bluuebunny/crossref_metadata_2025 huggingface dataset:
Ozone over the Western Mediterranean Sea – results from two years of shipborne measurements
Authors: Velchev K. , Cavalli F. , Hjorth J. , Marmer E. , Vignati E. , Dentener F. , Raes F.
Published: April 2010

Abstract. Ozone, along with other air pollutants, has been measured for two years from a monitoring station placed on a cruise ship that follows a regular track in the Western Mediterranean between April and October. Conditions favoring high ozone levels have been studied by analysis of weather maps and back trajectories. This analysis was focused on a transect over the open sea in the South Western Mediterranean between Tunis and Palma de Mallorca. High ozone levels were found in situations with an anticyclonic circulation over the Western Mediterranean when subsidence brings air masses down from altitudes between 1000 and 3500 m a.s.l. Analysis of composite meteorological maps suggest a relevant contribution of breeze circulation to subsidence during events with high surface ozone concentrations; this points to an important contribution from local ozone formation. A detailed back trajectory analysis of the origin of air masses with high ozone concentrations was carried out for two "hot spots" for ozone pollution, found along the coast south of Genova and between Napoli and Palermo, respectively. While it was found that the influence of plumes from areas with high pollutant levels might explain most episodes in the Northwestern transect, such "local" influences appeared to be of minor importance within the Napoli-Palermo transect.
Observed and simulated global distribution and budget of atmospheric C2−C5 alkanes
Authors: Pozzer A. , Pollmann J. , Taraborrelli D. , Jöckel P. , Helmig D. , Tans P. , Hueber J. , Lelieveld J.
Published: April 2010

Abstract. The primary sources and atmospheric chemistry of C2−C5 alkanes have been incorporated into the atmospheric chemistry general circulation model EMAC. Model output is compared with new observations from the NOAA/ESRL GMD cooperative air sampling network. Based on the global coverage of the data, two different anthropogenic emission datasets for C4−C5 alkanes, widely used in the modelling community, are evaluated. We show that the model reproduces the main atmospheric features of the C2−C5 alkanes (e.g., seasonality). While the simulated values of ethane and propane are within a 20% range of the measurements, larger deviations are found for the other tracers. Finally the effect of C3−C5 alkanes on the concentration of acetone and acetaldehyde are assessed. Their chemical sources are largely controlled by the reaction with OH, while the reactions with NO3 and Cl contribute only to a little extent. The total amount of acetone produced by propane, i-butane and i-pentane oxidation is 11.2 Tg/yr, 4.2 Tg/yr and 5.8 Tg/yr, respectively. Moreover, 3.1, 3.3, 1.4 and 4.8 Tg/yr of acetaldehyde are formed by the oxidation of propane, n-butane, n-pentane and i-pentane, respectively.
The impact of marine organics on the air quality of the western United States
Authors: Gantt B. , Meskhidze N. , Carlton A. G.
Published: April 2010

Abstract. The impact of marine organic emissions to the air quality in coastal areas of the western United States is studied using the latest version of the US Environmental Protection Agency (EPA) regional-scale Community Multiscale Air Quality (CMAQv4.7) modeling system. Emissions of marine isoprene, monoterpenes, and primary organic matter (POM) from the ocean are implemented into the model to provide a comprehensive view of the connection between ocean biology and atmospheric chemistry and air pollution. Model simulations show that marine organics can increase the concentration of PM2.5 by 0.1–0.3 μg m−3 (up to 5%) in coastal cities. This increase in the PM2.5 concentration is primarily attributed to the POM emissions, with small contributions from the marine isoprene and monoterpenes. When marine organic emissions are included, organic carbon (OC) concentrations over the remote ocean are increased by up to 50% (25% in coastal areas), values consistent with recent observational findings. This study is the first to quantify the air quality impacts from marine POM and monoterpenes for the United States, and highlights the need for inclusion of marine organic emissions in air quality models.
Brown carbon in tar balls from smoldering biomass combustion
Authors: Chakrabarty R. K. , Moosmüller H. , Chen L.-W. A. , Lewis K. , Arnott W. P. , Mazzolen C. , Dubey M. , Wold C. E. , Hao W. M. , Kreidenweis S. M.
Published: April 2010

Abstract. We report the direct observation of large-scale production of spherical, carbonaceous particles – "tar balls" – from smoldering combustion of two commonly occurring dry mid-latitude fuels. Real-time measurements indicate that brown carbon is an important component of tar balls. The spectrum of the imaginary parts of their complex refractive indices can be described with a Lorentzian-like model with an effective resonance wavelength in the ultraviolet (UV) spectral region. Sensitivity calculations for aerosols containing traditional organic carbon (no absorption at visible and UV wavelengths) and brown carbon suggest that accounting for UV absorption by brown carbon leads to a significant increase in aerosol radiative forcing efficiency and increased atmospheric warming. Since particles from smoldering combustion account for nearly three-fourths of the total carbonaceous aerosol mass emitted globally, inclusion of the optical properties of tar balls into radiative forcing models has significance for the Earth's radiation budget, optical remote sensing, and understanding of anomalous UV absorption in the troposphere.
Two-moment bulk stratiform cloud microphysics in the GFDL AM3 GCM: description, evaluation, and sensitivity tests
Authors: Salzmann M. , Ming Y. , Golaz J.-C. , Ginoux P. A. , Morrison H. , Gettelman A. , Krämer M. , Donner L. J.
Published: April 2010

Abstract. A new stratiform cloud scheme including a two-moment bulk microphysics module, a cloud cover parameterization allowing ice supersaturation, and an ice nucleation parameterization has been implemented into the recently developed GFDL AM3 general circulation model (GCM) as part of an effort to treat aerosol-cloud-radiation interactions more realistically. Unlike the original scheme, the new scheme facilitates the study of cloud-ice-aerosol interactions via influences of dust and sulfate on ice nucleation. While liquid and cloud ice water path associated with stratiform clouds are similar for the new and the original scheme, column integrated droplet numbers and global frequency distributions (PDFs) of droplet effective radii differ significantly. This difference is in part due to a difference in the implementation of the Wegener-Bergeron-Findeisen (WBF) mechanism, which leads to a larger contribution from super-cooled droplets in the original scheme. Clouds are more likely to be either completely glaciated or liquid due to the WBF mechanism in the new scheme. Super-saturations over ice simulated with the new scheme are in qualitative agreement with observations, and PDFs of ice numbers and effective radii appear reasonable in the light of observations. Especially, the temperature dependence of ice numbers qualitatively agrees with in-situ observations. The global average long-wave cloud forcing decreases in comparison to the original scheme as expected when super-saturation over ice is allowed. Anthropogenic aerosols lead to a larger decrease in short-wave absorption (SWABS) in the new model setup, but outgoing long-wave radiation (OLR) decreases as well, so that the net effect of including anthropogenic aerosols on the net radiation at the top of the atmosphere (netradTOA = SWABS-OLR) is of similar magnitude for the new and the original scheme.
Perfluorocarbons in the global atmosphere: tetrafluoromethane, hexafluoroethane, and octafluoropropane
Authors: Mühle J. , Ganesan A. L. , Miller B. R. , Salameh P. K. , Harth C. M. , Greally B. R. , Rigby M. , Porter L. W. , Steele L. P. , Trudinger C. M. , Krummel P. B. , O'Doherty S. , Fraser P. J. , Simmonds P. G. , Prinn R. G. , Weiss R. F.
Published: April 2010

Abstract. We present atmospheric baseline growth rates from the 1970s to the present for the long-lived, strongly infrared-absorbing perfluorocarbons (PFCs) tetrafluoromethane (CF4), hexafluoroethane (C2F6), and octafluoropropane (C3F8) in both hemispheres, measured with improved accuracies (~1–2%) and improved precisions (<0.3%, or <0.2 ppt (parts-per-trillion), for CF4; <1.5%, or <0.06 ppt, for C2F6; <4.5%, or <0.02 ppt, for C3F8) within the Advanced Global Atmospheric Gases Experiment (AGAGE). Pre-industrial background values of 34.7±0.2 ppt CF4 and 0.1±0.02 ppt C2F6 were measured in air extracted from Greenland ice and Antarctic firn. Anthropogenic sources are thought to be primary aluminum production (CF4, C2F6, C3F8), semiconductor production (C2F6, CF4, C3F8) and refrigeration use (C3F8). Global emissions calculated with the AGAGE 2-D 12-box model are significantly higher than most previous emission estimates. The sum of CF4 and C2F6 emissions estimated from aluminum production and non-metal production are lower than observed global top-down emissions, with gaps of ~6.4–7.6 Gg/yr CF4 in recent years. The significant discrepancies between previous CF4, C2F6, and C3F8 emission estimates and observed global top-down emissions estimated from AGAGE measurements emphasize the need for more accurate, transparent, and complete emission reporting, and for verification with atmospheric measurements to assess the emission sources of these long-lived and potent greenhouse gases, which alter the radiative budget of the atmosphere essentially permanently once emitted.
Seasonal variations of aerosol size distributions based on long-term measurements at the high altitude Himalayan site of Nepal Climate Observatory-Pyramid (5079 m), Nepal
Authors: Sellegri K. , Laj P. , Venzac H. , Boulon J. , Picard D. , Villani P. , Bonasoni P. , Marinoni A. , Cristofanelli P. , Vuillermoz E.
Published: April 2010

Abstract. The present paper investigates the diurnal and seasonal variability of the aerosol total number concentration, number and volume size distribution between 10 nm and 10 μm, from a combination of a scanning mobility particle sizer (SMPS) and an optical counter (OPC), performed over a two-year period (May 2006–May 2008) at the Nepal Climate Observatory-Pyramid (NCO-P) research station, (5079 m a.s.l.). The annual average number concentration measured over the two-year period at the NCO-P is 860 cm−3. Total concentrations show a strong seasonality with maxima during pre-monsoon and post-monsoon seasons and minima during the dry and monsoon seasons. A diurnal variation is also clearly observed, with maxima between 09:00 and 12:00 UTC. The aerosol concentration maxima are mainly due to nucleation processes during the post-monsoon season, as witnessed by high nucleation mode integrated number concentrations, and to transport of high levels of pollution from the plains by valley breezes during the pre-monsoon season, as demonstrated by high accumulation mode integrated number concentrations. Night-time number concentration of particles (from 03:00 to 08:00 NST) are relatively low throughout the year (from 450 cm−3 during the monsoon season to 675 cm−3 during the pre-monsoon season), indicating the level of free_tropospheric background, as a result of downslope winds during this part of the day. However, it was found that these background concentrations are strongly influenced by the daytime concentrations, as they show the same seasonal variability. The resulting free troposphere (FT)/residual layer concentrations are found to be two times higher than at other lower altitudes European sites, such as the Jungfraujoch. Night-time measurements were subsequently selected to study the FT composition according to different air masses, and the effect of long range transport to the station.
Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds
Authors: Williams B. J. , Goldstein A. H. , Kreisberg N. M. , Hering S. V. , Worsnop D. R. , Ulbrich I. M. , Docherty K. S. , Jimenez J. L.
Published: April 2010

Abstract. We report the first hourly in-situ measurements of speciated organic aerosol (OA) composition in an urban environment. Field measurements were made in southern California at the University of California–Riverside during the 2005 Study of Organic Aerosol at Riverside (SOAR), which included two separate measurement periods: a summer study (15 July–15 August) and a fall study (31 October–28 November). Hourly measurements of over 300 semivolatile and nonvolatile organic compounds were made using the thermal desorption aerosol gas chromatograph (TAG). Positive matrix factorization (PMF) was performed on a subset of these compounds to identify major components contributing to submicron (i.e., PM1) OA at the site, as measured by an aerosol mass spectrometer (AMS). PMF analysis was performed on an 11-day focus period in each season, representing average seasonal conditions during the summer and a period of urban influence during the fall. As a result of this analysis, we identify multiple types of primary and secondary OA (POA and SOA). Secondary sources contribute substantially to fine OA mass at Riverside, which commonly receives regional air masses that pass through metropolitan Los Angeles during the summer. Four individual summertime SOA components are defined, and when combined, they contribute an average 88% of the total fine OA mass during summer afternoons. These sources appear to be mostly from the oxidation of anthropogenic precursor gases, with one SOA component having contributions from oxygenated biogenics. During the fall, three out of four aerosol components which contain SOA are inseparable from covarying primary emissions, and therefore we can not estimate the fraction of total OA that is secondary in nature during the fall study. Identified primary OA components are attributed to vehicle emissions, food cooking, primary biogenics, and biomass burning aerosol. While a distinction between local and regional vehicle emissions is made, a combination of these two factors accounted for approximately 11% of observed submicron OA during both sampling periods. Food cooking operations contributed ~10% of submicron OA mass during the summer, but was not separable from SOA during the fall due to high covariance of sources. Biomass burning aerosol contributed a larger fraction of fine OA mass during the fall (~11%) than compared to summer (~7%). Primary biogenic aerosol was also identified during the summer, contributing ~1% of the OA, but not during the fall. While the contribution of both local and regional primary vehicle OA accounts for only ~11% of total OA during both seasons, gas-phase vehicle emissions likely create a substantial fraction of the observed SOA as a result of atmospheric processing.
Effects of climate-induced changes in isoprene emissions after the eruption of Mount Pinatubo
Authors: Telford P. J. , Lathière J. , Abraham N. L. , Braesicke P. , Johnson C. E. , Morgenstern O. , O'Connor F. M. , Pike R. C. , Wild O. , Young P. J. , Beerling D. , Hewitt C. N. , Pyle J. A.
Published: April 2010

Abstract. In the 1990s the rates of increase of greenhouse gas concentrations, most notably of methane, were observed to change, for reasons that have yet to be fully determined. This period included the eruption of Mt. Pinatubo and an El Niño warm event, both of which affect biogeochemical processes, by changes in temperature, precipitation and radiation. We examine the impact of these changes in climate on global isoprene emissions and the effect these climate dependent emissions have on the hydroxy radical, OH, the dominant sink for methane. We model a reduction of isoprene emissions in the early 1990s, with a maximum decrease of 40 Tg(C)/yr in late 1992 and early 1993, a change of 9%. This reduction is caused by the cooler, drier conditions following the eruption of Mt. Pinatubo. Isoprene emissions are reduced both directly, by changes in temperature and a soil moisture dependent suppression factor, and indirectly through reductions in the total biomass. The reduction in isoprene emissions causes increases of tropospheric OH which lead to an increased sink for methane of up to 5 Tg/year, comparable to estimated source changes over the time period studied.
Isoprene emissions modelling for West Africa using MEGAN
Authors: Ferreira J. , Reeves C. E. , Murphy J. G. , Garcia-Carreras L. , Parker D. J. , Oram D. E.
Published: April 2010

Abstract. Isoprene emissions are the largest source of reactive carbon to the atmosphere, with the tropics being a major source region. These natural emissions are expected to change with changing climate and human impact on land use. As part of the African Monsoon Multidisciplinary Analyses (AMMA) project the Model of Emissions of Gases and Aerosols from Nature (MEGAN) has been used to estimate the spatial and temporal distribution of isoprene emissions over the West African region. During the AMMA field campaign, carried out in July and August 2006, isoprene mixing ratios were measured on board the FAAM BAe-146 aircraft. These data have been used to evaluate the model performance. MEGAN was firstly applied to a large area covering much of West Africa from the Gulf of Guinea in the south to the desert in the north and was able to capture the large scale spatial distribution of isoprene emissions as inferred from the observed isoprene mixing ratios. In particular the model captures the transition from the forested area in the south to the bare soils in the north, but some discrepancies have been identified over the bare soil, mainly due to the emission factors used. Sensitivity analyses were performed to assess the model response to changes in driving parameters, namely Leaf Area Index (LAI), Emission Factors (EF), temperature and solar radiation. A high resolution simulation was made of a limited area south of Niamey, Niger, where the higher concentrations of isoprene were observed. This is used to evaluate the model's ability to simulate smaller scale spatial features and to examine the influence of the driving parameters on an hourly basis through a case study of a flight on 17 August 2006. This study highlights the complex interactions between land surface processes and the meteorological dynamics and chemical composition of the PBL. This has implications for quantifying the impact of biogenic emissions on the atmospheric composition over West Africa and any changes that may occur with changing climate.
Seasonal variations and spatial distribution of carbonaceous aerosols in Taiwan
Authors: Chou C. C.-K. , Lee C. T. , Cheng M. T. , Yuan C. S. , Chen S. J. , Wu Y. L. , Hsu W. C. , Lung S. C. , Hsu S. C. , Lin C. Y. , Liu S. C.
Published: April 2010

Abstract. To investigate the physico-chemical properties of aerosols in Taiwan, an observation network was initiated in 2003. In this work, the measurements of the mass concentration and carbonaceous composition of PM10 and PM2.5 are presented. Analysis on the data collected in the first 5-years, from 2003 to 2007, showed that there was a very strong contrast in the aerosol field between the rural and the urban/suburban stations. The five-year means of EC at the respective stations ranged from 0.9±0.04 to 4.2±0.1 μgC m−3. In rural areas, EC accounted for 2–3% of PM10 and 3–5% of PM2.5 mass loadings, comparing to 4–6% of PM10 and 4–8% of PM2.5 in the urban areas. It was found that the spatial distribution of EC was consistent with CO and NOx across the network stations, suggesting that the levels of EC over Taiwan were dominated by local sources. The measured OC was split into POC and SOC counterparts following the EC tracer method. Five-year means of POC ranged from 1.8±0.1 to 9.7±0.2 μgC m−3 among the stations. It was estimated that the POM contributed 5–17% of PM10 and 7–18% of PM2.5 in Taiwan. On the other hand, the five-year means of SOC ranged from 1.5±0.1 to 3.8±0.3 μgC m−3. The mass fractions of SOM were estimated to be 9–19% in PM10 and 14–22% in PM2.5. The results showed that the SOC did not exhibit significant urban-rural contrast as did the POC and EC. A significant cross-station correlation between SOC and total oxidant was observed, which means the spatial distribution of SOC in Taiwan was dominated by the oxidant mixing ratio. Besides, correlation was also found between SOC and particulate nitrate, implying that the precursors of SOA were mainly from local anthropogenic sources. In addition to the spatial distribution, the carbonaceous aerosols also exhibited distinct seasonality. In northern Taiwan, the concentrations of all the three carbonaceous components (EC, POC, and SOC) reached their respective minima in the fall season. POC and EC increased drastically in winter and peaked in spring, whereas the SOC was characterized by a bimodal pattern with the maximal concentration in winter and a second mode in summertime. In southern Taiwan, minimal levels of POC and EC occurred consistently in summer and the maxima were observed in winter, whereas the SOC peaked in summer and declined in wintertime. The discrepancies in the seasonality of carbonaceous aerosols between northern and southern Taiwan were most likely caused by the seasonal meteorological settings that dominated the dispersion of air pollutants. Moreover, it was inferred that the Asian pollution outbreaks could have shifted the seasonal maxima of air pollutants from winter to spring in the northern Taiwan, and that the biogenic SOA precursors were responsible to the elevated SOC concentrations in summer.
Enhancement of marine cloud albedo via controlled sea spray injections: a global model study of the influence of emission rates, microphysics and transport
Authors: Korhonen H. , Carslaw K. S. , Romakkaniemi S.
Published: April 2010

Abstract. Modification of cloud albedo by controlled emission of sea spray particles into the atmosphere has been suggested as a possible geoengineering option to slow global warming. Previous global studies have imposed changes in cloud drop concentration in low level clouds to explore the radiative and climatic effects. Here, we use a global aerosol transport model to quantify how an imposed flux of sea spray particles affects the natural aerosol processes, the particle size distribution, and concentrations of cloud drops. We assume that the proposed fleet of vessels emits sea spray particles with a wind speed-dependent flux into four regions of persistent stratocumulus cloud off the western coasts of continents. The model results show that fractional changes in cloud drop number concentration (CDNC) vary substantially between the four regions because of differences in wind speed (which affects the spray efficiency of the vessels), transport and particle deposition rates, and because of variations in aerosols from natural and anthropogenic sources. Using spray emission rates comparable to those implied by previous studies we find that the predicted CDNC changes are very small (maximum 20%) and in one of the four regions even negative. The weak or negative effect is because the added particles suppress the in-cloud supersaturation and prevent existing aerosol particles from forming cloud drops. A scenario with five times higher emissions (considerably higher than previously assumed) increases CDNC on average by 45–163%, but median concentrations are still below the 375 cm−3 assumed in previous studies. An inadvertent effect of the spray emissions is that sulphur dioxide concentrations are suppressed by 1–2% in the seeded regions and sulphuric acid vapour by 64–68% due to chemical reactions on the additional salt particles. The impact of this suppression on existing aerosol is negligible in the model, but should be investigated further in the real environment so that inadvertent impacts can be excluded.
Measurement of atmospheric nitrous acid at Blodgett Forest during BEARPEX2007
Authors: Ren X. , Gao H. , Zhou X. , Crounse J. D. , Wennberg P. O. , Browne E. C. , LaFranchi B. W. , Cohen R. C. , McKay M. , Goldstein A. H. , Mao J.
Published: April 2010

Abstract. Nitrous acid (HONO) is an important precursor of the hydroxyl radical (OH) in the lower troposphere. Understanding HONO chemistry, particularly its sources and contribution to HOx (=OH+HO2) production, is very important for understanding atmospheric oxidation processes. A highly sensitive instrument for detecting atmospheric HONO based on aqueous long path absorption photometry (LOPAP) was deployed in the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) at Blodgett Forest, California in late summer 2007. The median diurnal variation shows minimum HONO levels of about 20–30 pptv during the day and maximum levels of about 60–70 pptv at night, a diurnal pattern quite different from the results at various other forested sites. Measured HONO/NO2 ratios for a 24-h period ranged from 0.05 to 0.13 with a mean ratio of 0.07. Speciation of reactive nitrogen compounds (NOy) indicates that HONO accounted for only ~3% of total NOy. However, due to the fast HONO loss through photolysis, a strong HONO source (1.59 ppbv day−1) existed in this environment in order to sustain the observed HONO levels, indicating the significant role of HONO in NOy cycling. The LOPAP HONO measurements were compared to the HONO measurements made with a Chemical Ionization Mass Spectrometer (CIMS) over a three-day period. Good agreement was obtained between the measurements from the two different techniques. Using the expansive suite of photochemical and meteorological measurements, the contribution of HONO photolysis to HOx budget was calculated to be relatively small (6%) compared to results from other forested sites. The lower HONO mixing ratio and thus its smaller contribution to HOx production are attributed to the unique meteorological conditions and low acid precipitation at Blodgett Forest. Further studies of HONO in this kind of environment are needed to test this hypothesis and to improve our understanding of atmospheric oxidation and nitrogen budget.
Estimation of Antarctic ozone loss from Ground-based total column measurements
Authors: Kuttippurath J. , Goutail F. , Pommereau J.-P. , Lefèvre F. , Roscoe H. K. , Pazmiño A. , Feng W. , Chipperfield M. P.
Published: April 2010

Abstract. The passive ozone method is used to estimate ozone loss from ground-based measurements in the Antarctic. A sensitivity study shows that the O3 loss can be estimated within an accuracy of ~4%. The method is then applied to the observations from Amundsen-Scott/South Pole, Arrival Heights, Belgrano, Concordia, Dumont d'Urville, Faraday, Halley, Marambio, Neumayer, Rothera, Syowa and Zhongshan for the diagnosis of ozone loss in the Antarctic. On average, the five-day running mean of the vortex averaged ozone column loss deduced from the ground-based stations shows about 53% in 2009, 59% in 2008, 55% in 2007, 56% in 2006 and 61% in 2005. The observed O3 loss and loss rates are in very good agreement with the satellite observations (Ozone Monitoring Instrument and Sciamachy) and are well reproduced by the model (Reprobus and SLIMCAT) calculations. The historical ground-based total ozone measurements show that the depletion started in the late 1970s, reached a maximum in the early 1990s, stabilising afterwards at this level until present, with the exception of 2002, the year of an early vortex break-up. There is no indication of significant recovery yet. At southern mid-latitudes, a total ozone reduction of 40–50% is observed at the newly installed station Rio Gallegos and 25–35% at Kerguelen in October–November of 2008–2009 and 2005–2009 (except 2008) respectively, and of 10–20% at Macquarie Island in July–August of 2006–2009. This illustrates the significance of measurements at the edges of Antarctica.
Anthropogenic aerosol radiative forcing in Asia derived from regional models with atmospheric and aerosol data assimilation
Authors: Chung C. E. , Ramanathan V. , Carmichael G. , Kulkarni S. , Tang Y. , Adhikary B. , Leung L. R. , Qian Y.
Published: April 2010

Abstract. A high-resolution estimate of monthly 3-D aerosol solar heating rates and surface solar fluxes in Asia from 2001 to 2004 is described here. This product stems from an Asian aerosol assimilation project, in which a) the PNNL regional model bounded by the NCEP reanalyses was used to provide meteorology, b) MODIS and AERONET data were integrated for aerosol observations, c) the Iowa aerosol/chemistry model STEM-2K1 used the PNNL meteorology and assimilated aerosol observations, and d) 3-D (X-Y-Z) aerosol simulations from the STEM-2K1 were used in the Scripps Monte-Carlo Aerosol Cloud Radiation (MACR) model to produce total and anthropogenic aerosol direct solar forcing for average cloudy skies. The MACR model and STEM both used the PNNL model resolution of 0.45°×0.4° in the horizontal and of 23 layers in the troposphere. The 2001–2004 averaged anthropogenic all-sky aerosol forcing is -1.3 W m-2 (TOA), +7.3 W m-2 (atmosphere) and -8.6 W m-2 (surface) averaged in Asia (60–138° E and Eq. -45° N). In the absence of AERONET SSA assimilation, absorbing aerosol concentration (especially BC aerosol) is much smaller, giving -2.3 W m-2 (TOA), +4.5 W m-2 (atmosphere) and -6.8 W mm-2 (surface), averaged in Asia. In the vertical, monthly forcing is mainly concentrated below 600 hPa with maxima around 800 hPa. Seasonally, low-level forcing is far larger in dry season than in wet season in South Asia, whereas the wet season forcing exceeds the dry season forcing in East Asia. The anthropogenic forcing in the present study is similar to that in Chung et al. (2005) in overall magnitude but the former offers fine-scale features and simulated vertical profiles. The interannual variability of the computed anthropogenic forcing is significant and extremely large over major emission outflow areas. Given the interannual variability, the present study's estimate is within the implicated range of the 1999 INDOEX result. However, NCAR/CCSM3's anthropogenic aerosol forcing is much smaller than the present study's estimate at the surface, and is outside of what the INDOEX findings can support.
Technical note: Vapor pressure estimation methods applied to secondary organic aerosol constituents from α-pinene oxidation: an intercomparison study
Authors: Compernolle S. , Ceulemans K. , Müller J.-F.
Published: April 2010

Abstract. We applied and compared seven vapor pressure estimation methods to the condensable compounds generated in the oxidation of α-pinene, as described by the state-of-the-art mechanism of the BOREAM model (Capouet et al., 2008). Several of these methods had to be extended in order to treat functional groups such as hydroperoxides and peroxy acyl nitrates. Large differences in the estimated vapor pressures are reported, which will inevitably lead to large differences in aerosol formation simulations. Cautioning remarks are given for some vapor pressure estimation methods.
Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland
Authors: Liu D. , Flynn M. , Gysel M. , Créso Targino A. , Crawford I. , Bower K. , Choularton T. , Juranyi Z. , Steinbacher M. , Hüglin C. , Curtius J. , Kampus M. , Petzold A. , Weingartner E. , Baltensperger U. , Coe H.
Published: April 2010

Abstract. Black carbon (BC) mass, size distribution and mixing state in sub-micron aerosols were characterized from late February to March 2007 using a single particle incandescence method at the high alpine research station Jungfraujoch (JFJ), Switzerland (46.33° N, 7.59° E, 3580 m a.s.l.). JFJ is a ground based location, which is at times exposed to continental free tropospheric air. A median mass absorption coefficient (MAC) of 10.2±3.2 m2 g−1 at λ = 630 nm was derived by comparing single particle incandescence measurements of black carbon mass with continuous measurements of absorption coefficient. This value is comparable with other estimates at this location. The aerosols measured at the site were mostly well mixed and aged during transportation via the free troposphere. Pollutant sources were traced by air mass back trajectories, trace gases concentrations and the mass loading of BC. In southeasterly wind directions, mixed or convective weather types provided the potential to vent polluted boundary layer air from the southern Alpine area and industrial northern Italy, delivering enhanced BC mass loading and CN concentrations to the JFJ. The aerosol loadings at this site were also significantly influenced by precipitation, which led to the removal of BC from the atmosphere. Precipitation events were shown to remove about 65% of the BC mass from the free tropospheric background reducing the mean loading from 10±5 ngm−3 to 4±2 ngm−3. Overall, 40±15% of the observed BC particles within the detectable size range were mixed with large amounts of non-refractory materials present as a thick coating around the BC core. The growth of particle size into the accumulation mode was positively linked with the degree of BC mixing, suggesting the important role of condensable materials in increasing particle size as well as enhancing BC mixing state. It is the first time that BC mass, size distribution and mixing state are reported in the free troposphere over Europe. These ground based measurements also provide the first temporal study of BC in the European free troposphere quantitatively measured by single particle methods. At the present time there is only limited information of BC and its mixing state in the free troposphere, especially above Europe. The results reported in this paper provide an important constraint on modelled representation of BC.
Study of spatiotemporal variation of atmospheric mercury and its human exposure around an integrated steel plant, India
Authors: Pervez S. , Koshle A. , Pervez Y.
Published: April 2010

Abstract. Mercury release by coal combustion has been significantly increased in India. Mercury content in coal has been analyzed to 0.272 ppm by Central Pollution Control Board. Toxicological effects of elemental Hg (Hg0) exposure include respiratory and renal failures, cardiac arrest, and cerebral oedema, while subclinical exposure may induce kidney, behavioral, and cognitive dysfunctions. The present work is focused on dispersion pattern and inter-phase exchange phenomena of ambient mercury between air-particulate matter evaluations of alongwith dominance of various major routes of human exposure-dose response using regression analysis around an integrated steel plant in central India. Source-downwind type stratified random sampling plan using longitudinal study design has been adopted for ambient monitoring of total mercury, while representative sampling plant has been adopted for persona exposure-dose response study In space-time framework. Control sites and subjects have been chosen from uncontaminated area (100 km away from any industrial activities). 06 ambient air monitoring stations and 17 subjects from workers, non-workers but local residents' categories and from controlled sites have been chosen for the study. Samples of mercury biomarkers (blood, breast milk and urine) have also been collected from same subjects in each month during sampling period. The sampling period was March 2005 to February 2006 . Samples of 30% acidified KMnO4 for air-Hg absorption, PM10, RPM and biological samples were analyzed for total mercury by ICP-AES using standard methods. Local soils and ground water were also monitored for total mercury content during the sampling period. Results have shown that mercury concentration is very high compared to prescribed limits in all receptors. Results of exchange phenomenon have shown the higher transfer of mercury from air to particulate during combustion in steel plant environment due to presence of huge amount of iron particles, in contrast to results obtained in other industrial locations earlier. Plant workers have shown 1.5 to 2.5 times higher personal RPM-Hg levels compared to Category 2 and 20–30 times higher than Category 3. All biomarkers have shown higher Hg presence compared to prescribed standards. Regression analysis between exposure routes and bio-receptors has been investigated. Dominance status of selected routes of bio-accumulation has been varied from category to category.
A comprehensive characterisation of Asian dust storm particles: chemical composition, reactivity to SO2, and hygroscopic property
Authors: Ma Q. , Liu Y. , Liu C. , Ma J. , He H.
Published: April 2010

Abstract. Mineral dust comprises of a significant fraction of the globe's aerosol loading. Yet it remains the largest uncertainty in future climate predictions due to the complexity in its components and physico-chemical properties. Multi-analysis methods, including SEM-EDX, FTIR, BET, TPD/mass, and Knudsen cell/mass, were used in the present study to characterise Asian dust storm particles. The morphology, element fraction, source distribution, true uptake coefficient of SO2 and hygroscopic behaviour were studied. The major components of Asian dust storm particles were found to consist of aluminosilicate, SiO2, and CaCO3, which were coated with organic compounds and inorganic nitrate. The dust storm particles have a low reactivity to SO2 (true uptake coefficient of 5.767×10−6) which limits the conversion of SO2 to sulfate during a dust storm period. The low reactivity also demonstrated that the heterogeneous reaction of SO2, in both dry and humid air conditions, had little effect on the hygroscopic behaviour of the dust particles. These results indicate that the impact of dust storms on atmospheric SO2 removal should not be overestimated.
Response of tropical stratospheric O3, NO2 and NO3 to the equatorial Quasi-Biennial Oscillation and to temperature as seen from GOMOS/ENVISAT
Authors: Hauchecorne A. , Bertaux J. L. , Dalaudier F. , Keckhut P. , Lemennais P. , Bekki S. , Marchand M. , Lebrun J. C. , Kyrölä E. , Tamminen J. , Sofieva V. , Fussen D. , Vanhellemont F. , Fanton d'Andon O. , Barrot G. , Blanot L. , Fehr T. , Saavedra de Miguel L.
Published: April 2010

Abstract. The stellar occultation spectrometer GOMOS (Global Ozone Monitoring by Occultation of Stars) on ESA's Envisat satellite measures vertical profiles O3, NO2 and NO3 with a high long-term stability due to the self-calibrating nature of the technique. More than 6 years of GOMOS data from August 2002 to end 2008 have been analysed to study the inter-annual variation of O3, NO2 and NO3 in the tropics. It is shown that the QBO of the equatorial wind induces variations in the local concentration larger than 10% for O3 and larger than 25% for NO2. Quasi-Biennial Oscillation signals can be found in the evolution of the three constituents up to at least 45 km. We found that NO3 is positively correlated with temperature up to 40 km in the region where it is in chemical equilibrium with O3. Above 40 km, NO3 is no more in equilibrium during night and its concentration is correlated with both O3 and NO2. For O3 and NO2, our results confirm the existence of a transition from a dynamical control of O3 below 28 km with O3 correlated with NO2 and temperature and a chemical/temperature control between 28 and 38 km with O3 anti-correlated with NO2 and temperature. Above 38 km and up to 50 km a regime never described before is found with both O3 and NO2 anti-correlated with temperature. For the NO2/temperature anti-correlation, our proposed explanation is the modulation of the N2O ascent in the upper stratosphere by the QBO and the modulation of the Brewer-Dobson circulation. The oxidation of N2O is the main source of NOy in this altitude region. An enhancement of the ascending motion will cool adiabatically the atmosphere and will increase the amount of N2O concentration available for NOy formation.
Climate effects of seasonally varying biomass burning emitted carbonaceous aerosols (BBCA)
Authors: Jeong G.-R. , Wang C.
Published: April 2010

Abstract. The climate impact of the seasonality of Biomass Burning emitted Carbonaceous Aerosols (BBCA) has been studied using an aerosol-climate model coupled with a slab ocean model in a set of 60-year long simulations driven by BBCA emission data with and without seasonal variation, respectively. The model run with seasonally varying emission of BBCA leads to an increase in external mixture of carbonaceous aerosols and a decrease in internal mixtures of carbonaceous aerosols relative to those in the run with constant annual BBCA emissions, resulting from different strengths of source/sink processes. We find that the differences in atmospheric direct radiative forcing (DRF) caused by BBCA seasonality are in phase with the differences in column concentrations of an external mixture of carbonaceous aerosols in space and time; thus, the differences in surface temperature and heat fluxes are limited to the biomass burning source regions. In contrast, the differences in all-sky radiative forcing at the top of the atmosphere and at the earth's surface extend beyond the BBCA source regions due to climate feedback through cloud distribution and precipitation. The seasonality of biomass burning emissions uniquely affects the global distributions of high-level clouds and convective precipitation, which indicate an impact on atmospheric circulation. We especially find that the Inter-Tropical Convergence Zone (ITCZ) shifts northward when the seasonality of BBCA emissions is included in the model, compared to the case otherwise configured. In addition, the climate response to the periodic climate forcing of BBCA is not static in biomass burning seasons but dynamically extends into non-biomass seasons as well. The climate effects in contrasting biomass burning seasons occur in the springtime in northern Tropics with the largest difference in precipitation and mixed aerosol abundance caused by the seasonality of BBCA.
Atmospheric pollutant outflow from southern Asia: a review
Authors: Lawrence M. G. , Lelieveld J.
Published: April 2010

Abstract. Southern Asia is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal with the trade winds, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects.
Estimated total emissions of trace gases from the Canberra wildfires of 2003: a new method using satellite measurements of aerosol optical depth and the MOZART chemical transport model
Authors: Paton-Walsh C. , Emmons L. K. , Wilson S. R.
Published: April 2010

Abstract. In this paper we describe a new method for estimating trace gas emissions from large vegetation fires using measurements of aerosol optical depth from the MODIS instruments onboard NASA's Terra and Aqua satellites, combined with the atmospheric chemical transport model MOZART. The model allows for an estimate of double counting of enhanced levels of aerosol optical depth in consecutive satellite overpasses. Using this method we infer an estimated total emission of 10±3 Tg of carbon monoxide from the Canberra fires of 2003. Emissions estimates for several other trace gases are also given. An assessment of the uncertainties in the new method is made and we show that our estimate agrees (within expected uncertainties) with estimates made using current conventional methods of multiplying together factors for the area burned, fuel load, the combustion efficiency and the emission factor for carbon monoxide. The new method for estimating emissions from large vegetation fires described in this paper has some significant uncertainties, but these are mainly quantifiable and largely independent of the uncertainties inherent in conventional techniques. Thus we conclude that the new method is a useful additional tool for characterising emissions from vegetation fires.
Will climate change increase ozone depletion from low-energy-electron precipitation?
Authors: Baumgaertner A. J. G. , Jöckel P. , Dameris M. , Crutzen P. J.
Published: April 2010

Abstract. We investigate the effects of a strengthened Brewer-Dobson circulation on the transport of nitric oxide (NO) produced by energetic particle precipitation. During periods of high geomagnetic activity, low-energy-electron precipitation is responsible for winter time ozone loss in the polar middle atmosphere between 1 and 6 hPa. However, as climate change is expected to increase the strength of the Brewer-Dobson circulation, the enhancements of NOx concentrations are expected to be transported to lower altitudes in extra-tropical regions, becoming even more significant in the ozone budget. We use simulations with the chemistry climate model system ECHAM5/MESSy to compare present day effects of low-energy-electron precipitation with expected effects in a climate change scenario for the year 2100. In years of strong geomagnetic activity, similar to that observed in 2003, an additional polar ozone loss of up to 0.5 μmol/mol at 5 hPa is found. However, this would be approximately compensated by an ozone enhancement originating from a stronger poleward transport of ozone from lower latitudes caused by a strengthened Brewer-Dobson circulation, as well as by slower photochemical ozone loss reactions in a stratosphere cooled by risen greenhouse gas concentrations.
On the use of ATSR fire count data to estimate the seasonal and interannual variability of vegetation fire emissions
Authors: Schultz M. G.
Published: April 2010

Abstract. Biomass burning has long been recognised as an important source of trace gases and aerosols in the atmosphere. The burning of vegetation has a repeating seasonal pattern, but the intensity of burning and the exact localisation of fires vary considerably from year to year. Recent studies have demonstrated the high interannual variability of the emissions that are associated with biomass burning. In this paper we present a methodology using active fire counts from the Along-Track Scanning Radiometer (ATSR) sensor on board the ERS-2 satellite to estimate the seasonal and interannual variability of global biomass burning emissions in the time period 1996--2000. From the ATSR data, we compute relative scaling factors of burning intensity for each month, which are then applied to a standard inventory for carbon monoxide emissions from biomass burning. The new, time-resolved inventory is evaluated using the few existing multi-year burned area observations on continental scales.