bluuebunny/crossref_metadata_2025 huggingface dataset:
A new transport mechanism of biomass burning from Indochina as identified by modeling studies
Authors: Lin C.-Y. , Hsu H. M. , Lee Y. H. , Kuo C. H. , Sheng Y.-F. , Chu D. A.
Published: April 2010

Abstract. Biomass burning in the Indochina Peninsula (Indochina) is one of the important ozone sources in the low troposphere over East Asia in springtime. MODIS data showed that nearly 20 000 fires or more occurred annually in spring only from 2000 to 2007. In our tracer modeling study, we identified a new mechanism transporting the tracer over Indochina that is significantly different from the vertical transport mechanism over the areas around the equator such as Indonesia and Malaysia. Simulation results demonstrate that the leeside trough over Indochina played a dominant role in the uplift of the tracer below 3 km, and that the strong westerlies prevailed above 3 km to transport the tracer. They provided the fundamental mechanisms a major impact on the air quality downwind from Indochina over East Asia. And the climatological importance of such leeside trough is also discussed.
The exchange of SVOCs across the air-sea interface in Singapore's coastal environment
Authors: He J. , Balasubramanian R.
Published: April 2010

Abstract. Coastal areas are vulnerable to the accumulation of semi-volatile organic compounds such as PAHs, OCPs and PCBs from atmospheric inputs. Dry particulate and wet depositions, and air-water diffusive exchange in the Singapore's south coastal area, where most of chemical and oil refinery industries are situated in, were estimated. Based on a yearly dataset, the mean annual dry particulate deposition fluxes of ∑16PAHs, ∑7OCPs and ∑21PCBs were 1328.8±961.1 μg m−2 y−1, 5421.4±3426.7 ng m−2 y−1 and 811.8±578.3 ng m−2 y−1, and the wet deposition of ∑16PAHs and ∑7OCPs were 6667.1±1745.2 and 115.4±98.3 μg m−2 y−1, respectively. Seasonal variation of atmospheric depositions was influenced by meteorological conditions. Air-water gas exchange fluxes had negative values for PAHs, HCHs and DDXs, indicating Singapore's south coast as a sink for the above-mentioned SVOCs. The relative contribution of each depositional process to the total atmospheric input was assessed by annual fluxes. The profile of dry particulate deposition, wet deposition and gas exchange fluxes seemed to be correlated with individual pollutant's properties such as molecular weight and Henry's law constant, etc. For the water column partitioning, the organic carbon-normalized partition coefficients between particulate and dissolved phases (KOC) for both PAHs and OCPs were obtained. The relationships between KOC of PAHs and OCPs and their respective octanol-water partition coefficient (KOW) were examined. In addition, both adsorption onto combustion-derived soot carbon and absorption into natural organic matter for PAHs in marine water column were investigated. Enrichment factors in the sea-surface microlayer (SML) of the particulate phase were 1.2~7.1 and 3.0~4.9 for PAHs and OCPs, and those of dissolved phase were 1.1~4.9 and 1.6~4.2 for PAHs and OCPs, respectively. These enrichment factors are relatively higher than those reported for nearby coastal areas, which are most likely due to more organic surfactants floating in the south coastal surface of Singapore.
Chemical apportionment of southern African aerosol mass and optical depth
Authors: Magi B. I.
Published: April 2010

Abstract. We investigate the aerosol mass apportionment and derive aerosol optical properties that characterize the aerosol over extratropical and tropical southern Africa during the biomass burning season. We find that 54% and 83% of the extratropical and tropical aerosol mass, respectively, is composed of carbonaceous species, consistent with the fact that the major source of particulate matter in southern Africa is biomass burning. This mass apportionment implies that carbonaceous species in the form of organic carbon (OC) and black carbon (BC) play a critical role in the aerosol optical properties. By combining the in situ measurements of aerosol mass concentrations with concurrent measurements of aerosol optical properties at a wavelength of 550 nm, we find that 80–90% of the aerosol scattering is due to carbonaceous aerosol, where our derived mass scattering cross sections (MSC) for OC and BC are 3.9±0.6 m2/g and 1.6±0.2 m2/g, respectively. Our derived values of mass absorption cross sections (MAC) for OC and BC are 0.7±0.6 m2/g and 8.2±1.1 m2/g, respectively. The values of MAC imply that 26–27% of the aerosol absorption in southern Africa is due to OC, with the remainder due to BC. Our results provide important constraints for aerosol properties in a region dominated by biomass burning and should be integrated into climate models to improve aerosol simulations.
Origin of aerosol particles in the mid latitude and subtropical upper troposphere and lowermost stratosphere from cluster analysis of CARIBIC data
Authors: Köppe M. , Hermann M. , Brenninkmeijer C. A. M. , Heintzenberg J. , Schlager H. , Schuck T. , Slemr F. , Sprung D. , van Velthoven P. F. J. , Wiedensohler A. , Zahn A. , Ziereis H.
Published: April 2010

Abstract. The origin of aerosol particles in the upper troposphere and lowermost stratosphere over the Eurasian continent was investigated by applying cluster analysis methods to in situ measured data. Number concentrations of submicrometer aerosol particles and trace gas mixing ratios derived by the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) measurement system on flights between Germany and South-East Asia were used for this analysis. Four cluster analysis methods were applied to a test data set and their capability of separating the data points into scientifically reasonable clusters was assessed. The best method was applied to seasonal data subsets for summer and winter resulting in five cluster or air mass types: stratosphere, tropopause, free troposphere, high clouds, and boundary layer influenced. Other source clusters, like aircraft emissions could not be resolved in the present data set with the used methods. While the cluster separation works satisfactory well for the summer data, in winter interpretation is more difficult, which is attributed to either different vertical transport pathways or different chemical lifetimes in the two seasons. The geographical distribution of the clusters together with histograms for nucleation and Aitken mode particles within each cluster are presented. Aitken mode particle number concentrations show a clear vertical gradient with the lowest values in the lowermost stratosphere (750–2820 particles/cm3 STP, minimum of the two 25%- and maximum of the two 75%-percentiles of both seasons) and the highest values for the boundary-layer-influenced air (4290–22 760 particles/cm3 STP). Nucleation mode particles are also highest in the boundary-layer-influenced air (1260–29 500 particles/cm3 STP, but are lowest in the free troposphere (0–450 particles/cm3 STP). The given submicrometer particle number concentrations represent the first statistically sound data set for the upper troposphere and lowermost stratosphere over the Eurasian continent.
Rapid formation of isoprene photo-oxidation products observed in Amazonia
Authors: Karl T. , Guenther A. , Turnipseed A. , Artaxo P. , Martin S.
Published: April 2010

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian aerosol characterization experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. A recently suggested novel pathway for isoprene peroxy radicals could explain the observed discrepancy and reconcile the rapid formation of these VOCs. Furthermore, if generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in substantial underestimates of modelled OH reactivity that could explain a major fraction of the missing OH sink over forests which has previously been attributed to a missing source of primary biogenic VOCs.
Positive sampling artifact of carbonaceous aerosols and its influence on the thermal-optical split of OC/EC
Authors: Cheng Y. , He K. B. , Duan F. K. , Zheng M. , Ma Y. L. , Tan J. H.
Published: April 2010

Abstract. Accurate measurement of carbonaceous aerosols is challenging, due to the sampling artifact and the problems of the split of OC/EC. Two approaches have been used to account for the positive artifact: backup quartz approach in which a backup quartz filter is placed either behind a front quartz filter (QBQ) or in a parallel port behind a Teflon filter (QBT), and organic denuder approach in which an organic denuder is placed upstream of the quartz filter. Both approaches were evaluated in Beijing, China, from January to February 2009. 10% of the OC captured by the bare quartz filter was from the positive artifact. The origin of backup OC was quantitatively evaluated by the denuder-based method. All of the QBQ-OC was from gaseous organics passing through the front filter, but the QBQ had not reached equilibrium with gas phase due to the relative small sampling volume resulting in an undercorrection of the positive artifact by 3.7%. QBT-OC was from both gaseous organics passing through the front filter (82%) and the evaporated organic carbon (18%), thus overcorrecting the positive artifact by 6.3%. Even the positive artifact-contributed QBT-OC was found to overestimate the positive artifact, perhaps due to the difference in the adsorption properties of the loaded filter and the filter without particle loading. Re-partitioning of PC and EC was performed by the multiple linear regression approach. The attenuation coefficient of PC was twofold higher than that of EC, indicating PC was darker than EC, resulting in the underestimation of native EC by TOT-split-EC. It was also found that PC formed on the bare quartz filter (45.56 m2/g) was darker than that formed on the denuded filter (38.64 m2/g), indicating that the underestimation for the bare quartz filter was more significant.
Technical Note Formal blind intercomparison of OH measurements: results from the international campaign HOxComp
Authors: Schlosser E. , Brauers T. , Dorn H.-P. , Fuchs H. , Häseler R. , Hofzumahaus A. , Holland F. , Wahner A. , Kanaya Y. , Kajii Y. , Miyamoto K. , Nishida S. , Watanabe K. , Yoshino A. , Kubistin D. , Martinez M. , Rudolf M. , Harder H. , Berresheim H. , Elste T. , Plass-Dülmer C. , Stange G. , Schurath U.
Published: April 2010

Abstract. Hydroxyl radicals (OH) are the major oxidizing species in the troposphere. Because of their central importance, absolute measurements of their concentrations are needed to validate chemical mechanisms of atmospheric models. The extremely low and highly variable concentrations in the troposphere, however, make measurements of OH difficult. Three techniques are currently used worldwide for tropospheric observations of OH after about 30 years of technical developments: Differential Optical Laser Absorption Spectroscopy (DOAS), Laser-Induced Fluorescence Spectroscopy (LIF), and Chemical Ionisation Mass Spectrometry (CIMS). Even though many measurement campaigns with OH data were published, the question of accuracy and precision is still under discussion. Here, we report results of the first formal, blind intercomparison of these techniques. Six OH instruments (4 LIF, 1 CIMS, 1 DOAS) participated successfully in the ground-based, international HOxComp campaign carried out in Jülich, Germany, in summer 2005. Comparisons were performed for three days in ambient air (3 LIF, 1 CIMS) and for six days in the atmosphere simulation chamber SAPHIR (3 LIF, 1 DOAS). All instruments were found to measure tropospheric OH concentrations with high sensitivity and good time resolution. The pairwise correlations between different data sets were linear and yielded high correlation coefficients (r2=0.75−0.96). Excellent absolute agreement was observed for the instruments at the SAPHIR chamber, yielding slopes between 1.01 and 1.13 in the linear regressions. In ambient air, the slopes deviated from unity by factors of 1.06 to 1.69, which can partly be explained by the stated instrumental accuracies. In addition, sampling inhomogeneities and calibration problems have apparently contributed to the discrepancies. The absolute intercepts of the linear regressions did not exceed 0.6×106 cm−3, mostly being insignificant and of minor importance for daytime observations of OH. No relevant interferences with respect to ozone, water vapour, NOx and peroxy radicals could be detected. The HOxComp campaign has demonstrated that OH can be measured reasonably well by current instruments, but also that there is still room for improvement of calibrations.
Determination of OM/OC ratios and specific attenuation coefficients (SAC) in ambient fine PM at a rural site in southern Ontario: implications for emission sources, particle aging, and radiative forcing
Authors: Chan T. W. , Huang L. , Leaitch W. R. , Sharma S. , Brook J. R. , Slowik J. G. , Abbatt J. P. D. , Brickell P. C. , Liggio J. , Li S.-M. , Moosmüller H.
Published: April 2010

Abstract. Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in southern Ontario during intensive studies in 2005 and 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. These results were compared to the organic aerosol mass concentration (OM) measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b_asp) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC) were also derived. According to the results, the POC mass is proportional to the approximated oxygen mass in the aerosols and OM/OC ratios can be estimated directly from thermal measurements. The study also suggests that the air masses from the south, with relatively low OC/EC ratios, high EC, sulphate contents and OM/OC ratios, were originated from urban and industrial emissions and subsequently experienced photo-oxidations in the atmosphere, implying that the oxygenated organics could come from both primary and secondary sources. Whereas the air masses from the north, with relatively high OC/EC ratios, low EC, sulphate contents and OM/OC ratios, were dominant by the background clean air with relatively larger contributions from biogenic emissions. The mean SAC derived from the 2005 and 2007 studies are 4.9 m2 g−1 and 3.8 m2 g−1, respectively. When POC mass approaching zero (i.e. the impact of atmospheric aging is minimized), the SAC for primary emitted soot is estimated to be 5.8 m2 g−1 and 6.3 m2 g−1 for the northern and southern air masses, respectively, supported by the corresponding values when particulate sulphate concentration approaches zero. A decreasing trend in the SAC value with atmospheric aging of the aerosol was observed at the site, suggesting that during the study, the light absorption enhancement due to the presence of coating on particles was likely to be offset by the decrease in light absorption caused by increasing soot particle diameter and collapsing of soot particle structure. This result may imply that model simulations of atmospheric warming by BC could be 50% too high.
Elevated large-scale dust veil originated in the Taklimakan Desert: intercontinental transport and 3-dimensional structure captured by CALIPSO and regional and global models
Authors: Yumimoto K. , Eguchi K. , Uno I. , Takemura T. , Liu Z. , Shimizu A. , Sugimoto N.
Published: April 2010

Abstract. An intense dust storm occurred during 19–20 May 2007 over the Taklimakan Desert in northwestern China. In the following days, the space-borne lidar CALIOP tracked an optically thin, highly elevated, horizontally extensive dust veil that was transported intercontinentally over the eastern Asia, Pacific Ocean, North America, and Atlantic Ocean. A global aerosol transport model (SPRINTARS) also simulated the dust veil quite well and provided a 3-D view of the dust intercontinental transport. The SPRINTARS simulation revealed that the dust veil travels at 4–10 km altitudes with a thickness of 1–4 km along the isentropic surface between 310 K and 340 K. The transport speed is about 1500 km/d. The estimated dust amounts exported to the Pacific is 30.8 Gg, of which 65% is deposited in the Pacific and 18% is transported to the North Atlantic. These results imply that the dust veil can fertilize the open oceans, provide background dust to the atmosphere remote from the sources. The entrainment mechanism that injects dust particles into the free atmosphere is important for understanding the formation of the dust veil and the subsequent long-range transport. We used a regional dust transport model (RC4) to analyze the dust emission and entrainment over the source region. The RC4 analysis revealed that strong northeasterly surface winds associated with a low pressure invade into the Taklimakan Desert through the east side corridor and form a strong up-slope wind along the high and steep mountainside of the Tibetan Plateau, blowing up large amounts of dust into the air. The updraft further brings the lofted dust particles up to the free troposphere (about 9 km MSL) where the westerly generally blows. The peculiar terrain surrounding the Taklimakan Desert plays the key role in the entrainment of dust to the free troposphere to form the dust veil.
Effect of biomass burning on marine stratocumulus clouds off the California coast
Authors: Brioude J. , Cooper O. R. , Feingold G. , Trainer M. , Freitas S. R. , Kowal D. , Ayers J.K. , Prins E. , Minnis P. , McKeen S. A. , Frost G. J. , Hsie E.-Y.
Published: April 2010

Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning on marine stratocumulus clouds has been examined in June and July of 2006–2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. The combined effect is an indirect radiative forcing of −7.45% (cooling effect) on average, with a bias due to meteorology of +0.89%. Further away from the coast, the biomass burning aerosols, which are located within the boundary layer, reduce the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.33% (warming effect) with a bias of +0.49%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.
On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models
Authors: Merkel A. W. , Marsh D. R. , Gettelman A. , Jensen E. J.
Published: April 2010

Abstract. The distribution of ice layers in the polar summer mesosphere (called polar mesospheric clouds or PMCs) is sensitive to background atmospheric conditions and therefore affected by global-scale dynamics. To investigate this coupling it is necessary to simulate the global distribution of PMCs within a 3-dimensional (3-D) model that couples large-scale dynamics with cloud microphysics. However, modeling PMC microphysics within 3-D global chemistry climate models (GCCM) is a challenge due to the high computational cost associated with particle following (Lagrangian) or sectional microphysical calculations. By characterizing the relationship between the PMC radius, ice water content (iwc), and local temperature (T) from an ensemble of simulations from the sectional microphysical model, the Community Aerosol and Radiation Model for Atmospheres (CARMA), we determined that these variables have a fundamental stable relationship that is independent of the cloud time history. For our purposes we use this relationship to provide a bulk parameterization of PMC microphysics to be included into multidimensional models. However, this relationship has the potential to be used in other applications to characterize PMCs. We use a parameterization of the relationship to predict the particle effective radius using only the local temperature and ice water content in a 3-D GCCM for decadal scale PMC simulations. Such a parameterization allows for theoretical ice cloud microphysics to be applied in the GCCM to simulate growth, sublimation and sedimentation of ice particles without keeping track of the time history of each ice particle size or particle size bin. This approach produces realistic PMC simulations including estimates of the optical properties of PMCs. We validate the relationship with PMC data from the Solar Occultation for Ice Experiment (SOFIE).
Technical Note: Sensitivity of 1-D smoke plume rise models to the inclusion of environmental wind drag
Authors: Freitas S. R. , Longo K. M. , Trentmann J. , Latham D.
Published: April 2010

Abstract. We revisit the parameterization of the vertical transport of hot gases and particles emitted from biomass burning, described in Freitas et al. (2007), to include the effects of environmental wind on transport and dilution of the smoke plume at the cloud scale. Typically, the final vertical height that the smoke plumes reach is controlled by the thermodynamic stability of the atmospheric environment and the surface heat flux released by the fire. However, the presence of a strong horizontal wind can enhance the lateral entrainment and induce additional drag, particularly for small fires, impacting the smoke injection height. This process is quantitatively represented by introducing an additional entrainment term to account for organized inflow of a mass of cooler and drier ambient air into the plume and its drag by momentum transfer. An extended set of equations including the horizontal motion of the plume and the additional increase of the plume radius is solved to explicitly simulate the time evolution of the plume rise with the additional mass and momentum. One-dimensional (1-D) model results are presented for two deforestation fires in the Amazon basin with sizes of 10 and 50 ha under calm and windy atmospheric environments. The results are compared to corresponding simulations generated by the complex non-hydrostatic three dimensional (3-D) Active Tracer High resolution Atmospheric Model (ATHAM). We show that the 1-D model results compare well with the full 3-D simulations. The 1-D model may thus be used in field situations where extensive computing facilities are not available, especially under conditions for which several optional cases must be studied.
UV Raman lidar measurements of relative humidity for the characterization of cirrus cloud microphysical properties
Authors: Di Girolamo P. , Summa D. , Lin R.-F. , Maestri T. , Rizzi R. , Masiello G.
Published: April 2010

Abstract. Raman lidar measurements performed in Potenza by the Raman lidar system BASIL in the presence of cirrus clouds are discussed. Measurements were performed on 6 September 2004 in the frame of Italian phase of the EAQUATE Experiment. The major feature of BASIL is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour, and consequently relative humidity, both in daytime and night-time, based on the application of the rotational and vibrational Raman lidar techniques in the UV. BASIL is also capable to provide measurements of the particle backscatter and extinction coefficient, and consequently lidar ratio (at the time of these measurements only at one wavelength), which are fundamental to infer geometrical and microphysical properties of clouds. A case study is discussed in order to assess the capability of Raman lidars to measure humidity in presence of cirrus clouds, both below and inside the cloud. While air inside the cloud layers is observed to be always under-saturated with respect to water, both ice super-saturation and under-saturation conditions are found inside these clouds. Upper tropospheric moistening is observed below the lower cloud layer. The synergic use of the data derived from the ground based Raman Lidar and of spectral radiances measured by the NAST-I Airborne Spectrometer allows to determine the temporal evolution of the atmospheric cooling/heating rates due to the presence of the cirrus cloud anvil. Lidar measurements beneath the cirrus cloud layer have been interpreted using a 1-D cirrus cloud model with explicit microphysics. The 1-D simulations indicates that sedimentation-moistening has contributed significantly to the moist anomaly, but other mechanisms are also contributing. This result supports the hypothesis that the observed mid-tropospheric humidification is a real feature which is strongly influenced by the sublimation of precipitating ice crystals. Results illustrated in this study demonstrate that Raman lidars, like the one used in this study, can resolve the spatial and temporal scales required for the study of cirrus cloud microphysical processes and appears sensitive enough to reveal and quantify upper tropospheric humidification associated with cirrus cloud sublimation.
The impact of dust on sulfate aerosol, CN and CCN during an East Asian dust storm
Authors: Manktelow P. T. , Carslaw K. S. , Mann G. W. , Spracklen D. V.
Published: April 2010

Abstract. A global model of aerosol microphysics is used to simulate a large East Asian dust storm during the ACE-Asia experiment. We use the model together with size resolved measurements of aerosol number concentration and composition to examine how dust modified the production of sulfate aerosol and the particle size distribution in East Asian outflow. Simulated size distributions and mass concentrations of dust, sub- and super-micron sulfate agree well with observations from the C-130 aircraft. Modelled mass concentrations of fine sulfate (Dp<1.3 μm) decrease by ~10% due to uptake of sulfur species onto super-micron dust. We estimate that dust enhanced the mass concentration of coarse sulfate (Dp<1.0 μm) by more than an order of magnitude, but total sulfate concentrations increase by less than 2% because decreases in fine sulfate have a compensating effect. Our analysis shows that the sulfate associated with dust can be explained largely by the uptake of H2SO4 rather than reaction of SO2 on the dust surface, which we assume is suppressed once the particles are coated in sulfate. We suggest that many previous model investigations significantly overestimated SO2 oxidation on East Asian dust, possibly due to the neglect of surface saturation effects. We extend previous model experiments by examining how dust modified existing particle concentrations in Asian outflow. Total particle concentrations modelled in the dust-pollution plume are reduced by up to 20%, but we predict that dust led to less than 10% depletion in particles large enough to act as cloud condensation nuclei. Our analysis suggests that E. Asian dust storms have only a minor impact on sulfate particles present at climate-relevant sizes.
Seasonal variation of aliphatic amines in marine sub-micrometer particles at the Cape Verde islands
Authors: Müller C. , Iinuma Y. , Karstensen J. , van Pinxteren D. , Lehmann S. , Gnauk T. , Herrmann H.
Published: April 2010

Abstract. Monomethylamine (MA), dimethylamine (DMA) and diethylamine (DEA) were detected at non-negligible concentrations in sub-micrometer particles at the Cap Verde Atmospheric Observatory (CVAO) located on the island of São Vicente in Cape Verde during algal blooms in 2007. The concentrations of these amines in five stage impactor samples ranged from 0 to 30 pg m−3 for MA, 130 to 360 pg m−3 for DMA and 5 to 110 pg m−3 for DEA during the spring bloom in May 2007 and 2 to 520 pg m−3 for MA, 100 to 1400 pg m−3 for DMA, 90 to 760 pg m−3 for DEA during an unexpected winter algal bloom in December 2007. Anomalously high Saharan dust deposition and intensive ocean layer deepening were found at the Atmospheric Observatory and the associated Ocean Observatory during algal bloom periods. The highest amine concentrations in fine particles (impactor stage 2, 0.14–0.42 μm) indicates that amines are likely taken up from the gas phase into the acidic sub-micrometer particles. The contribution of amines to the organic carbon (OC) content ranged from 0.2 to 2.5%C in the winter months, indicating the importance of this class of compounds to the carbon cycle in the marine environment. Furthermore, aliphatic amines originating from marine biological sources likely contribute significantly to the organic nitrogen in the marine atmosphere. The average contribution of the amines to the total detected nitrogen content in submicron particles can be non-negligible, especially in the winter months (0.1% N to 1.5% N in the sum of nitrate, ammonium and amines). This indicates that these smaller aliphatic amines can be important for the carbon and the nitrogen cycles in the remote marine environment.
Numerical simulations of contrail-to-cirrus transition – Part 2: Impact of initial ice crystal number, radiation, stratification, secondary nucleation and layer depth
Authors: Unterstrasser S. , Gierens K.
Published: April 2010

Abstract. Simulations of contrail-to-cirrus transition were performed with an LES model. In Part 1 the impact of relative humidity, temperature and vertical wind shear was explored in a detailed parametric study. Here, we study atmospheric parameters (like stratification and depth of the supersaturated layer) and processes which may affect the contrail evolution. Under suitable conditions (controlled by the radiation scenario and stratification) radiative heating lifts the contrail-cirrus and prolongs its lifetime. The radiation scenario affects the radiance incident on the contrail layer and is characterised herein by the season, time of day and the presence of lower-level cloudiness. The potential of contrail-driven secondary nucleation, both via heterogeneous nucleation of preactivated soot cores (from former contrail ice crystals) and homogeneous nucleation is investigated. It turned out that in our model the pure contrail dynamics (triggered by radiative heating) does not suffice to force homogeneous freezing of ambient liquid aerosol particles. Our model results suggest that heterogeneous nucleation of preactivated soot cores is unimportant mainly because the relative humidity does not exceed ice saturation substantially close to the contrail core. Contrail evolution is not controlled by the depth of the supersaturated layer as long as it exceeds roughly 500 m. Deep fallstreaks however need thicker layers. A variation of the initial ice crystal number is effective during the whole evolution of a contrail which implies that engine modifications that lead to lower soot emissions would lead to optically thinner and shorter living contrail-cirrus.
Changes in the production rate of secondary aerosol particles in central Europe in view of decreasing SO2 emissions between 1996 and 2006
Authors: Hamed A. , Birmili W. , Joutsensaari J. , Mikkonen S. , Asmi A. , Wehner B. , Spindler G. , Jaatinen A. , Uhse K. , Wiedensohler A. , Lehtinen K. E. J. , Laaksonen A.
Published: April 2010

Abstract. In anthropogenically influenced atmospheres, sulphur dioxide (SO2) is the main precursor of gaseous sulphuric acid (H2SO4), which in turn forms new aerosol particles (diameter <10 nm) through nucleation. As a result of socio-economic changes, East Germany has seen a dramatic decrease in anthropogenic SO2 emissions between 1989 and present, as documented by routine air quality measurements in many locations. Using two different data sets of experimental particle number size distributions (3–750 nm) from the research station Melpitz (1996–1997 and 2003–2006) we have attempted to evaluate the possible influence of changing SO2 concentrations on the frequency and intensity of new particle formation (NPF). Between the two periods SO2 concentrations decreased on average by 65%, while the frequency of NPF events dropped by 45%. In addition, the average formation rate of 3 nm particles decreased by 68%. The trends were statistically significant, therefore suggesting a connection between the availability of anthropogenic SO2 and the production of new particle number. A contrasting finding was the increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H2SO4, the SO2 concentration, and global radiation intensity, we could define the characteristic range of atmospheric conditions under which particle formation events at the Melpitz site take place or not. While the connection between anthropogenic SO2, H2SO4 and NPF appears very plausible, our analysis yielded no significant evidence whether decreasing SO2 concentrations did affect the production of cloud condensation nuclei (CCN).
Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride
Authors: Bertram T. H. , Thornton J. A.
Published: April 2010

Abstract. The heterogeneous reaction of N2O5 on mixed organic-inorganic aerosol particles was investigated using an entrained aerosol flow tube coupled to a custom-built chemical ionization mass spectrometer. Laboratory results on aqueous particles confirm a strong dependence of the reactive uptake coefficient (γ) on particle liquid water, for particle water concentrations below 15 M, and the molar ratio of particle water to nitrate. Measurements of γ(N2O5) on mixed chloride-nitrate particles indicate that the presence of trace chloride can negate the suppression of γ(N2O5) at high nitrate loadings with implications for polluted coastal regions. These results are used to construct a new parameterization for γ(N2O5), that when coupled to an aerosol thermodynamics model, can be used within regional and/or global chemical transport models.
A modelling study of photochemical regimes over Europe: robustness and variability
Authors: Beekmann M. , Vautard R.
Published: April 2010

Abstract. The variability of the relative sensitivity to volatile organic compounds (VOC) or NOx emissions, the chemical regime, over Europe during summers 2001 to 2003 is simulated with a regional scale transport-chemistry model. The robustness of chemical regimes is shown. A VOC sensitive regime over North-Western Europe and a mainly NOx sensitive regime over the Mediterranean basin and Eastern Europe are found, confirming earlier published results. The chemical regime time variability, its robustness to several environmental factors (seasonality, interannual variability) and to model uncertainty are thoroughly analysed. The chemical regime spatial structure only slightly depends on the ozone target considered (daily ozone maximum or AOT40, SOMO35, ...). Differences between particular years and summer months are weak. Day to day variability is significant but does not change the occurrence of one or another chemical regime over North-Western Europe and the Mediterranean basin. Expected decreases in anthropogenic NOx emissions over Europe since the last and for the next few decades have shifted and will shift chemical regimes to more NOx sensitive. The predictive and explanatory use of chemical regime indicator species is also investigated. For all cases but near ship tracks over the Mediterranean basin, the spatial pattern of chemical regimes appears to be robust with respect to model uncertainty.
The representation of dust transport and missing urban sources as major issues for the simulation of PM episodes in a Mediterranean area
Authors: Flaounas E. , Coll I. , Armengaud A. , Schmechtig C.
Published: April 2010

Abstract. Due to its adverse effects on human health, atmospheric particulate matter (PM) constitutes a growing challenge for air quality management. It is also a complex subject of study. The understanding of its atmospheric evolution is indeed made difficult by the wide number of sources and the numerous processes that govern its evolution in the troposphere. As a consequence, the representation of particulate matter in chemistry-transport models needs to be permanently evaluated and enhanced in order to refine our comprehension of PM pollution events and to propose consistent environmental policies. The study presented here focuses on a summer particulate pollution episode that occurred on the French Mediterranean coast. It aims at identifying the constitutive elements of this episode and to discuss its representation within a eulerian model. We first highlight the major role of dust transport from western Africa in the formation of a multi-day PM event. This result shows that dust import has to be regarded as a potentially major participant to PM events in Europe, even when considering moderate peak values. In parallel we focus on a lack of diurnal variability in the model, which is attributed to missing urban sources in standard emission inventories, and notably the resuspension of particles by urban road traffic. Through a sensitivity study based on PM and NOx measurements, we could assess the amplitude of this lack as well as the need to reconsider road traffic PM sources. In parallel, by coupling the CHIMERE-DUST model outputs to our simulation, we could show that the representation of transcontinental dust transport is a necessity for a better simulation of atmospheric particles in Southern Europe, and – in the frame of air quality management – for the quantification of the anthropogenic part of particulate matter pollution.
Aerosol hygroscopicity at high (99 to 100%) relative humidities
Authors: Ruehl C. R. , Chuang P. Y. , Nenes A.
Published: April 2010

Abstract. The hygroscopicity of an aerosol largely determines its influence on climate and, for smaller particles, atmospheric lifetime. While much aerosol hygroscopicity data is available at lower relative humidities (RH) and under cloud formation conditions (RH>100%), relatively little data is available at high RH (99.2 to 99.9%). We measured the size of droplets at high RH that had formed on particles composed of one of seven compounds with dry diameters between 0.1 and 0.5 μm, and calculated the hygroscopicity of these compounds. We use a parameterization of the Kelvin term, in addition to a standard parameterization (κ) of the Raoult term, to express the hygroscopicity of surface-active compounds. For inorganic compounds, hygroscopicity could reliably be predicted using water activity data and assuming a surface tension of pure water. In contrast, most organics exhibited a slight to mild increase in hygroscopicity with droplet diameter. This trend was strongest for sodium dodecyl sulfate (SDS), the most surface-active compound studied. The results suggest that partitioning of surface-active compounds away from the bulk solution, which reduces hygroscopicity, dominates any increases in hygroscopicity due to reduced surface tension. This is opposite to what is typically assumed for soluble surfactants. Furthermore, we saw no evidence that micellization limits SDS activity in micron-sized solution droplets, as observed in macroscopic solutions. These results suggest that while the high-RH hygroscopicity of inorganic compounds can be reliably predicted using readily available data, surface-activity parameters obtained from macroscopic solutions with organic solutes may be inappropriate for calculations of the hygroscopicity of micron-sized droplets.
Extreme Saharan dust event over the southern Iberian Peninsula in september 2007: active and passive remote sensing from surface and satellite
Authors: Guerrero-Rascado J. L. , Olmo F. J. , Avilés-Rodríguez I. , Navas-Guzmán F. , Pérez-Ramírez D. , Lyamani H. , Alados Arboledas L.
Published: April 2010

Abstract. This study investigates aerosol optical properties during the extreme Saharan dust event detected from 3 to 7 September 2007 over Granada, southern Iberian Peninsula, with both active and passive remote sensing instrumentation from surface and satellite. The intensity of the event was visualized on the aerosol optical depth series obtained by the sun-photometer Cimel CE 318-4 operated at Granada in the framework of AERONET from August 2004 until December 2008 (level 2 data). A combination of large aerosol optical depth (0.86–1.50) at 500 nm, and reduced Angström exponent (0.1–0.25) in the range 440–870 nm, was detected on 6 September during daytime. This Saharan dust event also affected other Iberian Peninsula stations included in AERONET (El Arenosillo and Évora stations). During the most intense stage, on 6 September, maximum aerosol backscatter values were a factor of 8 higher than other maxima during this Saharan dust event. Values up to 1.5×10−2 km−1 sr−1 at 355 and 532 nm were detected in the layer with the greatest aerosol load between 3–4 km a.s.l., although aerosol particles were also detected up to 5.5 km a.s.l. In this stage of the event, dust particles at these altitudes showed a backscatter-related Angström exponent between −0.44 and 0.53 for the two spectral intervals considered. The results from different measurements (active/passive and ground-based/satellite) reveal the importance of performing multi-instrumental measurements to properly characterize the contribution of different aerosol types from different sources during extreme events.
Heterogeneous freezing of droplets with immersed mineral dust particles – measurements and parameterization
Authors: Niedermeier D. , Hartmann S. , Shaw R. A. , Covert D. , Mentel Th. F. , Schneider J. , Poulain L. , Reitz P. , Spindler C. , Clauss T. , Kiselev A. , Hallbauer E. , Wex H. , Mildenberger K. , Stratmann F.
Published: April 2010

Abstract. During the measurement campaign FROST (FReezing Of duST), LACIS (Leipzig Aerosol Cloud Interaction Simulator) was used to investigate the immersion freezing behavior of coated and uncoated Arizona Test Dust (ATD) particles with a mobility diameter of 300 nm. Particles were coated with succinic acid (C4H6O4), sulfuric acid (H2SO4, two different coating conditions), and ammonium sulfate ((NH4)2SO4). Ice fractions at temperatures between 233.15 K and 240.65 K were determined for all types of particles acting as IN (Ice Nuclei). In this temperature range, uncoated particles and those coated with C4H6O4 or small amounts of H2SO4 started to act as IN at higher temperatures compared to particles with larger amounts of H2SO4 or (NH4)2SO4 coatings. Although the latter two showed similar hygroscopic growth and droplet activation behavior, they differed in their ability to act as IN. ATD particles coated with (NH4)2SO4 were the most inefficient IN. The ability of the investigated particles to act as IN was found not to be related to water activity for the freezing process investigated, however, in LACIS, the supercooled droplets were activated and highly diluted before the freezing occurred. Applying the measurement results, a parameterization, based on a simplified CNT (Classical Nucleation Theory) type nucleation rate expression, was developed. The simplified theory allows us to determine that thermodynamic changes at the surface are dominating the change in nucleating ability, rather than changes in surface area or kinetic effects.
The chemistry of OH and HO2 radicals in the boundary layer over the tropical Atlantic Ocean
Authors: Whalley L. K. , Furneaux K. L. , Goddard A. , Lee J. D. , Mahajan A. , Oetjen H. , Read K. A. , Kaaden N. , Carpenter L. J. , Lewis A. C. , Plane J. M. C. , Saltzman E. S. , Wiedensohler A. , Heard D. E.
Published: April 2010

Abstract. Fluorescence Assay by Gas Expansion (FAGE) has been used to detect ambient levels of OH and HO2 radicals at the Cape Verde Atmospheric Observatory, located in the tropical Atlantic marine boundary layer, during May and June 2007. Midday radical concentrations were high, with maximum concentrations of 9×106 molecule cm−3 and 6×108 molecule cm−3 observed for OH and HO2, respectively. A box model incorporating the detailed Master Chemical Mechanism, extended to include halogen chemistry, and constrained by all available measurements including halogen and nitrogen oxides, has been used to assess the chemical and physical parameters controlling the radical chemistry. IO and BrO, although present only at a few pptv, constituted ~23% of the instantaneous sinks for HO2. Modelled HO2 was sensitive to both HCHO concentration and the rate of heterogeneous loss to the ocean surface and aerosols. However, a unique combination of these parameters could not be found that gave optimised (to within 15%) agreement during both the day and night. The results imply a missing nighttime source of HO2. The model underpredicted the daytime (sunrise to sunset) OH concentration by 12%. Photolysis of HOI and HOBr accounted for ~13% of the instantaneous rate of OH formation. Taking into account that halogen oxides increase the oxidation of NOx (NO→NO2), and in turn reduce the rate of formation of OH from the reaction of HO2 with NO, OH concentrations were estimated to be 10% higher overall due to the presence of halogens. The increase in modelled OH from halogen chemistry gives an estimated 10% shorter lifetime for methane in this region, and the inclusion of halogen chemistry is necessary to model the observed daily cycle of ozone destruction that is observed at the surface. Due to surface losses, we hypothesise that HO2 concentrations increase with height and therefore contribute a larger fraction of the ozone destruction than at the surface.
Correlations of mesospheric winds with subtle motion of the Arctic polar vortex
Authors: Bhattacharya Y. , Gerrard A. J.
Published: April 2010

Abstract. This paper investigates the relationship between high latitude upper mesospheric winds and the state of the stratospheric polar vortex in the absence of major sudden stratospheric warmings. A ground based Michelson Interferometer stationed at Resolute Bay (74°43´ N, 94°58´ W) in the Canadian High Arctic is used to measure mesopause region neutral winds using the hydroxyl (OH) Meinel-band airglow emission (central altitude of ~85 km). These observed winds are compared to analysis winds in the upper stratosphere during November and December of 1995 and 1996; years characterized as cold, stable polar vortex periods. Correlation of mesopause wind speeds with those from the upper stratosphere is found to be significant for the 1996 season when the polar vortex is subtly displaced off its initial location by a strong Aleutian High. These mesopause winds are observed to lead stratospheric winds by approximately two days with increasing (decreasing) mesospheric winds predictive of decreasing (increasing) stratospheric winds. No statistically significant correlations are found for the 1995 season when there is no such displacement of the polar vortex.