Atmospheric Environment (v.50, #C)

Validation of a new method for directional dust monitoring by Hugh Datson; David Hall; Bill Birch (1-8).
Fugitive dust from industrial sites is problematic to quantify and can be associated with nuisance complaints. Despite significant limitations, the British Standard 1747 Part 5 (BS 1747:5) directional dust gauge remains preferred for monitoring fugitive dust flux on site boundaries. An alternative directional dust gauge, DustScan, was developed at the University of Leeds, UK, and uses cylindrical adhesive ‘sticky pads’ to sample dust in flux. With this sampler, dust capture is measured as soiling, as opposed to mass, with the BS 1747:5 sampler. An Aerosol Test Tunnel (ATT) was developed to evaluate the performance of the DustScan sampler. Atmospheric turbulence was simulated using a coarse grid generator and maintained as rough-wall channel flow by roughness elements fixed to its floor and roof of the ATT. A polydisperse test dust was introduced upwind to form a cloud at the sampler. DustScan directional dust gauges were repeatedly exposed to aliquots of test dust at wind speeds of 2–10 m s−1 in the ATT. Dust soiling levels either side of the gauge's centreline (relative to the incident direction) were compared to demonstrate that the DustScan sampler is directionally accurate. Much lower proportions of antithetic sampling (dust catch on the downwind face of the gauge) occurred than for the BS 1747:5 sampler. The sampled particle size selection was related to the ratio of particle stop distance (s) to sampler diameter (D) ratio, s/D, showing that the particle size cut point fell with increasing wind speeds. A preliminary assessment of collection efficiency (CE) was made by determining dust mass after controlled ignition of selected sticky pad samples. Although dust saturation of the sticky pads can lead to sample loss over prolonged exposure periods, this loss is relatively small over the 1–2 week intervals established as appropriate for the DustScan sampler. This need for shorter sampling intervals is considered to outweigh the convenience of the longer exposure time but significantly poorer dust sampling characteristics of the BS 1747:5 sampler.► A new method for fugitive dust monitoring was validated in wind tunnel experiments. ► DustScan is unpowered, cylindrical, with removable adhesive dust collection media. ► Exposed to aliquots of known dust at 2–10 m s−1 in the wind tunnel experiments. ► DustScan was directionally accurate at all wind speeds tested. ► Antithetic dust catch proportions were much lower than for the BS 1747 Part 5 gauge.
Keywords: Dust gauge; Dust; DustScan; Directional dust; Fugitive dust; Soiling;

Agricultural field burning plays an important role in atmospheric pollution and climate change. This work aims to develop a detailed emission inventory for agricultural burning in China with a high spatial and temporal resolution. Province-specific statistical data, distributed by the Chinese national government, and results from scientific literature were utilized to estimate the total emissions for the base year 2006. Emissions were allocated to a 1 km grid and a 10-day interval by using the Moderate Resolution Imaging Spectroradiometer (MODIS) Thermal Anomalies/Fire product (MOD/MYD14A1). The estimated annual emission ranges, with a 90% confidence interval, are 68 (51–85) Tg CO2 yr−1, 4 (2–7) Tg CO yr−1, 0.25 (0.08–0.46) Tg CH4 yr−1, 2.2 (1.08–3.46) Tg NMOCs yr−1, 0.23 (0.08–0.41) Tg NOx yr−1, 0.09 (0.03–0.17) Tg NH3 yr−1, 0.02 (0.01–0.03) Tg SO2 yr−1, 0.03 (0.01–0.05) Tg BC yr−1, 0.1 (0.04–0.17) Tg OC yr−1, 0.27 (0.13–0.42) Tg PM2.5 yr−1, 0.31 (0.12–0.53) Tg PM10 yr−1. Provinces with the highest emissions are Anhui, Guizhou and Hunan. Spatially, agricultural fires are mostly located in the North China Plain, where the occurrence of fires is concentrated in early and late June (over 75% of the whole year) with another smaller peak in early October. This pattern corresponds with sowing and harvesting times for the main crops: wheat and maize. The temporal fire variation of two other agricultural zones in northeast China and south China are also detailed in our study. Our inventory, with a relatively high spatiotemporal resolution (1 km grid and 10 days), could meet the need of global and regional air quality simulations.► Emission estimation for crop residue field burning in China. ► Relatively high spatiotemporal resolution: 1 km and 10 days. ► 8-year MODIS Thermal Anomalies/Fire products were used to allocate the emissions. ► Detailed discussion of spatiotemporal distribution of agricultural open fire.
Keywords: China; Crop residue; Fire emission; MODIS;

Reduction of gaseous and particulate emissions from small-scale wood combustion with a catalytic combustor by A. Hukkanen; T. Kaivosoja; O. Sippula; K. Nuutinen; J. Jokiniemi; J. Tissari (16-23).
In this study, a catalytic combustor was used on a wood stove as a secondary emission reduction measure. An experimental comparison of emissions was done from combustion experiments with and without the catalyst. Samples were collected from gasification and burn out phases and from the whole combustion cycle (from start-up to burn out). Concentrations of carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2) and organic gaseous carbon (OGC), temperature and pressure were measured online directly from the flue gas stack. With the catalyst, the O2 concentration in the flue gas was lower and the temperature higher than without the catalyst, due to the large amount of unburnt compounds which were oxidized by the catalyst. Reductions of 21% for CO and 14% for OGC were achieved during the whole combustion cycle. During the burn out phase, a reduction as high as 80% was achieved for CO. PM1 (particle mass below aerodynamic size of 1 μm) was reduced by 30% during the whole combustion cycle. During gasification, a 44% reduction of PM1 was achieved but there was no reduction during burn out. The organic and elemental carbon analyzed from PM1 had reduced also only during gasification by 56% and 37%, respectively. The particle emission reductions were notable and it can be concluded that the catalyst affects the particles through oxidation of condensable organic vapors and oxidation of soot particles. The catalyst has potential as a secondary emission reduction method but in order to achieve low emissions, also improved combustion technology for emission reduction needs to be developed.► A catalyst for reducing emissions from a batch-wise fired wood stove was studied. ► The catalyst enhanced the oxidation of carbon monoxide and organic gaseous compounds. ► Carbon monoxide, which is difficult to oxidize otherwise, was reduced during the burn out phase by nearly 80%. ► Reduction of particulate mass below particle aerodynamic size of 1 μm, including both organic matter and soot, was observed. ► Catalyst is a potential method but primary emission reduction methods should also be applied.
Keywords: Wood combustion; Catalyst; Carbon monoxide; Organic gaseous compounds; Fine particles;

In vitro toxicological characterization of particulate emissions from residential biomass heating systems based on old and new technologies by Pasi I. Jalava; Mikko S. Happo; Joachim Kelz; Thomas Brunner; Pasi Hakulinen; Jorma Mäki-Paakkanen; Annika Hukkanen; Jorma Jokiniemi; Ingwald Obernberger; Maija-Riitta Hirvonen (24-35).
Residential wood combustion causes major effects on the air quality on a global scale. The ambient particulate levels are known to be responsible for severe adverse health effects that include e.g. cardio-respiratory illnesses and cancer related effects, even mortality. It is known that biomass combustion derived emissions are affected by combustion technology, fuel being used and user-related practices. There are also indications that the health related toxicological effects are influenced by these parameters. This study we evaluated toxicological effects of particulate emissions (PM1) from seven different residential wood combusting furnaces. Two appliances i.e. log wood boiler and stove represented old batch combustion technology, whereas stove and tiled stove were designated as new batch combustion as three modern automated boilers were a log wood boiler, a woodchip boiler and a pellet boiler. The PM1 samples from the furnaces were collected in an experimental setup with a Dekati® gravimetric impactor on PTFE filters with the samples being weighed and extracted from the substrates and prior to toxicological analyses. The toxicological analyses were conducted after a 24-hour exposure of the mouse RAW 264.7 macrophage cell line to four doses of emission particle samples and analysis of levels of the proinflammatory cytokine TNFα, chemokine MIP-2, cytotoxicity with three different methods (MTT, PI, cell cycle analysis) and genotoxicity with the comet assay. In the correlation analysis all the toxicological results were compared with the chemical composition of the samples. All the samples induced dose-dependent increases in the studied parameters. Combustion technology greatly affected the emissions and the concomitant toxicological responses. The modern automated boilers were usually the least potent inducers of most of the parameters while emissions from the old technology log wood boiler were the most potent. In correlation analysis, the PAH and other organic composition and inorganic ash composition affected the toxicological responses differently. In conclusion, combustion technology largely affects the particulate emissions and their toxic potential this being reflected in substantially larger responses in devices with incomplete combustion. These differences become emphasized when the large emission factors from old technology appliances are taken into account.► Combustion technology of the seven furnaces affected emissions and their toxicology. ► Toxicological responses were much larger for the old technology. ► Best performance was seen with automated continuous combustion. ► Toxicology can be applied when trying to decrease harmful particulate levels.
Keywords: Small-scale wood combustion; Particulate matter; Cytotoxicity; Genotoxicity; Inflammation; Chemical composition;

14C-Based source assessment of carbonaceous aerosols at a rural site by Xuesong Sun; Min Hu; Song Guo; Kexin Liu; Liping Zhou (36-40).
Radiocarbon (14C) has become a powerful tracer in source apportionments of atmospheric carbonaceous particles. Fine particles (PM2.5) were collected at a rural site of Beijing in the summer and winter of 2007. The fractions of contemporary carbon (f C) in total carbon (TC) and elemental carbon (EC) are presented using 14C measurements. This value directly represents the contemporary biogenic contribution, since recently living biomass and biogenic organic compound emissions have f C = 1, whereas anthropogenic emissions from fossil carbon have f C = 0 because the 14C in the latter has completely decayed. The measured f C (TC) values range from 0.30 to 0.38 (n = 12) in winter and 0.31 to 0.44 (n = 12) in summer, respectively. The levels of f C values are lower than those from other rural sites in the world, indicating that the Yufa site was heavily influenced by anthropogenic emissions. The high TC concentrations in winter with the lower average f C (TC) suggest that coal burning for residential heating was significant contributors to the TC concentrations. The sources of contemporary carbon are primary emissions due to biomass burning, and biogenic secondary organic aerosol. Biomass burning was a dominant contributor in the winter. Fossil fuels represented 80–87% of EC in both seasons.► Radiocarbon (14C) as source apportionment tool. ► A contribution of fossil versus biogenic carbon is estimated. ► Coal combustion is a dominant source of carbonaceous aerosol during the wintertime heating period. ► Anthropogenic emissions have a major impact on regional air quality.
Keywords: Carbonaceous aerosols; Radiocarbon; Source apportionment; Anthropogenic emission;

Seasonal variability in airborne bacterial communities at a high-elevation site by Robert M. Bowers; Ian B. McCubbin; Anna G. Hallar; Noah Fierer (41-49).
Although bacteria are ubiquitous in the near-surface atmosphere, the temporal dynamics of airborne bacterial communities have not been well-studied. We examined seasonal shifts in bacterial abundances, the relative contribution of bacteria to total aerosol loads, and bacterial community structure at a high-elevation research station in northern Colorado, USA. Aerosol samples were collected from the near-surface atmosphere over 5–10 days during each of the four calendar seasons. Bacterial abundances varied by season with the highest concentrations observed during the fall and spring seasons, consistent with the changes in total particle concentrations, with bacterial cells often representing a large fraction (22% on average) of the total near-surface aerosol particles >0.5 μm. Bacterial community composition, determined via barcoded pyrosequencing, also varied significantly by season. The dominant taxa in the spring, winter, and second half of the fall sampling periods (when the ground was snow covered) were bacterial taxa commonly found in other cold environments while the summer and first half of the fall samples contained taxa that were likely derived from soil and leaf-surface environments. Bacteria are clearly an important component of atmospheric aerosols with the abundance and composition of these airborne bacterial communities shaped by seasonal shifts in atmospheric conditions and the conditions of the local terrestrial environment.► Total particle and bacterial concentrations vary by season. ► Bacteria represent a large proportion of the near-surface atmospheric aerosol >0.5 μm. ► Bacterial community composition changed significantly across the four seasons. ► Seasonal shifts in airborne bacterial communities linked to shifts in bacterial source environments.
Keywords: Primary biological aerosol; High altitude site; Storm Peak Laboratory; Bacteria; Community; Colorado Rocky Mountains;

Vertical distribution of optical and micro-physical properties of ambient aerosols during dry haze periods in Shanghai by Yonghang Chen; Qiong Liu; Fuhai Geng; Hua Zhang; Changjie Cai; Tingting Xu; Xiaojun Ma; Hao Li (50-59).
Based on the lidar data obtained from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite of NASA (National Aeronautics and Space Administration), the vertical distributions of aerosols are revealed during dry haze periods in the Shanghai vicinity by analyzing the optical and micro-physical parameters including total attenuated backscatter coefficient (TABC), volume depolarization ratio (VDR) and total attenuated color ratio (TACR). The preliminary conclusion is that when dry haze occurs in the Shanghai vicinity, smoke and maritime aerosols are the major types in summer and autumn and aerosols might be affected by long-distance transport of dust in spring; lower troposphere below 2 km is the layer polluted most severely and aerosol scattering with relatively irregular shape is much stronger than that of aerosols with relatively regular shape within 2–10 km in middle and upper troposphere; relatively large aerosols appear more frequently in lower (0–2 km) and middle troposphere (2–6 km) than those in upper troposphere (6–10 km). In addition, HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model is applied to analyze the aerosol sources during two typical episodes. The results indicate that the middle and upper troposphere in the Shanghai vicinity are affected by the long-distance transport of dusts from northwest of China or other upstream regions. The high aerosol concentrations in the Shanghai vicinity are mainly caused not only by local human activities but also by the long-distance transport from other places.► The vertical distributions of aerosol TABC, VDR and TACR have been analyzed. ► Scattering from aerosols decreases with the increase of altitudes from 0 to 10 km. ► The irregularity of aerosols increases with increased altitudes. ► The relatively larger particles appear more frequently in the lower and upper. ► Smoke and maritime aerosols are the major dry aerosol types.
Keywords: CALIPSO satellite; Dry haze; Aerosols; Optical properties; Vertical distribution;

Atmospheric dry and wet deposition of mercury in Toronto by Xiaotong Zhang; Zia Siddiqi; Xinjie Song; Khakhathi L. Mandiwana; Muhammad Yousaf; Julia Lu (60-65).
Atmospheric mercury (Hg) speciation and deposition are critical in understanding the cycling of mercury in the environment. To estimate the dry and wet deposition of mercury in an urban environment, concentrations of gaseous elemental mercury (GEM), gaseous oxidized inorganic mercury (GOIM), mercury associated with particles having size less than 2.5 μm (Hg(p) < 2.5) (December 2003–November 2004) and total particulate mercury (THg(p)) (June 2004–December 2004) in the atmosphere, as well as the concentrations of methyl mercury (MeHg) and total mercury (THg) in atmospheric precipitation samples (June 2005–January 2006 and September 2007–March 2008), were measured in downtown Toronto, Canada.The dry deposition rates of GOIM, Hg(p) < 2.5 μm and THg(p) estimated between December 2003 and December 2004 were 0.17–2.33 μg m−2 month−1, 0.04–0.32 μg m−2 month−1 and 0.17–1.11 μg m−2 month−1, respectively, while the wet deposition rates of methyl mercury and total mercury between June 2005–January 2006 and September 2007–March 2008 were 0.01–0.08 μg m−2 month−1 and 0.32–8.48 μg m−2 month−1, respectively. The total dry deposition (7.66–26.06 μg m−2 a−1, calculated as the sum of GOIM and THg(p) deposition) and the total wet deposition (= the wet deposition of total mercury = 18.60 μg m−2 a−1) contributed proportionally to the total atmospheric Hg deposition in Toronto.► Concentrations of atmospheric Hg species were measured and Hg dry and wet deposition rates estimated in Toronto, Canada. ► Deposition rates of Hg are dependent on seasonal changes. ► Dry and wet depositions contribute proportionally to the total atmospheric Hg deposition.
Keywords: Speciation; Mercury species; Wet deposition; Dry deposition; Urban atmosphere; Cold vapor atomic fluorescence Spectrophotometer;

Raman lidar observations of a Saharan dust outbreak event: Characterization of the dust optical properties and determination of particle size and microphysical parameters by Paolo Di Girolamo; Donato Summa; Rohini Bhawar; Tatiana Di Iorio; Marco Cacciani; Igor Veselovskii; Oleg Dubovik; Alexey Kolgotin (66-78).
The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36 h from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, capturing the signature of a severe Saharan dust outbreak episode. The data clearly reveal the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5 km above ground level (a.g.l.) and an upper layer extending between 3.0 and 6.0 km a.g.l. The time evolution of the dust cloud is illustrated and discussed in the paper in terms of several optical parameters (particle backscatter ratio at 532 and 1064 nm, the colour ratio and the backscatter Angström parameter).An inversion algorithm was used to retrieve particle size and microphysical parameters, i.e., mean and effective radius, number, surface area, volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution (PSD), from the multi-wavelength lidar data of particle backscattering, extinction and depolarization. The retrieval scheme employs Tikhonov’s inversion with regularization and makes use of kernel functions for randomly oriented spheroids. Size and microphysical parameters of dust particles are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the presence of a fine mode with radii of 0.1–0.2 μm and a coarse mode with radii of 3–5 μm both in the lower and upper dust layers, and the dominance in the upper dust layer of a coarse mode with radii of 4–5 μm. Effective radius varies with altitude in the range 0.1–1.5 μm, while volume concentration is found to not exceed 92 μm3 cm−3. The real and imaginary part of the complex refractive index vary in the range 1.4–1.6 and 0.004–0.008, respectively.► Dust size and microphysical parameters determined from multi-wavelength lidar data. ► Application of a retrieval scheme using kernel functions for spheroidal particles. ► Lidar measurements compared with simultaneous photometer and literature data. ► Measurements reveal a partial hygroscopic behaviour of the sounded dust particles. ► Results allow to identify the deliquescence point and to compute the growth factor.
Keywords: Raman lidar; Saharan dust; Spheroids; Microphysics; COPS;

Household materials as emission sources of naphthalene in Canadian homes and their contribution to indoor air by Dong Hwa Kang; Dong Hee Choi; Doyun Won; Wenping Yang; Hans Schleibinger; Jacinthe David (79-87).
The objective of this study was to identify household materials that may contribute to the indoor naphthalene concentration in Canadian homes. Ninety-nine household materials including building materials, furnishings, and consumer products were tested. These materials included well-known naphthalene-containing products such as mothballs as well as building and consumer products where naphthalene could have been either added as part of a liquid formulation or used as a chemical intermediate in the manufacture of solid materials and product components. A fast screening method was used to determine the naphthalene concentration in a micro-scale test chamber. The tested materials were ranked based on the naphthalene emission strength combined with the amount of products typically used in homes. As expected, the results showed that mothballs, which had the highest emission factor, are one of the predominant sources. Interestingly, vinyl and wooden furniture with high emission factors and painted walls and ceiling with large surface areas were found to be important sources with the source strength even larger than those of mothballs when maximum emission factors were assumed for these building materials and furnishings. This suggests that some building materials and furnishings could be significant contributors to indoor naphthalene concentrations. This study shows that selecting materials with lower naphthalene emission factors could be one of many ways to reduce the indoor naphthalene concentration.► We test 99 household materials to determine sources of naphthalene in homes. ► We analyze scenarios on naphthalene concentrations for different material selections. ► Furniture can be high emitters of naphthalene, in addition to mothballs. ► Selecting low emitting materials is important to reduce indoor concentrations.
Keywords: Naphthalene; Household materials; Emission source; Canadian homes; Exposure; Micro-scale chamber;

An atmospheric emission inventory of anthropogenic and biogenic sources for Lebanon by Antoine Waked; Charbel Afif; Christian Seigneur (88-96).
A temporally-resolved and spatially-distributed emission inventory was developed for Lebanon to provide quantitative information for air pollution studies as well as for use as input to air quality models. This inventory covers major anthropogenic and biogenic sources in the region with 5 km spatial resolution for Lebanon and 1 km spatial resolution for its capital city Beirut and its suburbs. The results obtained for CO, NO x , SO2, NMVOC, NH3, PM10 and PM2.5 for the year 2010 were 563, 75, 62, 115, 4, 12, and 9 Gg, respectively. About 93% of CO emissions, 67% of NMVOC emissions and 52% of NO x emissions are calculated to originate from the on-road transport sector while 73% of SO2 emissions, 62% of PM10 emissions and 59% of PM2.5 emissions are calculated to originate from power plants and industrial sources. The spatial allocation of emissions shows that the city of Beirut and its suburbs encounter a large fraction of the emissions from the on-road transport sector while urban areas such as Zouk Mikael, Jieh, Chekka and Selaata are mostly affected by emissions originating from the industrial and energy production sectors. Temporal profiles were developed for several emission sectors.► First temporally and spatially-resolved emission inventory developed for Lebanon. ► Grids of 5 km × 5 km over Lebanon and 1 km × 1 km over Greater Beirut area. ► Transport sector (modelled as Tier 3) is the major source of pollutants. ► Major role of industries in PM10 and PM2.5 emissions. ► Discrepancies in seasonal emission profiles inter and intra-emission sectors.
Keywords: Emissions; Air quality; Lebanon; Gridded inventory; Temporal profiles;

Hygroscopicity is a critical property for evaluating aerosol’s environmental and climate impacts. Traditional view always considered hygroscopic behavior of aerosol as a water adsorption/absorption–desorption cycle in which the size, water content and morphology etc. are well characterized. However, the chemical reactions between coexisting components in mixed particles during humidifying-dehumidifying process are almost neglected. In this study, we found that there exists synergistic effect among Ca(NO3)2, CaCO3 and H2C2O4 mixtures during humidifying process. Substitution of strong acid (HNO3) by medium acid (H2C2O4) take place during vapor absorption on Ca(NO3)2/H2C2O4 mixture. Moreover, the presence of nitrate exhibits a promotive effect to the reaction between H2C2O4 and CaCO3 under ambient condition. These results provoke us to rethink the hygroscopic behavior of mixed aerosol in which chemical reaction can greatly change the chemical composition, mixing state and consequently environmental and climate impacts.► Synergistic effect among mixed aerosol exists during humidifying process. ► The coexisting Ca(NO3)2 promoted the reaction in CaCO3/H2C2O4 mixture. ► Substitution of HNO3 by H2C2O4 occurs during the humidifying process of Ca(NO3)2/H2C2O4 mixture. ► The physicochemical properties of mixtures were greatly changed after humidifying process.
Keywords: Oxalate; Mineral dust; Mixed aerosol; Hygroscopic behavior; Synergistic effect;

Outdoor near-roadway, community and residential pollen, carbon dioxide and particulate matter measurements in the urban core of an agricultural region in central CA by Derek G. Shendell; Jennifer H. Therkorn; Naomichi Yamamoto; Qingyu Meng; Sarah W. Kelly; Christine A. Foster (103-111).
We can control asthma through proper clinical and environmental management and education. The U.S. population is growing, urbanizing and aging; seniors of low-to-middle income families are working and living longer. We conducted community-based participatory research in Visalia, Tulare County, California with a prospective, cross-sectional repeated measures design and quantitative and qualitative process; home environment and health-related outcomes data were collected. In this paper, we presented results of the air quality sampling—pollen, carbon dioxide (CO2) and particulate matter (PM) outdoors away from most major sources (agricultural fields, large pollinating trees, etc)—at a community central site close to a mobile line source and participant homes in the cooling season, July, 2009. Weather was hot and dry with light winds; diurnal variation ranged between 65–107 °F (18–42 °C) and 12–76% relative humidity at the study’s central site. Co-located active (reference) and passive (PAAS) samplers were used for pollen; passive monitoring for CO2 (Telaire 7001) and active sampling for PM were conducted. Overall, we observed spatial variability in CO2, fine PM (PM2.5), and pollen counts. Weekday and study week average CO2 and PM2.5 concentrations were higher near study homes compared to central site sampling points, but peak measures and overnight/pre-dawn time period averages were elevated at the central site. Pollen counts were typically lower at homes—even if grass, trees, flowers or potted plants were present—compared to the central site closer to and generally downwind from commercial agricultural tree production. Data are new; the nine-county San Joaquin Valley has one pollen count station in the national network, and two of four government outdoor air monitoring stations in the county are in national parks. We suggest—given poor air quality in large part due to PM—adding routine pollen counts to regional/state agency air monitoring sites and more CO2 and PM monitoring.► Weekday and study week mean CO2 and PM2.5 concentrations were higher near homes. ► Daily peak measures, however, were elevated at a central site near the freeway. ► Overnight/pre-dawn time period averages were elevated at a central site (SJVC). ► Residential pollen counts were lower than SJVC near agricultural tree production. ► Outdoor central site air quality alone insufficiently describes exposure in homes.
Keywords: Carbon dioxide; Near roadway measurements; Pollen; Particulate matter; Spatial heterogeneity;

Short term temporal variability in the photochemically mediated alteration of chromophoric dissolved organic matter (CDOM) in rainwater by Robert J. Kieber; Mary Beth Adams; Joan D. Willey; Robert F. Whitehead; G. Brooks Avery; Katherine M. Mullaugh; Ralph N. Mead (112-119).
The goal of the research presented here was to determine the impact of photochemistry on the abundance and spectral qualities of chromophoric dissolved organic matter (CDOM) in precipitation. The relationship between sunlight and CDOM in rainwater was complex with both production and photobleaching of optical properties occurring simultaneously in different regions of the fluorescence excitation emission spectra (EEMs) over relatively short time scales. Spectral slope was inversely correlated with the observed changes in total integrated fluorescence suggesting that photo-induced modifications in the molecular weight of CDOM were occurring along with fluctuations in its optical properties. Atmospheric condensate collected near a high traffic roadway had a response to sunlight similar to authentic rainwater suggesting some fraction of the CDOM in atmospheric waters is derived from local anthropogenic gas phase sources. There was a dramatic increase in fluorescence in two samples photolyzed with photosynthetically active radiation only (PAR; 400–700 nm) compared to analogous samples exposed to full spectrum sunlight indicating that this less energetic light is capable of producing photochemically labile compounds in rainwater. The observed temporal variability in the molecular level response of CDOM to sunlight is important because it may alter the spectral attenuation and the amount of solar radiation reaching the earth’s surface.► Photoproduction and bleaching of optical properties occur simultaneously in rainwater. ► Rainwater contains fluorescence in a region unique from surface waters or aerosols. ► Molecular weight changes in CDOM correlated with fluctuations in optical properties. ► PAR is capable of producing optically active compounds in rainwater. ► Some fraction of CDOM in rain is derived from local anthropogenic gas phase sources.
Keywords: Chromophoric dissolved organic matter; CDOM; Photochemistry; Rain;

Roadside vegetation barriers have been suggested as a potential mitigation strategy for near-road air pollution. However, there is still a lack of mechanistic understanding of how roadside barriers affect pollutant transport and transformation on and near roadways, especially under different meteorological conditions and barrier properties. In this study, we incorporated the representations of particle aerodynamics and deposition mechanisms into the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) model, and explored the effects of vegetation barriers on near-road particulate air pollution by comparing the simulation results against field measurements. The model shows generally adequate agreement with concentrations of particles larger than 50 nm, but tends to overpredict concentrations of particles less than 50 nm behind a vegetation barrier. Sensitivity tests were performed by comparing two different particle dry deposition models and varying the vegetation density and local meteorology. It was found that an increase in leaf area density (LAD) further reduces particle concentration, but the responses were non-linear. Increases in wind speed were shown to enhance particle impaction, but reduce particle diffusion, which result in reduction in concentration for particles larger than 50 nm but have a minimal effect on particles smaller than 50 nm. Further improvements in representing particle deposition and aerodynamics in near-road environments are needed to fully capture the complex effects of roadside vegetation barriers.► Particle size distributions behind a roadside vegetation barrier were modeled. ► The model shows adequate agreement with concentrations of particles >50 nm. ► The model tends to overpredict concentrations of praticles <50 nm. ► Further improvements in flow simulations and LAD representations are needed.
Keywords: Air quality; Aerosol; Vegetation; Dry deposition; Ecosystem services;

Hourly measurements of airborne particle number concentration (a metric dominated by ultrafine particles) at two sites in London and a site in Birmingham show that over a period of a few months in late 2007 concentrations were reduced by between 30 and 59%. At the London kerbside site particle number emissions from vehicles were reduced by 65% compared to emissions of NOx. These reductions occurred at the same time as the introduction of “sulphur free” diesel fuel and the London Low Emission Zone for heavy goods vehicles, and in view of the reduction in Birmingham and the limited change in vehicle technologies at that time, is probably primarily due to the change in fuel sulphur. There is an absence of any similar reduction in the concentration of the regulated air quality mass metrics which may provide an opportunity for further evaluating the effects of ultrafine particle concentrations on human health.► Time series of particle number counts measured at 3 sites from 2005 to 2010 were analysed. ► The time series show a marked reduction in concentration occurring in late 2007 which did not affect other pollutants. ► Changes in particle size distributions occurred at the same time. ► The reduction is attributed primarily to the introduction of sulphur free (<10 ppm) diesel fuel.
Keywords: Particulate matter; Particle number count; Sulphur free fuel; Low Emission Zone;

The immission and deposition levels of selected pollutants occurring in the area of a typical Polish village have been presented. In the course of a year-long research project (2009–2010), concentration levels of gaseous compounds in the air were determined (SO2, NO2, C6H6), as well as the level of solid particles deposition with the consideration of their chemical composition (Mn, Zn, Pb, Ni, Cd, Cu). Measurements were conducted in the area of rural settlements and at the site of plantation fields adjacent to the village. Classical analytical techniques (AAS, GC, IC) and biomonitoring with the use of mosses and lichens were used for the purposes of the study. Air quality in rural areas is determined mostly by the influence of the local sources (agricultural and uncontrolled emission) and that the quantity of toxicants enriching the environment depends on cyclical weather states periods characteristic for the temperate climate. The spatial location of the village and meteorological conditions conducive to the spread and dilution of pollutants. Average monthly and the average annual concentrations of the classic gaseous atmosphere quality indicators do not entail the atmosphere's serious degradation. The presence of heavy metals and size of their deposition in the dust have shown that air quality is not at a satisfactory level. The deposition of solid particles is determined by the partition in the formation of emissions between uncontrolled and agricultural sources. The major source of the gas pollutants is associated with uncontrolled emission from residential and farm buildings.► Long-term measurements of air quality in the rural area. ► Satisfactory air quality in the case of gaseous pollutants. ► Large particulate matter in the local troposphere. ► Gas pollutants mainly from residential and farm buildings. ► The partition in the formation of solid particles from both sources.
Keywords: Dust; Heavy metals; Gaseous pollutants; Biomonitoring; Passive samplers; Rural area;

Modeling air pollutant emissions from Indian auto-rickshaws: Model development and implications for fleet emission rate estimates by Andrew P. Grieshop; Daniel Boland; Conor C.O. Reynolds; Brian Gouge; Joshua S. Apte; Steven N. Rogak; Milind Kandlikar (148-156).
Chassis dynamometer tests were conducted on 40 Indian auto-rickshaws with 3 different fuel–engine combinations operating on the Indian Drive Cycle (IDC). Second-by-second (1 Hz) data were collected and used to develop velocity-acceleration look-up table models for fuel consumption and emissions of CO2, CO, total hydrocarbons (THC), oxides of nitrogen (NOx) and fine particulate matter (PM2.5) for each fuel–engine combination. Models were constructed based on group-average vehicle activity and emissions data in order to represent the performance of a ‘typical’ vehicle. The models accurately estimated full-cycle emissions for most species, though pollutants with more variable emission rates (e.g., PM2.5) were associated with larger errors. Vehicle emissions data showed large variability for single vehicles (‘intra-vehicle variability’) and within the test group (‘inter-vehicle variability’), complicating the development of a single model to represent a vehicle population. To evaluate the impact of this variability, sensitivity analyses were conducted using vehicle activity data other than the IDC as model input. Inter-vehicle variability dominated the uncertainty in vehicle emission modeling. ‘Leave-one-out’ analyses indicated that the model outputs were relatively insensitive to the specific sample of vehicles and that the vehicle samples were likely a reasonable representation of the Delhi fleet. Intra-vehicle variability in emissions was also substantial, though had a relatively minor impact on model performance. The models were used to assess whether the IDC, used for emission factor development in India, accurately represents emissions from on-road driving. Modeling based on Global Positioning System (GPS) activity data from real-world auto-rickshaws suggests that, relative to on-road vehicles in Delhi, the IDC systematically under-estimates fuel use and emissions; real-word auto-rickshaws consume 15% more fuel and emit 49% more THC and 16% more PM2.5. The models developed in this study can be used to further explore the impact of varying vehicle activity patterns on emissions in efforts to manage air quality and mitigate air pollution exposure and air pollution related health impacts.Display Omitted► Laboratory dynamometer tests of Indian three-wheelers measured real-time emissions. ► Testing captured real-world emission variability among and within vehicles. ► Models predicting vehicle emissions based on vehicle activity were developed. ► Models were evaluated using real-world vehicle activity data from Delhi. ► Fuel use and some emissions are underestimated by regulatory testing in India.
Keywords: Vehicle emissions model; Vehicle fleet; Megacity; Micro-scale; India; Particulate matter;

Temporal and spatial variation characteristics of atmospheric emissions of Cd, Cr, and Pb from coal in China by Hezhong Tian; Ke Cheng; Yan Wang; Dan Zhao; Long Lu; Wenxiao Jia; Jiming Hao (157-163).
Multiple-year inventory of atmospheric emissions of cadmium (Cd), chromium (Cr), and lead (Pb) from coal burning in China have been established for the period 1980–2008 by using best available emission factors and annual activity data which are specified by different sub-categories of combustion facilities, coal types, and air pollution control devices. Our results show that the total emissions of Cd, Cr, and Pb have rapidly increased from 31.14 t, 1019.07 t, and 2671.73 t in 1980 to 261.52 t, 8593.35 t, and 12 561.77 t in 2008, respectively. The industrial sector ranks as the leading source, contributing ∼88.3%, ∼86.7%, and ∼81.8% of the total Cd, Cr, and Pb emissions, respectively. Remarkably uneven spatial allocation features are observed. The emissions are primarily concentrated in the provinces of the northern and eastern region of China owing to the dramatic difference in coal use by the industrial and power sectors. Monthly temporal emission profiles for different sectors are established by using indexes such as monthly thermal electricity generation, monthly gross industrial output values and monthly average ambient temperature. For the power plants, there are two peaks during cold and hot season while for the industrial sector, emissions are most substantial in the summer and autumn season. Further, uncertainties in the bottom-up inventories are quantified by Monte Carlo simulation, and the overall uncertainties are demonstrated as −16% to 45% for Cd, −13% to 20% for Cr, and −21% to 48% for Pb, respectively. To better understand the emissions of these metals and to adopt effective measures to prevent poisoning, more specific data collection and analysis are necessary.► Atmospheric emission inventories of Cd, Cr, and Pb from coal in China are established. ► Cd, Cr, and Pb emissions are mainly concentrated in the Northern and Eastern region. ► Industrial coal burning contributes the largest proportion of Cd, Cr, and Pb emission. ► Monthly emission profiles for different sectors by regions show remarkable variation. ► Uncertainties in the inventory are quantified by bootstrap and Monte Carlo simulation.
Keywords: Cadmium; Chromium; Lead; Atmospheric emission inventory; Coal burning; Temporal and spatial distribution;

Summertime aerosol chemical composition in the Eastern Mediterranean and its sensitivity to temperature by Ulas Im; Kostas Markakis; Mustafa Koçak; Evangelos Gerasopoulos; Nikos Daskalakis; Nikolaos Mihalopoulos; Anastasia Poupkou; Tayfun Kındap; Alper Unal; Maria Kanakidou (164-173).
The impact of ambient temperature on the levels and chemical composition of aerosols over the Eastern Mediterranean in July 2004 is investigated using the WRF/CMAQ model system coupled with the MEGAN biogenic emissions model. CMAQ is able to capture the observed mean aerosol concentrations over the studied period. Non-sea-salt sulfate (nss-SO4 2−) is calculated to be the major aerosol component contributing by 63%, 16% and 40% to the fine (PM2.5), coarse (PM2.5–10) and total particulate matter mass (PM10), respectively. PM2.5 to PM10 mass ratios reach more than 80% over the large urban agglomerations but decrease to 45% at downwind locations suggesting coagulation and condensation on coarse particles. Higher temperatures increase biogenic emissions, enhance spatially-averaged biogenic secondary organic aerosol (SOA, by 0.01 ± 0.00 μg m−3 K−1) and nitrate (NO3 ) aerosol concentrations (by 0.02 ± 0.02 μg m−3 K−1). They reduce nss-SO4 2− (by −0.04 ± 0.07 μg m−3 K−1), induced by significant reduction in the cloud cover (90% K−1) and subsequent aqueous-phase production. The PM2.5 concentrations show a very small positive response to temperature changes, increasing by 0.003 ± 0.042 μg m−3 K−1 (0.04% K−1) due to the compensation of organic carbon increases by nss-SO4 2− reductions. Locally, larger changes are computed, with nss-SO4 2− and NO3 in fine aerosols reduced by up to 0.62 μg m−3 K−1 and 0.80 μg m−3 K−1, respectively. Increases as high as 0.097 μg m−3 K−1 and 0.034 μg m−3 K−1 are calculated for organic and elemental carbon, respectively. Results show that changes in temperature modify not only the aerosol mass but also its chemical composition.► PM2.5 to PM10 ratios decrease from >80% over the urban regions to 45% downwind. ► Organic aerosols dominate urban sites and inorganic aerosols downwind sites. ► Warmer temperatures enhance secondary organic aerosol and decrease sulfate. ► Small temperature response of PM2.5 due to organic and nss-sulfate changes. ► Significant geographical differences in temperature response of PM2.5 components.
Keywords: Aerosol chemical composition; Temperature change; Eastern Mediterranean; Megacity;

Influence of Asian outflow on Rishiri Island, northernmost Japan: Application of radon as a tracer for characterizing fetch regions and evaluating a global 3D model by Chunmao Zhu; Hisayuki Yoshikawa-Inoue; Hidekadzu Matsueda; Yosuke Sawa; Yosuke Niwa; Akira Wada; Hiroshi Tanimoto (174-181).
Atmospheric 222Rn was monitored from December 2008 to November 2010 on Rishiri Island (45°07′N, 141°12′E), northernmost Japan. Seasonal 222Rn variation was characterized by high concentrations from November to February and low concentrations from May to July, caused by the alternation of continental and maritime fetch regions. 222Rn tracer and back trajectory cluster analyses indicated that the predominant continental fetch region was southeastern Siberia and northeastern China. 222Rn emitted from China and South Korea, whose economies are growing rapidly, did not significantly affect the Rishiri site. The major maritime fetch region was the Sea of Okhotsk and the Bering Sea. A global three-dimensional model (NICAM-TM) accurately simulated 222Rn concentrations on Rishiri Island and in the seasonal fetch regions. The time series of 222Rn data will make it possible to evaluate the sources and sinks of atmospheric greenhouse gases being monitored at Rishiri Island, which complements other sites in the Asia–Pacific rim region, and to validate model simulations used to examine trans-boundary air pollution.► Use radon and back trajectory to estimate fetch regions at Rishiri Island. ► Predominant continental fetch regions are southeastern Siberia and northeastern China. ► The major maritime fetch regions are the Sea of Okhotsk and the Bering Sea. ► A global 3D model accurately simulated radon and seasonal fetch regions.
Keywords: Asian outflow; Fetch regions; Radon-222; Back trajectory analysis; Model evaluation;

Influence of continental outflow on aerosol chemical characteristics over the Arabian Sea during winter by Ashwini Kumar; A.K. Sudheer; Vineet Goswami; Ravi Bhushan (182-191).
The chemical composition of aerosol over the Arabian Sea was investigated during December 2007. Elemental Carbon (EC), Organic Carbon (OC), water soluble organic and inorganic constituents and crustal elements (Al, Fe, Ca, and Mg) were measured in total suspended particulate samples (TSP) collected from marine boundary layer of the Arabian Sea when the oceanic region is influenced by continental outflow. Anthropogenic and natural mineral aerosol originating from continental regions dominates the aerosol composition contributing ∼88% of total aerosol mass. The sea-salt aerosol comprises only ∼12% of TSP. The carbonaceous aerosol exhibits spatial trend similar to that of K+ suggesting major source could be biomass burning. Secondary organic aerosol (SOA) contribution estimated by EC-tracer method suggests that up to 67% of OC can be of secondary origin. Average water soluble organic carbon to OC ratio is ∼0.9, indicates significant formation of SOA during transport of continental air masses. These results demonstrate the dominance of continental aerosol over the Arabian Sea during wintertime where deposition may have major impact on surface ocean biogeochemistry.► Aerosol characteristics were studied over Arabian Sea during continental outflow. ► Continental aerosol dominates total measured aerosol mass (∼88%). ► The sea-salt aerosol comprises only ∼12%. ► Secondary organic carbon estimated up to 67% of total organic carbon.
Keywords: Arabian Sea; Marine aerosol; Elemental and organic carbon; Aerosol composition;

The Alaska-adapted WRF/Chem was used to examine the benefits of the proposed North American Emission Control Area (ECA) for air quality along the Alaska coasts. Simulations were performed alternatively assuming the emissions of 2000, and the emissions of 2000 reduced by the proposed ECA-reductions. In response to the emission reductions, reductions in sulfur (nitrogen) compounds reached up to 9 km (2 km) height. Reductions of sulfate- and nitrate-in-clouds were highest at the top of the atmospheric boundary layer. The strongest reductions occurred over the ECA and the international sea-lanes for sulfur- and nitrogen-compounds, respectively. Along the Gulf of Alaska, sulfur- and nitrogen-compound concentrations decreased significantly in response to the reduced ship-emissions. They decreased over Alaska despite of unchanged emissions in Alaska. PM2.5-speciation only marginally changed in response to the reduced ship-emissions.► ECA-related SO2- and NOx-ship-emission reductions improve air quality in Alaska. ► The PM2.5-speciation marginally changes in response to the reduced ship-emissions. ► Air quality in the Gulf of Alaska improves significantly due to ECA reduced ship-emission.
Keywords: Ship-emissions; Alaska; ECA; Air quality; Aerosols;

Very high levels of ambient particulate matter (PM) are frequently encountered in the north of Italy and air quality limits are regularly exceeded. To obtain quantitative information on the pollution sources and to gain understanding of the dynamics of pollution episodes in this populated area PM10 and/or PM2.5 samples were collected daily at nine urban to regional sites distributed over the central Po Plain and one site in the Valtelline Valley. In total, 23 five-week winter campaigns and one comparative summer/autumn campaign (2007–2009) were organized. The PM was analyzed for 61 chemical constituents and a data-base was built up consisting of approx. 70000 records of the concentrations and their associated uncertainty. In addition 14C/12C ratios were determined in PM10 from four sites.Primary and secondary sources were quantified using macro-tracer methods in combination with chemical mass balance modelling and positive matrix factorization and the combined results were computed by probability- and sensitivity analysis. Monte Carlo simulations yielded probability distributions for seven source categories contributing to the carbonaceous fraction of PM and five major source categories contributing to the PM10 and PM2.5 mass.Despite large uncertainties in the combined source contribution estimates the paper demonstrates that secondary aerosol formed simultaneously over the Po Plain is the main responsible for the typical, rapid build-up of air pollution after clean-air episodes. Next to secondary sources, the most important sources are primary emissions from road transport followed by biomass burning (BB). In the Valtelline Valley, higher contributions from BB and lower contributions from secondary sources were observed.► Source apportionment for PM10 and PM2.5 in North Italy during winter. ► Probabilistic uncertainties in the combined results were high. ► Secondary aerosol was the dominating source in the Po Plain (54–75%). ► Traffic was the highest primary source in the Po Plain (16–17%). ► Biomass burning was the second highest primary source in the Po Plain (10–12%).
Keywords: Source apportionment; Receptor models; Macro-tracers; 14C; Carbonaceous aerosol;

Products and mechanism of the reaction of Cl atoms with unsaturated alcohols by Ana Rodríguez; Diana Rodríguez; Amparo Soto; Iván Bravo; Yolanda Diaz-de-Mera; Alberto Notario; Alfonso Aranda (214-224).
The products of the chlorine atom initiated oxidation of different unsaturated alcohols were determined at atmospheric pressure and ambient temperature, in a 400 L teflon reaction chamber using GC–FID and GC–MS for the analysis. The major products detected (with molar yields in brackets) are: chloroacetaldehyde (50 ± 8%) and acrolein (27 ± 2%) from allyl alcohol; acetaldehyde (77 ± 11%), chloroacetaldehyde (75 ± 18%), and methyl vinyl ketone (17 ± 2%) from 3-buten-2-ol; acetone (55 ± 4%) and chloroacetaldehyde (59 ± 8%) from 2-methyl-3-buten-2-ol; chloroacetone (18 ± 1%) and methacrolein (8 ± 1%) from 2-methyl-2-propen-1-ol; acetaldehyde (20 ± 1%), crotonaldehyde (6 ± 3%), 3-choloro-4-hydroxy-2-butanone (2 ± 2%) and 2-chloro-propanal (4 ± 5%) from crotyl alcohol; and acetone (24 ± 3%) from 3-methyl-2-buten-1-ol. The experimental data suggests that addition of Cl to the double bond of the unsaturated alcohol is the dominant reaction pathway compared to the H-abstraction channel.► Atmospheric degradation of different unsaturated alcohols with Cl atoms is investigated using smog chamber/GC techniques. ► The identified and quantified gas-phase products were mainly carbonyl compounds. ► The addition of Cl to the double bond of the unsaturated alcohol is the dominant reaction pathway. ► The H-abstraction channel cannot be excluded.
Keywords: Chlorine atoms; Unsaturated alcohols; Reaction products; Gas phase mechanism;

Fractionation of secondary organic carbon in aerosol in relation to the trafficborne emission of semivolatile organic compounds by Zang-Ho Shon; Ki-Hyun Kim; Sang-Keun Song; Young-Zoo Chae; Chan Goo Park; Kweon Jung (225-233).
The environmental behavior of particle-bound secondary organic carbon (SOC) was investigated with respect to its fractionation at four urban sites in Seoul, a megacity in Korea from Feb to Dec 2009. Empirical estimates of SOC formation were comparatively evaluated using the multiple linear regression and constrained mass balance (i.e., CO and EC tracers) methods. The SOC fraction estimates were significantly different depending on the applied methods. The multiple linear regression method used for the estimation of SOC fraction was more reliable than the constrained mass balance approach due to the limited number of available daily PM measurement during each season. Seasonal and spatial patterns in the SOC fractions were examined at the four urban sites. Seasonally averaged SOC fractions ranged from 15 to 65% of the total organic carbon concentration. According to this study, the SOC fractions were significantly high in the spring and summer relative to other seasons.► In this study, the fraction of SOC was quantified based on empirical methods. ► Method was developed by considering the major ionic compositions in 4 urban sites. ► SOC fractions were affected directly by photochemical oxidations of VOC.
Keywords: Secondary organic carbon; Multiple linear regression; CO tracer; EC tracer; Seoul;

Aerosol optical and radiative properties during summer and winter seasons over Lahore and Karachi by Khan Alam; Thomas Trautmann; Thomas Blaschke; Hussain Majid (234-245).
The study of aerosol optical and radiative properties presented here focuses on a geographic region in which there exist significant gaps in our knowledge. These properties have been analyzed through the ground-based Aerosol Robotic Network (AERONET) over the two megacities of Lahore and Karachi for summer (April–June) and winter (December–February) of 2010–11. During the study period the monthly mean aerosol optical depth (AOD) at 500 nm over Lahore ranged from 0.57 ± 0.18 to 0.76 ± 0.38, and the monthly mean Ångström exponent (<alpha>) ranged from 0.39 ± 0.17 to 1.22 ± 0.13. Likewise, over Karachi the monthly mean AOD ranged from 0.33 ± 0.11 to 0.63 ± 0.28 and the <alpha> values varied between 0.29 ± 0.08 to 0.95 ± 0.22. The average AOD values in summer and winter are 0.66 ± 0.30, 0.50 ± 0.18 and 0.67 ± 0.40, 0.34 ± 0.12 in Lahore and Karachi respectively. The relationship between the Absorption Ångström Exponent (AAE) and the Extinction Ångström Exponent (EAE) provided an indication of the relative proportions of urban-industrial and mineral dust aerosols over the two sites. The volume size distributions were higher over Lahore than over Karachi during both seasons. The single scattering albedo (SSA) ranged from 0.83 ± 0.02 (440 nm) to 0.91 ± 0.05 (1020 nm) over Lahore and from 0.88 ± 0.02 (440 nm) to 0.97 ± 0.01 (1020 nm) over Karachi. The lower SSA values over Lahore suggest that absorbing aerosols are more dominant over Lahore than over Karachi. The average aerosol radiative forcing (ARF) values in summer at the surface and the top of atmosphere (TOA) are −101.6 ± 8.2, −63.3 ± 9.5 and −19 ± 4.35, −20 ± 3.1 over Lahore and Karachi respectively. Likewise, the average ARF values in winter at the surface and TOA are −90.3 ± 21.03, −57 ± 6.35 and −26 ± 7, −16 ± 2.3 over Lahore and Karachi respectively. The averaged aerosol ARF values over Lahore and Karachi for the entire period covered by the observations were −22.5 ± 5.9 W m−2 and −18 ± 2.2 W m−2 at the TOA and −96 ± 13 W m−2 and −60 ± 6.8 W m−2 at the surface, respectively, giving an averaged atmospheric forcing of 74.56 ± 16.8 W m−2 over Lahore and 41.85 ± 6.4 W m−2 over Karachi, which indicates significant heating of the atmosphere at both sites. The average heating rate during summer was 2.3 ± 0.1 and 1.2 ± 0.2 K day−1 and during winter was 1.8 ± 0.4 and 1.1 ± 0.1 K day−1 over Lahore and Karachi respectively.► For the first time aerosol optical properties have analyzed in two cities of Pakistan. ► AAE vs. EAE provide an indication of urban-industrial and mineral dust aerosols. ► SSA and RI values suggest that anthropogenic aerosols are dominated at Lahore than at Karachi. ► Large differences between surface and TOA forcing reveal significant heating in the atmosphere. ► The AERONET-SBDART correlation coefficients are 0.99 for Lahore and 0.98 for Karachi.
Keywords: Aerosol optical depth; Ångström exponent; SSA; Radiative forcing; Lahore; Karachi;

Spectral dependency of light scattering/absorption and hygroscopicity of pollution and dust aerosols in Northeast Asia by Sihye Lee; Soon-Chang Yoon; Sang-Woo Kim; Yong Pyo Kim; Young Sung Ghim; Ji-Hyoung Kim; Chang-Hee Kang; Young Joon Kim; Lim-Seok Chang; Suk-Jo Lee (246-254).
Ground-based in-situ measurements were performed to investigate the spectral optical properties and hygroscopicity of light scattering and absorbing aerosols in pollution and dust plumes in Northeast Asia. The scattering Ångström exponents of pollution plumes are high, ranging from 0.8 to 1.8, because light scattering aerosols consist of relatively fine particles such as sulfate, nitrate, ammonium and carbonaceous particles. Pollution case having high organic carbon (OC) exhibits a relatively high absorption Ångström exponent (AAE), in the range of 1.0–1.5 due to the absorption by refractory OC at near-UV spectral region. Among the different pollution cases, the AAE is the highest in a polluted dust plume; this can be attributed to the strong wavelength dependence of light absorption by dust particles. The mass absorption cross section (MAC), which represents the ability of light-absorbing aerosols to absorb a photon, is 4.2–8.3 m2 g−1, and it is high when black carbon is mixed with OC and dust particles. The MAC decreases with increasing relative humidity, especially for pollution plume with a high OC content and for dust plume. Under humid conditions, hygroscopic chemical species can absorb water vapor, thus growing in size and enhancing aerosol light scattering, but the MAC decreases because of the possible shielding effects of absorbing aerosols with water uptake.► Pollution case having high OC exhibits a high absorption Ångström exponent. ► Mass absorption cross section is the highest when BC is mixed with dust particles. ► Mass absorption cross section decreases with increasing RH. ► Absorbing aerosols can cause the shielding effects with water uptake.
Keywords: Light-absorbing aerosol; Organic carbon; Mass absorption cross section; Relative humidity;

The Upper Green River Basin (UGRB) in Wyoming experiences ozone episodes in the winter when the air is relatively stagnant and the ground is covered by snow. A modeling study was carried out to assess relative contributions of oxides of nitrogen (NOx) and individual volatile organic compounds (VOCs), and nitrous acid (HONO) in winter ozone formation episodes in this region. The conditions of two ozone episodes, one in February 2008 and one in March 2011, were represented using a simplified box model with all pollutants present initially, but with the detailed SAPRC-07 chemical mechanism adapted for the temperature and radiation conditions arising from the high surface albedo of the snow that was present. Sensitivity calculations were conducted to assess effects of varying HONO inputs, ambient VOC speciation, and changing treatments of temperature and lighting conditions. The locations modeled were found to be quite different in VOC speciation and sensitivities to VOC and NOx emissions, with one site modeled for the 2008 episode being highly NOx-sensitive and insensitive to VOCs and HONO, and the other 2008 site and both 2011 sites being very sensitive to changes in VOC and HONO inputs. Incremental reactivity scales calculated for VOC-sensitive conditions in the UGRB predict far lower relative contributions of alkanes to ozone formation than in the traditional urban-based MIR scale and that the major contributors to ozone formation were the alkenes and the aromatics, despite their relatively small mass contributions. The reactivity scales are affected by the variable ambient VOC speciation and uncertainties in ambient HONO levels. These box model calculations are useful for indicating general sensitivities and reactivity characteristics of these winter UGRB episodes, but fully three-dimensional models will be required to assess ozone abatement strategies in the UGRB.► A detailed analysis of the “winter ozone problem”. ► Application of maximum incremental VOC reactivity to ozone formation. ► Upper Green River Basin (UGRB) of Wyoming, large natural gas-producing area.
Keywords: Winter ozone; Natural gas production; Incremental VOC reactivity; Upper Green River Basin; SAPRC-07 mechanism;

Integrated single particle-bulk chemical approach for the characterization of local and long range sources of particulate pollutants by Beatrice Moroni; David Cappelletti; Fabio Marmottini; Francesco Scardazza; Luca Ferrero; Ezio Bolzacchini (267-277).
The feasibility of an integrated approach based on multivariate statistical analysis and individual particle micro-analyses to characterize airborne particulate matter (PM) sampled at urban and regional background sites was tested. The proposed methodology encompasses data from ICP–AES, GC–MS and SEM–EDS analyses on ground and vertical profile PM samples.Source apportionment analysis of bulk chemical data allowed the identification and quantification of five distinct source categories for the fine and coarse particle size ranges. Results of quantitative phase analysis were included in the statistical investigation in order to correlate type and relevance of PM sources with relative abundance and texture of particles at ground level. Results were finally evaluated in the light of back-trajectory calculations and atmospheric vertical profile measurements. This approach allowed to discriminate between local from Saharan dust crustal contributions, and urban from regional secondary aerosol anthropogenic inputs.► Combined bulk and SEM–EDS chemical analyses of ground and tethered balloon PM samples. ► Statistical treatment of the results by PCA/APCS and cluster analysis. ► Discrimination between local sources and long range dust intrusions. ► Significant contribution by Saharan and secondary aerosol dust intrusions to total PM. ► Reconstruction of the pattern and dynamic evolution of the lower troposphere.
Keywords: Airborne dust; Multivariate source apportionment (PCA/APCS); SEM–EDS; Image analysis; Tethered balloon sampling; Saharan/NE-Europe dust intrusions;

Chemical composition and size distribution of airborne particulate matters in Beijing during the 2008 Olympics by Xingru Li; Lili Wang; Yuesi Wang; Tianxue Wen; Yongjie Yang; Yanan Zhao; Yingfeng Wang (278-286).
Size-segregated aerosol samples were collected daily in Beijing from 1 Jun. to 20 Sep. during the Beijing Olympic Games in 2008 to investigate aerosol concentrations, particle size distributions, and sources as well as the effects of pollution control measures on the chemical compositions (including Water-soluble ions, trace elements, elemental carbon (EC), and organic carbon (OC)) in aerosols of different sizes. Water-soluble ions, EC, OC, and trace elements accounted for 45.0%, 1.6%, 14.7%, and 11.4% of the total particle mass (PM), respectively. Approximately 56%, 56%, 30%, 71% and 55% of the PM, water-soluble ions, trace elements, EC and OC, respectively, were associated with particles smaller than 2.1 μm. Sulfate, nitrate, and ammonium were the dominant ions, which together accounted for approximately 77% of total water-soluble ions. The crustal elements accounted for the majority of the trace elements present. Different sources showed different mass size distributions. Anthropogenic source compounds, such as sulfate, nitrate, ammonium, OC, EC, and toxic elements, were mainly present in fine mode aerosols, whereas crustal elements, such as Al, Fe, Ca, Mg and Ba, primarily occurred in the coarse mode. SO 4 2 − and NH 4 + concentrations were strongly correlated (r 2 = 0.90, slope = 1.63) in the fine mode, thereby indicating that SO 4 2 − was mainly present as (NH4)2SO4; in contrast, a weak correlation between SO 4 2 − and NH 4 + (r 2 = 0.18, slope = 0.54) was observed in the coarse mode, indicating that SO 4 2 − was associated with other ions. Similarly, SO 4 2 − and NO 3 − exhibited a stronger correlation in the fine mode than in the coarse mode, indicating that SO 4 2 − and NO 3 − were formed via the same in-cloud processes in fine particles. The OC/EC ratio and the correlations between EC and OC concentrations showed that the sources of carbonaceous species were secondary organic carbon from fine particles and the long-range transport of coarse carbonaceous particles from biomass burning. The concentrations of atmospheric pollutants declined during the 2008 Olympic Games, indicating that the pollution control measures were effective in decreasing particulate air pollution in Beijing.► The concentrations of atmospheric particulate matters, water-soluble ions, trace elements, EC and OC were studied. ► The size distributions of those compounds were discussed. ► The correlations between Sulfate and Ammonium, Sulfate and Nitrate were studied to research the source of those secondary inorganic ions. ► The ratios and correlation of OC and EC were discussed to research the source of carbonaceous. ► The effects of pollution control measures on air pollution were discussed.
Keywords: Chemical compositions; Mass size distribution; Source; Pollution control measures;

An elevation-based regional model for interpolating sulphur and nitrogen deposition by Jiří Kopáček; Maximilian Posch; Josef Hejzlar; Filip Oulehle; Alena Volková (287-296).
We developed and tested a regression model, interpolating long-term sequences of observed atmospheric deposition of SO4 2−, NO3 , and NH4 + in the upper Vltava river catchment (Czech Republic) to its three sub-regions, differing in elevation and forest cover. The model provides more realistic estimates of wet and total S and N depositions and their inter-annual variability in the study catchment than the available European deposition sequences, especially in the case of wet S deposition prior to 1997. In the model, ion fluxes are calculated as the product of the precipitation volume and ion concentrations, which both are derived as empirical functions of elevation and time. The long-term sequences of ion concentrations are based on measured deposition data at 19 stations and their relationships with central European emission trends of SO2, NOx, and NH3 for years with no measurements. Exponential relationships between elevation and precipitation volume (positive) and elevation and ion concentrations (negative) are used to convert the long-term sequences of precipitation and concentrations into values for individual elevations. Throughfall fluxes (TF) of S and N in the forest areas are calculated from their fluxes in precipitation (PF), using long-term sequences of TF:PF ratios, based on measured fluxes and the S and N emission trends. The calculated fluxes of S and reactive nitrogen (NO3–N and NH4–N) explain 80% and 56% of the variability in their measured fluxes, respectively, along an elevation gradient from 275 to 1334 m.► We developed a model, converting average trends in S and N deposition to sub-regions. ► Deposition fluxes in the model are functions of elevation, forest cover, and time. ► The model was compared with measured data and EMEP deposition trends. ► The model can provide detail input data to other models (e.g., MAGIC or INCA-N).
Keywords: Atmospheric deposition; Sulphur; Nitrogen; Vltava river;

In the early fall of 2010 a survey questionnaire was conducted to assess residential wood combustion (RWC) practices in the 18 districts of mainland Portugal. This paper describes and analyses the results from a bottom-up approach, based on this telephone survey, which enabled the characterisation of RWC practices in each district. Additionally, emission factors and source profiles obtained from different RWC tests, allowed the estimation of CO, CO2, PM2.5 and particulate organic compound emissions on a country-scale. The type and number of RWC appliances, each with their specific emissions factor and the amount and type of fuel used vary significantly on a district scale. The energy consumption in RWC appliances was estimated to be 35 342 TJ y−1. The estimated emissions of PM2.5 from RWC in Portugal (10.96 kt y−1) represent 30% of the estimate for different source activities reported in a recent inventory. The national emissions of OC and EC were estimated to be 5.32 and 0.53 kt y−1, respectively. It was also estimated that the total CO2 emissions from RWC in Portugal are 1.7 Mt y−1. The levoglucosan emissions contribute with between 7.8% and 16.1% of PM2.5 emissions from RWC.► RWC is one of the largest sources of fine particle emissions in Portugal. ► An assessment of RWC practices was made through a national scale survey. ► Total of wood used in Portugal in 2010 was 1.95 Mt for heating and cooking purposes. ► The estimated emissions of PM2.5 from RWC in Portugal were 10.96 kt y−1. ► The global levoglucosan emissions for Portugal were estimated to be 1.2 kt y−1.
Keywords: Survey questionnaire; Wood species; Burning appliances; Emission factors; Inventory;

Sensitivity of hazardous air pollutant emissions to the combustion of blends of petroleum diesel and biodiesel fuel by Kento T. Magara- Gomez; Michael R. Olson; Tomoaki Okuda; Kenneth A. Walz; James J. Schauer (307-313).
Emission rates and composition of known hazardous air pollutants in the exhaust gas from a commercial agriculture tractor, burning a range of biodiesel blends operating at two different load conditions were investigated to better understand the emission characteristics of biodiesel fuel. Ultra-Low Sulfur Petroleum Diesel (ULSD) fuel was blended with soybean oil and beef tallow based biodiesel to examine fuels containing 0% (B0), 50% (B50) and 100% (B100) soybean oil based biodiesel, and 50% (B50T) and 100% (B100T) beef tallow biodiesel. Samples were collected using a dilution source sampler to simulate atmospheric dilution. Particulate matter and exhaust gases were analyzed for carbonyls, Volatile Organic Compounds (VOCs), and Polycyclic Aromatic Hydrocarbons (PAHs) to determine their respective emission rates. This analysis is focused on the emissions of organic compounds classified by the US EPA as air toxics and include 2,2,4 trimethylpentane, benzene, toluene, ethylbenzene, m-, p- and o-xylene, formaldehyde, acetaldehyde and methylethyl ketone. Emission rates of 2,2,4 trimethylpentane, toluene, ethylbenzene, m-, p- and o-xylene decreased more than 90% for B50, B100 and B100T blends; decreases in emission rates of benzene, formaldehyde and acetaldehyde were more modest, producing values between 23 and 67%, and methyl ethyl ketone showed decreases not exceeding 7% for the studied biodiesel blends. PAHs emission rates were reduced by 66% for B50, 84% for B100, and by 89% for B100T. The overall emissions of toxic organic compounds were calculated and expressed as benzene equivalents. The largest contributors of toxic risk were found to be formaldehyde and acetaldehyde. Reductions in formaldehyde emissions were 23% for B50 and 42% for B100 soybean, and 40% for B100T beef tallow compared to B0. Similarly, acetaldehyde reductions were 34% for B50 and 53% for B100 soybean biodiesel and 42% for B100T beef tallow biodiesel.► We evaluate the sensitivity of HAP emissions to blends of diesel and biodiesel fuels. ► Hazardous air pollutant emissions decrease with increasing content of biodiesel. ► Acetaldehyde and formaldehyde are the main contributors to toxicity of diesel exhaust.
Keywords: Hazardous air pollutants; Biodiesel; Benzene; Acetaldehyde; Formaldehyde; Toxicity;

Long term monitoring of the chemical composition of precipitation and wet deposition fluxes over three Sahelian savannas by D. Laouali; C. Galy-Lacaux; B. Diop; C. Delon; D. Orange; J.P. Lacaux; A. Akpo; F. Lavenu; E. Gardrat; P. Castera (314-327).
The purpose of this study is to analyze a long term database of the chemical composition of precipitation at three African dry savanna sites in the Sahel. The precipitation samples were collected during the monsoon season at Agoufou (15°20′N, 01°29′W, Mali) from 2004 to 2006, Banizoumbou (13°31′N, 02°38′E, Niger) from 1994 to 2009 and Katibougou (12°56′N, 07°32′ W, Mali) from 1997 to 2008. pH and major inorganic and organic ions in precipitation were analyzed by ionic chromatography. A characterization of mean precipitation chemistry with the associated wet deposition fluxes for each species is presented. The first important result is that interannual variability of all volume-weighted mean (VWM) concentrations is low, ranging between ±5% and ±25%. Acidity in dry savannas is low and indicates the strong alkaline nature of the precipitation. The average annual pH at Agoufou is 6.28, 5.75 at Banizoumbou and 5.54 at Katibougou. This result is correlated with the important terrigenous contribution measured in the chemical content of precipitation, implying acidity neutralization by mineral species such as Ca2+ and NH4 +. Mg2+ and K+ are found to play a minor role in neutralization. Enrichment factor calculations for Ca2+, SO4 2−, K+ and Mg2+ with respect to the sea reference reveal a significant influence of Saharan and Sahelian crustal sources. VWM concentrations of these species dominate the composition of measured precipitation. An estimation of the potential particulate and gas contribution to the total precipitation composition is given for each site: At Agoufou, the mean relative contribution in rainwater is 80% for particles and 20% for gases, while at the Banizoumbou and Katibougou sites, results indicate 70% for particles and 30% for gases. The high particulate phase contribution to precipitation emphasizes the importance of multiphase processes between gases and particles in the atmospheric chemistry typical of African semi-arid savanna ecosystems. The second highest contribution is nitrogenous, with high VWM concentrations of NO3 and NH4 + measured at the three sites. Monthly evolution of NO3 and NH4 + concentrations are studied in relation to gaseous emission sources in the Sahelian region, i.e. biogenic soil emission and ammonia sources from animals. The calculated wet nitrogen deposition flux presents a regular increase throughout the wet season at the three sites. Results suggest total mean nitrogen deposition fluxes of 1.80 kg N ha−1 yr−1 at Agoufou, 2.10 kg N ha−1 yr−1 at Banizoumbou, and 3.30 kg N ha−1 yr−1 at Katibougou. The marine contribution is lower, 23% at Agoufou, 17% at Banizoumbou and 13% at Katibougou. The last contribution concerns organic acidity, which ranges from 5% at Agoufou, 10% at Banizoumbou to 14% at Katibougou. Terrigenous and marine contributions present a negative gradient, whereas nitrogenous and organic contributions a positive gradient along the Sahelian transect defined by Agoufou–Banizoumbou–Katibougou.► Analysis of quality controlled rain chemical data for three sahelian savannas in Africa. ► Characterization of mean precipitation chemistry composition for each chemical species. ► Characterization of mean deposition fluxes for each chemical species. ► Interannual and seasonal variability of concentrations and deposition. ► Focus on nitrogen deposition fluxes in Sahelian ecosystems.
Keywords: African semi-arid ecosystems; Mineral species; Nitrogenous compounds; Neutralization factor; Atmospheric chemistry; Sahelian savannas;

The relationship between aviation activities and ultrafine particulate matter concentrations near a mid-sized airport by Hsiao-Hsien Hsu; Gary Adamkiewicz; E. Andres Houseman; Jose Vallarino; Steven J. Melly; Roger L. Wayson; John D. Spengler; Jonathan I. Levy (328-337).
Aircraft contribute to emissions of ultrafine particulate matter (UFP) and other air pollutants, with corresponding impacts on community-level exposures near active airports. However, it is challenging to isolate the contribution of aircraft from local road traffic and other nearby combustion sources. In this study, we used high-resolution monitoring and flight activity data to quantify contributions from landing and take-off operations (LTO) to UFP concentrations. UFP concentrations were monitored with 1-min resolution at four monitoring sites surrounding T.F. Green Airport in Warwick, RI, in three one-week campaigns across different seasons in 2007 and 2008. Along with pollutant monitoring, wind data were collected and runway-specific LTO data were obtained from airport officials. We developed regression models in which wind speed and direction were included as a nonparametric smooth spatial term using thin-plate splines applied to wind velocity vectors and fitted using linear mixed models. To better pinpoint the timing in the LTO cycle most contributing to elevated concentrations, we used regression models with lag terms for flight activity (ranging from 5 min before to 5 min after the departure or arrival). Results suggest positive associations between UFP concentrations and LTO activities, especially for departures when an aircraft moves near or passes a monitoring site. Departures of jet engine aircrafts on a runway proximate to one of the monitors have a maximal impact 1 min prior to take-off, with median absolute contributions during those minutes of 7400 particles cm−3 (range: 1100–70,000 particles cm−3). Across all observations, our models indicate median (95th, 99th percentile) percent contribution for all LTO activities of 9.8% (54%, 72%) and 6.6% (39%, 55%) for the two sites proximate to the airport's principal runway, and 4.7% (24%, 36%) and 1.8% (22%, 31%) for the remaining two sites. Our analysis illustrates the complexity of aviation impacts on local air quality and allows for quantification of the marginal contribution of LTO activity relative to other nearby sources.► Aircraft contribute to emissions of ultrafine particulate matter (UFP). ► We use monitoring data and flight activity to quantify UFP contributed by aircraft. ► Wind speed/direction and flight activity lag terms predict measured concentrations. ► Aircraft contribute 15–30% of UFP near-airport fenceline during operating hours. ► Regression models of continuous monitoring data can inform source attribution.
Keywords: Air quality; Aircraft; Ground measurements; Regression; Source attribution; Ultrafine particulate matter;

Analysis of heavy pollution episodes in selected cities of northern China by Dongsheng Ji; Yuesi Wang; Lili Wang; Liangfu Chen; Bo Hu; Guiqian Tang; Jinyuan Xin; Tao Song; Tianxue Wen; Yang Sun; Yuepeng Pan; Zirui Liu (338-348).
The analysis of air pollution episodes greatly aids in understanding air pollution and formulating policies to improve air quality. In this study, variations in the distribution of PM10 concentrations were analyzed using data collected from the air quality monitoring network in northern China set up by the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP, CAS) and the air quality monitoring network of the Beijing Municipal Environmental Protection Bureau (BJEPB). The results showed that there were two severe regional PM10 pollution episodes recorded from October 27, 2009, to November 10, 2009. During these pollution episodes, the highest daily PM10 concentration reached 600 μg m−3 in Shijiazhuang, which is far above the daily PM10 limit of 150 μg m−3. These aerosol pollution episodes were accompanied by regional haze and low visibility ranges. Synoptic patterns and long-range transport were the main factors controlling the regional air pollution processes. Transport patterns affected by synoptic cycle resulted in the spatial and temporal variations of PM10 and PM2.5 during the period studied. Conditions with light winds, temperature inversion and low mixed layer heights contributed to the buildup of PM10 and PM2.5 as well as gas-to-particle processing. In Beijing, the concentrations of sulfate and nitrate accounted for ∼1/3 of the PM10 mass and ∼2/3 of the PM2.5 mass, part of which is attributed to the additional secondary conversion of SO4 2− from SO2 and NO3 from NOx during high-pollution days. Stationary anthropogenic sources were still a major contributor to pollution in these two episodes based on the NOx/SO2 ratios. To address regional air pollution, more attention should be paid to the increases in emissions and the higher frequency of haze days, which are associated with degraded visibility, that have accompanied the rapid economic development in northern China.► Two severe regional PM10 pollution episodes were recorded in northern China. ► The highest daily mean concentration of PM10 reached 600 μg m−3 in Shijiazhuang. ► These two episodes were accompanied by regional haze and low visibility ranges. ► Region-wide anthropogenic features and the transport patterns affected by synoptic cycle resulted in the severe episodes.
Keywords: PM10; PM2.5; Northern China; Air pollution episodes; Temperature inversion;

The chemical composition of surface snow in the Arctic: Examining marine, terrestrial, and atmospheric influences by Laura Krnavek; William R. Simpson; Daniel Carlson; Florent Domine; Thomas A. Douglas; Matthew Sturm (349-359).
We collected surface snow samples during three years (2004, 2005, and 2007) in Arctic Alaska and from the adjoining frozen Arctic Ocean during springtime in environments that span most Arctic terrains including land, thin and thick first-year sea ice, and multi-year sea ice. The snow was analyzed for Br, Cl, SO4 2−, NO3 , NH4 +, Na+, K+, Mg2+ and Ca2+. Source fractionation processes and atmospheric influences are important modification mechanisms that influence the ions. We find that Cl, K+ and Mg2+ are primarily sourced by unfractionated sea salt and only show deviations from sea salt composition at low Na+ concentrations. Bromide and Ca2+ are highly influenced by atmospheric processes that are evident at low sea salt tracer concentrations. Calcium enrichments are due to the addition of non-sea salt (nss) Ca2+ from dust and possibly other sources. Bromide enrichments are due to the addition of nss-Br and bromide depletions are due to bromine activation to the gas phase. Sulfate is affected by source fractionation at high Na+ concentrations and by atmospheric addition at low Na+ concentrations. Nitrate and NH4 + are not correlated with sea salt and show less concentration variability than sea salt ions. Modifications are related to time-integrated air–snow exchange fluxes for Br, SO4 2− and Ca2+ and are in good agreement with observations of related gas-phase and aerosol species. This work reinforces our understanding of air–snow exchanges and their importance for atmospheric chemistry in the Arctic.► Surface snow composition was measured in 936 samples from 4 arctic environments. ► Air–snow exchange and source fractionation are modify snow composition. ► Correlation plots to sea salt tracer elucidate dominant modification mechanisms. ► Time-integrated snow–air fluxes are consistent with atmospheric measurements.
Keywords: Snow; Chemical composition; Ionic composition; Fractionation; Sea salt; Air–snow flux;

Multi-decadal variation of the net downward shortwave radiation over south Asia: The solar dimming effect by H.D. Kambezidis; D.G. Kaskaoutis; Shailesh Kumar Kharol; K. Krishna Moorthy; S.K. Satheesh; M.C.R. Kalapureddy; K.V.S. Badarinath; Anu Rani Sharma; M. Wild (360-372).
The solar radiation flux at the earth's surface has gone through decadal changes of decreasing and increasing trends over the globe. These phenomena known as dimming and brightening, respectively, have attracted the scientific interest in relation to the changes in radiative balance and climate. Despite the interest in the solar dimming/brightening phenomenon in various parts of the world, south Asia has not attracted great scientific attention so far. The present work uses the net downward shortwave radiation (NDSWR) values derived from satellites (Modern Era Retrospective-analysis for Research and Applications, MERRA 2D) in order to examine the multi-decadal variations in the incoming solar radiation over south Asia for the period of 1979–2004. From the analysis it is seen that solar dimming continues over south Asia with a trend of −0.54 Wm−2 yr−1. Assuming clear skies an average decrease of −0.05 Wm−2 yr−1 in NDSWR was observed, which is attributed to increased aerosol emissions over the region. There is evidence that the increase in cloud optical depth plays the major role for the solar dimming over the area. The cloud optical depth (MERRA retrievals) has increased by 10.7% during the study period, with the largest increase to be detected for the high-level (atmospheric pressure P < 400 hPa) clouds (31.2%). Nevertheless, the decrease in solar radiation and the role of aerosols and clouds exhibit large monthly and seasonal variations directly affected by the local monsoon system, the anthropogenic and natural aerosol emissions. All these aspects are examined in detail aiming at shedding light into the solar dimming phenomenon over a densely populated area.► The net downward shortwave radiation over south Asia is used in this study for the period 1979–2004. ► The multi-decadal variation in the incoming solar radiation over the area is investigated. ► The solar dimming effect seems to continue over south Asia with a trend of −0.54 W m−2 yr−1. ► The increase in cloud optical depth seems to play major role for the solar dimming effect over the area.
Keywords: Solar dimming; NDSWR; MERRA; South Asia; Aerosols;

Lord Kelvin (William Thomson) made careful, calibrated measurements of the atmospheric Potential Gradient (PG) at three sites on the east side of Arran in 1859. The PG was always anomalously high in easterly and north-easterly winds. Positive space charge from sea spray may have contributed to the high PG at two coastal sites, but measurements made on Goatfell, inland and 100–175 m above sea level are unlikely to have been affected by spray. Instead, pollution from the Scottish mainland seems the more likely cause of the high PG at Goatfell, which varied from 300 to 1000 Vm−1 on 10th–11th October 1859, corresponding to smoke levels from 0.2 to 0.8 mgm−3. Gaussian plume calculations, based on the atmospheric conditions described by Lord Kelvin, and constrained by early Glaswegian pollution measurements, indicate a substantial source region located on the Scottish mainland, 20–40 km from Arran, emitting between 10–104  kg s−1.
Keywords: Black carbon; Smoke proxy; Lord Kelvin; Historical pollution; Aerosol; Atmospheric electricity;

Sensitivity of desert dust emissions to model horizontal grid spacing during the Bodélé Dust Experiment 2005 by Christel Bouet; Guy Cautenet; Gilles Bergametti; Béatrice Marticorena; Martin C. Todd; Richard Washington (377-380).
The impact of model horizontal grid spacing on meteorology and dust emissions in the Bodélé depression was investigated during the well-documented period of the Bodélé Dust Experiment 2005 (BoDEx 2005). Five horizontal grid spacing ranging from 100 km to 5 km were tested. The main conclusion of these sensitivity tests is that the meteorology of the Bodélé depression is quite insensitive to model horizontal grid spacing below 50 km in agreement with Todd et al.'s (2008b) results. Below 50 km, dust emissions also appear relatively insensitive to model mesh size, the influence of model horizontal grid spacing on dust emissions tending towards an asymptotic behavior as model mesh size is reduced.
Keywords: Bodélé depression; Mesoscale modeling; Model horizontal grid spacing; Desert dust;

Kalman filter-based air quality forecast adjustment by Koen De Ridder; Ujjwal Kumar; Dirk Lauwaet; Lisa Blyth; Wouter Lefebvre (381-384).
We evaluate a Kalman Filter (KF) based adaptive regression method for the correction of deterministic air quality forecasts. In this method, corrected forecast concentrations are obtained by linear regression, using the free model forecast values as predictors, and estimating the regression coefficients dynamically by means of the KF technique. Basically, this method exploits the information regarding the mismatch between the deterministic forecast and observations of the prior period to calculate regression coefficients for the correction of the next forecast step.We considered model output generated by the deterministic regional air quality model AURORA over northern Belgium for the year 2007, together with observed values at a few tens of stations. It was found that, for daily mean PM10 concentrations, and averaged over the monitoring stations, the correction scheme reduced the root mean square error from 15.9 to 10.5 μg m−3, largely thanks to the bias reduction from 8.8 to 0.5 μg m−3. The correlation coefficient increased from 0.65 to 0.73. For daily maximum O3 concentrations, the root mean square error was reduced from 25.9 to 17.2 μg m−3, the bias from 7.9 to 0.2 μg m−3, and the correlation coefficient increased from 0.60 to 0.79.We also implemented a non-adaptive linear regression scheme to the same data. It was found that the adaptive regression method outperformed this simpler scheme consistently, demonstrating the relevance of the dynamic KF-based method for use in the correction of deterministic air quality forecasts.
Keywords: Air quality; Deterministic forecast; Kalman filter; Adaptive regression;

New Directions: Adapting air quality management to climate change: A must for planning by A.R. Ravishankara; John P. Dawson; Darrell A. Winner (387-389).
While adaptation to climate change is primarily thought of as a water, weather, and infrastructure issue, air quality and air quality management are important aspects of climate change adaptation. Air quality and climate change are so heavily intertwined that air quality needs to be considered not only for mitigation strategies but also in management of and adapting to climate change.
Keywords: Climate change; Adaptation; Air quality;