bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory experiments on the effect of organic acids and metals on the charge transfer during ice crystal – graupel collision under the conditions similar to stratiform clouds
Authors: Jish Prakash P. , Pradeep Kumar P.
Published: April 2010

Abstract. Laboratory investigations have been carried out to find the sign and magnitude of charge transfer during the collision between ice crystals and graupel in the presence of supercooled water droplets inside the cylindrical steel chamber kept inside a walk-in cold room, which can reach a temperature of −30 °C. The experiments were performed with pure water (Milli-Q, 18.2 Megohms-cm) and with trace amounts of organic acids and metals at low Rime Accretion Rate (<0.40 g m−2 s-1) applicable to stratiform clouds in the temperature range −5 to −27 °C. The ice crystals and supercooled droplets collided with the graupel target at a constant impact velocity of 2.2 m/s. The presence of trace chemicals (organics or metals) saw significant increase in the magnitude of charge transferred per crystal collision to the graupel. These experiments therefore suggest that the presence of trace amounts of organics or metals in cloud water can significantly alter the electrical structure of stratiform clouds.
Determination of particulate lead during MILAGRO/MCMA-2006 using Aerosol Mass Spectrometry
Authors: Salcedo D. , Onasch T. B. , Aiken A. C. , Williams L. R. , de Foy B. , Cubison M. J. , Worsnop D. R. , Molina L. T. , Jimenez J. L.
Published: April 2010

Abstract. We report the first measurements of particulate lead (Pb) from Aerodyne Aerosol Mass Spectrometers, which were deployed in and around Mexico City during the Megacity Initiative: Local and Global Research Observations (MILAGRO)/Mexico City Metropolitan Area 2006 (MCMA-2006) field campaigns. The high resolution mass spectrometer of one of the AMS instruments (HR-AMS) and the measured isotopic ratios unequivocally prove the detection of Pb in ambient particles. A substantial fraction of the lead evaporated slowly from the vaporizer of the instruments, which is indicative of species with low volatility at 600 °C. A model was developed in order to estimate the ambient particulate Pb entering the AMS from the signals in the "open" and the "closed" (or "background") mass spectrum modes of the AMS. The model suggests the presence of at least two lead fractions with ~25% of the Pb signal exhibiting rapid evaporation (1/e decay constant, τ<0.1 s) and ~75% exhibiting slow evaporation (τ~2.4 min) at the T0 urban supersite and a different fraction (70% prompt and 30% slow evaporation) at a site northwest from the metropolitan area (PEMEX site). From laboratory experiments with pure Pb(NO3)2 particles, we estimated that the Pb ionization efficiency relative to nitrate (RIEPb) is 0.5. Comparison of time series of AMS Pb with other measurements carried out at T0 (using Proton Induced X-ray Emission (PIXE), Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) and single-particle counts from an Aerosol Time-of-Fight Mass Spectrometer (ATOFMS)) shows similar levels (for PIXE and ICP-MS) and substantial correlation. During part of the campaign, sampling at T0 was alternated every 10 min with an Aerosol Concentrator, which enabled the detection of signals for PbCl+ and PbS+ ions. PbS+ displays the signature of a slowly evaporating species, while PbCl+ appears to arise only from fast evaporation, which is likely due to the higher vapor pressure of the compounds generating PbCl+. This is consistent with the evaporation model results. Levels of particulate Pb measured at T0 were similar to previous studies in Mexico City. Pb shows a diurnal cycle with a maximum in the early morning, which is typical of primary urban pollutants. Pb shows correlation with Zn, consistent with previous studies, while the sources of Pb appear to be at least partially disjoint from those of particulate chloride. Back trajectory analysis of the T0 Pb data suggests the presence of sources inside the urban area SSW and N of T0, with different chemical forms of Pb being associated with different source locations. High signals due to particulate lead were also detected in the PEMEX site; again, no correlation between Pb and chloride plumes was observed, suggesting mostly different sources for both species.
The roles of sulfuric acid in new particle formation and growth in the mega-city of Beijing
Authors: Yue D. L. , Hu M. , Zhang R. Y. , Wang Z. B. , Zheng J. , Wu Z. J. , Wiedensohler A. , He L. Y. , Huang X. F. , Zhu T.
Published: April 2010

Abstract. Simultaneous measurements of gaseous sulfuric acid and particle number size distributions were performed to investigate aerosol nucleation and growth during CAREBeijing-2008. The analysis of the measured aerosols and sulfuric acid with an aerosol dynamic model shows the dominant role of sulfuric acid in new particle formation (NPF) process but also in the subsequent growth in Beijing. Based on the data of twelve NPF events, the average formation rates (2–13 cm−3 s−1) show a linear correlation with the sulfuric acid concentrations (R2=0.85). Coagulation seems to play a significant role in reducing the number concentration of nucleation mode particles with the ratio of the coagulation loss to formation rate being 0.41±0.16. The apparent growth rates vary from 3 to 11 nm h−1. Condensation of sulfuric acid and its subsequent neutralization by ammonia and coagulation contribute to the apparent particle growth on average 45±18% and 34±17%, respectively. The 30% higher concentration of sulfate than organic compounds in particles during the seven sulfur-rich NPF events but 20% lower concentration of sulfate during the five sulfur-poor type suggest that organic compounds are an important contributor to the growth of the freshly nucleated particles, especially during the sulfur-poor cases.
Improvements in the profiles and distributions of nitric acid and nitrogen dioxide with the LIMS version 6 dataset
Authors: Remsberg E. , Natarajan M. , Marshall T. , Gordley L. L. , Thompson R. E. , Lingenfelser G.
Published: April 2010

Abstract. The quality of the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) nitric acid (HNO3) and nitrogen dioxide (NO2) profiles and distributions of 1978/1979 is described after their processing with an updated, Version 6 (V6) algorithm and subsequent archival in 2002. Estimates of the precision and accuracy of both of those species are developed and provided herein. The character of the V6 HNO3 profiles is relatively unchanged from that of the earlier LIMS Version 5 (V5) profiles, except in the upper stratosphere where the interfering effects of CO2 are accounted for better with V6. The accuracy of the retrieved V6 NO2 is also significantly better in the middle and upper stratosphere, due to improvements in its spectral line parameters and in the reduced biases for the accompanying V6 temperature and water vapor profiles. As a result of these important updates, there is better agreement with theoretical calculations for profiles of the HNO3/NO2 ratio, day-to-night NO2 ratio, and with estimates of the production of NO2 in the mesosphere and its descent to the upper stratosphere during polar night. The improved precisions and more frequent retrievals of the profiles along the LIMS orbit tracks provide for better continuity and detail in map analyses of these two species on pressure surfaces. It is judged that the chemical effects of the oxides of nitrogen on ozone can be examined quantitatively throughout the stratosphere with the LIMS V6 data, and that the findings will be more compatible with those obtained from measurements of the same species from subsequent satellite sensors.
Kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB): the influence of interfacial transport and bulk diffusion on the oxidation of oleic acid by ozone
Authors: Shiraiwa M. , Pfrang C. , Pöschl U.
Published: April 2010

Abstract. We present a novel kinetic multi-layer model that explicitly resolves mass transport and chemical reaction at the surface and in the bulk of aerosol particles (KM-SUB). The model is based on the PRA framework of gas-particle interactions (Pöschl et al., 2007), and it includes reversible adsorption, surface reactions and surface-bulk exchange as well as bulk diffusion and reaction. Unlike earlier models, KM-SUB does not require simplifying assumptions about steady-state conditions and radial mixing. The temporal evolution and concentration profiles of volatile and non-volatile species at the gas-particle interface and in the particle bulk can be modeled along with surface concentrations and gas uptake coefficients. In this study we explore and exemplify the effects of bulk diffusion on the rate of reactive gas uptake for a simple reference system, the ozonolysis of oleic acid particles, in comparison to experimental data and earlier model studies. We demonstrate how KM-SUB can be used to interpret and analyze experimental data from laboratory studies, and how the results can be extrapolated to atmospheric conditions. In particular, we show how interfacial transport and bulk transport, i.e., surface accommodation, bulk accommodation and bulk diffusion, influence the kinetics of the chemical reaction. Sensitivity studies suggest that in fine air particulate matter oleic acid and compounds with similar reactivity against ozone (C=C double bonds) can reach chemical lifetimes of multiple hours only if they are embedded in a (semi-)solid matrix with very low diffusion coefficients (≤10−10 cm2 s−1). Depending on the complexity of the investigated system, unlimited numbers of volatile and non-volatile species and chemical reactions can be flexibly added and treated with KM-SUB. We propose and intend to pursue the application of KM-SUB as a basis for the development of a detailed master mechanism of aerosol chemistry as well as for the derivation of simplified but realistic parameterizations for large-scale atmospheric and climate models.
Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles
Authors: Devasthale A. , Willén U. , Karlsson K.-G. , Jones C. G.
Published: April 2010

Abstract. Temperature inversions are one of the dominant features of the Arctic atmosphere and play a crucial role in various processes by controlling the transfer of mass and moisture fluxes through the lower troposphere. It is therefore essential that they are accurately quantified, monitored and simulated as realistically as possible over the Arctic regions. In the present study, the characteristics of inversions in terms of frequency and strength are quantified for the entire Arctic Ocean for summer and winter seasons of 2003 to 2008 using the AIRS data for the clear-sky conditions. The probability density functions (PDFs) of the inversion strength are also presented for every summer and winter month. Our analysis shows that although the inversion frequency along the coastal regions of Arctic decreases from June to August, inversions are still seen in almost each profile retrieved over the inner Arctic region. In winter, inversions are ubiquitous and are also present in every profile analysed over the inner Arctic region. When averaged over the entire study area (70° N–90° N), the inversion frequency in summer ranges from 69% to 86% for the ascending passes and 72% to 86% for the descending passes. For winter, the frequency values are 88% to 91% for the ascending passes and 89% to 92% for the descending passes of AIRS/AQUA. The PDFs of inversion strength for the summer months are narrow and right-skewed (or positively skewed), while in winter, they are much broader. In summer months, the mean values of inversion strength for the entire study area range from 2.5 K to 3.9 K, while in winter, they range from 7.8 K to 8.9 K. The standard deviation of the inversion strength is double in winter compared to summer. The inversions in the summer months of 2007 were very strong compared to other years. The warming in the troposphere of about 1.5 K to 3.0 K vertically extending up to 400 hPa was observed in the summer months of 2007.
Influence of relative humidity and temperature on the production of pinonaldehyde and OH radicals from the ozonolysis of α-pinene
Authors: Tillmann R. , Hallquist M. , Jonsson Å. M. , Kiendler-Scharr A. , Saathoff H. , Iinuma Y. , Mentel Th. F.
Published: April 2010

Abstract. The ozonolysis of α-pinene has been investigated under dry and humid conditions in the temperature range of 243–303 K. The results provided new insight into the role of water and temperature in the degradation mechanism of α-pinene and in the formation of secondary organic aerosols (SOA). The SOA yields were higher at humid conditions than at dry conditions. The water induced gain was largest for the lowest temperatures investigated (243 and 253 K). The increase in the SOA yields was dominated by water (and temperature) effects on the organic product distribution, whilst physical uptake of water was negligible. This will be demonstrated for the example of pinonaldehyde (PA) which was formed as a~major product in the humid experiments with total molar yields of 0.30±0.06 at 303 K and 0.15±0.03 at 243 K. In the dry experiments the molar yields of PA were only 0.07±0.02 at 303 K and 0.02±0.02 at 253 K. The observed partitioning of PA as a function of the SOA mass present at 303 K limited the effective vapour pressure of pure PA pPA0 to the range of 0.01–0.001 Pa, 3–4 orders of magnitude lower than literature values. The corresponding mass partitioning coefficient was determined to KPA=0.005±0.004 m3/μg and the total mass yield αPA.total=0.37±0.08. At 303 K PA preferably stayed in the gas-phase, whereas at 253 K and 243 K it exclusively partitioned into the particulate phase. PA could thus account at least for half of the water induced gain in SOA mass at 253 K. The corresponding effect was negligible at 303 K because the PA preferably remained in the gas-phase. The yield of OH radicals, which were produced in the ozonolysis, was indirectly determined by means of the yield of cyclohexanone formed in the reaction of OH radicals with cyclohexane. OH yields of the α-pinene ozonolysis were determined to 0.67±0.17 for humid and 0.54±0.13 for dry conditions at 303 K, indicating a water dependent path of OH radical formation. For 253 and 243 K OH yields could be estimated to 0.5 with no significant difference between the dry and humid experiments. This is the first clear indication for OH radical formation by α-pinene ozonolysis at such low temperatures.
The impact of the 1783–1784 AD Laki eruption on global aerosol formation processes and cloud condensation nuclei
Authors: Schmidt A. , Carslaw K. S. , Mann G. W. , Wilson B. M. , Breider T. J. , Pickering S. J. , Thordarson T.
Published: April 2010

Abstract. The 1783–1784 AD Laki flood lava eruption commenced on 8 June 1783 and released 122 Tg of sulphur dioxide gas over the course of 8 months into the upper troposphere and lower stratosphere above Iceland. Previous studies have examined the impact of the Laki eruption on sulphate aerosol and climate using general circulation models. Here, we study the impact on aerosol microphysical processes, including the nucleation of new particles and their growth to cloud condensation nuclei (CCN) using a comprehensive Global Model of Aerosol Processes (GLOMAP). Total particle concentrations in the free troposphere increase by a factor ~16 over large parts of the Northern Hemisphere in the 3 months following the onset of the eruption. Particle concentrations in the boundary layer increase by a factor 2 to 5 in regions as far away as North America, the Middle East and Asia due to long-range transport of nucleated particles. CCN concentrations (at 0.22% supersaturation) increase by a factor 65 in the upper troposphere with maximum changes in 3-month zonal mean concentrations of ~1400 cm−3 at high northern latitudes. 3-month zonal mean CCN concentrations in the boundary layer at the latitude of the eruption increase by up to a factor 26, and averaged over the Northern Hemisphere, the eruption caused a factor 4 increase in CCN concentrations at low-level cloud altitude. The simulations show that the Laki eruption would have completely dominated as a source of CCN in the pre-industrial atmosphere. The model also suggests an impact of the eruption in the Southern Hemisphere, where CCN concentrations are increased by up to a factor 1.4 at 20° S. Our model simulations suggest that the impact of an equivalent wintertime eruption on upper tropospheric CCN concentrations is only about one-third of that of a summertime eruption. The simulations show that the microphysical processes leading to the growth of particles to CCN sizes are fundamentally different after an eruption when compared to the unperturbed atmosphere, underlining the importance of using a fully coupled microphysics model when studying long-lasting, high-latitude eruptions.
Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons
Authors: Voss P. B. , Zaveri R. A. , Flocke F. M. , Mao H. , Hartley T. P. , DeAmicis P. , Deonandan I. , Contreras-Jiménez G. , Martínez-Antonio O. , Figueroa Estrada M. , Greenberg D. , Campos T. L. , Weinheimer A. J. , Knapp D. J. , Montzka D. D. , Crounse J. D. , Wennberg P. O. , Apel E. , Madronich S. , de Foy B.
Published: April 2010

Abstract. One of the major objectives of the Megacities Initiative: Local And Global Research Observations (MILAGRO-2006) campaign was to investigate the long-range transport of polluted Mexico City Metropolitan Area (MCMA) outflow and determine its downwind impacts on air quality and climate. Six research aircraft, including the National Center for Atmospheric Research (NCAR) C-130, made extensive chemical, aerosol, and radiation measurements above MCMA and more than 1000 km downwind in order to characterize the evolution of the outflow as it aged and dispersed over the Mesa Alta and Gulf of Mexico. As part of this effort, free-floating Controlled-Meteorological (CMET) balloons, commanded to change altitude via satellite, made repeated profile measurements of winds and state variables within the advecting outflow. In this paper, we present an analysis based on the data from two CMET balloons that were launched near Mexico City on the afternoon of 18 March 2006 and floated downwind with the MCMA pollution for nearly 30 h. The repeating profile measurements show the evolving structure of the outflow in considerable detail: its stability and stratification, interaction with other air masses, mixing episodes, and dispersion into the regional background. Air parcel trajectories, computed directly from the balloon wind profiles, show three different transport pathways on 18–19 March: (a) high-altitude advection of the top of the MCMA mixed layer, (b) mid-level outflow over the Sierra Madre Oriental followed by decoupling and isolated transport over the Gulf, and (c) low-altitude outflow with entrainment into a cleaner westerly jet below the plateau. The C-130 aircraft intercepted the balloon-based trajectories three times on 19 March, once along each of these pathways. In all three cases, distinct peaks in the urban tracer signatures and LIDAR backscatter imagery were consistent with MCMA pollution. The coherence of the high-altitude outflow was well preserved after one day whereas that lower in the atmosphere was more widely dispersed over the same time period. Other C-130 intercepts of polluted air are shown to have likely originated outside of MCMA. These findings, and the aircraft intercepts in particular, should prove useful in answering a range of scientific questions pertaining to the transport, transformation, and downwind impacts of megacity air pollution.
Characterization of particle cloud droplet activity and composition in the free troposphere and the boundary layer during INTEX-B
Authors: Roberts G. C. , Day D. A. , Russell L. M. , Dunlea E. J. , Jimenez J. L. , Tomlinson J. M. , Collins D. R. , Shinozuka Y. , Clarke A. D.
Published: April 2010

Abstract. Measurements of cloud condensation nuclei (CCN), aerosol size distributions, and submicron aerosol composition were made as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign during spring 2006. Measurements were conducted from an aircraft platform over the Northeastern Pacific and Western North America with a focus on how the transport and evolution of Asian pollution across the Pacific Ocean affected CCN properties. A broad range of air masses were sampled and here we focus on three distinct air mass types defined geographically: the Pacific free troposphere (FT), the marine boundary layer (MBL), and the polluted continental boundary layer in the California Central Valley (CCV). These observations add to the few observations of CCN in the FT. CCN concentrations showed a large range of concentrations between air masses, however CCN activity was similar for the MBL and CCV (κ~0.2–0.25). FT air masses showed evidence of long-range transport from Asia and CCN activity was consistently higher than for the boundary layer air masses. Bulk chemical measurements predicted CCN activity reasonably well for the CCV and FT air masses. Decreasing trends in κ with organic mass fraction were observed for the combination of the FT and CCV air masses and can be explained by the measured soluble inorganic chemical components. Changes in hygroscopicity associated with differences in the non-refractory organic composition were too small to be distinguished from the simultaneous changes in inorganic ion composition in the FT and MBL, although measurements for the large organic fractions (0.6–0.8) found in the CCV showed values of the organic fraction hygroscopicity consistent with other polluted regions (κorg~0.1–0.2). A comparison of CCN-derived κ (for particles at the critical diameter) to TDMA-derived κ (for particles at 100 nm diameter) showed similar trends, however the CCN-derived κ values were significantly higher.
On microphysical processes of noctilucent clouds (NLC): observations and modeling of mean and width of the particle size-distribution
Authors: Baumgarten G. , Fiedler J. , Rapp M.
Published: April 2010

Abstract. Noctilucent clouds (NLC) in the polar summer mesopause region have been observed in Norway (69° N, 16° E) between 1998 and 2009 by 3-color lidar technique. Assuming a mono-modal Gaussian size distribution we deduce mean and width of the particle sizes throughout the clouds. We observe a quasi linear relationship between distribution width and mean of the particle size at the top of the clouds and a deviation from this behavior for particle sizes larger than 40 nm, most often in the lower part of the layer. The vertically integrated particle properties show that 65% of the data follows the linear relationship with a slope of 0.42±0.02. For the vertically resolved particle properties (Δz=0.15 km) the slope is smaller and only 0.39±0.03. We compare our observations to microphysical modeling of noctilucent clouds and find that the distribution width depends on turbulence, the time that turbulence can act (cloud age), and the sampling volume/time (atmospheric variability). The model results nicely reproduce the measurements and show that the observed slope can be explained by eddy diffusion profiles as observed from rocket measurements.
In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O3, IO, OIO and NOx
Authors: Huang R.-J. , Seitz K. , Buxmann J. , Poehler D. , Hornsby K. E. , Carpenter L. J. , Platt U. , Hoffmann T.
Published: April 2010

Abstract. "Single-point" in situ measurements of molecular iodine (I2) were carried out in the coastal marine boundary layer (MBL) using diffusion denuders in combination with a gas chromatography-mass spectrometry (GC-MS) method. Comparison measurements were taken at Mace Head and Mweenish Bay, on the West Coast of Ireland. The observed mixing ratios of I2 at Mweenish Bay are much higher than that at Mace Head, indicating the emissions of I2 are correlated with the local algal biomass density and algae species. The concentration levels of I2 were found to correlate inversely with tidal height and correlate positively with the concentration levels of O3 in the surrounding air. However, the released I2 can also lead to O3 destruction via the reaction of O3 with iodine atoms that are formed by the photolysis of I2 during the day and via the reaction of I2 with NOx at night. IO and OIO were measured by long-path differential optical absorption spectroscopy (LP-DOAS). The results show that the concentrations of both daytime and nighttime IO are correlated with the mixing ratios of I2. OIO was observed not only during the day but also, for the first time at both Mace Head and Mweenish Bay, at night. In addition, I2 was measured simultaneously by the LP-DOAS technique and compared with the "single-point" in situ measurement. The results suggest that the local algae sources dominate the inorganic iodine chemistry at Mace Head and Mweenish Bay.
Water uptake and chemical composition of fresh aerosols generated in open burning of biomass
Authors: Carrico C. M. , Petters M. D. , Kreidenweis S. M. , Sullivan A. P. , McMeeking G. R. , Levin E. J. T. , Malm W. C. , Collett J. L.
Published: April 2010

Abstract. As part of the Fire Lab at Missoula Experiments (FLAME) in 2006–2007, we examined hygroscopic properties of particles emitted from open combustion of 33 select biomass fuels. Measurements of humidification growth factors for subsaturated water relative humidity (RH) conditions were made with a hygroscopic tandem differential mobility analyzer (HTDMA) for dry particle diameters of 50, 100 and 250 nm. Results were then fit to a single-parameter model to obtain the hygroscopicity parameter, κ. Particles in freshly emitted biomass smoke exhibited a wide range of hygroscopicity (individual modes with 0<κ<1.0), spanning a range from the hygroscopicity of fresh diesel soot emissions to that of pure inorganic salts commonly found in the ambient aerosol. Smoke aerosols dominated by carbonaceous species typically had a unimodal growth factor with corresponding mean κ=0.1 (range of 0<κ<0.4). Those with a substantial inorganic mass fraction typically separated into less- and more-hygroscopic modes at high RH, the latter with mean κ=0.4 (range of 0.1<κ<1). The bimodal κ distributions were indicative of smoke chemical heterogeneity at a single particle size, whereas heterogeneity as a function of size was indicated by typically decreasing κ values with increasing dry particle diameters. Hygroscopicity varied strongly with biomass fuel type and, to a lesser extent, with combustion conditions. Among the most hygroscopic smokes were those from palmetto, rice straw, and sawgrass, while smoke particles from coniferous species such as spruces, firs, pines, and duffs were among the least hygroscopic. Overall, hygroscopicity decreased with increasing ratios of total carbon to inorganic ions as measured in PM2.5 filter samples. Despite aerosol heterogeneity, reconstructions of κ using PM2.5 bulk chemical composition data fell along a 1:1 line with measured ensemble κ values.
Effects of relative humidity on aerosol light scattering in the Arctic
Authors: Zieger P. , Fierz-Schmidhauser R. , Gysel M. , Ström J. , Henne S. , Yttri K. E. , Baltensperger U. , Weingartner E.
Published: April 2010

Abstract. Aerosol particles experience hygroscopic growth in the ambient atmosphere. Their optical properties – especially the aerosol light scattering – are therefore strongly dependent on the ambient relative humidity (RH). In-situ light scattering measurements of long-term observations are usually performed under dry conditions (RH<30–40%). The knowledge of this RH effect is of eminent importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. This study combines measurements and model calculations to describe the RH effect on aerosol light scattering for the first time of aerosol particles present in summer and fall at the high Arctic. For this purpose, a field campaign was carried out from July to October 2008 at the Zeppelin station in Ny-Ålesund, Svalbard. The aerosol light scattering coefficient σsp(λ) was measured at three distinct wavelengths (λ=450, 550, and 700 nm) at dry and at various, predefined RH conditions between 20% and 95% with a recently developed humidified nephelometer (WetNeph) and with a second nephelometer measuring at dry conditions (DryNeph). In addition, the aerosol size distribution and the aerosol absorption coefficient were measured. The scattering enhancement factor f(RH,λ) is the key parameter to describe the RH effect on σsp(λ) and is defined as the RH dependent σsp(RH,λ) divided by the corresponding dry σsp(RHdry,λ). During our campaign the average f(RH=85%, λ=550 nm) was 3.24±0.63 (mean ± standard deviation), and no clear wavelength dependence of f(RH,λ) was observed. This means that the ambient scattering coefficients at RH=85% were on average about three times higher than the dry measured in-situ scattering coefficients. The RH dependency of the recorded f(RH,λ) can be well described by an empirical one-parameter equation. We used a simplified method to retrieve an apparent hygroscopic growth factor g, defined as the aerosol particle diameter at a certain RH divided by the dry diameter, using the WetNeph, the DryNeph, the aerosol size distribution measurements and Mie theory. With this approach we found on average for g values of 1.61±0.12 (mean ± standard deviation). No clear seasonal shift of f(RH,λ) was observed during the 3-month period, while aerosol properties (size and chemical composition) clearly changed with time. While the beginning of the campaign was mainly characterized by smaller and less hygroscopic particles, the end was dominated by larger and more hygroscopic particles. This suggests that compensating effects of hygroscopicity and size determined the temporal stability of f(RH,λ). During sea salt influenced periods, distinct deliquescence transitions were observed. At the end we give a method on how to transfer the dry in-situ measured aerosol scattering coefficients to ambient values for the aerosol measured during summer and fall at this location.
Low sensitivity of cloud condensation nuclei to changes in the sea-air flux of dimethyl-sulphide
Authors: Woodhouse M. T. , Carslaw K. S. , Mann G. W. , Vallina S. M. , Vogt M. , Halloran P. R. , Boucher O.
Published: April 2010

Abstract. The emission of dimethylsulphide (DMS) gas by phytoplankton and the subsequent formation of aerosol has long been suggested as an important climate regulation mechanism. The key aerosol quantity is the number concentration of cloud condensation nuclei (CCN), but until recently global models did not include the necessary aerosol physics to quantify CCN. Here we use a global aerosol microphysics model to calculate the sensitivity of CCN to changes in DMS emission using multiple present-day and future sea-surface DMS climatologies. Calculated annual fluxes of DMS to the atmosphere for the five model-derived and one observations based present day climatologies are in the range 15.1 to 32.3 Tg a−1 sulphur. The impact of DMS climatology on surface level CCN concentrations was calculated in terms of summer and winter hemispheric mean values of ΔCCN/ΔFluxDMS, which varied between −51 and +147 cm−3/(mg m−2 day−1 sulphur), with a mean of 56 cm−3/(mg m−2 day−1 sulphur). The range is due to CCN production in the atmosphere being strongly dependent on the spatial distribution of the emitted DMS. The DMS flux from a future globally warmed climatology was 0.2 Tg a−1 sulphur higher than present day with a mean CCN response of 95 cm−3/(mg m−2 day−1 sulphur) relative to present day. The largest CCN response was seen in the southern Ocean, contributing to a Southern Hemisphere mean annual increase of less than 0.2%. We show that the changes in DMS flux and CCN concentration between the present day and global warming scenario are similar to interannual differences due to variability in windspeed. In summary, although DMS makes a significant contribution to global marine CCN concentrations, the sensitivity of CCN to potential future changes in DMS flux is very low. This finding, together with the predicted small changes in future seawater DMS concentrations, suggests that the role of DMS in climate regulation is very weak.
Impacts of HONO sources on the photochemistry in Mexico City during the MCMA-2006/MILAGO Campaign
Authors: Li G. , Lei W. , Zavala M. , Volkamer R. , Dusanter S. , Stevens P. , Molina L. T.
Published: April 2010

Abstract. The contribution of HONO sources to the photochemistry in Mexico City is investigated during the MCMA-2006/MILAGO Campaign using the WRF-CHEM model. Besides the homogeneous reaction of NO with OH, four additional HONO sources are considered in the WRF-CHEM model: secondary HONO formation from NO2 heterogeneous reaction with semivolatile organics, NO2 reaction with freshly emitted soot, NO2 heterogeneous reaction on aerosol and ground surfaces. The WRF-CHEM model with the five HONO sources performs reasonably well in tracking the observed diurnal variation of HONO concentrations. The HONO sources included are found to significantly improve the HOx (OH+HO2) simulations during daytime and the partition of NO/NO2 in the morning. The HONO sources also accelerate the accumulation of O3 concentrations in the morning by about 2 h and subsequently result in a noticeable enhancement of O3 concentrations over the course of the day with a midday average of about 6 ppb. Furthermore, these HONO sources play a very important role in the formation of secondary aerosols in the morning. They substantially enhance the secondary organic aerosol concentrations by a factor of 2 on average in the morning, although contribute less during the rest of the day. The simulated nitrate and ammonium aerosols are also remarkably enhanced in the morning when the four HONO sources are added, in good agreement with the measurements. The impact of the HONO sources on the sulfate aerosols is negligible because of the inefficient conversion of H2SO4 from SO2 reacting with OH.
A detailed aerosol mixing state model for investigating interactions between mixing state, semivolatile partitioning, and coagulation
Authors: Lu J. , Bowman F. M.
Published: April 2010

Abstract. A new method for describing externally mixed particles, the Detailed Aerosol Mixing State (DAMS) representation, is presented in this study. This novel method classifies aerosols by both composition and size, using a user-specified mixing criterion to define boundaries between compositional populations. Interactions between aerosol mixing state, semivolatile partitioning, and coagulation are investigated with a Lagrangian box model that incorporates the DAMS approach. Model results predict that mixing state affects the amount and types of semivolatile organics that partition to available aerosol phases, causing external mixtures to produce a more size-varying composition than internal mixtures. Both coagulation and condensation contribute to the mixing of emitted particles, producing a collection of multiple compositionally distinct aerosol populations that exists somewhere between the extremes of a strictly external or internal mixture. The selection of mixing criteria has a significant impact on the size and type of individual populations that compose the modeled aerosol mixture.
Joint spatial variability of aerosol, clouds and rainfall in the Himalayas from satellite data
Authors: Shrestha P. , Barros A. P.
Published: April 2010

Abstract. Satellite-based precipitation, Aerosol Optical Depth (AOD), Cloud Optical Depth (COD), and Aerosol Index (AI) data were used to characterize the linkages among landform and the intra-annual variability of aerosols, cloudiness and rainfall in the Himalayas using Empirical Orthogonal Function (EOF) analysis. The first modes of AOD and AI show the presence of two branches of dust aerosol: over the Indus River basin and the Thar Desert with a sharp west-east gradient parallel to the southern slopes of the Himalayas – the southern Branch; and the second against the slopes of the Tian Shan and over the Takla Makan Desert in the Tibetan Plateau – the northern branch. The second EOF mode of AOD accounts for about 10% of overall variance of AOD. It is attached to the foothills of the Himalayas east of the Aravalli range peaking in April-May followed by a sharp decrease between June and July during the first active phase of the monsoon. The first and second EOF modes of COD and precipitation show consistent patterns against the Central and Eastern Himalayas and along the ocean-land boundaries in western India and the Bay of Bengal. The break in cloudiness and rainfall between the winter and the monsoon seasons is captured well by the second EOF mode of COD and rainfall concurrent with the aerosol build up mode (March-April-May) over the region depicted by the second mode of AOD. The results show that the Aravalli range separates the two different modes of aerosol variability over northern India with dust aerosols to the west and polluted mixed aerosols to the east consistent with its role in regional circulation and precipitations patterns as per Barros et al. (2004) and Chiao and Barros (2006). The region of spatial overlap of the modes of variability of aerosols, clouds and rainfall is captured by the second EOF of MODIS AOD along the southern slopes of the Himalayas east of the Aravalli. It is proposed that this mode maps the area where the indirect radiative effect of aerosols on cloud properties and rainfall is pronounced.
Long term measurements of sulfur dioxide, nitrogen dioxide, ammonia, nitric acid and ozone in Africa using passive samplers
Authors: Adon M. , Galy-Lacaux C. , Yoboué V. , Delon C. , Lacaux J. P. , Castera P. , Gardrat E. , Pienaar J. , Al Ourabi H. , Laouali D. , Diop B. , Sigha-Nkamdjou L. , Akpo A. , Tathy J. P. , Lavenu F. , Mougin E.
Published: April 2010

Abstract. In this paper, we present the long term monitoring of ambient gaseous concentrations within the framework of the IDAF (IGAC-DEBITS-AFRICA) program. This study proposes for the first time to study long term gases concentrations (1998–2007) by determining the ambient concentration of the inorganic gases, i.e., SO2, NO2, HNO3, NH3 and O3 using passive samplers at seven remote sites in West and Central Africa. Sites are representative of a great African ecosystem and are located according a transect: dry savannas-wet savannas-forests with Banizoumbou (Niger), Katibougou and Agoufou (Mali), Djougou (Benin), Lamto (Cote d'Ivoire), Zoetele (Cameroon) and Bomassa (Congo). The validation and inter-comparison studies conducted with the IDAF passive samplers assure the quality and the control of the measurement technique to show the accuracy of the measurements. For each type of African ecosystems, we have studied the long term data series to document the levels of gaseous surface concentrations and the seasonal and interannual variations analyzed as a function of emission sources variations. We have tried to compare West and Central African gases concentrations to the results obtained in other parts of the world. Results show that the annual mean concentrations of NO2, NH3, HNO3 measured in dry savannas are higher than those measured in wet savannas and forests that have quite similar concentrations. Annual mean NO2 concentrations vary from 0.9±0.2 in forests to 2.4±0.4 ppb in the dry savannas, NH3 from 3.9±1.4 to 7.4±0.8 ppb, HNO3 from 0.2±0.1 to 0.5±0.2 ppb. Annual mean O3 and SO2 concentrations are lower for all the ecosystems and range from 4.0±0.4 to 14.0±2.8 and from 0.3±0.1 to 1.0±0.2 ppb, respectively. A focus on dry savannas processes involved in gases emission is presented in this work, explaining the high concentrations of all gases measured on the three dry savannas sites. For all gases, seasonal concentrations are higher in the wet season of dry savannas. Conversely, concentrations are higher in the dry season of wet savannas. In forest, we measure no significant difference between wet and dry seasons. This unique database of long term gases concentrations monitoring is available at: http://www.obs-mip.fr/idaf/.
Temporal and spatial variations of aerosol physical and chemical properties over West Africa: AMMA aircraft campaign in summer 2006
Authors: Matsuki A. , Quennehen B. , Schwarzenboeck A. , Crumeyrolle S. , Venzac H. , Laj P. , Gomes L.
Published: April 2010

Abstract. While West Africa is recognized as being one of the global hot-spots of atmospheric aerosols, the presence of West African Monsoon is expected to create significant spatial and temporal variations in the regional aerosol properties through mixing particles from various sources (mineral dust, biomass burning, sulfates, sea salt). To improve our understanding of the complexity of the aerosol-cloud system in that region, the African Monsoon Multidisciplinary Analysis (AMMA) project has been launched, providing valuable data sets of in-situ and remote sensing measurements including satellites for extended modeling. The French ATR-42 research aircraft was deployed in Niamey, Niger (13°30' N, 02°05' E) in summer 2006, during the three special observation periods (SOPs) of AMMA. These three SOPs covered both dry and wet periods before and after the onset of the Western African Monsoon. State of the art physico-chemical aerosol measurements on the ATR-42 showed a notable seasonal transition in averaged number size distributions where (i) the Aitken mode is dominating over the accumulation mode during the dry season preceding the monsoon arrival and (ii) the accumulation mode increasingly gained importance after the onset of the West African monsoon and even dominated the Aitken mode after the monsoon had fully developed. An extended analysis of the vertical dependence of size spectra, comparing the three observation periods, revealed that the decreasing concentration of the Aitken mode particles, as we move from SOP1 (June) to SOP2a1 (July), and SOP2a2 (August), was less pronounced in the monsoon layer as compared to the overlying Saharan dust layer and free troposphere. In order to facilitate to all partners within the AMMA community radiative transfer calculations, validation of satellite remote sensors, and detailed transport modeling, the parameters describing the mean log-normally fitted number size distributions as a function of altitude and special observation periods were summarized and subsequently related to simultaneously performed measurements of major aerosol particle chemical composition. Extended TEM-EDX analysis of the chemical composition of single aerosol particles revealed dominance of mineral dust (aluminosilicate) even in the submicron particle size range during the dry period, gradually replaced by prevailing biomass burning and sulfate particles, after the onset the monsoon period. The spatial and temporal evolution from SOP1 to SOP2a1 and SOP2a2 of the particle physical and chemical properties and associated aerosol hygroscopic properties are remarkably consistent.
The chemical and microphysical properties of secondary organic aerosols from Holm Oak emissions
Authors: Lang-Yona N. , Rudich Y. , Mentel Th. F. , Buchholz A. , Kiendler-Scharr A. , Kleist E. , Spindler C. , Tillmann R. , Wildt J.
Published: April 2010

Abstract. The Mediterranean region is expected to experience substantial climatic change in the next 50 years. But, possible effects of climate change on biogenic volatile organic compound (VOC) emissions as well as on the formation of secondary organic aerosols (SOA) produced from these VOC are yet unexplored. To address such issues, the effects of temperature and light intensity on the VOC emissions of Mediterranean Holm Oak have been studied in the Jülich plant aerosol atmosphere chamber, as well as the optical and microphysical properties of the resulting SOA. Monoterpenes dominated the VOC emissions from Holm Oak (97.5%) and temperature increase enhanced the emission strength under variation of the emission pattern. The amount of SOA increased linearly with the emission strength with a fractional mass yield of 5.7±1%, independent of the detailed emission pattern. The particles were highly scattering with no absorption abilities. Their average hygroscopic growth factor was 1.13±0.03 at 90% RH with a critical diameter of droplet activation of 100±4 nm at a supersaturation of 0.4%. All microphysical properties did not depend on the detailed emission pattern, in accordance with an invariant O/C ratio (0.57(+0.03/−0.1)) of the SOA observed by high resolution aerosol mass spectrometry. The increase of Holm oak emissions with temperature (≈20% per degree) was stronger than e.g. for Boreal tree species (≈10% per degree). Increasing mean temperature in Mediterranean areas therefore may have a stronger impact on VOC emissions and SOA formation than in areas with Boreal forests.
Biogenic oxidized organic functional groups in aerosol particles from a mountain forest site and their similarities to laboratory chamber products
Authors: Schwartz R. E. , Russell L. M. , Sjosted S. J. , Vlasenko A. , Slowik J. G. , Abbatt J. P. D. , Macdonald A. M. , Li S. M. , Liggio J. , Toom-Sauntry D. , Leaitch W. R.
Published: April 2010

Abstract. Submicron particles collected at Whistler, British Columbia, at 1020 masl during May and June 2008 on Teflon filters were analyzed by Fourier transform infrared (FTIR) and X-ray fluorescence (XRF) techniques for organic functional groups (OFG) and elemental composition. Organic mass (OM) ranged from less than 0.5 to 3.1μg m−3, with a project mean and standard deviation of 1.3±1.0 μg m−3 and 0.21±0.16 μg m−3 for OM and sulfate, respectively. On average, organic hydroxyl, alkane, and carboxylic acid groups represented 34%, 33%, and 23% of OM, respectively. Ketone, amine and organosulfate groups constituted 6%, 5%, and <1% of the average organic aerosol composition, respectively. Measurements of volatile organic compounds (VOC), including isoprene and monoterpenes from biogenic VOC (BVOC) emissions and their oxidation products (methyl-vinylketone/methacrolein, MVK/MACR), were made using co-located proton transfer reaction mass spectrometry (PTR-MS). We present chemically-specific evidence of OFG associated with BVOC emissions. Positive matrix factorization (PMF) analysis attributed 65% of the campaign OM to biogenic sources, based on the correlations of one factor to monoterpenes and MVK/MACR. The remaining fraction was attributed to anthropogenic sources based on a correlation to sulfate. The functional group composition of the biogenic factor (consisting of 32% alkane, 25% carboxylic acid, 2% organic hydroxyl, 16% ketone, and 6% amine groups) was similar to that of secondary organic aerosol (SOA) reported from the oxidation of BVOCs in laboratory chamber studies, providing evidence that the magnitude and chemical composition of biogenic SOA simulated in the laboratory is similar to that found in actual atmospheric conditions. The biogenic factor OM is also correlated to dust elements, indicating that dust may act as a non-acidic SOA sink. This role is supported by the organic functional group composition and morphology of single particles, which were analyzed by scanning transmission X-ray microscopy near edge X-ray absorption fine structure (STXM-NEXAFS).