bluuebunny/crossref_metadata_2025 huggingface dataset:
Latitudinal variation in the multiphase chemical processing of inorganic halogens and related species over the eastern North and South Atlantic Oceans
Authors: Keene W. C. , Long M. S. , Pszenny A. A. P. , Sander R. , Maben J. R. , Wall A. J. , O'Halloran T. L. , Kerkweg A. , Fischer E. V. , Schrems O.
Published: April 2010

Abstract. Volatile inorganic and size-resolved particulate Cl- and Br-species were measured in near-surface air over a broad range of conditions within four distinct regimes (European – EURO, North African – N-AFR, the Intertropical Convergence Zone – ITCZ, and South Atlantic – S-ATL) along a latitudinal gradient from 51° N to 18° S through the eastern Atlantic Ocean. Processes within each regime were interpreted in conjunction with box-model calculations. Median dry-deposition fluxes of sea salt, oxidized N, and oxidized non-sea-salt S varied by factors of 25, 17, and 9, respectively, among the regimes. Sea-salt production was the primary source for inorganic Cl and Br. Acidification and dechlorination of sea salt primarily by HNO3 sustained HCl mixing ratios ranging from medians of 82 (ITCZ) to 682 (EURO) pmol mol−1. Aerosol pHs inferred from HCl phase partitioning with super-μm size fractions (~3 for EURO to the low 4 s for ITCZ) were similar to modeled values. Within all regimes, the dominant sources for atomic Cl were BrCl photolysis and ClO+NO. Maxima in atomic Cl ranged from 2.1 to 7.8×104 cm−3 in the ITCZ and N-AFR regimes, respectively. Because SO2 solubility over the aerosol pH range was low, S(IV) oxidation by hypohalous acids was unimportant under most conditions. Measured particulate Br− (median enrichment factor=0.25) was greater and volatile inorganic Br less than simulated values. Reaction with atomic Br was an important sink for O3 (5% in EURO to 46% in N-AFR). Formation of halogen nitrates accelerated the oxidation of NOx (NO+NO2) primarily via hydrolysis reactions involving S aerosol. Relative to simulations with no halogens, lower NOx coupled with direct reactions involving halogens yielded lower OH (by 20% to 54%) in all regimes. Halogen chemistry resulted in net O3 destruction and steady-state mixing ratios that were lower by 22% (EURO) to 62% (N-AFR) relative to "no-halogen" runs.
The sensitivity of CO and aerosol transport to the temporal and vertical distribution of North American boreal fire emissions
Authors: Chen Y. , Li Q. , Randerson J. T. , Lyons E. A. , Kahn R. A. , Nelson D. L. , Diner D. J.
Published: April 2010

Abstract. Forest fires in Alaska and West Canada represent important sources of aerosols and trace gases in North America. Among the largest uncertainties when modeling forest fire effects are the timing and injection height of biomass burning emissions. Here we simulate CO and aerosols over North America during the 2004 fire season, using the GEOS-Chem chemical transport model. We apply different temporal distributions and injection height profiles to the biomass burning emissions, and compare model results with satellite-, aircraft-, and ground-based measurements. We find that averaged over the fire season, the use of finer temporal resolved biomass burning emissions usually decreases CO and aerosol concentrations near the fire source region, and often enhances long-range transport. Among the individual temporal constraints, switching from monthly to 8-day time intervals for emissions has the largest effect on CO and aerosol distributions, and shows better agreement with measured day-to-day variability. Injection height substantially modifies the surface concentrations and vertical profiles of pollutants near the source region. In comparison with CO, the simulation of black carbon aerosol is more sensitive to the temporal and injection height distribution of emissions. The use of MISR-derived injection height improves agreement with surface aerosol measurements near the fire source. Our results indicate that the discrepancies between model simulations and MOPITT CO measurements near the Hudson Bay can not be attributed solely to the representation of injection height within the model. Frequent occurrence of strong convection in North America during summer tends to limit the influence of injection height distribution of fire emissions in Alaska and West Canada on CO and aerosol distributions over eastern North America.
Retrieval of cloud liquid water distributions from a single scanning microwave radiometer aboard a moving platform – Part 1: Field trial results from the Wakasa Bay experiment
Authors: Huang D. , Gasiewksi A. , Wiscombe W.
Published: April 2010

Abstract. Tomographic methods offer a new promise for retrieving three-dimensional distributions of cloud liquid water from path-integrated radiometric measurements by passive sensors. A mobile cloud tomography system using only a single scanning microwave radiometer has many advantages over a fixed system using multiple distinctly-located radiometers, e.g., efficient and flexible data collection. Part 1 (this paper) examines the results from a limited cloud tomography trial carried out during the 2003 AMSR-E validation campaign at Wakasa Bay of the Sea of Japan. During the tomographic test, the Polarimetric Scanning Radiometer (PSR) and Microwave Imaging Radiometer (MIR) aboard the NASA P-3 research aircraft scanned through a system of low-level clouds and thus provided a useful dataset for testing the cloud tomography method. We conduct three retrieval runs with a constrained inversion algorithm using, respectively the PSR, MIR, and combined PSR and MSR data. The liquid water paths calculated from the PSR retrieval are consistent with that from the MIR retrieval. The retrieved cloud field based on the combined data appears to be physically plausible and consistent with the cloud image obtained by a cloud radar. It is unfortunate that there were no in-situ cloud measurements during the experiment that can be used to quantitatively validate the tomographic retrievals. Nevertheless, we find that some vertically-uniform clouds appear at high altitudes in the retrieved fields where the radar image shows clear sky. This is likely due to flawed data collection geometry, which, in turn, is determined by the radiometer scan strategy, and aircraft altitude and moving speed. This sets the stage for Part 2 of this study that aims at possible improvements of the mobile cloud tomography approach by a group of sensitivity studies using observation system simulation experiments.
New particle formation and growth at a remote, sub-tropical coastal location
Authors: Modini R. L. , Ristovski Z. D. , Johnson G. R. , He C. , Surawski N. , Morawska L. , Suni T. , Kulmala M.
Published: April 2010

Abstract. A month-long intensive measurement campaign was conducted in March/April 2007 at Agnes Water, a remote coastal site just south of the Great Barrier Reef on the east coast of Australia. Particle and ion size distributions were continuously measured during the campaign. Coastal nucleation events were observed in clean, marine air masses coming from the south-east on 65% of the days. The events usually began at ~10:00 local time and lasted for 1–4 h. They were characterised by the appearance of a nucleation mode with a peak diameter of ~10 nm. The freshly nucleated particles grew within 1–4 h up to sizes of 20–50 nm. The events occurred when solar intensity was high (~1000 W m−2) and RH was low (~60%). Interestingly, the events were not related to tide height. The volatile and hygroscopic properties of freshly nucleated particles (17–22.5 nm), simultaneously measured with a volatility-hygroscopicity-tandem differential mobility analyser (VH-TDMA), were used to infer chemical composition. The majority of the volume of these particles was attributed to internally mixed sulphate and organic components. After ruling out coagulation as a source of significant particle growth, we conclude that the condensation of sulphate and/or organic vapours was most likely responsible for driving particle growth during the nucleation events. We cannot make any direct conclusions regarding the chemical species that participated in the initial particle nucleation. However, we suggest that nucleation may have resulted from the photo-oxidation products of unknown sulphur or organic vapours emitted from the waters of Hervey Bay, or from the formation of DMS-derived sulphate clusters over the open ocean that were activated to observable particles by condensable vapours emitted from the nutrient rich waters around Fraser Island or Hervey Bay. Furthermore, a unique and particularly strong nucleation event was observed during northerly wind. The event began early one morning (08:00) and lasted almost the entire day resulting in the production of a large number of ~80 nm particles (average modal concentration during the event was 3200 cm−3). The Great Barrier Reef was the most likely source of precursor vapours responsible for this event.
Contrasting atmospheric boundary layer chemistry of methylhydroperoxide (CH3OOH) and hydrogen peroxide (H2O2) above polar snow
Authors: Frey M. M. , Hutterli M. A. , Chen G. , Sjostedt S. J. , Burkhart J. F. , Friel D. K. , Bales R. C.
Published: April 2010

Abstract. Atmospheric hydroperoxides (ROOH) were measured at Summit, Greenland (72.97° N, 38.77° W) in summer 2003 (SUM03) and spring 2004 (SUM04) and South Pole in December 2003 (SP03). The two dominant hydroperoxides were H2O2 and CH3OOH (from here on MHP) with average(±1σ) mixing ratios of 1448(±688) pptv, 204(±162) and 278(±67) for H2O2 and 578(±377) pptv, 139(±101) pptv and 138(±89) pptv for MHP, respectively. In early spring, MHP dominated the ROOH budget and showed night time maxima and daytime minima, out of phase with the diurnal cycle of H2O2, suggesting that the organic peroxide is controlled by photochemistry, while H2O2 is largely influenced by temperature driven exchange between the atmosphere and snow. Highly constrained photochemical box model runs yielded median ratios between modeled and observed MHP of 52%, 148% and 3% for SUM03, SUM04 and SP03, respectively. At Summit firn air measurements and model calculations suggest a daytime sink of MHP in the upper snow pack, which decreases in strength through the spring season into the summer. Up to 50% of the estimated sink rates of 1–5×1011 molecules m−3 s−1 equivalent to 24–96 pptv h−1 can be explained by photolysis and reaction with the OH radical in firn air and in the quasi-liquid layer on snow grains. Rapid processing of MHP in surface snow is expected to contribute significantly to a photochemical snow pack source of formaldehyde (CH2O). Conversely, summer levels of MHP at South Pole are inconsistent with the prevailing high NO concentrations, and cannot be explained currently by known photochemical precursors or transport, thus suggesting a missing source. Simultaneous measurements of H2O2, MHP and CH2O allow to constrain the NO background today and potentially also in the past using ice cores, although it seems less likely that MHP is preserved in firn and ice.
Global distribution of upper tropospheric formic acid from the ACE-FTS
Authors: González Abad G. , Bernath P. F. , Boone C. D. , McLeod S. D. , Manney G. L. , Toon G. C.
Published: April 2010

Abstract. We present the first near global upper tropospheric distribution of formic acid (HCOOH) observed from the space using solar occultation measurements from the Fourier transform spectrometer (FTS) on board the Atmospheric Chemistry Experiment (ACE) satellite. Using a new set of spectroscopic line parameters recently published for formic acid, we have retrieved the concentrations of HCOOH between 5 km and the tropopause for ACE-FTS observations from February 2004 to September 2007. We observe a significant seasonal dependence for the HCOOH concentrations related to vegetation growth and biomass burning. We estimate an emission ratio of 0.0051±0.0015 for HCOOH relative to CO for tropical South American fires using a selected set of data for September 2004. Results from the balloon-borne MkIV Fourier transform spectrometer are also presented and used to validate the ACE measurements.
Kinetic modeling of nucleation experiments involving SO2 and OH: new insights into the underlying nucleation mechanisms
Authors: Du H. , Yu F.
Published: April 2010

Abstract. Nucleation is an important source of atmospheric aerosols which have significant climatic and health implications. Despite intensive theoretical and field studies during past decades, the dominant nucleation mechanism in the lower troposphere remains to be mysterious. Several recent laboratory studies on atmospheric nucleation may shed light on this important problem. However, the most interesting finding from those studies was based on the H2SO4 concentration whose accuracy has not yet been evaluated by any other methods. Moreover, the threshold H2SO4 concentration needed to reach the same degree of nucleation reported by two separate nucleation studies varies by about one order of magnitude. In this study, we apply a recently updated kinetic nucleation model to study the nucleation phenomena observed in those recent experiments. We show that the H2SO4 concentration can be estimated with a higher level of accuracy with the kinetic model by constraining the simulated particle size distributions with observed ones. We find that the H2SO4 concentration was underestimated in those studies by a factor of ~2 to 4. More importantly, by comparing the derived thermodynamic properties associated with the nucleation process, we conclude that different unknown species may participate in the two separate nucleation experimental studies, which may explain the large difference in the reported threshold H2SO4 concentration. Although the unknown species involved has yet to be identified, the derived values of thermodynamic properties can serve as a valuable guideline for the search of their chemical identities using advanced quantum-chemical approaches.
Evaluating the potential of IASI ozone observations to constrain simulated surface ozone concentrations
Authors: Foret G. , Beekmann M. , Eremenko M. , Hamaoui L. , Schmechtig C. , Keim C. , Dufour G. , Boynard A. , Ung A.
Published: April 2010

Abstract. A tracer study has been performed for two summers in 2003 and 2004 with a regional chemistry- transport model in order to evaluate the potential constraint that tropospheric ozone observations from nadir viewing infrared sounders like IASI or TES exert on modeled near surface ozone. As these instruments show high sensitivity in the free troposphere, but low sensitivity at ground, our study addresses which amount of this information is transferred to ground through vertical transport processes. Within the European model domain, and within a time span of 4 days, only ozone like tracers initialised in vertical layers above 500 hPa are transported to the surface. For a tracer initialised between 800 and 700 hPa, seven percent reaches the surface within one to three days, when averaging over the whole European model domain, but more than double of it over the Mediterranean sea. These results are confirmed by a second tracer study taking into account averaging kernels related to IASI retrievals.
Trans-Pacific transport of Asian dust and CO: accumulation of biomass burning CO in the subtropics and dipole structure of transport
Authors: Nam J. , Wang Y. , Luo C. , Chu D. A.
Published: April 2010

Abstract. In May 2003, both MODIS aerosol optical depth (AOD) and carbon monoxide (CO) measurements from MOPITT show significant trans-Pacific transport to North America. We apply the global chemical transport model, GEOS-Chem, to analyze the main features of the long-range transport events. Enhancements of MOPITT CO over the tropical Pacific are much broader than MODIS AOD enhancements. We find in model simulations that a substantial fraction of the CO enhancements in the subtropics in May is due to biomass burning in Southeast Asia in April. Biomass burning CO was recirculated into the subtropical high-pressure system and lingered for a much longer period than aerosols transported at higher latitudes. Simulated AOD enhancements are due to a combination of dust, sulfate, and organic and elemental carbons. Dust contribution dominates the AOD enhancements in early May. Model results indicate that dust transport takes place at higher altitude than the other aerosols. MODIS observations indicate a bias in model simulated pathway of dust AOD transport. Sensitivities of dust transport pathways are analyzed in the model. The dipole structure of transport over the Pacific is found to be the key factor leading to the high sensitivity of simulated transport pathways to source location and wind field.
Rates and regimes of photochemical ozone production over Central East China in June 2006: a box model analysis using comprehensive measurements of ozone precursors
Authors: Kanaya Y. , Pochanart P. , Liu Y. , Li J. , Tanimoto H. , Kato S. , Suthawaree J. , Inomata S. , Taketani F. , Okuzawa K. , Kawamura K. , Akimoto H. , Wang Z. F.
Published: April 2010

Abstract. An observation-based box model approach was undertaken to estimate concentrations of OH, HO2, and RO2 radicals and the net photochemical production rate of ozone at the top of Mount Tai, located in the middle of Central East China, in June 2006. The model calculation was constrained by the measurements of O3, H2O, CO, NO, NO2, hydrocarbon, HCHO, and CH3CHO concentrations, and temperature and J values. The net production rate of ozone was estimated to be 6.4 ppb h−1 as a 6-h average (09:00–15:00 CST), suggesting 58 ppb of ozone is produced in one day. Thus the daytime buildup of ozone recorded at the mountain top as 23 ppb on average is likely affected by in situ photochemistry as well as by the upward transport of polluted air mass in the daytime. On days with high ozone concentrations (hourly values exceeding 100 ppb at least once), in situ photochemistry was more active than it was on low ozone days, suggesting that in situ photochemistry is an important factor controlling ozone concentrations. Sensitivity model runs for which different NOx and hydrocarbon concentrations were assumed suggested that the ozone production occurred normally under NOx-limited conditions, with some exceptional periods (under volatile-organic-compound-limited conditions) in which there was fresh pollution. We also examined the possible influence of the heterogeneous loss of gaseous HO2 radicals in contact with aerosol particle surfaces on the rate and regimes of ozone production.
Evidence of the water-cage effect on the photolysis of NO3- and FeOH2+, and its implications for the photochemistry at the air-water interface of atmospheric droplets
Authors: Nissenson P. , Dabdub D. , Das R. , Maurino V. , Minero C. , Vione D.
Published: April 2010

Abstract. Experiments are conducted to determine the photolysis quantum yields of nitrate, FeOH2+, and H2O2 in the bulk and at the surface layer of water. Results show that the quantum yields of nitrate and FeOH2+ are enhanced at the surface compared to the bulk due to a reduced water-cage surrounding the photo-fragments (•OH+•NO2 and Fe2++•OH, respectively). However, no evidence is found for an enhanced quantum yield for H2O2 at the surface. The photolysis rate constant distribution within nitrate, FeOH2+, and H2O2 aerosols is calculated by combining the quantum yield data with Mie theory calculations of light intensity. Values for the photolysis rate constant of nitrate and FeOH2+ are significantly higher at the surface than in the bulk due to enhanced quantum yields at the surface. The results concerning the rates of photolysis of these photoactive species are applied to the assessment of the reaction between benzene and •OH in the presence of •OH scavengers in an atmospherically relevant scenario. For a droplet of 1μm radius, a large fraction of the total •OH-benzene reaction (15% for H2O2, 20% for nitrate, and 35% for FeOH2+) occurs in the surface layer, which accounts for just 0.15% of the droplet volume. By neglecting the surface effects on photochemistry, the rate of the important reactions could be underestimated by a considerable amount.
Annual particle flux observations over a heterogeneous urban area
Authors: Järvi L. , Rannik Ü. , Mammarella I. , Sogachev A. , Aalto P. P. , Keronen P. , Siivola E. , Kulmala M. , Vesala T.
Published: April 2010

Abstract. Long-term eddy covariance (EC) particle number flux measurements for the size range 6 nm to 5 μm were performed at the SMEAR III station over urban area in Helsinki, Finland. Heterogeneous urban environment allowed us to study the effect of different land-use classes in different wind directions on the measured fluxes. The particle fluxes were observed to be the highest from the road direction during weekdays with day-time median flux 0.8×109 m−2 s−1. Particle fluxes showed a~clear dependence on traffic rates and mixing conditions of the boundary layer. In the direction of road, the larger particle fluxes were dominated by smaller sizes. Footprint analysis was performed by using numerical modeling and emission rate of particles from road was estimated to be 0.8×1012 s−1 m−1 during day-time. With typical traffic rate of 2500 vehicles per hour this corresponds to average emission rate of 1.2×1015 vehicles−1 km−1. The particle fluxes from vegetated area were the lowest with daytime median fluxes below 0.2×109 m−2 s−1. During weekends and nights the particle fluxes were low from all land use sectors being in the order of 0.02–0.1×109 m−2 s−1. On annual scale, the highest fluxes were measured in winter when emissions from stationary combustion sources are higher.
Elevated nitrogen-containing particles observed in Asian dust aerosol samples collected at the marine boundary layer of the Bohai Sea and the Yellow Sea
Authors: Geng H. , Park Y.-M. , Hwang H.-J. , Kang S. , Ro C.-U.
Published: April 2010

Abstract. Low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA) shows powerful advantages for the characterization of ambient particulate matter in environmental and geological applications. By the application of the low-Z particle EPMA single particle analysis, an overall examination of 1800 coarse and fine particles (aerodynamic diameters: 2.5–10 μm and 1.0–2.5 μm, respectively) in six samples collected on 28 April–1 May 2006 in the marine boundary layer (MBL) of the Bohai Sea and Yellow Sea was conducted. Three samples (D1, D2, and D3) were collected along the Bohai Bay, Bohai Straits, and Yellow Sea near Korea during an Asian dust storm event while the other three samples (N3, N2, and N1) were collected on normal days. Based on X-ray spectral and secondary electron image data, 15 different types of particles were identified, in which soil-derived particles were encountered with the largest frequency, followed by (C, N, O)-rich droplets (likely the mixture of organic matter and NH4NO3), particles of marine origin, and carbonaceous, Fe-rich, fly ash, and (C, N, O, S)-rich droplet particles. Results show that during the Asian dust storm event relative abundances of the (C, N, O)-rich droplets and the nitrate-containing secondary soil-derived particles were markedly increased (on average by a factor of 4.5 and 2, respectively in coarse fraction and by a factor of 1.9 and 1.5, respectively in fine fraction) in the MBL of the Bohai Sea and Yellow Sea, implying that Asian dust aerosols in springtime are an important carrier of gaseous inorganic nitrogen species, especially NOx (or HNO3) and NH3.
Evaluation of the volatility basis-set approach for the simulation of organic aerosol formation in the Mexico City metropolitan area
Authors: Tsimpidi A. P. , Karydis V. A. , Zavala M. , Lei W. , Molina L. , Ulbrich I. M. , Jimenez J. L. , Pandis S. N.
Published: April 2010

Abstract. New primary and secondary organic aerosol modules have been added to PMCAMx, a three dimensional chemical transport model (CTM), for use with the SAPRC99 chemistry mechanism based on recent smog chamber studies. The new modeling framework is based on the volatility basis-set approach: both primary and secondary organic components are assumed to be semivolatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. This new framework with the use of the new volatility basis parameters for low-NOx and high-NOx conditions tends to predict 4–6 times higher anthropogenic SOA concentrations than those predicted with older generation of models. The resulting PMCAMx-2008 was applied in Mexico City Metropolitan Area (MCMA) for approximately a week during April of 2003. The emission inventory, which uses as starting point the MCMA 2004 official inventory, is modified and the primary organic aerosol (POA) emissions are distributed by volatility based on dilution experiments. The predicted organic aerosol (OA) concentrations peak in the center of Mexico City reaching values above 40 μg m−3. The model predictions are compared with Aerosol Mass Spectrometry (AMS) observations and their Positive Matrix Factorization (PMF) analysis. The model reproduces both Hydrocarbon-like Organic Aerosol (HOA) and Oxygenated Organic Aerosol (OOA) concentrations and diurnal profiles. The small OA underprediction during the rush hour periods and overprediction in the afternoon suggest potential improvements to the description of fresh primary organic emissions and the formation of the oxygenated organic aerosols respectively, although they may also be due to errors in the simulation of dispersion and vertical mixing. However, the AMS OOA data are not specific enough to prove that the model reproduces the organic aerosol observations for the right reasons. Other combinations of contributions of primary, aged primary, and secondary organic aerosol production rates may lead to similar results. The model results suggest strongly that during the simulated period transport of OA from outside the city was a significant contributor to the observed OA levels. Future simulations should use a larger domain in order to test whether the regional OA can be predicted with current SOA parameterizations. Sensitivity tests indicate that the predicted OA concentration is especially sensitive to the volatility distribution of the emissions in the lower volatility bins.
Chinese SO2 pollution over Europe – Part 1: Airborne trace gas measurements and source identification by particle dispersion model simulations
Authors: Fiedler V. , Nau R. , Ludmann S. , Arnold F. , Schlager H. , Stohl A.
Published: April 2010

Abstract. A large SO2-rich pollution plume of Chinese origin was detected by aircraft based CIMS (Chemical Ionization Mass Spectrometry) measurements at 3–7.5 km altitude over the North Atlantic on 3 May 2006 during the INTEX (Intercontinental Chemical Transport Experiment) campaign. Additional trace gases (NO, NOy, CO, H2O) were measured and used for comparison and source identification. All measurements took place aboard the German research aircraft Falcon. The atmospheric SO2 mole fraction was markedly increased inside the plume and reached up to 900 pmol/mol. The measured ratio SO2/NOy of 1.4 suggests combustion of coal or fuel with a very high sulfur content as a source of the excess SO2. Accompanying FLEXPART particle dispersion model simulations indicate that the probed pollution plume originated at low altitudes over densely populated and industrialized areas in eastern China about 8–12 days prior to the measurements.
Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site
Authors: Shantz N. C. , Chang R. Y.-W. , Slowik J. G. , Abbatt J. P. D. , Leaitch W. R.
Published: April 2010

Abstract. Growth rates of water droplets were measured with a static diffusion cloud condensation chamber in May–June 2007 at a rural field site in Southern Ontario, Canada, 70 km north of Toronto. Observations were made during periods when the winds were from the south and the site was impacted by anthropogenic air from the US and Southern Ontario as well as during a 5-day period of northerly wind flow when the aerosol was dominated by biogenic sources. The growth of droplets on anthropogenic size-selected particles centred at 0.1 μm diameter and composed of approximately 40% organic and 60% ammonium sulphate (AS) by mass, was delayed on the order of 1 second compared to a pure AS aerosol. Simulations of the growth rate indicate that a lowering of the water mass accommodation coefficient from αc=1 to an average of αc=0.044 is needed (assuming an insoluble organic with hygroscopicity parameter, κorg, of zero). In contrast, the growth rate of the aerosol of biogenic character, consisting of >80% organic, was similar to that of pure AS. Simulations of the predominantly biogenic aerosol show agreement between the observations and simulations when κorg=0.05–0.2 and αc=1. Inhibition of water uptake by the anthropogenic organic applied to an adiabatic cloud parcel model in the form of a constant low αc increases the number of droplets in a cloud compared to pure AS. If the αc is assumed to increase with increasing liquid water on the droplets, then the number of droplets decreases which could diminish the indirect effect. The slightly lower κorg in the biogenic case decreases the number of droplets in a cloud compared to pure AS.
Size-distributions of n-hydrocarbons, PAHs and hopanes and their sources in the urban, mountain and marine atmospheres over East Asia
Authors: Wang G. , Kawamura K. , Xie M. , Hu S. , Gao S. , Cao J. , An Z. , Wang Z.
Published: April 2010

Abstract. Size-segregated (9 stages) n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in the urban (Baoji city in inland China), mountain (Mt. Tai in east coastal China) and marine (Okinawa Island, Japan) atmospheres over East Asia were studied using a GC/MS technique. Concentrations of n-alkanes (1698±568 ng m−3 in winter and 487±145 ng m−3 in spring), PAHs (536±80 and 161±39 ng m−3), and hopanes (65±24 and 20±2.4 ng m−3) in the urban air are 1–2 orders of magnitude higher than those in the mountain aerosols and 2–3 orders of magnitude higher than those in the marine samples. Mass ratios of n-alkanes, PAHs and hopanes clearly demonstrate coal-burning emissions as the major source of the determined organic aerosols. Size distributions of fossil fuel derived n-alkane, PAHs and hopanes were found as a unimodal in most cases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived n-alkanes present a bimodal distribution with two peaks at the sizes of 0.7–1.1 μm and >4.7 μm in the summer mountain and spring marine samples. Among the three types of samples, geometric mean diameter (GMD) of the determined organics in fine mode (<2.1 μm) was the smallest (av. 0.63 μm in spring) in the urban samples and the largest (1.01 μm) in the marine samples, whereas the GMD in coarse mode (≥2.1 μm) was smallest (3.48 μm) in the marine aerosols and largest (4.04 μm) in the urban aerosols. The fine mode of GMDs in the urban and mountain samples were larger in winter than in spring and summer. Moreover, GMDs of 3- and 4-ring PAHs were larger than 5- and 6-ring PAHs in the three types of atmospheres. Such differences in GMDs may be interpreted by coagulation and repartitioning of organic compound during a long range transport from the inland continent to the marine site, suggesting that the size changes arising from these physical processes must be included in climate models in relevant to organic aerosols.
Interannual variability of tropospheric composition: the influence of changes in emissions, meteorology and clouds
Authors: Voulgarakis A. , Savage N. H. , Braesicke P. , Wild O. , Carver G. D. , Pyle J. A.
Published: April 2010

Abstract. We have run a chemistry transport model (CTM) to systematically examine the drivers of interannual variability of tropospheric composition. On a global scale, changing meteorology (winds, temperatures, humidity and clouds) is found to be the most important factor driving interannual variability of NO2 and ozone on the timescales considered. The strong influence of emissions is largely confined to areas where intense biomass burning events occur. For CO, interannual variability is almost solely driven by emission changes, while for OH meteorology dominates, with the radiative influence of clouds being a very strong contributor. Through a simple attribution analysis we conclude that changing cloudiness drives 25% of the interannual variability of OH over Europe by affecting shortwave radiation. Over Indonesia this figure is as high as 71%. Changes in cloudiness contribute a small but non-negligible amount (up to 6%) to the interannual variability of ozone over Europe and Indonesia. This suggests that future assessments of trends in tropospheric oxidizing capacity should account for interannual variability in cloudiness, a factor neglected in many previous studies. The approach followed in the current study can help explain observed tropospheric variability, such as the increases in ozone concentrations over Europe in 1998.
Quantifying transport into the Arctic lowermost stratosphere
Authors: Werner A. , Volk C. M. , Ivanova E. V. , Wetter T. , Schiller C. , Schlager H. , Konopka P.
Published: April 2010

Abstract. In-situ measurements of the long-lived trace gases N2O, CFC-11 (CCl3F), H-1211 (CBrClF2), CH4, O3 and H2O performed in the Arctic winter 2003 on board the high-altitude aircraft M55 Geophysica are presented and used to study transport into the lowermost stratosphere (LMS). Fractions of air in the LMS originating in i) the troposphere, ii) the extra-vortex stratosphere above 400 K and iii) the Arctic vortex above 400 K are determined using a simple mass balance calculation. The analysis exhibits a strong tropospheric influence of 50% or more in the lowest 20 K of the high-latitude LMS. Above this region the LMS is dominated by air masses having descended from above 400 K. Below the Arctic vortex region at potential temperatures above 360 K, air in the LMS is a mixture of extra-vortex stratospheric and vortex air masses. The vortex fraction increases from about 40% at 360 K to 100% at 400 K for equivalent latitudes >70° N. This influence of air masses descending through the bottom of the polar vortex increases over the course of the winter. By the end of winter a significant fraction of 30% vortex air in the LMS is found even at an equivalent latitude of 40° N. Since the chemical and dynamical history of vortex air is distinct from that of mid-latitude stratospheric air masses, this study implies that the composition of the mid- to high-latitude LMS during late winter and spring is significantly influenced by the Arctic vortex.
Airborne measurements of the nitric acid partitioning in persistent contrails
Authors: Schäuble D. , Voigt C. , Kärcher B. , Stock P. , Schlager H. , Krämer M. , Schiller C. , Bauer R. , Spelten N. , de Reus M. , Szakáll M. , Borrmann S. , Weers U. , Peter Th.
Published: April 2010

Abstract. This study reports the first systematic measurements of nitric acid (HNO3) uptake in contrail ice particles at typical aircraft cruise altitudes. During the CIRRUS-III campaign cirrus clouds and almost 40 persistent contrails were probed with in situ instruments over Germany and Northern Europe in November 2006. Besides reactive nitrogen, water vapor, cloud ice water content, ice particle size distributions, and condensation nuclei were measured during 6 flights. Contrails with ages up to 8 hours were detected at altitudes 10–11.5 km and temperatures 211–220 K. These contrails had a larger ice phase fraction of total nitric acid (HNO3ice/HNO3tot = 6%) than the ambient cirrus layers (3%). On average, the contrails contained twice as much HNO3ice as the cirrus clouds, 14 pmol/mol and 6 pmol/mol, respectively. Young contrails with ages below 1 h had a mean HNO3ice of 21 pmol/mol. The contrails had higher nitric acid to water molar ratios in ice and slightly higher ice water contents than the cirrus clouds under similar meteorological conditions. The differences in ice phase fractions and molar ratios between developing contrails and cirrus are likely caused by high plume concentrations of HNO3 prior to contrail formation. The location of the measurements in the top region of frontal cirrus layers might account for slight differences in the ice water content between contrails and adjacent cirrus clouds. The observed dependence of molar ratios as a function of the mean ice particle diameter suggests that ice-bound HNO3 concentrations are controlled by uptake of exhaust HNO3 in the freezing plume aerosols in young contrails and subsequent trapping of ambient HNO3 in growing ice particles in older (age > 1 h) contrails.
Stochastic fields method for sub-grid scale emission heterogeneity in mesoscale atmospheric dispersion models
Authors: Cassiani M. , Vinuesa J. F. , Galmarini S. , Denby B.
Published: April 2010

Abstract. The stochastic fields method for turbulent reacting flows has been applied to the issue of sub-grid scale emission heterogeneity in a mesoscale model. This method is a solution technique for the probability density function (PDF) transport equation and can be seen as a straightforward extension of currently used mesoscale dispersion models. It has been implemented in an existing mesoscale model and the results compared with Large-Eddy Simulation (LES) data devised to test specifically the effect of sub-grid scale emission heterogeneity on boundary layer concentration fluctuations. The sub-grid scale emission variability is assimilated in the model as a PDF of the emissions. The stochastic fields method shows excellent agreement with the LES data without the need of any additional model constants, nor the adjustment of the constants already used in the mesoscale model. The stochastic fields method solves transport equations of the concentration PDF for dispersing scalars and therefore it possesses the ability to handle chemistry of any complexity without closure assumptions. This study shows for the first time the feasibility of applying this method to mesoscale chemical transport models.
A modelling system for the exhaust emissions of marine traffic and its application in the Baltic Sea area
Authors: Jalkanen J.-P. , Brink A. , Kalli J. , Pettersson H. , Kukkonen J. , Stipa T.
Published: April 2010

Abstract. A method is presented for the evaluation of the exhaust emissions of marine traffic, based on the messages provided by the Automatic Identification System (AIS), which enable the identification and location determination of ships. The use of the AIS data enables the positioning of ship emissions with a high spatial resolution, which is limited only by the inaccuracies of the Global Positioning System (typically a few metres) that is used in vessel navigation. The emissions are computed based on the relationship of the instantaneous speed to the design speed, and these computations also take into account the detailed technical information of the ships' engines. The modelling of emissions is also based on a few basic equations of ship design, including the modelling of the propelling power of each vessel in terms of its speed. We have also investigated the effect of waves on the consumption of fuel, and on the emissions to the atmosphere. The predictions of fuel consumption were compared with the actual values obtained from the shipowners. For a RoPax vessel, the predicted and reported values of fuel consumption agreed within an accuracy of 6%. According to the data analysis and model computations, the emissions of NOx, SOx and CO2 originating from ships in the Baltic Sea in 2007 were in total 400 kt, 138 kt and 19 Mt, respectively. A breakdown of emissions by flag state, ship's type and year of construction is also presented. The modelling system can be used as a decision support tool in the case of issues concerning, e.g., health effects caused by shipping emissions, the construction of emission-based fairway dues systems or emissions trading. The computation of emissions can also be automated, which will save resources in constructing emission inventories. Both the methodologies and the emission computation program can be applied in any sea region in the world, provided that the AIS data from that specific region are available.
Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)
Authors: Kamphus M. , Ettner-Mahl M. , Drewnick F. , Keller L. , Cziczo D. J. , Mertes S. , Borrmann S. , Curtius J.
Published: April 2010

Abstract. Two different single particle mass spectrometers were operated in parallel at the Swiss High Alpine Research Station Jungfraujoch (JFJ, 3580 m a.s.l.) during the Cloud and Aerosol Characterization Experiment (CLACE 6) in February and March 2007. During mixed phase cloud events ice crystals from 5 μm up to 20 μm were separated from large ice aggregates, non-activated, interstitial aerosol particles and supercooled droplets using an Ice-Counterflow Virtual Impactor (Ice-CVI). During one cloud period supercooled droplets were additionally sampled and analyzed by changing the Ice-CVI setup. The small ice particles and droplets were evaporated by injection into dry air inside the Ice-CVI. The resulting ice and droplet residues (IR and DR) were analyzed for size and composition by two single particle mass spectrometers: a custom-built Single Particle Laser-Ablation Time-of-Flight Mass Spectrometer (SPLAT) and a commercial Aerosol Time of Flight Mass Spectrometer (ATOFMS, TSI Model 3800). During CLACE 6 the SPLAT instrument characterized 355 individual ice residues that produced a mass spectrum for at least one polarity and the ATOFMS measured 152 particles. The mass spectra were binned in classes, based on the combination of dominating substances, such as mineral dust, sulfate, potassium and elemental carbon or organic material. The derived chemical information from the ice residues is compared to the JFJ ambient aerosol that was sampled while the measurement station was out of clouds (several thousand particles analyzed by SPLAT and ATOFMS) and to the composition of the residues of supercooled cloud droplets (SPLAT: 162 cloud droplet residues analyzed, ATOFMS: 1094). The measurements showed that mineral dust particles were strongly enhanced in the ice particle residues. 57% of the SPLAT spectra from ice residues were dominated by signatures from mineral compounds, and 78% of the ATOFMS spectra. Sulfate and nitrate containing particles were strongly depleted in the ice residues. Sulfate was found to dominate the droplet residues (~90% of the particles). The results from the two different single particle mass spectrometers were generally in agreement. Differences in the results originate from several causes, such as the different wavelength of the desorption and ionisation lasers and different size-dependent particle detection efficiencies.
Ground-based lidar measurements from Ny-Ålesund during ASTAR 2007: a statistical overview
Authors: Hoffmann A. , Ritter C. , Stock M. , Shiobara M. , Lampert A. , Maturilli M. , Orgis T. , Neuber R. , Herber A.
Published: April 2010

Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) in March and April 2007, measurements obtained at the AWIPEV Research station in Ny-Ålesund, Spitsbergen (operated by the Alfred-Wegener-Institute for Polar and Marine Research and the Institut polaire français Paul-Emile Victor), supported the airborne campaign. This included Lidar data from the Koldewey Aerosol Raman Lidar (KARL) and the Micro Pulse Lidar (MPL), located in the atmospheric observatory as well as photometer data and the daily launched radiosonde. The MPL features nearly continuous measurements; the KARL was switched on whenever weather conditions allowed observations (145 h in 61 days). From 1 March to 30 April, 71 meteorological balloon soundings were performed and compared with the corresponding MPL measurements; photometer measurements are available from 18 March. For the KARL data, a statistical overview based on the optical properties backscatter ratio and volume depolarization can be given. The altitudes of the occurrence of the named features (subvisible and visible ice and water as well as mixed-phase clouds, aerosol layers) as well as their dependence on different air mass origins are analyzed. Although the spring 2007 was characterized by rather clean conditions, diverse case studies of cloud and aerosol occurrence during March and April 2007 are presented in more detail, including temporal development and main optical properties as backscatter, depolarization and extinction coefficients. Links between air mass origins and optical properties can be presumed but need further evidence.
Explicit calculation of indirect global warming potentials for halons using atmospheric models
Authors: Youn D. , Patten K. O. , Lin J.-T. , Wuebbles D. J.
Published: April 2010

Abstract. The concept of Global Warming Potentials (GWPs) has been extensively used in policy consideration as a relative index for comparing the climate impact of an emitted greenhouse gas (GHG), relative to carbon dioxide with equal mass emissions. Ozone depletion due to emission of chlorinated or brominated halocarbons leads to cooling of the climate system in the opposite direction to the direct warming contribution by halocarbons as GHGs. This cooling is a key indirect effect of the halocarbons on climatic radiative forcing, which is accounted for by indirect GWPs. With respect to climate, it is critical to understand net influences considering direct warming and indirect cooling effects for Halons. Until now, the indirect GWPs have been calculated using a para\\-meterized approach based on the concept of Equivalent Effective Stratospheric Chlorine (EESC) and the observed ozone depletion over the last few decades. As a step towards obtaining indirect GWPs through a more robust approach, we use atmospheric models to explicitly calculate the indirect GWPs of Halon-1211 and Halon-1301 for a 100-year time horizon. State-of-the-art global chemistry-transport models (CTMs) were used as the computational tools to derive more realistic ozone depletion changes caused by an added pulse emission of the two major Halons at the surface. The radiative forcings on climate from the ozone changes have been calculated for indirect GWPs using an atmospheric radiative transfer model (RTM). The simulated temporal variations of global average total column Halons after a pulse perturbation follow an exponential decay with an e-folding time which is consistent with the expected chemical lifetimes of the Halons. Our calculated indirect GWPs for the two Halons are smaller than past studies although direct GWPs agree with the published values. Nonetheless, our model-based assessment of the Halon indirect GWPs confirms the significant importance of indirect effects on climate.
Secondary organic material formed by methylglyoxal in aqueous aerosol mimics – Part 2: Product identification using Aerosol-CIMS
Authors: Sareen N. , Shapiro E. L. , Schwier A. N. , McNeill V. F.
Published: April 2010

Abstract. We used chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol-CIMS) to characterize secondary organic material formed by methylglyoxal with ammonium sulfate in aqueous aerosol mimics. Bulk reaction mixtures were diluted and atomized to form submicron aerosol particles. Organics were detected using Aerosol-CIMS in positive and negative ion mode using I− and H3O+·(H2O)n as reagent ions. The results are consistent with aldol condensation products, carbon-nitrogen species, sulfur-containing compounds, and oligomeric species up to 759 amu. These results support previous observations by us and others that ammonium sulfate plays a critical role in the SOA formation chemistry of dicarbonyl compounds.