and e-folding depth of ultraviolet/near-visible (UV/near-vis) actinic flux in the snowpack at each location. We have developed a simple and broadly applicable parameterization to calculate depth and wavelength dependent snowpack actinic flux that can be easily integrated into large-scale (e.g., 3-D) models of the atmosphere. The calculated e-folding depths of actinic flux at 305 nm, the peak wavelength of nitrate photolysis in the snowpack, are 8–12 cm near the stations and 15–31 cm away (〉11 km) from the stations. We find that the e-folding depth is strongly dependent on impurity content and wavelength in the UV/near-vis region, which explains the relatively shallow e-folding depths near stations where local activities lead to higher snow impurity levels. We calculate the lifetime of NO x in the snowpack interstitial air produced by photolysis of snowpack nitrate against wind pumping (τ wind pumping ) from the snowpack, and compare this to the calculated lifetime of NO x against chemical conversion to HNO 3 (τ chemical ) to determine whether the NO x produced at a given depth can escape from the snowpack to the overlying atmosphere. Comparison of τ wind pumping and τ chemical suggests efficient escape of photoproduced NO x in the snowpack to the overlying atmosphere throughout most of the photochemically active zone. Calculated vertical actinic flux profiles and observed snowpack nitrate concentrations are used to estimate the potential flux of NO x from the snowpack. Calculated NO x fluxes of 4.4 × 10 8 –3.8 × 10 9 molecules cm −2 s −1 in remote polar locations and 3.2–8.2 × 10 8 molecules cm −2 s −1 near polar stations for January at Dome C and South Pole and June at Summit suggest that NO x flux measurements near stations may be underestimating the amount of NO x emitted from the clean polar snowpack.

Description: The relative importance of impacts from climate change vs. emissions change on air pollution levels in the 21st century Atmospheric Chemistry and Physics, 13, 3569-3585, 2013 Author(s): G. B. Hedegaard, J. H. Christensen, and J. Brandt So far several studies have analysed the impacts of climate change on future air pollution levels. Significant changes due to impacts of climate change have been made clear. Nevertheless, these changes are not yet included in national, regional or global air pollution reduction strategies. The changes in future air pollution levels are caused by both impacts from climate change and anthropogenic emission changes, the importance of which needs to be quantified and compared. In this study we use the Danish Eulerian Hemispheric Model (DEHM) driven by meteorological input data from the coupled Atmosphere-Ocean General Circulation Model ECHAM5/MPI-OM and forced with the newly developed RCP4.5 emissions. The relative importance of the climate signal and the signal from changes in anthropogenic emissions on the future ozone, black carbon (BC), total particulate matter with a diameter below 2.5 μm (total PM 2.5 including BC, primary organic carbon (OC), mineral dust and secondary inorganic aerosols (SIA)) and total nitrogen (including NH x + NO y ) has been determined. For ozone, the impacts of anthropogenic emissions dominate, though a climate penalty is found in the Arctic region and northwestern Europe, where the signal from climate change dampens the effect from the projected emission reductions of anthropogenic ozone precursors. The investigated particles are even more dominated by the impacts from emission changes. For black carbon the emission signal dominates slightly at high latitudes, with an increase up to an order of magnitude larger, close to the emission sources in temperate and subtropical areas. Including all particulate matter with a diameter below 2.5 μm (total PM 2.5 ) enhances the dominance from emissions change. In contrast, total nitrogen (NH x + NO y ) in parts of the Arctic and at low latitudes is dominated by impacts of climate change.

Description: Climate and land use change impacts on global terrestrial ecosystems, fire, and river flows in the HadGEM2-ES Earth System Model using the Representative Concentration Pathways Biogeosciences Discussions, 10, 6171-6223, 2013 Author(s): R. A. Betts, N. Golding, P. Gonzalez, J. Gornall, R. Kahana, G. Kay, L. Mitchell, and A. Wiltshire A new generation of an Earth System Model now includes a number of land surface processes directly relevant to analyzing potential impacts of climate change. This model, HadGEM2-ES, allows us to assess the impacts of climate change, multiple interactions, and feedbacks as the model is run. This paper discusses the results of century-scale HadGEM2-ES simulations from an impacts perspective–specifically, terrestrial ecosystems and water resources–for four different scenarios following the Representative Concentration Pathways (RCPs), being used for next assessment report of the Intergovernmental Panel on Climate Change (IPCC). Over the 21st Century, simulated changes in global and continential-scale terrestrial ecosystems due to climate change appear to be very similar in all 4 RCPs, even though the level of global warming by the end of the 21st Century ranges from 2 °C in the lowest scenario to 5.5° in the highest. A warming climate generally favours broadleaf trees over needleleaf, needleleaf trees over shrubs, and shrubs over herbaceous vegetation, resulting in a poleward shift of temperate and boreal forests and woody tundra in all scenarios. Although climate related changes are slightly larger in scenarios of greater warming, the largest differences between scenarios arise at regional scales as a consequence of different patterns of anthropogenic land cover change. In the model, the scenario with the lowest global warming results in the most extensive decline in tropical forest cover due to a large expansion of agriculture. Under all four RCPs, fire potential could increase across extensive land areas, particularly tropical and sub-tropical latitudes. River outflows are simulated to increase with higher levels of CO 2 and global warming in all projections, with outflow increasing with mean temperature at the end of the 21st Century at the global scale and in North America, Asia, and Africa. In South America, Europe, and Australia, the relationship with climate warming and CO 2 rise is less clear, probably as a result of land cover change exerting a dominant effect in those regions.

Description: Horizontal distribution of Fukushima-derived radiocesium in zooplankton in the northwestern Pacific Ocean Biogeosciences Discussions, 10, 6143-6170, 2013 Author(s): M. Kitamura, Y. Kumamoto, H. Kawakami, E. C. Cruz, and K. Fujikura The magnitude of the 9.0 Tohoku earthquake and the ensuing tsunami on 11 March 2011, inflicted heavy damage on the Fukushima Dai-ichi nuclear power plant (FNPP1). Fission products were emitted, falling over a broad range in the northern hemisphere, and water contaminated with radionuclides leaked into the ocean. In this study, we described the horizontal distribution of the Fukushima-derived radiocesium in zooplankton and in seawater in the western North Pacific Ocean (500–2100 km from the FNPP1) 10 months after the accident. 134 Cs and 137 Cs were detected in zooplankton and seawater from all the stations. Because of its short half-lives, 134 Cs detected in our samples could only be derived from the FNPP1 accident. The highest 137 Cs activity in zooplankton was same order of magnitude as that one month after the accident, and average activity was one or two orders of magnitude higher than 137 Cs activities observed before the accident around Japan. Horizontally, the radiocesium activity concentrations in zooplankton were high at around 25° N while those in surface seawater were high at around the transition area between the Kuroshio and the Oyashio Currents (36–40° N). We observed subsurface radiocesium maxima in density range of the North Pacific Subtropical Mode Water and occurrence of many diel vertical migratory zooplanktons. These suggested that the high activity concentrations in the subtropical zooplankton at around 25° N were connected to the subsurface radiocesium and active vertical migration of zooplankton. However, the high activity concentrations of radiocesium in subsurface seawater did not necessarily follow the higher radiocesium activity in zooplankton. Biological characteristics of zooplankton community possibly influenced how large was contamination of radiocesium in the community but it is still unknown what kind of biological factors were important.

Description: Estimating carbonate parameters from hydrographic data for the intermediate and deep waters of the Southern Hemisphere Oceans Biogeosciences Discussions, 10, 6225-6257, 2013 Author(s): H. C. Bostock, S. E. Mikaloff Fletcher, and M. J. M. Williams Using GLODAP and CLIVAR ocean carbon data, we have developed several multiple linear regression (MLR) algorithms to estimate alkalinity and dissolved inorganic carbon (DIC) in the intermediate and deep waters of the Southern Hemisphere (south of 25° S) from only hydrographic data (temperature, salinity and dissolved oxygen). A Monte Carlo experiment was used to identify a potential density (σ θ ) of 27.5 as an optimal break point between the two regimes with different MLR algorithms. The algorithms provide a good estimate of DIC ( R 2 =0.98) and alkalinity ( R 2 =0.91), and excellent agreement for aragonite and calcite saturation states ( R 2 =0.99). Combining the algorithms with the CSIRO Atlas of Regional Seas (CARS), we have been able to map the calcite saturation horizon (CSH) and aragonite saturation horizon (ASH) for the Southern Ocean at a spatial resolution of 0.5°. These maps are more detailed and more consistent with oceanography than the gridded GLODAP data. The high resolution ASH map reveals a dramatic circumpolar shoaling at the Polar Front. North of 40° S the CSH is deepest in the Atlantic (~ 4000 m) and shallower in the Pacific Ocean (~ 2750 m), while the CSH sits between 3200 and 3400 m in the Indian Ocean.

Description: Pollution transport from North America to Greenland during summer 2008 Atmospheric Chemistry and Physics, 13, 3825-3848, 2013 Author(s): J. L. Thomas, J.-C. Raut, K. S. Law, L. Marelle, G. Ancellet, F. Ravetta, J. D. Fast, G. Pfister, L. K. Emmons, G. S. Diskin, A. Weinheimer, A. Roiger, and H. Schlager Ozone pollution transported to the Arctic is a significant concern because of the rapid, enhanced warming in high northern latitudes, which is caused, in part, by short-lived climate forcers, such as ozone. Long-range transport of pollution contributes to background and episodic ozone levels in the Arctic. However, the extent to which plumes are photochemically active during transport, particularly during the summer, is still uncertain. In this study, regional chemical transport model simulations are used to examine photochemical production of ozone in air masses originating from boreal fire and anthropogenic emissions over North America and during their transport toward the Arctic during early July 2008. Model results are evaluated using POLARCAT aircraft data collected over boreal fire source regions in Canada (ARCTAS-B) and several days downwind over Greenland (POLARCAT-France and POLARCAT-GRACE). Model results are generally in good agreement with the observations, except for certain trace gas species over boreal fire regions, in some cases indicating that the fire emissions are too low. Anthropogenic and biomass burning pollution (BB) from North America was rapidly uplifted during transport east and north to Greenland where pollution plumes were observed in the mid- and upper troposphere during POLARCAT. A model sensitivity study shows that CO levels are in better agreement with POLARCAT measurements (fresh and aged fire plumes) upon doubling CO emissions from fires. Analysis of model results, using ΔO 3 /ΔCO enhancement ratios, shows that pollution plumes formed ozone during transport towards the Arctic. Fresh anthropogenic plumes have average ΔO 3 /ΔCO enhancement ratios of 0.63 increasing to 0.92 for aged anthropogenic plumes, indicating additional ozone production during aging. Fresh fire plumes are only slightly enhanced in ozone (ΔO 3 /ΔCO=0.08), but form ozone downwind with ΔO 3 /ΔCO of 0.49 for aged BB plumes (model-based run). We estimate that aged anthropogenic and BB pollution together made an important contribution to ozone levels with an average contribution for latitudes 〉55° N of up to 6.5 ppbv (18%) from anthropogenic pollution and 3 ppbv (5.2%) from fire pollution in the model domain in summer 2008.

Description: Validation of an hourly resolved global aerosol model in answer to solar electricity generation information needs Atmospheric Chemistry and Physics, 13, 3777-3791, 2013 Author(s): M. Schroedter-Homscheidt and A. Oumbe Solar energy applications need global aerosol optical depth (AOD) information to derive historic surface solar irradiance databases from geostationary meteorological satellites reaching back to the 1980's. This paper validates the MATCH/DLR model originating in the climate community against AERONET ground measurements. Hourly or daily mean AOD model output is evaluated individually for all stations in Europe, Africa and the Middle East – an area highly interesting for solar energy applications being partly dominated by high aerosol loads. Overall, a bias of 0.02 and a root-mean-square error (RMSE) of 0.23 are found for daily mean AOD values, while the RMSE increases to 0.28 for hourly mean AOD values. Large differences between various regions and stations are found providing a feedback loop for the aerosol modelling community. The difference in using daily means versus hourly resolved modelling with respect to hourly resolved observations is evaluated. Nowadays state-of-the-art in solar resource assessment relies on monthly turbidity or AOD climatologies while at least hourly resolved irradiance time series are needed by the solar sector. Therefore, the contribution of higher temporally modelled AOD is evaluated.

Description: Montreal Protocol Benefits simulated with CCM SOCOL Atmospheric Chemistry and Physics, 13, 3811-3823, 2013 Author(s): T. Egorova, E. Rozanov, J. Gröbner, M. Hauser, and W. Schmutz Ozone depletion is caused by the anthropogenic increase of halogen-containing species in the atmosphere, which results in the enhancement of the concentration of reactive chlorine and bromine in the stratosphere. To reduce the influence of anthropogenic ozone-depleting substances (ODS), the Montreal Protocol was agreed by Governments in 1987, with several Amendments and Adjustments adopted later. In order to assess the benefits of the Montreal Protocol and its Amendments and Adjustments (MPA) on ozone and UV radiation, two different runs of the chemistry-climate model (CCM) SOCOL have been carried out. The first run was driven by the emission of ozone depleting substances (ODS) prescribed according to the restrictions of the MPA. For the second run we allow the ODS to grow by 3% annually. We find that the MPA would have saved up to 80% of the global annual total ozone by the end of the 21st century. Our calculations also show substantial changes of the stratospheric circulation pattern as well as in surface temperature and precipitations that could occur in the world without MPA implementations. To illustrate the changes in UV radiation at the surface and to emphasise certain features, which can only be seen for some particular regions if the influence of the cloud cover changes is accounted for, we calculate geographical distribution of the erythemally weighted irradiance ( E ery ). For the no Montreal Protocol simulation E ery increases by factor of 4 to 16 between the 1970s and 2100. For the scenario including the Montreal Protocol it is found that UV radiation starts to decrease in 2000, with continuous decline of 5% to 10% at middle latitudes in the both Northern and Southern Hemispheres.

Description: CLARA-SAL: a global 28 yr timeseries of Earth's black-sky surface albedo Atmospheric Chemistry and Physics, 13, 3743-3762, 2013 Author(s): A. Riihelä, T. Manninen, V. Laine, K. Andersson, and F. Kaspar We present a novel 28 yr dataset of Earth's black-sky surface albedo, derived from AVHRR instruments. The dataset is created using algorithms to separately derive the surface albedo for different land use areas globally. Snow, sea ice, open water and vegetation are all treated independently. The product features corrections for the atmospheric effect in satellite-observed surface radiances, a BRDF correction for the anisotropic reflectance properties of natural surfaces, and a novel topography correction of geolocation and radiometric accuracy of surface reflectance observations over mountainous areas. The dataset is based on a homogenized AVHRR radiance timeseries. The product is validated against quality-controlled in situ observations of clear-sky surface albedo at various BSRN sites around the world. Snow and ice albedo retrieval validation is given particular attention using BSRN sites over Antarctica, Greenland Climate Network stations on the Greenland Ice Sheet (GrIS), as well as sea ice albedo data from the SHEBA and Tara expeditions. The product quality is found to be comparable to other previous long-term surface albedo datasets from AVHRR.

Description: Spectral albedo of seasonal snow during intensive melt period at Sodankylä, beyond the Arctic Circle Atmospheric Chemistry and Physics, 13, 3793-3810, 2013 Author(s): O. Meinander, S. Kazadzis, A. Arola, A. Riihelä, P. Räisänen, R. Kivi, A. Kontu, R. Kouznetsov, M. Sofiev, J. Svensson, H. Suokanerva, V. Aaltonen, T. Manninen, J.-L. Roujean, and O. Hautecoeur We have measured spectral albedo, as well as ancillary parameters, of seasonal European Arctic snow at Sodankylä, Finland (67°22' N, 26°39' E). The springtime intensive melt period was observed during the Snow Reflectance Transition Experiment (SNORTEX) in April 2009. The upwelling and downwelling spectral irradiance, measured at 290–550 nm with a double monochromator spectroradiometer, revealed albedo values of ~0.5–0.7 for the ultraviolet and visible range, both under clear sky and variable cloudiness. During the most intensive snowmelt period of four days, albedo decreased from 0.65 to 0.45 at 330 nm, and from 0.72 to 0.53 at 450 nm. In the literature, the UV and VIS albedo for clean snow are ~0.97–0.99, consistent with the extremely small absorption coefficient of ice in this spectral region. Our low albedo values were supported by two independent simultaneous broadband albedo measurements, and simulated albedo data. We explain the low albedo values to be due to (i) large snow grain sizes up to ~3 mm in diameter; (ii) meltwater surrounding the grains and increasing the effective grain size; (iii) absorption caused by impurities in the snow, with concentration of elemental carbon (black carbon) in snow of 87 ppb, and organic carbon 2894 ppb, at the time of albedo measurements. The high concentrations of carbon, detected by the thermal–optical method, were due to air masses originating from the Kola Peninsula, Russia, where mining and refining industries are located.

Description: Investigation of radiative effects of the optically thick dust layer over the Indian tropical region Annales Geophysicae, 31, 647-663, 2013 Author(s): S. K. Das, J.-P. Chen, M. Venkat Ratnam, and A. Jayaraman Optical and physical properties of aerosols derived from multi-satellite observations (MODIS-Aqua, OMI-Aura, MISR-Terra, CALIOP-CALIPSO) have been used to estimate radiative effects of the dust layer over southern India. The vertical distribution of aerosol radiative forcing and heating rates are calculated with 100 m resolution in the lower atmosphere, using temperature and relative humidity data from balloon-borne radiosonde observations. The present study investigates the optically thick dust layer of optical thickness 0.18 ± 0.06 at an altitude of 2.5 ± 0.7 km over Gadanki, transported from the Thar Desert, producing radiative forcing and heating rate of 11.5 ± 3.3 W m −2 and 0.6 ± 0.26 K day −1 , respectively, with a forcing efficiency of 43 W m −2 and an effective heating rate of 4 K day −1 per unit dust optical depth. Presence of the dust layer increases radiative forcing by 60% and heating rate by 60 times at that altitude compared to non-dusty cloud-free days. Calculation shows that the radiative effects of the dust layer strongly depend on the boundary layer aerosol type and mass loading. An increase of 25% of heating by the dust layer is found over relatively cleaner regions than urban regions in southern India and further 15% of heating increases over the marine region. Such heating differences in free troposphere may have significant consequences in the atmospheric circulation and hydrological cycle over the tropical Indian region.

Description: Productivity of aboveground coarse wood biomass and stand age related to soil hydrology of Amazonian forests in the Purus-Madeira interfluvial area Biogeosciences Discussions, 10, 6417-6459, 2013 Author(s): B. B. L. Cintra, J. Schietti, T. Emillio, D. Martins, G. Moulatlet, P. Souza, C. Levis, C. A. Quesada, and J. Schöngart The ongoing demand for information on forest productivity has increased the number of permanent monitoring plots across the Amazon. Those plots, however, do not comprise the whole diversity of forest types in the Amazon. The complex effects of soil, climate and hydrology on the productivity of seasonally waterlogged interfluvial wetland forests are still poorly understood. The presented study is the first field-based estimate for tree ages and wood biomass productivity in the vast interfluvial region between the Purus and Madeira rivers. We estimate stand age and wood biomass productivity by a combination of tree-ring data and allometric equations for biomass stocks of eight plots distributed along 600 km in the Purus-Madeira interfluvial area that is crossed by the BR-319 highway. We relate stand age and wood biomass productivity to hydrological and edaphic conditions. Mean productivity and stand age were 5.6 ± 1.1 Mg ha −1 yr −1 and 102 ± 18 yr, respectively. There is a strong relationship between tree age and diameter, as well as between mean diameter increment and mean wood density within a plot. Regarding the soil hydromorphic properties we find a positive correlation with wood biomass productivity and a negative relationship with stand age. Productivity also shows a positive correlation with the superficial phosphorus concentration. In addition, superficial phosphorus concentration increases with enhanced soil hydromorphic condition. We raise three hypotheses to explain these results: (1) the reduction of iron molecules on the saturated soils with plinthite layers close to the surface releases available phosphorous for the plants; (2) the poor structure of the saturated soils creates an environmental filter selecting tree species of faster growth rates and shorter life spans and (3) plant growth on saturated soil is favored during the dry season, since there should be low restrictions for soil water availability.

Description: Top-down estimate of surface flux in the Los Angeles Basin using a mesoscale inverse modeling technique: assessing anthropogenic emissions of CO, NO x and CO 2 and their impacts Atmospheric Chemistry and Physics, 13, 3661-3677, 2013 Author(s): J. Brioude, W. M. Angevine, R. Ahmadov, S.-W. Kim, S. Evan, S. A. McKeen, E.-Y. Hsie, G. J. Frost, J. A. Neuman, I. B. Pollack, J. Peischl, T. B. Ryerson, J. Holloway, S. S. Brown, J. B. Nowak, J. M. Roberts, S. C. Wofsy, G. W. Santoni, T. Oda, and M. Trainer We present top-down estimates of anthropogenic CO, NO x and CO 2 surface fluxes at mesoscale using a Lagrangian model in combination with three different WRF model configurations, driven by data from aircraft flights during the CALNEX campaign in southern California in May–June 2010. The US EPA National Emission Inventory 2005 (NEI 2005) was the prior in the CO and NO x inversion calculations. The flux ratio inversion method, based on linear relationships between chemical species, was used to calculate the CO 2 inventory without prior knowledge of CO 2 surface fluxes. The inversion was applied to each flight to estimate the variability of single-flight-based flux estimates. In Los Angeles (LA) County, the uncertainties on CO and NO x fluxes were 10% and 15%, respectively. Compared with NEI 2005, the CO posterior emissions were lower by 43% in LA County and by 37% in the South Coast Air Basin (SoCAB). NO x posterior emissions were lower by 32% in LA County and by 27% in the SoCAB. NO x posterior emissions were 40% lower on weekends relative to weekdays. The CO 2 posterior estimates were 183 Tg yr −1 in SoCAB. A flight during ITCT (Intercontinental Transport and Chemical Transformation) in 2002 was used to estimate emissions in the LA Basin in 2002. From 2002 to 2010, the CO and NO x posterior emissions decreased by 41% and 37%, respectively, in agreement with previous studies. Over the same time period, CO 2 emissions increased by 10% in LA County but decreased by 4% in the SoCAB, a statistically insignificant change. Overall, the posterior estimates were in good agreement with the California Air Resources Board (CARB) inventory, with differences of 15% or less. However, the posterior spatial distribution in the basin was significantly different from CARB for NO x emissions. WRF-Chem mesoscale chemical-transport model simulations allowed an evaluation of differences in chemistry using different inventory assumptions, including NEI 2005, a gridded CARB inventory and the posterior inventories derived in this study. The biases in WRF-Chem ozone were reduced and correlations were increased using the posterior from this study compared with simulations with the two bottom-up inventories, suggesting that improving the spatial distribution of ozone precursor surface emissions is also important in mesoscale chemistry simulations.

Description: Arctic aerosol life cycle: linking aerosol size distributions observed between 2000 and 2010 with air mass transport and precipitation at Zeppelin station, Ny-Ålesund, Svalbard Atmospheric Chemistry and Physics, 13, 3643-3660, 2013 Author(s): P. Tunved, J. Ström, and R. Krejci In this study we present a qualitative and quantitative assessment of more than 10 yr of aerosol number size distribution data observed in the Arctic environment (Mt. Zeppelin (78°56' N, 11°53' E, 474 m a.s.l.), Ny Ålesund, Svalbard). We provide statistics on both seasonal and diurnal characteristics of the aerosol observations and conclude that the Arctic aerosol number size distribution and related parameters such as integral mass and surface area exhibit a very pronounced seasonal variation. This seasonal variation seems to be controlled by both dominating source as well as meteorological conditions. Three distinctly different periods can be identified during the Arctic year: the haze period characterized by a dominating accumulation mode aerosol (March–May), followed by the sunlit summer period with low abundance of accumulation mode particles but high concentration of small particles which are likely to be recently and locally formed (June–August). The rest of the year is characterized by a comparably low concentration of accumulation mode particles and negligible abundance of ultrafine particles (September–February). A minimum in aerosol mass and number concentration is usually observed during September/October. We further show that the transition between the different regimes is fast, suggesting rapid change in the conditions defining their appearance. A source climatology based on trajectory analysis is provided, and it is shown that there is a strong seasonality of dominating source areas, with Eurasia dominating during the Autumn–Winter period and dominance of North Atlantic air during the summer months. We also show that new-particle formation events are rather common phenomena in the Arctic during summer, and this is the result of photochemical production of nucleating/condensing species in combination with low condensation sink. It is also suggested that wet removal may play a key role in defining the Arctic aerosol year, via the removal of accumulation mode size particles, which in turn have a pivotal role in facilitating the conditions favorable for new-particle formation events. In summary the aerosol Arctic year seems to be at least qualitatively predictable based on the knowledge of seasonality of transport paths and associated source areas, meteorological conditions and removal processes.

Description: Assessment of the interannual variability and influence of the QBO and upwelling on tracer–tracer distributions of N 2 O and O 3 in the tropical lower stratosphere Atmospheric Chemistry and Physics, 13, 3619-3641, 2013 Author(s): F. Khosrawi, R. Müller, J. Urban, M. H. Proffitt, G. Stiller, M. Kiefer, S. Lossow, D. Kinnison, F. Olschewski, M. Riese, and D. Murtagh A modified form of tracer–tracer correlations of N 2 O and O 3 has been used as a tool for the evaluation of atmospheric photochemical models. Applying this method, monthly averages of N 2 O and O 3 are derived for both hemispheres by partitioning the data into altitude (or potential temperature) bins and then averaging over a fixed interval of N 2 O. In a previous study, the method has been successfully applied to the evaluation of two chemical transport models (CTMs) and one chemistry–climate model (CCM) using a 1 yr climatology derived from the Odin Sub-Millimetre Radiometer (Odin/SMR). However, the applicability of a 1 yr climatology of monthly averages of N 2 O and O 3 has been questioned due to the inability of some CCMs to simulate a specific year for the evaluation of CCMs. In this study, satellite measurements from Odin/SMR, the Aura Microwave Limb Sounder (Aura/MLS), the Michelson Interferometer for Passive Atmospheric Sounding on ENVISAT (ENVISAT/MIPAS), and the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-1 and CRISTA-2) as well as model simulations from the Whole Atmosphere Community Climate Model (WACCM) are considered. By using seven to eight years of satellite measurements derived between 2003 and 2010 from Odin/SMR, Aura/MLS, ENVISAT/MIPAS and six years of model simulations from WACCM, the interannual variability of lower stratospheric monthly averages of N 2 O and O 3 is assessed. It is shown that the interannual variability of the monthly averages of N 2 O and O 3 is low, and thus can be easily distinguished from model deficiencies. Furthermore, it is investigated why large differences are found between Odin/SMR observations and model simulations from the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the atmospheric general circulation model ECHAM5/Messy1 for the Northern and Southern Hemisphere tropics (0° to 30° N and 0° to −30° S, respectively). The differences between model simulations and observations are most likely caused by an underestimation of the quasi-biennial oscillation and tropical upwelling by the models as well as due to biases and/or instrument noise from the satellite instruments. A realistic consideration of the QBO in the model reduces the differences between model simulation and observations significantly. Finally, an intercomparison between Odin/SMR, Aura/MLS, ENVISAT/MIPAS and WACCM was performed. The comparison shows that these data sets are generally in good agreement, although some known biases of the data sets are clearly visible in the monthly averages. Nevertheless, the differences caused by the uncertainties of the satellite data sets are sufficiently small and can be clearly distinguished from model deficiencies. Thus, the method applied in this study is not only a valuable tool for model evaluation, but also for satellite data intercomparisons.

Description: Sources and fate of terrestrial dissolved organic carbon in lakes of a Boreal Plains region recently affected by wildfire Biogeosciences Discussions, 10, 6093-6141, 2013 Author(s): D. Olefeldt, K. J. Devito, and M. R. Turetsky Downstream mineralization and sedimentation of terrestrial dissolved organic carbon (DOC) render lakes important for landscape carbon cycling in the boreal region, with regulating processes potentially sensitive to perturbations associated with climate change including increased occurrence of wildfire. In this study we assessed chemical composition and reactivity (during both dark and UV incubations) of DOC from lakes and terrestrial sources within a peatland-rich western boreal plains region partially affected by a recent wildfire. While wildfire was found to increase aromaticity of DOC in peat pore-water above the water table, it had no effect on concentrations or composition of DOC from peatland wells and neither affected mineral well or lake DOC characteristics. Lake DOC composition reflected a mixing of peatland and mineral groundwater, with a greater influence of mineral sources to lakes in coarse- than fine-textured settings. Peatland DOC was less biodegradable than mineral DOC, but both mineralization and sedimentation of peatland DOC increased substantially during UV incubations through selective removal of aromatic humic and fulvic acids. DOC composition in lakes with longer residence times had characteristics consistent with increased UV-mediated processing. We estimate that about half of terrestrial DOC inputs had been lost within lakes, mostly due to UV-mediated processes. The importance of within-lake losses of aromatic DOC from peatland sources through UV-mediated processes indicate that terrestrial-aquatic C linkages in the study region are largely disconnected from recent terrestrial primary productivity. Together, our results suggest that characteristics of the study region (climate, surface geology and lake morphometry) render linkages between terrestrial and aquatic C cycling insensitive to the effects of wildfire by determining dominant terrestrial sources and within-lake processes of DOC removal.

Description: Corrigendum to "Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds" published in Atmos. Chem. Phys., 13, 2857–2891, 2013 Atmospheric Chemistry and Physics, 13, 3693-3694, 2013 Author(s): J. E. Williams, P. F. J. van Velthoven, and C. A. M. Brenninkmeijer No abstract available.

Description: Low level jet intensification by mineral dust aerosols Annales Geophysicae, 31, 625-632, 2013 Author(s): O. Alizadeh Choobari, P. Zawar-Reza, and A. Sturman Modification of the intensity of a low level jet (LLJ) and near-surface wind speed by mineral dust is important as it has implications for dust emission and its long-range transport. Using the Weather Research and Forecasting with Chemistry (WRF/Chem) regional model, it is shown that direct radiative forcing by mineral dust reduces temperature in the lower atmosphere, but increases it in the layers aloft. The surface cooling is shown to be associated with a reduction of turbulent kinetic energy (TKE) and hence vertical mixing of horizontal momentum. Changes in the vertical profile of temperature over the regions that are under the influence of a LLJ are shown to result in an intensification of the LLJ and near-surface wind speed, but a decrease of winds aloft. These changes in the wind speed profile differ from results of previous research which suggested a decrease of wind speed in the lower atmosphere and its increase in the upper boundary layer.

Description: Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves Annales Geophysicae, 31, 599-624, 2013 Author(s): A. V. Artemyev, D. Mourenas, O. V. Agapitov, and V. V. Krasnoselskikh The lifetimes of electrons trapped in Earth's radiation belts can be calculated from quasi-linear pitch-angle diffusion by whistler-mode waves, provided that their frequency spectrum is broad enough and/or their average amplitude is not too large. Extensive comparisons between improved analytical lifetime estimates and full numerical calculations have been performed in a broad parameter range representative of a large part of the magnetosphere from L ~ 2 to 6. The effects of observed very oblique whistler waves are taken into account in both numerical and analytical calculations. Analytical lifetimes (and pitch-angle diffusion coefficients) are found to be in good agreement with full numerical calculations based on CRRES and Cluster hiss and lightning-generated wave measurements inside the plasmasphere and Cluster lower-band chorus waves measurements in the outer belt for electron energies ranging from 100 keV to 5 MeV. Comparisons with lifetimes recently obtained from electron flux measurements on SAMPEX, SCATHA, SAC-C and DEMETER also show reasonable agreement.

Description: Coherent amplitude modulation of electron-beam-driven Langmuir waves Annales Geophysicae, 31, 633-638, 2013 Author(s): K. Baumgärtel A linear approach to the phenomenon of irregular amplitude modulation of beam-driven Langmuir waves, developed in a previous paper, is extended to explain periodic modulation as well. It comes about by beating of the fastest growing mode of the instability with beam-aligned plasma oscillations. They are naturally generated in a uniform domain of beam–plasma interaction prior to the onset of the instability. Particle-in-cell (PIC) simulations support the results of the linear analysis.

Description: Formation and occurrence of dimer esters of pinene oxidation products in atmospheric aerosols Atmospheric Chemistry and Physics, 13, 3763-3776, 2013 Author(s): K. Kristensen, K. L. Enggrob, S. M. King, D. R. Worton, S. M. Platt, R. Mortensen, T. Rosenoern, J. D. Surratt, M. Bilde, A. H. Goldstein, and M. Glasius The formation of carboxylic acids and dimer esters from α-pinene oxidation was investigated in a smog chamber and in ambient aerosol samples collected during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX). Chamber experiments of α-pinene ozonolysis in dry air and at low NO x concentrations demonstrated formation of two dimer esters, pinyl-diaterpenyl (MW 358) and pinonyl-pinyl dimer ester (MW 368), under both low- and high-temperature conditions. Concentration levels of the pinyl-diaterpenyl dimer ester were lower than the assumed first-generation oxidation products cis -pinic and terpenylic acids, but similar to the second-generation oxidation products 3-methyl-1,2,3-butane tricarboxylic acid (MBTCA) and diaterpenylic acid acetate (DTAA). Dimer esters were observed within the first 30 min, indicating rapid production simultaneous to their structural precursors. However, the sampling time resolution precluded conclusive evidence regarding formation from gas- or particle-phase processes. CCN activities of the particles formed in the smog chamber displayed a modest variation during the course of experiments, with κ values in the range 0.06–0.09 (derived at a supersaturation of 0.19%). The pinyl-diaterpenyl dimer ester was also observed in ambient aerosol samples collected above a ponderosa pine forest in the Sierra Nevada Mountains of California during two seasonally distinct field campaigns in September 2007 and July 2009. The pinonyl-pinyl ester was observed for the first time in ambient air during the 2009 campaign, and although present at much lower concentrations, it was correlated with the abundance of the pinyl-diaterpenyl ester, suggesting similarities in their formation. The maximum concentration of the pinyl-diaterpenyl ester was almost 10 times higher during the warmer 2009 campaign relative to 2007, while the concentration of cis -pinic acid was approximately the same during both periods, and lack of correlation with levels of cis -pinic and terpenylic acids for both campaigns indicate that the formation of the pinyl-diaterpenyl ester was not controlled by their ambient abundance. In 2009 the concentration of the pinyl-diaterpenyl ester was well correlated with the concentration of DTAA, a supposed precursor of diaterpenylic acid, suggesting that the formation of pinyl-diaterpenyl dimer was closely related to DTAA. Generally, the pinyl-diaterpenyl ester was found at higher concentrations under higher temperature conditions, both in the smog-chamber study and in ambient air aerosol samples, and exhibited much higher concentrations at night relative to daytime in line with previous results. We conclude that analysis of pinyl dimer esters provides valuable information on pinene oxidation processes and should be included in studies of formation and photochemical aging of biogenic secondary organic aerosols, especially at high temperatures.