bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic model framework for aerosol and cloud surface chemistry and gas-particle interactions: Part 1 – general equations, parameters, and terminology
Authors: Pöschl U. , Rudich Y. , Ammann M.
Published: April 2010

Abstract. Aerosols and clouds play central roles in atmospheric chemistry and physics, climate, air pollution, and public health. The mechanistic understanding and predictability of aerosol and cloud properties, interactions, transformations, and effects are, however, still very limited. This is due not only to the limited availability of measurement data, but also to the limited applicability and compatibility of model formalisms used for the analysis, interpretation, and description of heterogeneous and multiphase processes. To support the investigation and elucidation of atmospheric aerosol and cloud surface chemistry and gas-particle interactions, we present a comprehensive kinetic model framework with consistent and unambiguous terminology and universally applicable rate equations and parameters. It allows to describe mass transport and chemical reactions at the gas-particle interface and to link aerosol and cloud surface processes with gas phase and particle bulk processes in systems with multiple chemical components and competing physicochemical processes. The key elements and essential aspects of the presented framework are: a simple and descriptive double-layer surface model (sorption layer and quasi-static layer); straightforward flux-based mass balance and rate equations; clear separation of mass transport and chemical reactions; well-defined rate parameters (uptake and accommodation coefficients, reaction and transport rate coefficients); clear distinction between gas phase, gas-surface, and surface-bulk transport (gas phase diffusion correction, surface and bulk accommodation); clear distinction between gas-surface, surface layer, and surface-bulk reactions (Langmuir-Hinshelwood and Eley-Rideal mechanisms); mechanistic description of concentration and time dependencies; flexible inclusion/omission of chemical species and physicochemical processes; flexible convolution/deconvolution of species and processes; and full compatibility with traditional resistor model formulations. Exemplary practical applications and model calculations illustrating the relevance of the above aspects will be presented in a companion paper (Ammann and Pöschl, 2005). We expect that the presented model framework will serve as a useful tool and basis for experimental and theoretical studies investigating and describing atmospheric aerosol and cloud surface chemistry and gas-particle interactions. In particular, it is meant to support the planning and design of laboratory experiments for the elucidation and determination of kinetic parameters; the establishment, evaluation, and quality assurance of comprehensive and self-consistent collections of rate parameters; and the development of detailed master mechanisms for process models and the derivation of simplified but yet realistic parameterizations for atmospheric and climate models.
Aerosol mass closure and reconstruction of the light scattering coefficient over the Eastern Mediterranean Sea during the MINOS campaign
Authors: Sciare J. , Oikonomou K. , Cachier H. , Mihalopoulos N. , Andreae M. O. , Maenhaut W. , Sarda-Estève R.
Published: April 2010

Abstract. As part of the Mediterranean Intensive Oxidant Study (MINOS) performed during August 2001 in the Eastern Mediterranean Region, intensive measurements of chemical and radiative properties of atmospheric aerosols were performed at two remote sites on Crete Island, located in the marine boundary layer (MBL), and in the lower free troposphere (FT), respectively. Gravimetric particulate mass, as well as chemically-derived masses of water soluble ions, organic and elemental carbon, and tracer elements for dust aerosols were measured for fine (<1.2 µm) and coarse (>1.2 µm) particles at the two sampling sites. Although strongly bound water, mainly associated with inorganic species, could have slightly altered our results (10% of the reconstructed mass), chemical mass closure was achieved most of the time for the fine and coarse size fractions and at both sites. Our conversion factor of 2.1 for organic carbon (OC) to particulate organic matter (POM) is at the upper end of those reported in the literature, but fits with the aged smoke particles collected during the campaign. The results indicate that this conversion factor changed during the campaign along with the BC/TC ratio. The particulate mass (PM) concentration for fine aerosols at the MBL and FT sites averaged 17.4±4.7 µg/m3 and 11.2±3.2 µg/m3, respectively, and is among the highest reported in the literature for remote sites; more than 90% of this PM was composed equally of ammonium sulfate and carbonaceous aerosols. Comparison between the MBL and FT sites showed a slight vertical gradient for PM that was not observed for dust aerosols, which averaged 10.5±4.8 and 11.7±5.0 µg/m3 for the MBL and FT sites, respectively. The results were used to reconstruct the ambient light scattering coefficient (σsp) that was measured at ambient Relative Humidity (RH) for fine particles at the MBL site. Reconstruction of σsp was achieved using ratios of wet to dry scattering, f(RH), that depend on RH for ammonium sulfate, but are kept equal to 1 for POM. This results in a low water adsorption for our organic-rich carbonaceous aerosols, although these aged biomass smoke aerosols are supposed to be highly oxidized. Mass scattering efficiencies of the main aerosol components were obtained by multivariate regression analysis, and were 2.66 and 4.19 m2/g (at the 95% confidence level) for dry ammonium sulfate and POM, respectively. The calculations indicate that one third of the reconstructed σsp was due to water uptake by ammonium sulfate aerosols, demonstrating their major role in the radiative aerosol properties in the eastern Mediterranean.
Characterization of aerosol particle episodes in Finland caused by wildfires in Eastern Europe
Authors: Niemi J. V. , Tervahattu H. , Vehkamäki H. , Martikainen J. , Laakso L. , Kulmala M. , Aarnio P. , Koskentalo T. , Sillanpää M. , Makkonen U.
Published: April 2010

Abstract. We studied the sources, compositions and size distributions of aerosol particles during long-range transport (LRT) PM2.5 episodes occurred on 12–15 August, 26–28 August and 5–6 September 2002 in Finland. Backward air mass trajectories, satellite detections of fire areas, and dispersion modelling results indicate that emissions from wildfires in Russia and other Eastern European countries arrived to Finland during the episodes. Individual particle analyses using scanning electron microscopy (SEM) coupled with energy dispersive X-ray analyses (EDX) showed that the proportion of S-rich particles increased during the episodes and they contained elevated fractions of K, which indicates emissions from biomass burning. These aerosols were mixed with S-rich emissions from fossil fuel burning during the transport, since air masses came through polluted areas of Europe. Minor amounts of coarse Ca-rich particles were also brought by LRT during the episodes, and they probably originated from wildfires and/or from Estonian and Russian oil-shale burning industrial areas. The ion chromatography analysis showed that concentrations of sulphate (SO42-), total nitrate (NO3-+HNO3(g)) and total ammonium (NH4++NH3(g)) increased during the episodes, but the ratio of total amount of these ions to PM10 concentration decreased indicating unusually high fractions of other chemical components. The particle number size distribution measurements with differential mobility particle sizer (DMPS) showed that the concentrations of 90–500 nm particles increased during the episodes, but the concentrations of particles smaller than 90nm decreased. The reduction of the smallest particles was caused by suppressed new particle formation due to the vapour and molecular cluster uptake of LRT particles. Our results show that the emissions from wildfires in Russian and other Eastern European deteriorated air quality on very large areas, even at the distance of over 1000 km from the fire areas.
The uptake of SO2 on Saharan dust: a flow tube study
Authors: Adams J. W. , Rodriguez D. , Cox R. A.
Published: April 2010

Abstract. The uptake of SO2 onto Saharan mineral dust from the Cape Verde Islands was investigated using a coated wall flow tube coupled to a mass spectrometer. The rate of loss of SO2 to the dust coating was measured and uptake coefficients were determined using the measured BET surface area of the sample. The uptake of SO2, with an initial concentration between (2–40)×1010 molecule cm-3 (0.62–12 µTorr), was found to be strongly time dependent over the first few hundred seconds of an experiment, with an initial uptake γ0,BET of (6.6±0.8)×10-5 (298 K), declining at longer times. The amount of SO2 adsorbed on the dust samples was measured over a range of SO2 concentrations and mineral dust loadings. The uptake of SO2 was found to be up to 98% irreversible over the timescale of these investigations. Experiments were also performed at 258 K, at a relative humidity of 27% and at 298 K in the presence of ozone. The initial uptake and the amount of SO2 taken up per unit area of BET dust surface was the same within error, irrespective of the conditions used; however the presence of ozone reduced the amount of SO2 released back into the gas-phase per unit area once exposure of the surface ended. Multiple uptakes to the same surface revealed a loss of surface reactivity, which did not return if the samples were exposed to gas-phase water, or left under vacuum overnight. A mechanism which accounts for the observed uptake behaviour is proposed and numerically modelled, allowing quantitative estimates of the rate and amount of SO2 removal in the atmosphere to be estimated. Removal of SO2 by mineral dust is predicted to be significant at high dust loadings.
Intercomparison of four different in-situ techniques for ambient formaldehyde measurements in urban air
Authors: Hak C. , Pundt I. , Kern C. , Platt U. , Dommen J. , Ordóñez C. , Prévôt A. S. H. , Junkermann W. , Astorga-Lloréns C. , Larsen B. R. , Mellqvist J. , Strandberg A. , Yu Y. , Galle B. , Kleffmann J. , Lörzer J. C. , Braathen G. O. , Volkamer R.
Published: April 2010

Abstract. Results from an intercomparison of several currently used in-situ techniques for the measurement of atmospheric formaldehyde (CH2O) are presented. The measurements were carried out at Bresso, an urban site in the periphery of Milan (Italy) as part of the FORMAT-I field campaign. Eight instruments were employed by six independent research groups using four different techniques: Differential Optical Absorption Spectroscopy (DOAS), Fourier Transform Infra Red (FTIR) interferometry, the fluorimetric Hantzsch reaction technique (five instruments) and a chromatographic technique employing C18-DNPH-cartridges (2,4-dinitrophenylhydrazine). White type multi-reflection systems were employed for the optical techniques in order to avoid spatial CH2O gradients and ensure the sampling of nearly the same air mass by all instruments. Between 23 and 31 July 2002, up to 13 ppbv of CH2O were observed. The concentrations lay well above the detection limits of all instruments. The formaldehyde concentrations determined with DOAS, FTIR and the Hantzsch instruments were found to agree within ±11%, with the exception of one Hantzsch instrument, which gave systematically higher values. The two hour integrated samples by DNPH yielded up to 25% lower concentrations than the data of the continuously measuring instruments averaged over the same time period. The consistency between the DOAS and the Hantzsch method was better than during previous intercomparisons in ambient air with slopes of the regression line not significantly differing from one. The differences between the individual Hantzsch instruments could be attributed in part to the calibration standards used. Possible systematic errors of the methods are discussed.
Influence of convective transport on tropospheric ozone and its precursors in a chemistry-climate model
Authors: Doherty R. M. , Stevenson D. S. , Collins W. J. , Sanderson M. G.
Published: April 2010

Abstract. The impact of convection on tropospheric O3 and its precursors has been examined in a coupled chemistry-climate model. There are two ways that convection affects O3. First, convection affects O3 by vertical mixing of O3 itself. Convection lifts lower tropospheric air to regions where the ozone lifetime is longer, whilst mass-balance subsidence mixes O3-rich upper tropospheric (UT) air downwards to regions where the O3 lifetime is shorter. This tends to decrease UT ozone and the overall tropospheric column of O3. Secondly, convection affects O3 by vertical mixing of ozone precursors. This affects O3 chemical production and destruction. Convection transports isoprene and its degradation products to the UT where they interact with lightning NOx to produce PAN, at the expense of NOx. The combined effect of NOx to PAN conversions and downward transport of lightning NOx results in UT NOx decreases. Convective lofting of NOx from surface sources appears relatively unimportant. Despite UT NOx decreases, UT O3 production increases as a result of UT HOx increases driven by isoprene oxidation chemistry. However, UT O3 tends to decrease, as the effect of convective overturning of O3 itself dominates over changes in O3 chemistry. The changes in tropical UT O3 are transported polewards resulting in a 15% decrease in the global tropospheric O3 burden. These results contrast with an earlier study that uses a model of similar chemical complexity. Differences in chemistry schemes - in particular isoprene-driven changes, as well as differences in convection schemes themselves, are the most likely causes of such discrepancies. Further modelling studies are needed to constrain this uncertainty range.
New insight into the atmospheric chloromethane budget gained using gained using
Authors: Keppler F. , Harper D. B. , Röckmann T. , Moore R. M. , Hamilton J. T. G.
Published: April 2010

Abstract. Atmospheric chloromethane (CH3Cl) plays an important role in stratospheric ozone destruction, but many uncertainties still exist regarding strengths of both sources and sinks and the processes leading to formation of this naturally occurring gas. Recent work has identified a novel chemical origin for CH3Cl, which can explain its production in a variety of terrestrial environments: The widespread structural component of plants, pectin, reacts readily with chloride ion to form CH3Cl at both ambient and elevated temperatures (Hamilton et al., 2003). It has been proposed that this abiotic chloride methylation process in terrestrial environments could be responsible for formation of a large proportion of atmospheric CH3Cl. However, more information is required to determine the global importance of this new source and its contribution to the atmospheric CH3Cl budget. A potentially powerful tool in studying the atmospheric CH3Cl budget is the use of stable carbon isotope ratios. In an accompanying paper it is reported that the reaction of CH3Cl with OH radical, the dominant sink for atmospheric CH3Cl, is accompanied by an unexpectedly large fractionation factor (Gola et al., 2005). Another recently published study shows that CH3Cl formed by the abiotic methylation process at ambient temperatures has a unique stable carbon isotope signature, extremely depleted in 13C, unequivocally distinguishing it from all other known sources (Keppler et al., 2004). Using these findings together with data existing in the literature, we here present three scenarios for an isotopic mass balance for atmospheric CH3Cl. Our calculations provide strong support for the proposal that the bulk fraction of atmospheric CH3Cl (1.8 to 2.5Tg yr−1) is produced by an abiotic chloride methylation process in terrestrial ecosystems, primarily located in tropical and subtropical areas, where turnover of biomass is highest. Furthermore our calculations also indicate that the microbial soil sink for CH3Cl is likely to be much larger (>1Tg yr−1) than that previously assumed.
Measurements of Black Carbon Specific Absorption in the Mexico City Metropolitan Area during the MCMA 2003 Field Campaign
Authors: Barnard J. C. , Kassianov E. I. , Ackerman T. P. , Frey S. , Johnson K. , Zuberi B. , Molina L. T. , Molina M. J. , Gaffney J. S. , Marley N. A.
Published: April 2010

Abstract. During the Mexico City Metropolitan Area (MCMA) field campaign of 2003, measurements of the shortwave radiation field, lidar backscatter, and atmospheric concentrations of black carbon (BC) permitted the inference of the BC carbon specific absorption, αλ, defined as the absorption cross section per unit mass (with units of m2/g). This diverse set of measurements allowed us to determine αλ in two ways. These methods – labeled I and II – are distinguished from one another in the manner that the columnar concentration of BC (with units of mg/m2 is determined. This concentration is found by using either surface measurements of BC concentration and lidar estimates of aerosol mixing heights, or a more rigorous method that relies on the columnar aerosol size distribution. The averaged values of αλ derived from these methods agree to about 20%, although we expect that the values obtained from method I are underestimated. These results, along with those of Schuster et al. (2005), suggest that in the MCMA, αλ is in a range of 8 to 10 m2/g at a wavelength of 550 nm. This range is somewhat lower than the commonly accepted value of 10 m2/g for a wavelength of 550 nm, but is consistent with the calculations of Fuller et al. (1999), who suggest that this value is too high.
Seasonal variations in the horizontal wind structure from 0–100 km above Rothera station, Antarctica (67° S, 68° W)
Authors: Hibbins R. E. , Shanklin J. D. , Espy P. J. , Jarvis M. J. , Riggin D. M. , Fritts D. C. , Lübken F.-J.
Published: April 2010

Abstract. A medium frequency spaced-antenna radar has been operating at Rothera station, Antarctica (67° S, 68° W) for two periods, between 1997–1998 and since 2002, measuring winds in the mesosphere and lower thermosphere. In this paper monthly mean winds are derived and presented along with three years of radiosonde balloon data for comparison with the HWM-93 model atmosphere and other high latitude southern hemisphere sites. The observed meridional winds are slightly more northwards than those predicted by the model above 80 km in the winter months and below 80 km in summer. In addition, the altitude of the summer time zero crossing of the zonal winds above the westward jet is overestimated by the model by up to 8 km. These data are then merged with the wind climatology obtained from falling sphere measurements made during the PORTA campaign at Rothera in early 1998 and the HWM-93 model atmosphere to generate a complete zonal wind climatology between 0 and 100 km as a benchmark for future studies at Rothera. A westwards (eastwards) maximum of 44 ms−1 at 67 km altitude occurs in mid December (62 ms−1 at 37 km in mid July). The 0 ms−1 wind contour reaches a maximum altitude of 90 km in mid November and a minimum altitude of 18 km in January extending into mid March at 75 km and early October at 76 km.
Characterization of high molecular weight compounds in urban atmospheric particles
Authors: Samburova V. , Kalberer M. , Zenobi R.
Published: April 2010

Abstract. The chemical nature of a large fraction of ambient organic aerosol particles is not known. However, high molecular weight compounds (often named humic-like substances) have recently been detected by several authors and these compounds seem to account for a significant fraction of the total organic aerosol mass. Due to the unknown chemical structure of these compounds a quantification as well as a determination of their molecular weight is difficult. In this paper we investigate water soluble humic-like substances in ambient urban aerosol using size exclusion chromatography-UV spectroscopy and laser desorption/ionization mass spectrometry. A careful method evaluation shows that both methods complement each other and that both are needed to learn more about the molecular weight distribution and the concentration of humic-like substances. An upper molecular weight limit of humic-like substances of about 700 Da and a concentration of 0.2–1.8 µg/m3 air can be estimated corresponding to 8–33% of the total organic carbon for an urban background site.
Optical and physical properties of aerosols in the boundary layer and free troposphere over the Amazon Basin during the biomass burning season
Authors: Chand D. , Guyon P. , Artaxo P. , Schmid O. , Frank G. P. , Rizzo L. V. , Mayol-Bracero O. L. , Gatti L. V. , Andreae M. O.
Published: April 2010

Abstract. As part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) campaign, detailed surface and airborne aerosol measurements were performed over the Amazon Basin during the dry to wet season from 16 September to 14 November 2002. Optical and physical properties of aerosols at the surface, boundary layer (BL) and free troposphere (FT) during the dry season are discussed in this article. Carbon monoxide (CO) is used as a tracer for biomass burning emissions. At the surface, good correlation among the light scattering coefficient (σs at 550 nm), PM2.5, and CO indicates that biomass burning is the main source of aerosols. Accumulation of haze during some of the large-scale biomass burning events led to high mass loadings (PM2.5=200 µgm−3), σs (1400 Mm−1), aerosol optical depth at 500 nm (3.0), and CO (3000 ppb). A few rainy episodes reduced the aerosol mass loading, number concentration (CN) and CO concentration by two orders of magnitude. The correlation analysis between σs and aerosol optical thickness shows that most of the optically active aerosols are confined to a layer with a scale height of 1660 m during the burning season. The average mass scattering and absorption efficiencies (532 nm) for small particles (diameter Dp<1.5 µm) at surface level are found to be 5.3 and 0.42 m2 g−1, respectively, when relating the aerosol optical properties to PM2.5 aerosols. The observed mean single scattering albedo (ωo at ~540 nm) for submicron aerosols at the surface (0.92±0.02) is significantly higher than reported previously. The scattering efficiency (dσs/dCN) of particles increases 2–10 times from the surface to the FT, most probably due to the combined affects of coagulation and condensation.
Technical note: The Lagrangian particle dispersion model FLEXPART version 6.2
Authors: Stohl A. , Forster C. , Frank A. , Seibert P. , Wotawa G.
Published: April 2010

Abstract. The Lagrangian particle dispersion model FLEXPART was originally (about 8 years ago) designed for calculating the long-range and mesoscale dispersion of air pollutants from point sources, such as after an accident in a nuclear power plant. In the meantime FLEXPART has evolved into a comprehensive tool for atmospheric transport modeling and analysis. Its application fields were extended from air pollution studies to other topics where atmospheric transport plays a role (e.g., exchange between the stratosphere and troposphere, or the global water cycle). It has evolved into a true community model that is now being used by at least 25 groups from 14 different countries and is seeing both operational and research applications. A user manual has been kept actual over the years and was distributed over an internet page along with the model's source code. However, so far there was no citeable description of FLEXPART. In this note we provide a description of FLEXPART's latest version (6.2).
CCN activation and cloud processing in simplified sectional aerosol models with low size resolution
Authors: Korhonen H. , Kerminen V.-M. , Lehtinen K. E. J. , Kulmala M.
Published: April 2010

Abstract. We investigate the influence of low size resolution, typical to sectional aerosol models in large scale applications, on cloud droplet activation and cloud processing of aerosol particles. A simplified cloud scheme with five approaches to determine the fraction of activated particles is compared with a detailed reference model under different atmospheric conditions. In general, activation approaches which assume a distribution profile within the critical model size sections predict the cloud droplet concentration most accurately under clean and moderately polluted conditions. In such cases, the deviation from the reference simulations is below 15% except for very low updraft velocities. In highly polluted cases, the concentration of cloud droplets is significantly overestimated due to the inability of the simplified scheme to account for the kinetic limitations of the droplet growth. Of the profiles examined, taking into account the local shape of the particle size distribution is the most accurate although in most cases the shape of the profile has little relevance. While the low resolution cloud model cannot reproduce the details of the out-of-the-cloud aerosol size distribution, it captures well the amount of sulphate produced in aqueous-phase reactions as well as the distribution of the sulphate between the cloud droplets. Overall, the simplified cloud scheme with low size resolution performs well for clean and moderately polluted regions that cover most of the Earth's surface and is therefore suitable for large scale models.
Aerosol optical properties at Lampedusa (Central Mediterranean) – 2. Determination of single scattering albedo at two wavelengths for different aerosol types
Authors: Meloni D. , di Sarra A. , Pace G. , Monteleone F.
Published: April 2010

Abstract. Aerosol optical properties were retrieved from direct and diffuse spectral irradiance measurements made by a multi-filter rotating shadowband radiometer (MFRSR) at the island of Lampedusa (35.5° N, 12.6° E), in the Central Mediterranean, in the period July 2001–September 2003. In a companion paper (Pace et al., 2005) the aerosol optical depth (AOD) and Ångström exponent were used together with airmass backward trajectories to identify and classify different aerosol types. The MFRSR diffuse-to-direct ratio (DDR) at 415.6 nm and 868.7 nm for aerosol classified as biomass burning-urban/industrial, originating primarily from the European continent, and desert dust, originating from the Sahara, is used in this study to estimate the aerosol single scattering albedo (SSA). A detailed radiative transfer model is initialized with the measured aerosol optical depth; calculations are performed at the two wavelengths varying the SSA values until the modelled DDR matches the MFRSR observations. Sensitivity studies are performed to estimate how uncertainties on AOD, DDR, asymmetry factor (g), and surface albedo influence the retrieved SSA values. The results show that a 3% variation of AOD or DDR produce a change of about 0.02 in the retrieved SSA value at 415.6 and 868.7 nm; a ±0.06 variation of the asymmetry factor g produces a change of the estimated SSA of <0.04 at 415.6 nm, and <0.06 at 868.7 nm; finally, an increase of the assumed surface albedo of 0.05 gives very small changes (0.01–0.02) in the retrieved SSA. The calculations show that the SSA of desert dust (DD) increases with wavelength, from 0.81±0.05 at 415.6 nm to 0.94±0.05 at 868.7 nm; on the contrary, the SSA of urban/industrial (UN) aerosols decreases from 0.96±0.02 at 415.6 nm to 0.87±0.07 at 868.7 nm; the SSA of biomass burning (BB) particles is 0.82±0.04 at 415.6 nm and 0.80±0.05 at 868.7 nm. Episodes of UN aerosols occur usually in June and July; BB aerosol episodes with large AOD and long duration are observed mainly in July and August, the driest months of the year, when the development of fires is favoured.
Sensitivity of Global Modeling Initiative chemistry and transport model simulations of radon-222 and lead-210 to input meteorological data
Authors: Considine D. B. , Bergmann D. J. , Liu H.
Published: April 2010

Abstract. We have used the Global Modeling Initiative chemistry and transport model to simulate the radionuclides radon-222 and lead-210 using three different sets of input meteorological information: 1. Output from the Goddard Space Flight Center Global Modeling and Assimilation Office GEOS-STRAT assimilation; 2. Output from the Goddard Institute for Space Studies GISS II′ general circulation model; and 3. Output from the National Center for Atmospheric Research MACCM3 general circulation model. We intercompare these simulations with observations to determine the variability resulting from the different meteorological data used to drive the model, and to assess the agreement of the simulations with observations at the surface and in the upper troposphere/lower stratosphere region. The observational datasets we use are primarily climatologies developed from multiple years of observations. In the upper troposphere/lower stratosphere region, climatological distributions of lead-210 were constructed from ~25 years of aircraft and balloon observations compiled into the US Environmental Measurements Laboratory RANDAB database. Taken as a whole, no simulation stands out as superior to the others. However, the simulation driven by the NCAR MACCM3 meteorological data compares better with lead-210 observations in the upper troposphere/lower stratosphere region. Comparisons of simulations made with and without convection show that the role played by convective transport and scavenging in the three simulations differs substantially. These differences may have implications for evaluation of the importance of very short-lived halogen-containing species on stratospheric halogen budgets.
High-precision isotope measurements of H216, H217, H218, and the Δ17O-anomaly of water vapor in the southern lowermost stratosphere
Authors: Franz P. , Röckmann T.
Published: April 2010

Abstract. We report the first high-precision measurements of δ18O and Δ17O at high southern latitudes that can resolve changes in the isotopic composition of water vapor in the lowermost stratosphere and upper troposphere. A strong increase of δ18O with decreasing mixing ratio above the tropopause is found. Since also the water vapor mixing ratio decreases above the tropopause, the isotope data can be explained by mixing of relatively moist air from the tropopause with dry stratospheric air. However, the nature of dehyration process that produced this dry stratospheric, e.g., fast transport from the extratropical tropopause or mixing with air from the dehydrated polar vortex, cannot be clearly identified. The magnitude of the Δ17O-anomaly (departure from mass-dependent fractionation (MDF)) was below 2 for each datapoint, and the mean is consistent with a zero anomaly in lower level stratospheric water vapor. Various transport histories for the stratospheric data are discussed based on the mixing ratio and isotope data.
Tropopause referenced ozone climatology and inter-annual variability (1994–2003) from the MOZAIC programme
Authors: Thouret V. , Cammas J.-P. , Sauvage B. , Athier G. , Zbinden R. , Nédélec P. , Simon P. , Karcher F.
Published: April 2010

Abstract. The MOZAIC programme collects ozone and water vapour data using automatic equipment installed on board five long-range Airbus A340 aircraft flying regularly all over the world since August 1994. Those measurements made between September 1994 and August 1996 allowed the first accurate ozone climatology at 9–12 km altitude to be generated. The seasonal variability of the tropopause height has always provided a problem when constructing climatologies in this region. To remove any signal from the seasonal and synoptic scale variability in tropopause height we have chosen in this further study of these and subsequent data to reference our climatology to the altitude of the tropopause. We define the tropopause as a mixing zone 30 hPa thick across the 2 pvu potential vorticity surface. A new ozone climatology is now available for levels characteristic of the upper troposphere (UT) and the lower stratosphere (LS) regardless of the seasonal variations of the tropopause over the period 1994–2003. More over, this new presentation has allowed an estimation of the monthly mean climatological ozone concentration at the tropopause showing a sine seasonal variation with a maximum in May (120 ppbv) and a minimum in November (65 ppbv). Besides, we present a first assessment of the inter-annual variability of ozone in this particular critical region. The overall increase in the UTLS is about 1%/yr for the 9 years sampled. However, enhanced concentrations about 10–15% higher than the other years were recorded in 1998 and 1999 in both the UT and the LS. This so-called "1998–1999 anomaly'' may be attributed to a combination of different processes involving large scale modes of atmospheric variability, circulation features and local or global pollution, but the most dominant one seems to involve the variability of the North Atlantic Oscillation (NAO) as we find a strong positive correlation (above 0.60) between ozone recorded in the upper troposphere and the NAO index. A strong anti-correlation is also found between ozone and the Northern Annular Mode (NAM) index, attributing the lower stratospheric variability to dynamical anomalies. Finally this analysis highlights the coupling between the troposphere, at least the upper one, and the stratosphere, at least the lower one.
Mid-latitude Tropospheric Ozone Columns from the MOZAIC program: climatology and interannual variability
Authors: Zbinden R. M. , Cammas J.-P. , Thouret V. , Nedelec P. , Karcher F. , Simon P.
Published: April 2010

Abstract. Several thousands ozone vertical profiles collected in the course of the MOZAIC program (Measurements of Ozone, Water Vapour, Carbon Monoxide and Nitrogen Oxides by In-Service Airbus Aircraft) from August 1994 to February 2002 are investigated to bring out climatological and interannual variability aspects. The study is centred on the most frequently visited MOZAIC airports, i.e. Frankfurt (Germany), Paris (France), New York (USA) and the cluster of Tokyo, Nagoya and Osaka (Japan). The analysis focuses on the vertical integration of ozone from the ground to the dynamical tropopause and the vertical integration of stratospheric-origin ozone throughout the troposphere. The characteristics of the MOZAIC profiles, frequency of flights, accuracy, precision, and depth of the troposphere observed, are presented. The climatological analysis shows that the Tropospheric Ozone Column (TOC) seasonal cycle ranges from a minimum wintertime at all four stations to a spring-summer maximum in Frankfurt, Paris, and New York. Over Japan, the maximum occurs in spring because of the earlier springtime sun. The invasion of monsoon air masses in the boundary layer and in the mid-troposphere then steeply diminishes the summertime value. Boundary layer contributions to the TOC are 10% higher in New York compare to Frankfurt and Paris during spring and summer, and are 10% higher in Japan compare to New York, Frankfurt and Paris during autumn and early spring. Local and remote anthropogenic emissions as well as biomass burning over upstream regions of Asia may be responsible of larger low- and mid-tropospheric contributions to the tropospheric ozone column over Japan throughout the year except during the summer-monsoon season. A simple Lagrangian analysis has shown that a minimum range of 10% of the TOC is of stratospheric-origin throughout the year. The investigation on the short-term trends of the TOC over the period 1995–2001 shows a linear increase of 0.7%/year in Frankfurt, 0.8%/year in Japan, 0.9%/year in Paris, and 1.1%/year in New York. Essential ingredients to these positive short-term trends are the continuous increase of wintertime tropospheric ozone columns from 1996 to 1999 and the positive contributions of the mid-troposphere whatever the season.
Eddy covariance measurements and parameterisation of traffic related particle emissions in an urban environment
Authors: Mårtensson E. M. , Nilsson E. D. , Buzorius G. , Johansson C.
Published: April 2010

Abstract. Urban aerosol sources are important due to the health effects of particles and their potential impact on climate. Our aim has been to quantify and parameterise the urban aerosol source number flux F (particles m-2 s-1), in order to help improve how this source is represented in air quality and climate models. We applied an aerosol eddy covariance flux system 118.0 m above the city of Stockholm. This allowed us to measure the aerosol number flux for particles with diameters >11 nm. Upward source fluxes dominated completely over deposition fluxes in the collected dataset. Therefore, the measured fluxes were regarded as a good approximation of the aerosol surface sources. Upward fluxes were parameterised using a traffic activity (TA) database, which is based on traffic intensity measurement. The footprint (area on the surface from which sources and sinks affect flux measurements, located at one point in space) of the eddy system covered road and building construction areas, forests and residential areas, as well as roads with high traffic density and smaller streets. We found pronounced diurnal cycles in the particle flux data, which were well correlated with the diurnal cycles in traffic activities, strongly supporting the conclusion that the major part of the aerosol fluxes was due to traffic emissions. The emission factor for the fleet mix in the measurement area EFfm=1.4±0.1×1014 veh-1 km-1 was deduced. This agrees fairly well with other studies, although this study has an advantage of representing the actual effective emission from a mixed vehicle fleet. Emission from other sources, not traffic related, account for a F0=14±18×106 m-2 s-1. The urban aerosol source flux can then be written as F=EFfmTA+F0. In a second attempt to find a parameterisation, the friction velocity U* normalised with the average friction velocity has been included, F=EF. This parameterisation results in a somewhat reduced emission factor, 1.3×1014 veh-1 km-1. When multiple linear regression have been used, two emission factors are found, one for light duty vehicles EFLDV=0.3±0.3×1014 veh-1 km-1 and one for heavy-duty vehicles, EFHDV=19.8±4.0×1014 veh-1 km-1, and F0=18±16×106 m-2 s-1. The results show that during weekdays ~70–80% of the emissions came from HDV.
Characterization of the organic composition of aerosols from Rondônia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds
Authors: Decesari S. , Fuzzi S. , Facchini M. C. , Mircea M. , Emblico L. , Cavalli F. , Maenhaut W. , Chi X. , Schkolnik G. , Falkovich A. , Rudich Y. , Claeys M. , Pashynska V. , Vas G. , Kourtchev I. , Vermeylen R. , Hoffer A. , Andreae M. O. , Tagliavini E. , Moretti F. , Artaxo P.
Published: April 2010

Abstract. The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of advanced analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations had decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6–8% of TC (9–11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Poly-hydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50–90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a lesser extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.
On the changing seasonal cycles and trends of ozone at Mace Head, Ireland
Authors: Carslaw D. C.
Published: April 2010

Abstract. A seasonal-trend decomposition technique based on a locally-weighted regression smoothing (Loess) approach has been used to decompose monthly ozone concentrations at Mace Head (Ireland) into trend, seasonal and irregular components. The trend component shows a steady increase from 1990–2004, which is confirmed by statistical testing that shows that ozone concentrations at Mace Head have increased at the p=0.06 level by 0.18±0.04 ppb yr−1. By considering different air mass origins using a trajectory analysis, it has been possible to separate air masses into "polluted" and "unpolluted" origins. The seasonal-trend decomposition technique confirms the different seasonal cycles of these air mass origins with unpolluted air mass maxima in April and polluted air mass maxima in July/August. A detailed consideration of the seasonal component reveals different behaviour depending on the air mass origin. For baseline unpolluted air arriving at Mace Head there has been a gradual increase in the seasonal amplitude, driven by a declining summertime component. The amplitude of the seasonal component of baseline air is controlled by a maximum in April and a minimum in July. For polluted air mass trajectories, there was a substantial reduction in the amplitude of the seasonal component from 1990–1997. However, post-1997 results indicate that the seasonal amplitude in polluted air masses arriving at Mace Head is increasing. Furthermore, there has been a shift in the months controlling the size of the seasonal amplitude in polluted air from a maximum in May and minimum in January in 1990 to a maximum in April and a minimum in July by 2001. These results indicate that the characteristics of baseline air are becoming more important in polluted air masses arriving at this location.
Improving cloud information over deserts from SCIAMACHY O2 A-band
Authors: Fournier N. , Stammes P. , de Graaf M. , van der A R. , Piters A. , Koelemeijer R. , Kokhanovsky A.
Published: April 2010

Abstract. The retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites is sensitive to light scattered by clouds. The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument on the Envisat satellite, principally designed to retrieve trace gases in the atmosphere, is also capable of detecting clouds. FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A-band) is a fast and robust algorithm providing cloud information from the O2 A-band for cloud correction of ozone. FRESCO provides a consistent set of cloud products by retrieving simultaneously effective cloud fraction and cloud top pressure. The FRESCO retrieved values are compared with both the SCIAMACHY Level 2 operational cloud fraction of OCRA (Optical Cloud Recognition Algorithm) and cloud information deduced from the MODIS instrument. The results correlate well, but FRESCO overestimates cloud fraction over deserts. Thus, to improve retrievals at these locations, the FRESCO surface albedo databases are decontaminated from the presence of desert dust aerosols. This is achieved by using a GOME Absorbing Aerosol Index. It is shown that this approach succeeds well in producing more accurate cloud information over the Sahara.
Atmospheric oxidation in the Mexico City Metropolitan Area (MCMA) during April 2003
Authors: Shirley T. R. , Brune W. H. , Ren X. , Mao J. , Lesher R. , Cardenas B. , Volkamer R. , Molina L. T. , Molina M. J. , Lamb B. , Velasco E. , Jobson T. , Alexander M.
Published: April 2010

Abstract. The Mexico City Metropolitan Area (MCMA) study in April 2003 had measurements of most atmospheric constituents including OH and HO2. It provided a unique opportunity to examine atmospheric oxidation in a megacity that has more pollution than typical US and European cities. OH typically reached 0.35 pptv (~7×106 cm−3), comparable to amounts observed in US cities, but HO2 reached 40 pptv in the early afternoon, more than observed in most US cities. A steady-state photochemical model simulated the measured OH and HO2 for day and night to within combined measurement and modeling uncertainties for 2/3 of the results. For OH, measured = 0.65 (modeled) + 0.026 pptv, with R2=0.80. For HO2, observed = 0.70 (modeled) + 3.4 pptv, with R2=0.64. Measurements tended to be higher during night and rush hour; the model was higher by ~30% during midday. With a large median measured OH reactivity of more than 120 s−1 during morning rush hour, median ozone production from observed HO2 reached 50 ppb hr−1; RO2 was calculated to have a similar ozone production rate. For both the HO2/OH ratio and the ozone production, the measured values have the essentially same dependence on NO as the modeled values. This similarity is unlike other urban studies in which the NO-dependence of the measured HO2/OH ratio was much less than the modeled ratio and the ozone production rate that was calculated from measured HO2 unexpectedly appeared to increase as a function of NO with no obvious peak.
The surface properties of SOA generated from limonene and toluene using specific molecular probes: exploration of a new experimental technique
Authors: Demirdjian B. , Rossi M. J.
Published: April 2010

Abstract. A new experimental technique of characterizing the aerosol-atmosphere surface has been explored using three examples: the secondary organic aerosols (SOA) resulting from the reaction of limonene with O3 and from the photooxidation of toluene in comparison with the combustion aerosol (soot) from a toluene diffusion flame. Rather than investigating the bulk composition of the aerosol by complete chemical analysis and identification of the many dozens if not more of constituent compounds we have interrogated the type and number of functional groups located at the aerosol surface by interacting them with specific molecular probes such as O3, NO2, N(CH3)3, and NH2OH to probe for the presence of oxidizable sites, acidic sites and carbonyl functionalities, respectively, that are present on the surface of the aerosol particle. In practice, typical amounts of one to a few mg of laboratory-generated SOA of limonene, toluene and soot have been deposited on a PTFE membrane filter that subsequently has been transferred to a molecular flow reactor used for the titration reaction of the surface functional groups by the molecular probes. Absolute amounts Ni with i=O3, NO2, N(CH3)3, NH2OH of probe molecules taken up by the filter sample measured using molecular beam sampling mass spectrometry have been converted into the number of surface group functionalities per unit surface area S using the aerosol particle distribution function (PDF) of limonene and toluene SOA and the BET total surface area of toluene flame soot to result in Ni/S. Arguments are presented that support the transfer of the PDF of the suspended to the aerosol collected on the Teflon filter.