Atmospheric Environment (v.46, #C)

Despite direct and indirect evidence suggesting that heterogeneous surfaces potentially play a key role in mercury chemistry, there is little known about mercury reactions and equilibrium processes that take place at atmospherically relevant surfaces. The lack of knowledge of mercury surface chemistry is a major gap for adequate modeling of mercury cycling. In part I of this review, we assessed the sources of uncertainty associated with existing kinetic parameters. In this part, we present evidence that supports surface–mercury interactions in the ecosystem elucidating the importance of heterogeneous and interfacial chemistry from a fundamental viewpoint. Consequently, we draw attention to the chemical processes that are missing and/or are inadequately incorporated in the atmospheric mercury models and highlight some of the recent advances in this field. We reveal that adsorption equilibrium of mercury species, most of which are not well characterized, to natural surfaces such as atmospheric particles and air/water interface are not known. Gas–liquid partitioning of mercury and its compounds are not adequately implemented. Equilibrium constants for aqueous phase complex formation with dissolved organic matters and formation of possible solid mercury clusters and nanoparticles are not considered in the global models. Potential heterogeneous mercury reduction reactions that can be important in mercury cycling require further evaluation which includes characterizing the influence of surfaces on mercury chemistry. The implementation of chemical processes for which information is available but not currently included in the models bears the potential of greatly reducing the uncertainties that are currently present in the models.► Numerous evidence of mercury–surface interactions exist. ► The lack of knowledge of mercury surface chemistry adds to uncertainty in mercury modeling. ► Mercury species, phase transition, and complex and solid formation are not well characterized. ► Aerosols, DOM, ice, snow packs, and vegetation surfaces influence mercury chemistry. ► Potential mercury reduction reactions important in mercury cycling are discussed.
Keywords: Mercury cycling; Mercury speciation; Mercury complexes Uncertainties; Heterogeneous chemistry Adsorption; Aerosols; Surface reaction; Aqueous reduction;

The Aggregate Risk Index: An intuitive tool providing the health risks of air pollution to health care community and public by Pierre Sicard; Charles Talbot; Olivia Lesne; Antoine Mangin; Nicolas Alexandre; Rémy Collomp (11-16).
In the framework of the European project PASODOBLE (FP7), we set up downstream information services by combining environmental and health data with a view to support the health care community and to improve vulnerable people welfare. Indeed there is a profound relationship between human health, well-being and air pollution levels. The main objectives are to establish correlations between air quality, exposure of populations and their reactivity, to develop and validate air quality indexes and to construct a prediction model of this sanitary index. This index will be implemented on 3 European sites: Greece (Athens and Thessaloniki), the Netherlands and “Provence Alpes Côte d’Azur” (South East of France). The selected region and cities are among the most affected by the atmospheric pollution in Europe and leads to serious sanitary concerns. The service aims to provide up-to-date, detailed information on air quality discomfort. The Aggregate Risk Index is based on the Cairncross’s concept, obtained from the Relative Risk associated with short-term exposure to common air pollutants and takes into account the possible effects of a mixture of pollutants. This communication tool, easy to use and intuitive, about the levels of air pollution and the associated health risks, will be used to communicate information to the general population, authorities and to the health care community and will provide advanced warning of potentially health-damaging air pollution events.► We discuss plausible air quality impacts on human health. ► We develop a tool to allow an assessment of additive effects of air pollutants and associated risks. ► We develop a communication tool easy to use and intuitive on the air quality impacts on health.
Keywords: Aggregate Risk Index; ARI; Air quality; Health; Pasodoble; Relative risk;

Wintertime PM2.5 concentrations during persistent, multi-day cold-air pools in a mountain valley by Geoffrey D. Silcox; Kerry E. Kelly; Erik T. Crosman; C. David Whiteman; Bruce L. Allen (17-24).
In January and February 2011, PM2.5 concentrations in residential and nonresidential areas of Salt Lake City, Utah, were elevated during days with persistent multi-day stable layers or cold-air pools (CAPs). Under most conditions the PM2.5 concentrations and atmospheric stability increased with time during these events, so that the highest PM2.5 concentrations were observed in long-lived CAPs. PM2.5 concentrations were generally observed to decrease with increasing elevation and were linearly related to the pre-sunrise valley heat deficit, an instantaneous measure of atmospheric stability. Decreases of up to 30 percent were observed as elevation increased from 1300 to 1600 m. During the CAP episode of 23–30 January, concentrations of PM2.5 increased roughly linearly with time at all elevations at the rate of about 6 μg (m3 day)−1. Higher elevation sites also experienced more rapid influxes of clean air during the mix-out of a CAP on 16 January, although short-lived episodes of higher concentrations occurred at times when polluted air was carried upslope from the residual CAP that persisted at lower elevations.► Series of persistent cold-air pools (CAP) formed in Salt Lake Valley 1 Jan - 20 Feb 2011. ► PM2.5 concentrations increased with time and CAP strength. ► Within CAPs, ground-level PM2.5 concentrations decreased with altitude. ► During 23–30 Jan CAP, rate of increase in PM2.5 concentration was linear at 6 μg (m3 day)−1. ► Breakup of CAP on 16 Jan 2011 occurred first at higher elevations.
Keywords: PM2.5; Altitude; Cold-air pools; Temperature inversions; Mix-out; Utah; Salt Lake Valley;

Number particle concentrations and fluxes were measured, synchronously with CO2 concentrations and fluxes, in an urban area. Measurements were taken with an eddy-correlation station located near the busiest road of the town of Lecce (Italy). Upward fluxes dominate completely over deposition and the area behaved as a source of aerosol and CO2 with an average particle flux FN  = 71,100 #/cm2 s (median 64,000 #/cm2 s) and an average CO2 flux FC  = 0.76 mg/m2 s (median 0.46 mg/m2 s). Pronounced diurnal and weekly cycles of FN and FC were observed, well correlated with measured traffic rate, TR , indicating that traffic is the main source of CO2 and particles in the area. Biogenic cycle on CO2 fluxes and concentrations was also distinguishable, decreasing the correlation between FN and FC . The relationships between particle and CO2 fluxes with TR , friction velocity and atmospheric stability were analysed. Measured FN /TR increased when friction velocity increased and, correspondingly, number concentration decreased. Particle fluxes showed a dependence on the atmospheric stability. These dependencies were used to derive an empirical parameterisation of aerosol concentration and fluxes, based on TR and micrometeorological parameters, that could be used to estimate traffic emissions, in real operating conditions, for applications in dispersion and climate modelling. Measured FC /TR showed a limited correlation with friction velocity and stability, because of the influence of the biogenic cycle, thereby micrometeorological parameters were not used in the parameterisation of FC .► Particle number and CO2 concentrations and fluxes were measured in an urban area. ► The urban area is a net source of traffic related particles and CO2. ► Daily cycles of concentrations and fluxes are correlated to vehicular traffic rate. ► The influence of micrometeorological parameters on fluxes was parameterised. ► CO2 and particle average emissions of vehicles fleet were estimated.
Keywords: Number particle flux; CO2 flux; Urban pollution; Eddy-correlation; Urban aerosol; Traffic emissions;

Simulated nitrogen inputs influence methane and nitrous oxide fluxes from a young larch plantation in northern Japan by Yong Suk Kim; Masakazu Imori; Makoto Watanabe; Ryusuke Hatano; Myong Jong Yi; Takayoshi Koike (36-44).
Future increases in nitrogen (N) deposition have the potential to change underground nutrient dynamics in forest ecosystems and alter the soil–atmosphere exchange of greenhouse gases (GHGs), such as methane (CH4) and nitrous oxide (N2O). To clarify changes in soil CH4 and N2O fluxes following N application, N input was initiated at the onset of our experiment and included two treatments (0 and 50 kg N m−2  yr−1) with four replicates in a young larch plantation in northern Japan. The N was added as an ammonium nitrate (NH4NO3) solution and distributed four times per year during two growing seasons. Soil GHG fluxes and soil variables were determined on ten occasions during a period that spanned the two growing seasons. Before the N application, no significant differences were observed in any of the soil variables between the two treatments. Ammonium–N (NH4–N) and nitrate–N (NO3–N) concentrations increased immediately after N applications in the 50 kg-N addition plot. With an increasing pool of inorganic-N, we found that soil CH4 uptake in the 50 kg-N addition plot decreased by 48% when compared to the Zero-N control plot. In particular, reduced CH4 uptake or CH4 emissions were observed in 50 kg-N addition soils immediately after N input events. Moreover, N inputs increased soil N2O emissions by an average of 69% in the 50 kg-N addition plot compared to the control during two growing seasons. At this experimental site, a negative spatial relationship was observed between soil CH4 uptake and the NH4–N concentration, and a positive spatial relationship was seen between soil N2O emissions and the NO3–N concentration, despite high inherent spatial variability in the soil CH4 flux. Overall, these results suggest that N deposition-induced increases in the availability of inorganic-N in the soil may affect processes linked to CH4 and N2O dynamics in cool-temperate forest soils, at least over the short term.► Simulated N application was conducted in a young larch plantation in northern Japan. ► Nitrogen inputs increased NH4–N and NO3–N concentrations in soil. ► Increased soil NH4–N concentration reduced soil CH4 uptake. ► Increased soil NO3–N concentration stimulated soil N2O emission.
Keywords: Nitrogen deposition; CH4; N2O; Soil GHG fluxes; Forest soil;

On-road diesel vehicle emission factors for nitrogen oxides and black carbon in two Chinese cities by Xing Wang; Dane Westerdahl; Jingnan Hu; Ye Wu; Hang Yin; Xiaochuan Pan; K. Max Zhang (45-55).
Nitrogen oxides (NO x ) and black carbon (BC) emission factors (EF) of 440 on-road diesel trucks were determined by conducting on-road chasing studies in Beijing and Chongqing, China, in the winter 2010. NO x and BC EF distributions are reported. The median NO x EFs for trucks sampled on level roads in Chongqing and Beijing are 40.0 and 47.4 g kg-fuel−1, respectively. The median BC EFs are 1.1 and 0.4 g kg-fuel−1in Chongqing and Beijing, respectively. In addition, a clear downward trend of BC EFs of on-road diesel trucks sampled in Beijing since 2008 is observed. Moreover, Beijing-registered trucks had the lowest BC EFs among the entire sample. These observations appear to reflect the effectiveness of emission standard and fuel quality standard implemented in Beijing (China IV) and nationwide (China III) in reducing BC (and likely overall particulate matter) emission. However, NO x EFs for Beijing-registered trucks did not show lower value than those from other regions. Unlike black carbon, there is no clear correlation between emission controls and NO x emissions from the sampled on-road trucks. Further analysis shows that trucks with high BC EFs do not usually have high NO x EFs, and vice versa, indicating that the current emission standards implemented in Beijing and nationwide have only limited impact on NO x emissions control. Therefore, effective multi-pollutant control strategies and in-use compliance programs are imperative to reduce the overall emissions from the transportation sector.► Over 400 on-road diesel trucks were sampled in Beijing and Chongqing, China. ► The NO x and black carbon (BC) emission factors of those 400 trucks were derived. ► The improved emissions and fuel standards are effective in reducing BC emissions. ► In contrast, we did not observe significant reduction in NO x emissions.
Keywords: Emission factor; Diesel; Climate change; Air pollution; Nitrogen oxides; Black carbon;

Long-term recovery of lakes in the Adirondack region of New York to decreases in acidic deposition by Kristin Waller; Charles Driscoll; Jason Lynch; Dani Newcomb; Karen Roy (56-64).
After years of adverse impacts to the acid-sensitive ecosystems of the eastern United States, the Acid Rain Program and Nitrogen Budget Program were developed to control sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions through market-based cap and trade systems. We used data from the National Atmospheric Deposition Program’s National Trends Network (NTN) and the U.S. EPA Temporally Integrated Monitoring of Ecosystems (TIME) program to evaluate the response of lake-watersheds in the Adirondack region of New York to changes in emissions of sulfur dioxide and nitrogen oxides resulting from the Acid Rain Program and the Nitrogen Budget Program. TIME is a long-term monitoring program designed to sample statistically selected subpopulations of lakes and streams across the eastern U.S. to quantify regional trends in surface water chemistry due to changes in atmospheric deposition. Decreases in wet sulfate deposition for the TIME lake-watersheds from 1991 to 2007 (−1.04 meq m−2-yr) generally corresponded with decreases in estimated lake sulfate flux (−1.46 ± 0.72 meq m−2-yr), suggesting declines in lake sulfate were largely driven by decreases in atmospheric deposition. Decreases in lake sulfate and to a lesser extent nitrate have generally coincided with increases in acid neutralizing capacity (ANC) resulting in shifts in lakes among ANC sensitivity classes. The percentage of acidic Adirondack lakes (ANC <0 μeq L−1) decreased from 15.5% (284 lakes) to 8.3% (152 lakes) since the implementation of the Acid Rain Program and the Nitrogen Budget Program. Two measures of ANC were considered in our analysis: ANC determined directly by Gran plot analysis (ANCG) and ANC calculated by major ion chemistry (ANCcalc = C B − C A). While these two metrics should theoretically show similar responses, ANCcalc (+2.03 μeq L−1-yr) increased at more than twice the rate as ANCG (+0.76 μeq L−1-yr). This discrepancy has important implications for assessments of lake recovery and appears to be due to compensatory increases in concentrations of naturally occurring organic acids coincident with decreases in lake concentrations of strong acid anions, as evidenced by increases in concentrations of dissolved organic carbon.► Recovery of Adirondack lakes from acid rain. ► Effectiveness of air quality management programs. ► Comparison of findings with other studies.
Keywords: Acid neutralizing capacity; Acid rain program; Adirondacks; Atmospheric deposition; Sulfate; TIME;

Occurrence, speciation and bioaccessibility of lead in Chinese rural household dust and the associated health risk to children by Zhixuan Han; Xiangyang Bi; Zhonggen Li; Wenlin Yang; Lixing Wang; Huan Yang; Fanglin Li; Zhendong Ma (65-70).
Lead (Pb) concentration, speciation and bioaccessibility were measured in 122 household dust samples collected in rural areas of eight provinces of China. The mean Pb concentration in the household dust was 208 mg kg−1, of which samples from sites in Hunan (538 mg kg−1) and Yunnan (280 mg kg−1) provinces exhibited the highest Pb concentrations while those from Shaanxi (96 mg kg−1) and Fujian (80 mg kg−1) provinces had a relatively low Pb content. The major fraction of Pb in the household dust samples was found to be strongly bound to Fe–Mn oxide phases (37%) while Pb present in minor fractions individually making up between 14 and 18% was characterized in falling orders as residual, carbonate, organic/sulphide, and exchangeable fractions by the sequential extraction method applied. Bioaccessible Pb making up an average proportion of 53% in the household dusts was significantly correlated to the Fe–Mn oxide phases of Pb. According to the Hazard Quotient (HQ), the ingestion of dust particles pose the highest risk to children in Chinese rural areas, followed by dermal contact and inhalation. Hazard Index (HI) values for most samples were lower than 1, indicating that the domestic Pb exposure in rural areas of China were relatively safe for children when they exposure to the household dust. However, dust Pb in 4.1% of the studied families having HI values higher than 1 may pose adverse health effect to the children.► Lead concentration, speciation and bioaccessibility in household dusts from Chinese rural areas were investigated. ► Pb in the household dusts was mainly associated with Fe–Mn oxides phase. ► The Fe–Mn oxides phase of Pb in the dusts contributed predominantly to the bioaccessible Pb pools. ► Ingestion of dust particles was the main route of children exposure to dust Pb and could result in a high risk.
Keywords: Lead (Pb); Household dust; Chinese rural area; Health risk;

A computational fluid dynamics (CFD) model that includes the carbon bond mechanism IV (CBM-IV) is developed and used to investigate reactive pollutant dispersion in and above a street canyon with an aspect ratio of 1. Fourteen emission scenarios of NOx and volatile organic compounds (VOCs) are considered. Dispersion types are classified into NO-type, NO2-type, and O3-type dispersion that exhibit concentration maxima at the street bottom, near the center of the street canyon, and above the street canyon, respectively. For the base emission scenario, the number of reactive species is 9 in the NO-type dispersion, 10 in the NO2-type dispersion, and 15 in the O3-type dispersion. As the NOx emission level decreases or the VOC emission level increases, some species in the O3-type dispersion are shifted to the NO2-type dispersion. The VOC-to-NOx emission ratio is found to be an important factor in determining the transition of dispersion type. In this transition process, OH plays a key role through a radical chain including HO2, RO, and RO2. Because of their high OH reactivities, XYL (xylene) and OLE (olefin carbon bond) among VOCs are largely responsible for the transition of dispersion type. The O3 sensitivity is examined by reducing NOx or VOC emission level by a half. Because the NO titration of O3 is more pronounced than the NO2 photolysis and the radical chain process in the street canyon, the O3 concentration therein is negatively correlated with the NOx emission level and weakly correlated with the VOC emission level. As a result, the street canyon is a negatively NOx-sensitive regime.► A CFD model coupled with the CBM-IV is developed. ► Dispersion types are classified into NO-type, NO2-type, and O3-type dispersion. ► The transition of dispersion type depends on the NOx-to-VOC emission ratio. ► OH is important through a radical chain (HO2, RO, and RO2) in the transition process. ► The street canyon is a negatively NOx-sensitive regime.
Keywords: Street canyon; CFD model; CBM-IV; VOC-to-NOx emission ratio; Dispersion type; O3 sensitivity;

Ammonia and hydrogen sulfide are hazardous substances that are regulated by the U.S. Environmental Protection Agency through community right-to-know legislation (EPCRA, ). The emissions of ammonia and hydrogen sulfide from large commercial layer facilities are of concern to legislators and nearby neighbors. Particulate matter (PM10 and PM2.5) released from layer houses are two of seven criteria pollutants for which EPA has set National Ambient Air Quality Standards as required by the Clean Air Act. Therefore, it is important to quantify the baseline emissions of these pollutants. The emissions of ammonia, hydrogen sulfide, carbon dioxide and PM from two California high-rise layer houses were monitored for two years from October 2007 to October 2009. Each house had 32,500 caged laying hens. The monitoring site was setup in compliance with a U.S. EPA-approved quality assurance project plan. The results showed the average daily mean emission rates of ammonia, hydrogen sulfide and carbon dioxide were 0.95 ± 0.67 (standard deviation) g d−1 bird−1, 1.27 ± 0.78 mg d−1 bird−1 and 91.4 ± 16.5 g d−1 bird−1, respectively. The average daily mean emission rates of PM2.5, PM10 and total suspended particulate (TSP) were 5.9 ± 12.6, 33.4 ± 27.4, and 78.0 ± 42.7 mg d−1 bird−1, respectively. It was observed that ammonia emission rates in summer were lower than in winter because the high airflow stabilized the manure by drying it. The reductions due to lower moisture content were greater than the increases due to higher temperature. However, PM10 emission rates in summer were higher than in winter because the drier conditions coupled with higher internal air velocities increased PM10 release from feathers, feed and manure.► The pollutants from two layer houses were continuously monitored for two years. ► Emission rate of ammonia was 0.95 g d−1 bird−1. ► Emission rate of PM10 was 33.4 mg d−1 bird−1. ► Ammonia emission rates in summer were lower than in winter. ► PM10 emission rates in summer were higher than in winter.
Keywords: Gases; Continuous monitoring; Sampling system; Concentration; Ventilation; Pollutant emission rate;

The present study estimates the temporal variability of the anthropogenic heat flux density (Q F) for three common land use types found in Singapore between October 2008 and March 2009. Q F is estimated by separately considering the major sources of waste heat in urban environments, which are heat release from vehicular traffic, buildings and human metabolism, respectively. The individual components of Q F are calculated by using a combination of top-down and bottom-up modelling approaches of energy consumption applied to the local context. Results show that over a 24-h period, magnitudes of mean hourly Q F reach maximum values of 113 W m−2 in the commercial, 17 W m−2 in the high-density public housing and 13 W m−2 in the low-density residential areas, respectively. Buildings are found to be the major source of anthropogenic heat (primarily related to space cooling) in each study area, contributing to between 49–82% of Q F on weekdays and 46–81% on weekends. The spatial and temporal variations of Q F are attributed to differences in traffic volume, building energy consumption and population density. This is one of the first anthropogenic heat studies carried out in a tropical city and the results show that Q F can be substantial and of the same order of magnitude as calculated for city centres in mid-latitude cities during winter time.► The anthropogenic heat flux density (Q F) was estimated for different land uses in Singapore. ► The largest mean hourly Q F estimate (113 W m−2) was found in the commercial area. ► Building-related emissions related to air-conditioning were the dominant contributor to anthropogenic heat. ► A distinct diurnal and weekly variability in the Q F estimates was observed.
Keywords: Anthropogenic heat; Waste heat; Energy use; Tropical urban climate; Singapore;

Cloud water composition over the southeastern Pacific Ocean during the VOCALS regional experiment by Katherine B. Benedict; Taehyoung Lee; Jeffrey L. Collett (104-114).
Relatively few measurements exist of cloud water composition over the open ocean, despite the importance of clouds as processors of atmospheric aerosols and trace gases in such regions. In order to improve understanding of cloud water composition in the southeast Pacific, and to determine the capacity of regional clouds for aqueous sulfate production, cloud water was collected aboard the NCAR C-130 during VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment) in October and November, 2008. A total of 72 cloud water samples were collected on 14 flights using the NCAR/CSU airborne cloud water collector. Cloud water samples were collected over a region extending from approximately 71–85° west and from approximately 18–30° south. Cloud water pH ranged from 2.9 to 7.2 with an average of 4.3. Samples were also analyzed for major inorganic ions, hydrogen peroxide, sulfur(IV), carboxylic and dicarboxylic acids, formaldehyde, total Fe and Mn, and total organic carbon. Sodium and chloride were the most abundant solutes, while organic matter was found to contribute only 12%, on average, of the total measured solute load. Cloud water and trace gas measurements aboard the aircraft were used to examine the importance of various oxidation pathways for in-cloud sulfate production. S(IV) oxidation by H2O2 was found to be the most important pathway and excess cloud water H2O2 concentrations revealed considerable potential for additional, rapid in-cloud sulfate production by this mechanism. S(IV) oxidation by ozone was important when cloud water pH climbed above 5.5 and was the fastest oxidation pathway 24% of the time.► A unique set of cloud water composition observations was made over the southeast Pacific. ► Cloud water pH ranged from 2.9 to 7.2 with an average of 4.3. ► Cloud water composition was dominated by sea salt components. ► Other important inputs were from sulfate, nitrate, ammonium, and organic matter. ► H2O2 was found to be the most important oxidant for in-cloud sulfate production.
Keywords: Sulfur oxidation; Cloud chemistry; Southeast Pacific; Chile;

Processes affecting concentrations of fine particulate matter (PM2.5) in the UK atmosphere by Roy M. Harrison; Duncan Laxen; Stephen Moorcroft; Kieran Laxen (115-124).
PM2.5 is now subject to a limit value and exposure-reduction targets across the European Union. This has led to a rapid expansion in PM2.5 monitoring across Europe and this paper reviews data collected in the United Kingdom in 2009. The expected gradient between rural, urban background and roadside sites is observed, although the roadside increment is generally rather small except for heavily trafficked street canyon locations. PM2.5:PM10 ratios decline from around 0.8 in southeast England to below 0.6 in Scotland consistent with a higher contribution of secondary particulate matter in southeast England. Average diurnal profiles of PM2.5 differ around the UK but have a common feature in a nocturnal minimum and a peak during the morning rush hour. Central and southern UK sites also show an evening peak following a concentration reduction during the mid afternoon which is not seen at northern UK sites and is attributed to evaporation of semi-volatile components, particularly ammonium nitrate. Concentrations of PM2.5 are typically highest in the winter months and lowest in the mid-summer consistent with better mixing and volatilisation of semi-volatile components in the warmer months of the year. Directional analysis shows a stronger association of PM2.5 with easterly winds associated with air masses from the European mainland than with the direction of local traffic sources.► Data from across the UK for 2009 are presented. ► Gradient observed between roadside, urban background and rural sites. ► PM2.5–PM10 ratios decline from SE to NW across Great Britain. ► Highest average concentrations at background sites are associated with easterly air masses and not nearby roads.
Keywords: Particulate matter; PM2.5; Diurnal variations; Polar plots;

Laboratory study of the effect of oxalic acid on the cloud condensation nuclei activity of mineral dust aerosol by Kelly M. Gierlus; Olga Laskina; Tricia L. Abernathy; Vicki H. Grassian (125-130).
Dicarboxylic acids, which make up a significant portion of the atmospheric organic aerosol, are emitted directly through biomass burning as well as produced through the oxidation of volatile organic compounds. Oxalic acid, the most abundant of the dicarboxylic acids, has been shown by recent field studies to be present in mineral dust aerosol particles. The presence of these internally mixed organic compounds can alter the water absorption and cloud condensation nuclei (CCN) abilities of mineral particles in the Earth’s atmosphere. The University of Iowa’s Multi-Analysis Aerosol Reactor System (MAARS) was used to measure the CCN activity of internally mixed particles that were generated from a mixture of either calcite or polystyrene latex spheres (PSLs) in an aqueous solution of oxalic acid. Although PSL is not a mineral dust component, it is used here as a non-reactive, insoluble particle. CCN measurements indicate that the internally mixed oxalate/calcite particles showed nearly identical CCN activity compared to the original calcite particles whereas oxalic acid/PSL internally mixed particles showed much greater CCN activity compared to PSL particles alone. This difference is due to the reaction of calcite with oxalic acid, which produces a relatively insoluble calcium oxalate coating on the particle surface and not a soluble coating as it does on the PSL particle. Our results suggest that atmospheric processing of mineral dust aerosol through heterogeneous processes will likely depend on the mineralogy and the specific chemistry involved. Increase in the CCN activity by incorporation of oxalic acid are only expected for unreactive insoluble dust particles that form a soluble coating.► Oxalic acid, the most abundant of the dicarboxylic acids, can be present in dust aerosol and impact the properties of dust. ► Heterogeneous processes of mineral dust with oxalic acid will depend on mineralogy. ► Impact of oxalic acid on dust properties depends on mineralogy. ► CCN activity of oxalate/calcite particles were similar to the unreacted calcite particles. ► CCN activity increases when the particle is unreactive and insoluble.
Keywords: Cloud chemistry; Mineral dust; Oxalic acid; CCN activity;

Bacterial pathogens in airborne particulate matter (PM) and in rainwater (RW) were detected using a robust and sensitive Real-Time PCR method. Both RW and PM were collected simultaneously in the tropical atmosphere of Singapore, which were then subjected to analysis for the presence of selected bacterial pathogens and potential pathogen of health concern (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Aeromonas hydrophila). These pathogens were found to be prevalent in both PM and RW samples with E. coli being the most prevalent potential pathogen in both types of samples. The temporal distribution of these pathogens in PM and RW was found to be similar to each other. Using the proposed microbiological technique, the atmospheric deposition (dry and wet deposition) of bacterial pathogens to lakes and reservoirs can be studied in view of growing concerns about the outbreak of waterborne diseases.► A sensitive RT-PCR method was employed for assessment of bacterial pathogens. ► Bacterial pathogens in rainwater and aerosols were studied. ► The prevalence of pathogens increased in air during the biomass burning period.
Keywords: Aerosols; Air quality; Bioaerosols; Pathogens; Rainwater;

Spatial distribution and magnification processes of mercury in snow from high-elevation glaciers in the Tibetan Plateau by Jie Huang; Shichang Kang; Qianggong Zhang; Matt G. Jenkins; Junming Guo; Guoshuai Zhang; Kang Wang (140-146).
The Tibetan Plateau is one of the most extreme cold regions in the world and a source of fresh water to 1.4 billion people. In this study, between 2008 and 2010, surface snow samples were retrieved in replicate from four high-elevation glaciers with an average elevation of 5200 m above sea level from the Tibetan Plateau and were analyzed for total Hg (HgT). The spatial distribution of Hg for glaciers and magnification processes of Hg in snow with increasing altitude over the Tibetan Plateau are investigated. The total Hg concentrations in snow samples ranged from <1 to 15 ng L−1, with the highest concentrations at Mt. Muztagata (8.56 ng L−1), and the lowest concentrations at Mt. Nyainqêntanglha (0.90 ng L−1). This may be explained by the high concentration and annual flux of particulate matter deposition at Mt. Muztagata, the maximum from which particulate matter loads decrease from northwest to southeast over the Tibetan Plateau. Because Hg deposited on the plateau is primarily associated with particulate matter, only 31% of Hg was lost (e.g., reemitted back to the atmosphere) during the transition of fresh snow to coarse-grained snow. This demonstrates that Hg in snow over the Tibetan Plateau may be less influenced by the effect of post-depositional processes such as reemission and photoreduction than that in the Arctic. Moreover, the increases of HgT with increasing altitude (“altitude effect”) found on four high-elevation glaciers (e.g., 3-fold in Mt. Muztagata) suggests that atmospheric Hg is cold-trapped and magnified toward low temperature and/or high-elevation regions, implying that the glaciers over the Tibetan Plateau play an important sink role for global Hg cycling. In the context of a warming climate, the Tibetan Plateau may shift from a current sink to a source in the future, and the released Hg may endanger the ecosystems and human health of these snow-fed regions.► The HgT concentrations in the surface snow of four typical glaciers were very low. ► Hg in snow may be less influenced by effect of post-depositional processes. ► The increasing trend in HgT with altitude was found on four high-elevation glaciers. ► The glaciers over the high-elevation regions may play a sink role for atmospheric Hg.
Keywords: Mercury; Snow; Cold-trapping; Glaciers; Tibetan Plateau;

Polycyclic aromatic hydrocarbons in background air in central Europe – Seasonal levels and limitations for source apportionment by Alice Dvorská; Klára Komprdová; Gerhard Lammel; Jana Klánová; Helena Plachá (147-154).
Positive matrix factorization (PMF) was applied on a large dataset of polycyclic aromatic hydrocarbon (PAH) concentrations determined in air at the central European background monitoring site Košetice, Czech Republic. The long-term (1996–2009) PAH median concentration in Košetice is about 6 times higher during winter than summer months. As the source apportionment of these pollutants is accompanied by concerns regarding the loss of the source signature during atmospheric transport, PMF was run on two winter PAH concentration data subsets stratified according to different ambient levels of oxidants. It is suggested, that the typical ambient air PAH pattern is largely preserved on a regional transport scale in winter in central Europe. However, the allocation of PMF model factors to particular PAH source categories (e.g., road traffic, residential wood combustion, residential and industrial coal combustion) could not be achieved due to (a) a high similarity of reference PAH profiles among each other and (b) variability in ambient reference PAH profiles. It is suggested, that the commonly studied set of EPA PAHs is not source category specific and thus not suitable for source apportionment. PAH source apportionment using more specific PAH and non-PAH markers is recommended.► Winter PAH levels are 6 times higher than summer levels in background central Europe. ► On the regional scale the ambient air PAH pattern is preserved in winter. ► The commonly studied set of EPA PAHs is not source category specific. ► EPA PAHs are not suitable for source apportionment.
Keywords: Polycyclic aromatic hydrocarbons; Source apportionment; Positive matrix factorization; Background site; Degradation;

Forecasting size-fractionated particle number concentrations in the urban atmosphere by Bjarke Mølgaard; Tareq Hussein; Jukka Corander; Kaarle Hämeri (155-163).
Airborne particulate matter affects human health, especially in urban areas where air pollutant concentrations are high. In order to reduce exposure to particulates and other pollutants it is essential to forecast concentrations of these. In this work we introduce a statistical model to forecast size-fractionated particle number concentrations. Our forecasting approach is based on a parametric regression model that utilises traffic intensity and meteorological parameters as covariates and has an autoregressive dependence structure for the error terms. We use a Bayesian framework with a Markov Chain Monte Carlo (MCMC) implementation to derive the forecasts numerically from a given set of learning data. The particle concentration forecast is provided as probability distributions for a few days ahead. For the development and test of the model we used weather and particle size distribution data from an urban background station in Helsinki, and traffic data. Comparison of forecast distributions and measurements shows that the adopted probabilistic characterisation of particle number concentrations is adequate. In particular, forecasts of the log number concentration of ultra-fine particles (diameter < 100 nm) for the upcoming day have R 2 equal to 0.67 (at 3 h time resolution). Our model is flexible and it may be implemented for other urban locations, provided that measurements of number concentrations, as well as measurements and forecasts of covariates are available.► Development of a statistical forecast model for particle number concentrations. ► Bayesian inference for the probability distributions. ► Model evaluation against long-term aerosol data in the urban background of Helsinki.
Keywords: Forecast; Aerosol; Number concentration; Statistics; Bayesian learning;

Ultrahigh-resolution FT-ICR mass spectrometry characterization of α-pinene ozonolysis SOA by Annie L. Putman; John H. Offenberg; Rebeka Fisseha; Shuvashish Kundu; Thom A. Rahn; Lynn R. Mazzoleni (164-172).
Secondary organic aerosol (SOA) of α-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were identified over the mass range of 100–850 u. Hydroxyl radicals formed during the ozonolysis of α-pinene might be expected to alter the composition of SOA, however a majority of the molecular formulas were identified in all three experiments and with a few exceptions they had similar relative abundances. Thus, the detailed composition of SOA was only slightly influenced by the presence or absence of hydroxyl radical scavenging hexane. The negative-ion mass spectra of the SOA contained four groups of peaks with increasing mass spectral complexity corresponding to increasing molecular weight. The mean values of O:C decreased from 0.55 to 0.42 with increasing molecular weight, but the mean value of H:C, approximately 1.5, did not change with increasing molecular weight. The molecular formulas with the highest relative abundances in Groups I and II contained 5–7 and 7–10 oxygen atoms and 3–4 and 5–7 double bond equivalents, respectively. The molecular formulas with the highest relative abundances in Groups III and IV contained 10–13 and 13–16 oxygen atoms and 7–9 and 9–11 double bond equivalents, respectively. Observations of the oxygen content and the double bond equivalents of the SOA products suggest a complex mixture of accretion reaction mechanisms, without an easily confirmable dominating pathway.► The overall detailed composition of SOA was only slightly influenced by the hexane concentration. ► The relative abundance of a few specific ions m/z 357, 367 and 539 substantially increased in the presence of hexane. ► The oxygen content and the double bond equivalents of SOA products suggest a complex mixture of accretion reactions. ► The relative abundance weighted O:C and OM:OC values for α-pinene SOA and limonene SOA samples were similar.
Keywords: Secondary organic aerosol; Water-soluble organic compounds; HR-MS;

Satellite aerosol remote sensing over urban areas is still a difficult task because of the high reflectance of the underlying surface. Many aerosol retrieval algorithms are appropriate for ‘dark’ pixels and provide aerosol products with low resolutions. In this paper, we present a new aerosol retrieval algorithm that applies the synergetic use of small satellite data and Moderate Resolution Imaging Spectroradiometer (MODIS) data. The algorithm was applied to data from the China HJ-1A/1B of the Environment and Disasters Monitoring Microsatellite Constellation Charge-Coupled Device (CCD) camera and Terra MODIS data. To downscale 500 m MODIS data, a new method based on mutual information was developed. By applying this algorithm to aerosol retrieval over Beijing City, we obtain the aerosol optical depth (AOD) with a 100 m × 100 m resolution. A comparison of our results to the ground measurement data from Aerosol Robotic Network (AERONET) sites and Huailai Remote Sensing Test Field, which are measured by CE318 automatic sun tracking photometer, shows a correlation coefficient of approximately 0.89 and a root-mean-square error (RMSE) of about 0.24. The uncertainty for AOD (τ) is found to be Δτ = ±0.05 ± 0.20τ. The algorithm could potentially be useful for other small satellite constellation data. High-resolution AOD is very useful and powerful for urban air quality monitoring and other applications.► A new AOD retrieval algorithm that applies the synergetic use of small satellite HJ-1 data and MODIS data over land. ► To downscale 500-m MODIS data, a new method based on mutual information (MI) was developed. ► Validation shows an RMSE of less than 0.24 and a correlation coefficient of approximately 0.89. ► The uncertainty for AOD (τ) is found to be Δτ = ±0.05 ± 0.20τ. ► The algorithm could potentially be useful for small satellite constellation data to derive AOD data at a high resolution.
Keywords: Aerosol optical depth; HJ-1; CCD; MODIS; Mutual information; Synergy;

Desorption kinetics and sources (fossil vs. contemporary) of the water soluble organic carbon (WSOC) component of aerosol particles were examined at two sites on the east coast of the United States. Experiments revealed that WSOC is released either rapidly as one homogeneous pool or via biphasic kinetics with one rapidly and one slowly desorbing pool. The majority (>85%) of WSOC was desorbed within the first 15 min of immersion in water, suggesting that this material can be rapidly incorporated into rainwater pre-depositionally or surface waters post-depositionally and transported through watersheds. Radiocarbon (14C) measurements showed that on average 12 ± 4% and 14 ± 2% of WSOC from sites in New York and Virginia, respectively, was derived from fossil sources. By contrast, mass balance calculations revealed water-insoluble organic carbon to have significantly greater fossil contributions. These findings suggest that contemporary biogenic aerosol OC is preferentially incorporated into the aqueous phase and may be transported relatively rapidly through watersheds and aquatic systems. In contrast, the more highly aged and fossil aerosol component remains in particulate form and is more likely to be retained on particles or in soils or aquatic sediments.► More than 85% of WSOC desorbs from aerosols within 15 min of immersion in water. ► 12–14% of east coast USA WSOC can be attributed to fossil fuel sources. ► WSOC is consistently enriched in contemporary sources relative to TOC and WINSOC.
Keywords: Water soluble organic carbon; Radiocarbon; Aerosols; Kinetics; Biogeochemical cycling;

Chloride depletion in sea-salt aerosols was studied using size-segregated inorganic ions data collected at a Canadian rural coastal site during a summer (June 29–July 15, 2002) and a fall campaign (October 25 – November 15, 2002). Three samples collected in the fall campaign had high concentrations of sea-salt and ammoniated sulfate and nitrate aerosols and were used to study the relative importance of different chemical reactions contributing to the depletion. The percentage depletion (Cl depletion(%)) increased substantially with decreasing particle size (up to 86% for particles in the size range of 1.0–3.1 μm). For particles >6.2 μm, the observed NO3 was responsible for all the depleted Cl; but less than a quarter of the depletion was explained by the HCl-released reaction between NaCl and HNO3; the rest of the depletion was likely due to the non-HCl-released reactions, e.g., between NaCl and N2O5. For particles in the size range of 3.1–6.2 μm, the NO3 was responsible for nearly 80–90% of all the depleted Cl via HCl-released and/or non-HCl-released reactions; the remaining depletion was likely due to the reactions releasing Cl2, HOCl, etc. Particles >3.1 μm were mostly neutral acidity while a portion of particles at 1.0–3.1 μm was acidic. SO4 2− was only responsible for Cl depletion(%) in acidic particles at 1.0–3.1 μm and the highest Cl depletion(%) was observed in acidic particles of this size range.► The percentage Cl depletion increased with decreasing particle size. ► Non-HCl-released reactions played a role in Cl depletion for particles >6.2 μm. ► Reactions releasing Cl2, HOCl also played a role for particles 3.1–6.2 μm. ► SO4 2− was only responsible for Cl depletion in acidic particles at 1.0–3.1 μm.
Keywords: Chlorine chemistry; Inorganic ions; Nitrogen species; Size-resolved aerosols;

Atmospheric organic nitrogen deposition in China by Y. Zhang; L. Song; X.J. Liu; W.Q. Li; S.H. Lü; L.X. Zheng; Z.C. Bai; G.Y. Cai; F.S. Zhang (195-204).
Precipitation samples have been collected and analyzed for organic and inorganic nitrogen (N) at 32 sites in China from 2005 to 2009. Our results suggest that dissolved organic nitrogen (DON) accounts for 28% of the total atmosphere bulk N deposition. Average annual DON deposition was 6.84 kg N ha−1 yr−1, ranging from 1.01 to 19.7 kg N ha−1 yr−1. The volume weighted average DON concentration was 77 μmol L−1, ranging from 13 to 190 μmol L−1, which was much higher than results obtained in other regions of the world. Analysis of seasonal variations of DON concentration, deposition, the ratio of DON to total dissolved N (TDN), rainfall and wind frequency roses revealed possible pollution sources in specific regions, e.g. agriculture, oceanic spray and re-suspension. Significant correlations of DON with TDN from results in this study and elsewhere indicate that atmospheric organic N species have similar anthropogenic pollution sources to atmospheric inorganic N species, and that DON deposition is an important part of the TDN deposition.► Rainwater was collected for determining DON at 32 sites in China in a 5-yr study. ► DON concentration and deposition averaged 77 μmol L-1 and 6.84 kg N ha-1 yr-1. ► DON is a significant source of deposited N (28%) but its composition is not clear.
Keywords: Atmospheric deposition; DON; DON/TDN; Rainfall; Seasonal variation;

Comparison of SAPRC99 and SAPRC07 mechanisms in photochemical modeling for central California by Sharon M. Shearer; Robert A. Harley; Ling Jin; Nancy J. Brown (205-216).
A condensed version of the SAPRC07 photochemical reaction mechanism is compared to an earlier version, SAPRC99, in a 3-dimensional air quality model applied to central California. The updated mechanism results in lower predicted ozone concentrations in all locations. A sensitivity analysis shows the 19% increase (at 1 atm and 300 K) in the OH + NO2 → HNO3 reaction rate coefficient contributes to decreases in predicted ozone concentrations in our study domain. This revision to SAPRC07 results in the largest ozone change of all the rate coefficient changes we examined. Also, lumping species to achieve a more computationally efficient mechanism, with respect to SAPRC99, has the effect of lowering ozone concentrations in the region studied. Although ozone concentrations in SAPRC07 simulations are decreased with respect to SAPRC99, the NOx and VOC emission sensitivities of the new mechanism are on the same order or greater than those in SAPRC99. The new mechanism is less sensitive to climate change related perturbations including increased temperature, water vapor concentration, and biogenic VOC emissions.► We compare a chemical mechanism (SAPRC07) to its predecessor in a 3-D AQM. ► Ozone concentrations are lower in new mechanism, increasing peak biases. ► We investigate differences that could contribute to the ozone reduction. ► We determine how use of SAPRC07 alters sensitivity studies performed with SAPRC99.
Keywords: Air quality modeling; Ozone; CMAQ; Photochemistry; Chemical mechanism; Temperature effects;

Lead concentrations in fine particulate matter after the phasing out of leaded gasoline in Xi’an, China by H.M. Xu; J.J. Cao; K.F. Ho; H. Ding; Y.M. Han; G.H. Wang; J.C. Chow; J.G. Watson; S.D. Khol; J. Qiang; W.T. Li (217-224).
Daily concentrations of lead (Pb) were determined for PM2.5 samples collected from an urban location in Xi’an, China from 2007 to 2009 to assess the effects of the phasing out of leaded gasoline in 2000. The Pb concentrations (annual average: 0.306 μg m−3, range: below detection limit to 2.631 μg m−3) have declined after the phasing out of leaded gasoline, but the concentrations were still higher than those reported in many other cities. Seasonal variations of Pb were significant, with high concentrations in winter, presumably due to the burning of coal, and low concentrations in summer, due to a deep mixed layer and scavenging of aerosols by precipitation. Correlation analyses and enrichment factor calculations both indicated that anthropogenic sources had a large influence on atmospheric Pb. The lead isotope ratios were low in winter (the average 207Pb/206Pb ratio was 0.843 ± 0.032; 208Pb/206Pb was 1.908 ± 0.058) and high in summer (207Pb/206Pb was 0.860 ± 0.032; 208Pb/206Pb was 2.039 ± 0.057), suggesting that coal combustion was the major Pb source in winter and vehicular emission was the major Pb source in summer. Positive Matrix Factorization receptor model indicated that there were five major sources for Pb in PM2.5. Coal combustion was the major contributor, accounting for 39.0% PM2.5 mass, followed by vehicular emissions (30.4%). Other contributors included 17.8% from industrial emissions, 11.6% from biomass burning, and 1.2% from fugitive dust.► Pb concentrations (average: 0.306 μg m−3 during 2007–2009) have declined after the phasing out of leaded gasoline. ► Pb concentrations in Xi’an are still higher than those reported in many other cities. ► Coal combustion was the strongest source for PM2.5 Mass (39.0%).
Keywords: Lead concentration; Lead isotope; PM2.5; Source apportionment; Xi’an;

Assessment of human health effects associated with particles requires knowledge of their emission factors and dispersion characteristics. A field experiment was recently conducted to determine the vertical and horizontal dispersion of particles emitted from highway vehicles. The measurements were conducted near the highway I-90 in Liverpool (NY) over a flat terrain, where the predominant dispersion mechanisms were atmospheric turbulence and traffic-produced turbulence (TPT). Real-time vertical number concentration measurements were made using several identical water condensation particle counters (WCPCs) over nine heights up to 10 m. Three sites (at distances of 15, 50, and 100 m from the highway) were selected to study the concentration profiles. As previously observed at other sites, particle concentrations decay with increasing distance from highways. At the site closest to the highway, the highest concentration was observed under a downwind condition with the average wind speed ∼1 ms−1. Under conditions of low wind speed, particles from the highway are observed even at locations upwind of the highway. The vertical profiles of particle concentrations at different measurement locations varied with wind speed, wind direction and distance to the highway. The correlation coefficients of particle concentrations at different elevations reveal the characteristics of the plume dispersion and its development in the horizontal and vertical directions. The experimental results suggest the need for three-dimensional modeling of particle plumes from highways and the importance of considering TPT for accurate prediction of particle dispersion near roadways.► Particle concentration and wind relationships are different at different sites. ► Obtained real-time particle distribution in vertical direction. ► Obtained particle vertical distribution at different wind conditions. ► Detected particles from traffic emission at upwind sites very close to a highway. ► Studied plume development from traffic emission in vertical direction.
Keywords: Vertical distribution; Concentration; Highway; Dispersion; Traffic; Plume; Traffic-produced turbulence; Ultrafine particle;

Path-integrated measurements of carbon dioxide in the urban canopy layer by Christian Büns; Wilhelm Kuttler (237-247).
Continuous CO2 concentration measurements have been recorded within the city center of Essen, Germany, using a path-integrated measuring system above a typical urban area over the course of nine months (February–October 2010). Mean monthly urban CO2 concentrations were 396 and 446 ppm in summer and winter, respectively, which were 8.5 % in average higher than at a nearby suburban measuring site. Urban-suburban differences mainly occur due to increased CO2 emissions from traffic and industry within the urban area, as well as domestic heating in winter.Among the analyzed meteorological variables, low wind velocities increased CO2 concentrations as well as high atmospheric stability within the urban boundary layer, respectively. The influence of wind direction reflects the heterogeneous distribution of local CO2 sources at the recording sites, particularly industrial point sources. Other point sources in the vicinity of the urban site strongly influence the additional point measurements but show no significant effect on the measured CO2 concentrations by the path-integrated measuring system. Within an eight-day case study, a significant positive correlation between CO2 concentration and traffic count (R  = 0.26; p  < 0.05) was found on weekdays using partial correlation analysis after excluding the influence of meteorological variables. This correlation diminishes when combined with the meteorological components, and mixing layer height shows the strongest negative correlation with measured urban CO2 (R  = −0.59). The path-integrated system provides CO2 concentrations on a greater temporal and spatial scale than common point measurements, which can be influenced by strong adjacent local CO2 sources.► Implementation of an open path-integrated system in an urban environment. ► Monthly mean CO2 concentration vary from 396–446 ppm between summer and winter. ► Strength of urban sources can overrule typical diurnal courses of CO2. ► Path-integrated system is able to provide representative results.
Keywords: Carbon dioxide; Path-integrated system; Open-path; TDL; Essen, Germany; Urban;

A model for inventory of ammonia emissions from agriculture in the Netherlands by G.L. Velthof; C. van Bruggen; C.M. Groenestein; B.J. de Haan; M.W. Hoogeveen; J.F.M. Huijsmans (248-255).
Agriculture is the major source of ammonia (NH3). Methodologies are needed to quantify national NH3 emissions and to identify the most effective options to mitigate NH3 emissions. Generally, NH3 emissions from agriculture are quantified using a nitrogen (N) flow approach, in which the NH3 emission is calculated from the N flows and NH3 emission factors. Because of the direct dependency between NH3 volatilization and Total Ammoniacal N (TAN; ammonium–N + N compounds readily broken down to ammonium) an approach based on TAN is preferred to calculate NH3 emission instead of an approach based on total N. A TAN-based NH3-inventory model was developed, called NEMA (National Emission Model for Ammonia). The total N excretion and the fraction of TAN in the excreted N are calculated from the feed composition and N digestibility of the components. TAN-based emission factors were derived or updated for housing systems, manure storage outside housing, manure application techniques, N fertilizer types, and grazing. The NEMA results show that the total NH3 emission from agriculture in the Netherlands in 2009 was 88.8 Gg NH3–N, of which 50% from housing, 37% from manure application, 9% from mineral N fertilizer, 3% from outside manure storage, and 1% from grazing. Cattle farming was the dominant source of NH3 in the Netherlands (about 50% of the total NH3 emission). The NH3 emission expressed as percentage of the excreted N was 22% of the excreted N for poultry, 20% for pigs, 15% for cattle, and 12% for other livestock, which is mainly related to differences in emissions from housing systems. The calculated ammonia emission was most sensitive to changes in the fraction of TAN in the excreted manure and to the emission factor of manure application. From 2011, NEMA will be used as official methodology to calculate the national NH3 emission from agriculture in the Netherlands.► Methodologies are needed to quantify national NH3 emissions from agriculture. ► The NH3 emission from agriculture in the Netherlands in 2009 was 88.8 Gg NH3–N. ► Largest sources of NH3 were housing (50% of total) and manure application (37%). ► Cattle farming was the dominant source of NH3 emission in the Netherlands.
Keywords: Ammonia; Agriculture; Inventory; Manure; Total ammoniacal nitrogen (TAN); Netherlands;

Due to the implications caused by mineral dust and sea-salt heterogeneous reactions with SO2, NO x and NH3 derivatives, this study aims to understand the interaction between gaseous and particulate phases; PM10 and PM2.5, in dust-rich and dust-poor environments. During dust outbreaks, the increase in PM10 and PM2.5 mass concentrations by 80 and 75%, respectively, was accompanied with approximately 30% decrease in water soluble inorganic ions. However, nitrate ion concentration, which increased by 36% during dust-rich episodes, was correlated with a 96% increase in gaseous HONO concentration. This implies a significant impact of dust storms on the tropospheric NO2 to HONO conversion and consequently the formation of nitrate in PMs. Products of the reaction between HONO and mineral dust render atmospheric aerosols more soluble and consequently higher nitrogen deposition fluxes were calculated.► In dust-rich episodes; Increase in PM10 (80%) and PM2.5 (75%) mass concentrations. ► Increase in PM10-nitrate (36%), and -chloride (30%) and PM2.5-nitrate (54%). ► Reaction rate of HNO3–CaCO3 becomes in the same order of magnitude as SO2–NaCl. ► A 96% increase in HONO(g) is accompanied by a 36% increase in particle nitrate. ► Conversion of calcite to soluble nitrate particles is enhanced over urban areas.
Keywords: Marine nutrients; Aerosol solubility; Total soluble nitrogen; Ionic composition; Heterogeneous gas–particle interaction;

Products of the OH radical-initiated reactions of 2- and 3-hexyl nitrate by Sara M. Aschmann; Janet Arey; Roger Atkinson (264-270).
Products of the gas-phase reaction of OH radicals with 2-hexyl nitrate (containing 13% 3-hexyl nitrate) have been investigated by gas chromatography with mass spectral and flame ionization detection, and by direct air sampling atmospheric pressure ionization tandem mass spectrometry. The products identified and quantified from 2-hexyl nitrate were: 2-hexanone (8.6 ± 1.3%), propanal (3.4 ± 0.8%), butanal (2.3 ± 0.6%) and 5-hydroxy-2-hexanone (25%), where the molar yields are given in parentheses. 3-Hexanone was observed from the 3-hexyl nitrate reaction, with a molar formation yield of 9.5 ± 2.1%. Organic nitrates of molecular weight 133, 161, 177 and 208 were also observed, and these are attributed to C4-carbonyl nitrate(s), C6-carbonyl-nitrates, C6-hydroxycarbonyl-nitrates and C6-dinitrates, respectively, and are expected to account for all or most of the non-quantified reaction products from OH + 2- and 3-hexyl nitrate. 5-Hydroxy-2-hexanone formation indicates that the CH3CH(ONO2)CH2CH2CH(O•)CH3 alkoxy radical dominantly reacts by isomerization.► Multifunctional nitrates are major products from OH radical reaction with 2- and 3-hexyl nitrate. ► Alkoxy radical reactions determine if the NOx in the alkyl nitrate is released by OH reaction. ► The CH3CH(ONO2)CH2CH2CH(O•)CH3 alkoxy radical from 2-hexyl nitrate dominantly isomerizes.
Keywords: 2-Hexyl nitrate; 3-Hexyl nitrate; Hydroxyl radical; Reaction products; Carbonyl-nitrates; Hydroxycarbonyl-nitrates;

Secondary organic aerosol (SOA) created from the photooxidation of a mixture of isoprene and dimethyl sulfide (DMS) was studied at different NO x concentrations (40–220 ppb) and humidities (12%, 42% and 80%) using a Teflon film indoor chamber. To study the effect of isoprene on DMS products, the major DMS photooxidation products, such as sulfuric acid, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA), were quantified in both the presence and the absence of isoprene using a Particle-Into-Liquid-Sampler coupled with Ion Chromatography (PILS-IC). The resulting PILS-IC data showed that the DMS aerosol yield significantly decreased due to the photooxidation of isoprene. A 35.2% DMS aerosol yield reduction was observed due to 800 ppb isoprene in 185 ppb NO x and 140 ppb DMS. Among the aerosol-phase DMS oxidation products, MSA was the most sensitive to the presence of isoprene (e.g., 46% reduction). The DMS aerosol product analysis indicates that isoprene oxidation affects the pathways of MSA formation on the aerosol surface. Using a new approach that implements an Organic Carbon (OC) analyzer, the isoprene SOA yield (Y iso) in the DMS/isoprene/NO x system was also estimated. The OC data showed that Y iso increased significantly with DMS compared to the Y iso without DMS. For example, Y iso with 80 ppb NO x and 840 ppb isoprene was increased by 124.6% due to 100 ppb DMS at RH = 42%. Our study suggests that the heterogeneous reactions of isoprene oxidation products with the highly acidic products (e.g., MSA and sulfuric acid) from DMS photooxidation can considerably contribute to the Y iso increase.► The impact of DMS on isoprene SOA yields at different humidity and NO x conditions. ► DMS aerosol products quantified using a PILS-IC. ► Isoprene SOA yields and DMS aerosol yields from photooxidation of isoprene and DMS.
Keywords: Secondary organic aerosol; Heterogeneous reaction; Isoprene; Dimethyl sulfide; Methanesulfonic acid;

Seasonal and diurnal variations of ozone at a high-altitude mountain baseline station in East Asia by Chang-Feng Ou Yang; Neng-Huei Lin; Guey-Rong Sheu; Chung-Te Lee; Jia-Lin Wang (279-288).
Continuous measurements of tropospheric ozone were conducted at the Lulin Atmospheric Background Station (LABS) at an altitude of 2862 m from April 2006 to the end of 2009. Distinct seasonal variations in the ozone concentration were observed at the LABS, with a springtime maximum and a summertime minimum. Based on a backward trajectory analysis, CO data, and ozonesondes, the springtime maximum was most likely caused by the long-range transport of air masses from Southeast Asia, where biomass burning was intense in spring. In contrast, a greater Pacific influence contributed to the summertime minimum. In addition to seasonal variations, a distinct diurnal pattern was also observed at the LABS, with a daytime minimum and a nighttime maximum. The daytime ozone minimum was presumably caused by sinks of dry deposition and NO titration during the up-slope transport of surface air. The higher nighttime values, however, could be the result of air subsidence at night bringing ozone aloft to the LABS. After filtering out the daytime data to remove possible local surface contributions, the average background ozone value for the period of 2006–2009 was approximately 36.6 ppb, increased from 32.3 ppb prior to data filtering, without any changes in the seasonal pattern. By applying HYSPLIT4 model analysis, the origins of the air masses contributing to the background ozone observed at the LABS were investigated.► Tropospheric ozone was measured at a high elevation site in East Asia. ► Mechanisms causing seasonal and diurnal variations of ozone were proposed. ► Springtime ozone maximum was mainly contributed by biomass burning over SE Asia. ► M–V circulation was proposed as the major driving force for the diurnal pattern. ► Origins of air masses shaping the seasonal background values were analyzed.
Keywords: Mountain–valley circulation; Long-range transport; Biomass burning;

Magnetic properties and correlation with heavy metals in urban street dust: A case study from the city of Lanzhou, China by Guan Wang; Frank Oldfield; Dunsheng Xia; Fahu Chen; Xiuming Liu; Weiguo Zhang (289-298).
We report results obtained from magnetic and geochemical measurements of 71 street dust samples from four distinct districts (residential, commercial and industrial) in Lanzhou, an industrial city in China. Magnetic properties and the concentrations of 17 elements (As, Ba, Bi, Cr, Cu, Mn, Ni, Pb, Ti, Zn, Fe, Si, Na, Mg, K, Ca, Al) are reported for each sample. Ferrimagnetic mineral concentrations are generally high in Lanzhou street dust, mainly due to grains above Stable Single Domain size. The highest concentrations of magnetic materials and heavy metals are in dusts from the two main industrial districts, Xigu and Chengguan. In the least polluted Anning district, some samples have magnetic properties more probably derived from arid areas to the north of the city. The two main industrial areas also show some differences in magnetic mineral assemblages suggesting that magnetic properties and magnetic-metal correlations may be of use in ascribing heavy metal contamination to distinct sources. Geochemical studies and the significant positive correlation between magnetic concentrations and those for Fe, As, Cu, Mn, Ni, Pb and Zn confirm that much of the heavy metal contamination in the study area is linked to combustion derived particulate emissions. The results confirm that a combined magnetic and geochemical approach can provide useful information on the types, levels and sources of heavy metals in street dust.► Magnetic and geochemical analyses identify differences between the districts studied. ► Coarse ferrimagnetic grains and hematite are the main magnetic minerals present. ► As, Cu, Mn, Ni, Pb and Zn concentrations are linked to combustion particulates. ► Dusts from desert sources to the north can be differentiated magnetically from polluted dusts.
Keywords: Magnetic properties; Heavy metal; Street dust; Lanzhou city;

Analysis of daily observations from 43 meteorological stations in the Inner Mongolia Autonomous Region, China, showed the distribution of spring dust storm events during 2000–2007. Guaizihu and Sunitezuoqi stations had the highest frequencies of dust storms. The interannual and seasonal variations of dust storms were closely related to weather conditions, especially the wind speed. A forward trajectory model and satellite observations were used to investigate the transport paths and dust layers of dust storms from Guaizihu and Sunitezuoqi stations to the China seas and their probability of influencing the seas during spring 2000–2007. Forward trajectories showed that dust storms at Guaizihu and Sunitezuoqi stations had the highest probability of affecting the Yellow Sea, followed by the Bohai Sea, the East China Sea, and the northern South China Sea. The dust particles from Sunitezuoqi station affected these four seas directly through coastal areas, while those from Guaizihu station were transported via the Inner Mongolian deserts and/or the Loess Plateau. The dust storms from Sunitezuoqi station impacting the four seas were characterized by a single dust source and a short transport distance, while those from Guaizihu station were characterized by multiple sources and relatively long transport distances. The dust particles from these two stations were mostly transported in a <4 km layer from the source regions to the seas. The satellite vertical profile also indicated that dust particles were mainly contained in a 0–4 km layer over the source regions and the four seas. An aerosol index retrieved from satellite observations and the estimated dust deposition also supported the influence derived from the forward trajectory model, with large aerosol index and dust deposition values occurring on the dust days affecting the four seas. The average deposition over the four seas was 18.7 g m−2 during spring 2000–2007.► Characteristics of transport of dust from two sources to the seas were different. ► Dust transported from sources to the seas were mostly contained in <4 km layer. ► Dust storms had different probability of influencing the four China seas. ► The influence was supported by aerosol index and simulated dust deposition.
Keywords: Dust storm; Transport; Deposition; Probability; The China seas;

Size-segregated mass concentration and water soluble inorganic ions in an urban aerosol of the Central Balkans (Belgrade) by D. Đorđević; A. Mihajlidi-Zelić; D. Relić; Lj. Ignjatović; J. Huremović; A.M. Stortini; A. Gambaro (309-317).
The distribution of nano/micron inorganic main ions in the size-segregated urban aerosol of Belgrade center was studied during the summer–autumn of 2008. The particle size distribution in the size ranges D p  ≤ 0.49 μm, 0.49 ≤  D p  ≤ 0.95 μm, 0.95 ≤  D p  ≤ 1.5 μm, 1.5 ≤  D p  ≤ 3.0 μm, 3.0 ≤  D p ≤ 7.2 μm and D p  ≥ 7.2 μm was measured. The aerosol samples were submitted to gravimetric and chemical analyses. The obtained mean mass concentration of the PM fractions was in accordance with an urban aerosol distribution. The aerosol mass concentrations were determined by gravimetric measurements (m GM) and, analyzed by ion chromatography for Na+, NH4 +, K+, Mg2+, Ca2+, Cl, NO3 , PO4 3− and SO4 2−. The mean random uncertainties associated with the determinations of Na+, NH4 +, K+, Mg2+, Ca2+, Cl, NO3 and SO4 2− were assessed. The absolute highest concentration is found for SO4 2− (1555.8 ± 973.6 ng m−3) in the range of D p  ≤ 0.49 μm with an average participation of 8.19% to the total mass of the particles. The highest coefficients of correlation were found between NH4 + and SO4 2−. Principal component analysis, PCA, was used for the identification and evaluation of the contributions of the main emission sources to the contents of water soluble ions in the urban aerosol. The formation of (NH4)2SO4 was found to be the dominant process. The influences of local urban (traffic) and regional industrial sources (nearby city Pančevo) were identified and a contribution of marine aerosol was observed.► The obtained distribution of the mean aerosol mass concentration was in accordance with an urban aerosol distribution. ► The absolute highest concentration is found for SO4 2− in nuclei mode with an average participation of 8.19%. ► The contribution of marine aerosol was identified as a significant component.
Keywords: Size distribution; Urban aerosols; Water soluble main ions;

The study analyses the added value of data assimilation for short-term air quality forecasting by means of three modelling experiments with sulphur oxides. Two ways of utilising the observations are considered: determination of the optimal model initial state and adjustment of the emission fluxes of atmospheric pollutants. It is demonstrated that the influence of the initial conditions on the predicted SOx concentrations disappears within less than a day in European-scale applications. Adjusting the emission fluxes had a longer lasting impact on the model results, frequently covering the whole forecast window. The two-week long data assimilation exercise for Southern Europe showed that the largest improvement of the model score with regard to individual monitoring sites was obtained for the stations with the worst initial model-measurement agreement. With the emission adjustment, a major improvement was achieved for the stations near the Etna volcano, the strongest source in the area, where the SO2 emission was reduced by almost 50% as a result of the data assimilation.► Two chemical data assimilation strategies are compared in modelling experiments. ► 3D-VAR and 4D-VAR assimilation of in-situ measurements. ► The most consistent improvements are obtained using emission rate adjustment with the 4D-VAR method. ► Emission adjustment with daily resolution too coarse in some cases.
Keywords: Data assimilation; Air quality forecasting; Model initialisation; Emission refinement; Numerical modelling;

In most cases, receptor models are applied to data from a single monitoring site even if there are multiple sampling locations in a given urban area. When it can be reasonably expected that the sites are affected by the same set of sources, it is possible to use the spatial variability of the source contributions to enhance the source apportionment. With the framework of positive matrix factorization, it is possible to enhance the results through an effective use of multiple site data. There have been several previous studies of the sources of ambient PM2.5 in St Louis, MO based on data from the US EPA chemical speciation network and the St Louis–Midwest Supersite. However, these different analyses identified different sets of sources including the omission of known major emission sources. A re-examination of the previous studies was undertaken using knowledge of the existing sources based on independent data and the resulting profiles were used to constrain the solution. These new solutions provide more realistic results in which the source impacts of all of the major sources could be assessed at each site.► An enhanced PMF model permits input of known source profiles. ► Sources have been simultaneously apportioned from three monitoring sites. ► All of the known sources can be resolved using the enhanced model. ► More realistic apportioned mass contributions have been obtained.
Keywords: Multilinear Engine; PMF; Target Transformation; Rotational control; Physical constraints; CPF;

Gas phase reaction of OH radicals with (E)-β-farnesene at 296 ± 2 K: Rate coefficient and carbonyl products by Ivan Kourtchev; Iustinian Bejan; John R. Sodeau; John C. Wenger (338-345).
The gas phase reaction of OH radicals with (E)-β-farnesene was investigated in a 3.91 m3 atmospheric simulation chamber at 296 ± 2 K and atmospheric pressure. The relative rate method was used to determine the reaction rate coefficient of (1.71 ± 0.21) × 10−10 cm3 molecule−1 s−1. Gas phase carbonyl products were collected using a denuder sampling technique and analyzed with GC/MS following derivatization with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA). The reaction products detected were acetone, 4-oxopentanal, 4-methylenehex-5-enal, 6-methylhept-5-en-2-one and (E)-4-methyl-8-methylenedeca-4,9-dienal. A minor reaction product with MW 112 was tentatively identified as 4-oxohex-5-enal or 2-methylenepentanedial. A mechanism for the OH radical-initiated oxidation of (E)-β-farnesene is proposed, which accounts for all of the products observed in this study. The results of this work indicate that the atmospheric reaction of (E)-β-farnesene with OH radicals has a lifetime of around 1 h and is a potential source of the ubiquitous carbonyls, acetone, 4-oxopentanal and 6-methylhept-5-en-2-one in the atmosphere.► Kinetics of the reactions of (E)-β-farnesene with OH radicals has been measured. ► A number of carbonyl compounds have been determined as reaction products. ► A reaction mechanism has been proposed to explain the majority of the products. ► The atmospheric implications of the results are considered.
Keywords: Sesquiterpenes; (E)-β-farnesene; 4-Oxopentanal; Hydroxyl radical; Rate coefficient; Kinetics;

Occurrence and air-seawater exchange of brominated flame retardants and Dechlorane Plus in the North Sea by Axel Möller; Zhiyong Xie; Armando Caba; Renate Sturm; Ralf Ebinghaus (346-353).
The occurrence, spatial and seasonal concentration variations in air and seawater and the air–seawater exchange of polybrominated diphenyl ethers (PBDEs), alternate brominated flame retardants (BFRs) and Dechlorane Plus (DP) were studied in the German part of the North Sea in 2010. BDE–209 and DP were found to be the dominating compounds, both in the atmosphere and in seawater. Sum PBDEs (∑10PBDEs) ranged from 0.31 to 10.7 pg m−3 in the atmosphere and from not detected (n.d.) to 10.5 pg L−1 in seawater, respectively. DP ranged from 0.13 to 22.3 pg m−3 and from 0.10 to 17.7 pg L−1 in air and seawater, respectively. Besides, four other BFRs including hexabromobenzene (HBB) and pentabromobenzene (PBBz) were detected. Elevated atmospheric concentrations were observed in continentally influenced air masses while highest seawater concentrations were observed at sampling stations close to the coast influenced by riverine discharge. The ratio of the two DP stereoisomers both in air and water was found to be close to the technical mixture at high concentrations but changed at lower concentrations giving first evidence for the alteration within the aquatic environment. Both dry air-seawater gas exchange and dry deposition are input pathways of BFRs and DP in the North Sea besides riverine discharge.► BDE–209 and DP are emitted via the atmosphere and rivers into the North Sea. ► High HBB concentrations in the North Sea occur during winter time and northerly winds. ► First evidence for the alteration of the DP stereoisomer ratio in (sea)-water. ► Possible BDE–209 degradates HBB and PBBz detected in the atmopshere. ► Air–seawater exchange in the North Sea is dominated by net deposition.
Keywords: Flame retardants; PBDE; Air–seawater exchange; Hexabromobenzene; Dechlorane plus; North Sea;

Ozone variability in the atmospheric boundary layer in Maryland and its implications for vertical transport model by Xiao-Ming Hu; David C. Doughty; Kevin J. Sanchez; Everette Joseph; Jose D. Fuentes (354-364).
Although much research has focused on daytime ozone (O3) distribution in the atmospheric boundary layer, there remain many unresolved processes related to O3 transport in the residual layer. To address such unresolved questions, a field study was conducted in Beltsville, MD during the summer of 2010 to study the spatial and temporal distribution of O3 and other pollutants using ground-based gas analyzers and ozonesondes. During elevated pollution events in the daytime, the convective boundary layer, which reached a maximum depth of about 2 km, had nearly uniform O3 levels of almost 100 parts per billion (ppbv). Due to intermittent and intense vertical turbulent motion, the residual layer became “leaky” and permitted vertical transport to enhance ground-level O3 mixing ratios by as much as 10–30 ppbv in a span of 0.5–3 h. Model simulations, using the Weather Research and Forecasting model with Chemistry (WRF/Chem), were carried out to investigate the impact of different treatments of vertical mixing on the simulation of O3 in the nocturnal boundary layer and residual layer. WRF/Chem model simulations provided realistic O3 vertical distribution during the daytime. During the nighttime, in the residual layer, model outputs resulted in higher O3 levels compared with the in-situ observations. Model sensitivity analyses showed that increasing the turbulent length scales and improved stability functions yielded improvements in the vertical transport of O3 within the residual layer. One key conclusion of this study is that models such as WRF/Chem require improved numerical algorithms to properly account for the nocturnal vertical transport of O3 in the residual region of the atmospheric boundary layer.► At times, the residual layer became leaky and permitted vertical transport to enhance surface O3. ► Ozone in the residual layer is highly variable. ► The current implementation of the ACM2 PBL scheme in WRF/Chem does not properly simulate the mixing of pollutants. ► Increasing the asymptotic length and using “long-tails” stability function improved the nighttime simulation.
Keywords: Ozonesonde; Beltsville; WRF/Chem; Residual layer; Nocturnal boundary layer;

Climatological information on the vertical distribution of aerosol in the lower atmosphere is needed to assess the effects of aerosols on climate. Altitude profiles of the backscatter coefficient (at 532 nm), color ratio (CR) and particle depolarization ratio (PDR) derived from space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite were used to investigate the climatological aspects of seasonal variation of aerosol vertical distribution over central Indo-Gangetic belt (IGB). Strong convective activity coupled with capping inversion lead to vertical extension (4–5 km) of aerosol distribution during the pre-monsoon (PrM) season. Trapping of pollution at low altitudes (below 1.5 km) by subsidence have been found during the late post-monsoon (PoM) and winter seasons. Combined results of CR and PDR suggest presence of elevated mineral dust particles during the PrM season, whereas fine mode and spherical (biomass burning/industrial pollution) particles are dominant during the PoM and winter seasons. The observations indicate a seasonal dependency of the aerosol vertical distribution over central IGB.► Examined climatological aspects of aerosol vertical distribution using CALIOP data. ► Formation of mixed boundary layer led vertical extension of dust aerosol in PrM. ► Trapping of pollution at low altitudes by subsidence was found in PoM and winter. ► Indicated a seasonal dependency of aerosol vertical distribution over central IGB.
Keywords: Aerosol vertical distribution; Space-borne lidar CALIOP; Color ratio (CR); Particle depolarization ratio (PDR); Aerosol backscatter; Capping inversion; Subsidence inversion;

Spatio-temporal variability of concentrations and speciation of particulate matter across Spain in the CALIOPE modeling system by M.T. Pay; P. Jiménez-Guerrero; O. Jorba; S. Basart; X. Querol; M. Pandolfi; J.M. Baldasano (376-396).
The CALIOPE high-resolution air quality modeling system (4 km × 4 km, 1 h) estimates particulate matter from two aerosol models, CMAQv4.5 (AERO4) and BSC-DREAM8b. While CMAQv4.5 calculates biogenic, anthropogenic and sea-salt aerosols; BSC-DREAM8b provides hourly estimates of the natural mineral dust contribution from North Africa deserts. This paper presents an evaluation of the CALIOPE system to reproduce the spatial and temporal variability levels of PM2.5, PM10 and chemical composition (nitrate, non-marine sulfate, ammonium, organic and elemental carbon, sea-salt, and desert dust) across Spain. The evaluation is performed against ground-based observations for the year 2004, when a number of time series of chemically speciated compounds were available. A new data set of Saharan dust PM10 concentration is used to evaluate the PM10 contribution modeled by BSC-DREAM8b. The results indicate that both natural aerosol sea-salt and desert dust accomplish the model performance criteria (MFE ≤ 75% and MFB ± 60%). Modeled PM10 sea-salt is highly dependent on wind speed and presents high correlation with experimental data in coastal areas (r = 0.67). The BSC-DREAM8b is able to reproduce the daily variability of the observed levels of desert dust and most of the outbreaks affecting southern Spain. Species in the equilibrium (e.g. sulfate/nitrate/ammonium) are highly correlated each other and show high dependency on ammonia emissions. Non-marine sulfate and ammonium are underestimated by a factor of 3. An underestimation of nitrate was also seen (factor of 2). Fine carbonaceous aerosols present the highest underestimations (factor of 4) in part related to the state-of-the-science concerning secondary organic aerosol formation pathways. Spatial and seasonal variability of PM2.5, PM10 and their chemical compounds increase the correlation with observations when multiplicative bias-correction factors for the aforementioned underestimated species are taking into account. Furthermore, simulated spatial and seasonal patterns of aerosol agree with those described in related studies based on experimental values.► CALIOPE system uses a high-resolution computational grid. ► CALIOPE system includes a modeling emission model specifically for Spain. ► CALIOPE simulate aerosol with a natural and anthropogenic origin. ► CALIOPE is evaluated to reproduce spatio-temporal variability levels of aerosols. ► A new data set of Saharan dust PM10 is used to evaluate the BSC-DREAM8b model.
Keywords: Aerosols; Desert dust; Air quality; Emissions; Geochemistry;

Mercury in particulate matter over Polish zone of the southern Baltic Sea by M. Beldowska; D. Saniewska; L. Falkowska; A. Lewandowska (397-404).
Important Hg transformations can occur at the air–water interface where polluted terrestrial air masses meet humid, halogen-rich marine air masses over the southern Baltic Sea. These chemical and physical processes include gas-to-particle conversion that led to an increase of Hg associated with coarse particles, which due to higher dry deposition rates, enhanced local scale deposition and limited the transport of this toxic trace metal. Daily (24 h) sampling of size-segregated atmospheric particles revealed the sea to be a sink for Hg during winter months and as a source of Hg during summer months. Poland is one of the major Hg emitters among the Baltic States according to International HELCOM Reports. Thus, important measurements in this region were conducted over a one-year period from December 18, 2007 to December 15, 2008. The range in concentrations of Hg in particulate matter (2–142 pg m−3) at the Polish site are comparable to other measurements at sites along the coastal areas of the Baltic Sea. Annual Hg(p) represents 1% of the total atmospheric Hg (HgTOT) under unpolluted or background ambient conditions. A major source of atmospheric Hg in this area is the combustion of fossil fuels, especially coal burning used for home heating. This was clearly seen in the statistically higher mean concentration of 24 pg m−3 observed during the heating season compared to the 15 pg m−3 measured during the non-heating season. Construction activities e.g., cement manufacturing, gravel extraction, and waste incineration during the warm season strongly influenced Hg concentrations and led to an increase in Hg(p) on working days compared to weekend days.► Manuscript contradicts the information that Polish coastal zone is the significant source of Hg. ► Coastal zone of Baltic Sea is both a sink and a source of Hg. ► Results show possible transformations of Hg in air, associated with climate changes.
Keywords: Hg in coarse and fine particles; Southern Baltic sea; Continental air masses; Maritime air masses;

Carbon dioxide variability during cold front passages and fair weather days at a forested mountaintop site by Temple R. Lee; Stephan F.J. De Wekker; Arlyn E. Andrews; Jonathan Kofler; Jonathan Williams (405-416).
This study describes temporal carbon dioxide (CO2) changes at a new meteorological site on a mountaintop in the Virginia Blue Ridge Mountains during the first year of measurements. Continental mountaintop locations are increasingly being used for CO2 monitoring, and investigations are needed to better understand measurements made at these locations. We focus on CO2 mixing ratio changes on days with cold front passages and on fair weather days. Changes in CO2 mixing ratios are largest during cold front passages outside the growing season and on clear, fair weather days in the growing season. 67% (60%) of the frontal passages during the non-growing (growing) season have larger postfrontal than prefrontal CO2 mixing ratios. The increase in CO2 mixing ratio around the frontal passage is short-lived and coincides with changes in CO and O3. The CO2 increase can therefore be used as an additional criterion to determine the timing of frontal passages at the mountaintop station. The CO2 increase can be explained by an accumulation of trace gases along frontal boundaries. The magnitude and duration of the CO2 increase is affected by the wind speed and direction that determine the source region of the postfrontal air. Southward-moving fronts result in the largest prolonged period of elevated CO2, consistent with the postfrontal advection of air from the Northeastern United States where anthropogenic contributions are relatively large compared to other areas in the footprint of the mountaintop station. These anthropogenic contributions to the CO2 changes are confirmed through concurrent CO measurements and output from NOAA’s CarbonTracker model.► We contrast CO2 changes during cold fronts and clear days at a forested mountaintop. ► CO2 variations are larger during cold fronts than on clear days. ► Wind shifts explain the magnitude and longevity of postfrontal CO2 increases. ► Consistent CO2 increases during fronts help determine the time of frontal passages. ► CO2 variations are well-captured with the CarbonTracker model.
Keywords: Carbon dioxide; Cold fronts; Blue Ridge Mountains;

Interpreting predictions from the SAPRC07 mechanism based on regional and continental simulations by W.T. Hutzell; D.J. Luecken; K.W. Appel; W.P.L. Carter (417-429).
The SAPRC07T mechanism is implemented and evaluated in the CMAQ air quality model. The implementation is described and tested with simulations over the United States for two periods. The evaluation compares results against observations for ozone and particulate matter as well as against predictions from the SAPRC-99 mechanism for the same simulation periods and model domain. Comparisons against SAPRC-99 results reveal largest differences over urban areas with low VOC to NO x ratios. Integrated rate analysis is used to investigate the chemical reactions responsible for these differences. Comparison against observations shows over predictions of ozone concentrations over the southeastern United States. The errors appear linked to failing to match the observations during early morning hours. We discuss the source of the errors in terms of both simulation inputs and the photochemical mechanism and recommend potential directions for improving applications with regional photochemical models.► SAPRC07T mechanism implemented in a model for ozone and particulate matter. ► Evaluation compared against observations and predictions from the SAPRC-99 mechanism. ► Comparisons against SAPRC-99 revealed largest differences in ozone over urban areas. ► Integrated rate analysis investigated the chemical reactions responsible. ► Ozone predictions overestimate observations so errors and improvements are discussed.
Keywords: SAPRC; Air quality model; Tropospheric photochemistry;

A methodology to retrieve Single Scattering Albedo (SSA) values employing the ratio of Direct to Diffuse Irradiances (DDR) is used and applied to the El Paso-Juarez Airshed, a challenging region where air masses interact. The TUV model was used to obtain the calculated DDR irradiances, and the experimental irradiances were obtained from a UV-MFRSR instrument located in the city of El Paso, Texas. The wavelengths used were 332 nm and 368 nm. The retrieved SSA values at both 332 nm and 368 nm were higher in a lightly polluted day (0.66–0.81 at 332 nm, and 0.61 to 0.80 at 368 nm) than in a heavier polluted day (0.56–0.70 at 332 nm and 0.53–0.66 at 368 nm).A sensitivity study of the ground albedo and the asymmetry parameter was performed, which indicated that the variation of the asymmetry parameter is a secondary effect in the retrievals of SSA. In addition, the variation of SSA values during the day was also analyzed for the El Paso-Juarez Airshed and linked to the flow of air masses into the region using HYSPLIT trajectories. A presence of absorptive aerosols was observed during the late morning and the middle of the day. This methodology can be applied in any area, and is particularly useful for cities that experience episodes of high PM concentrations.► Retrieval of the single scattering albedo, SSA, to characterize aerosols in situ. ► The methodology used is robust and can be applied to any region. ► It is applied to the El Paso-Juarez Airshed, a very challenging region to model. ► A sensitivity study of the relevant optical, physical parameters was also performed. ► The evolution of the SSA throughout the day for this region was analyzed.
Keywords: Aerosol optical properties; UV-MFRSR; Direct-to-diffuse irradiance ratio; Single scattering albedo; Asymmetry parameter; Tropospheric ultraviolet and visible model;

Likely seeding of cirrus clouds by stratospheric Kasatochi volcanic aerosol particles near a mid-latitude tropopause fold by James R. Campbell; Ellsworth J. Welton; Nickolay A. Krotkov; Kai Yang; Sebastian A. Stewart; Michael D. Fromm (441-448).
Following the explosive 7–8 August 2008 Mt. Kasatochi volcanic eruption in southwestern Alaska, a segment of the dispersing stratospheric aerosol layer was profiled beginning 16 August in continuous ground-based lidar measurements over the Mid-Atlantic coast of the eastern United States. On 17–18 August, the layer was displaced downward into the upper troposphere through turbulent mixing near a tropopause fold. Cirrus clouds and ice crystal fallstreaks were subsequently observed, having formed within the entrained layer. The likely seeding of these clouds by Kasatochi aerosol particles is discussed. Cloud formation is hypothesized as resulting from either preferential homogenous freezing of relatively large sulfate-based solution droplets deliquesced after mixing into the moist upper troposphere or through heterogeneous droplet activation by volcanic ash. Satellite-borne spectrometer measurements illustrate the evolution of elevated Kasatochi SO2 mass concentrations regionally and the spatial extent of the cirrus cloud band induced by likely particle seeding. Satellite-borne polarization lidar observations confirm ice crystal presence within the clouds. Geostationary satellite-based water vapor channel imagery depicts strong regional subsidence, symptomatic of tropopause folding, along a deepening trough in the sub-tropical westerlies. Regional radiosonde profiling confirms both the position of the fold and depth of upper-tropospheric subsidence. These data represent the first unambiguous observations of likely cloud seeding by stratospheric volcanic aerosol particles after mixing back into the upper troposphere.► Stratospheric volcanic aerosol entrained into upper troposphere downwind of eruption. ► Cirrus clouds formed, likely-seeded by enhanced sulfate droplet and ash presence. ► Comprehensive ground and satellite-based atmospheric observations are described. ► First unambiguous account of likely cirrus cloud seeding by aged volcanic aerosol.
Keywords: Aerosol indirect effect; Volcanic aerosol; Cloud seeding; Cirrus clouds; UTLS processes; Lidar;

Characterization and heterogeneity of coarse particles across an urban area by Pramod Kumar; Philip K. Hopke; Suresh Raja; Gary Casuccio; Traci L. Lersch; Roger R. West (449-459).
Coarse particles exposures are expected to be highly heterogeneous in an urban area. However, little data are available to explore the extent of heterogeneity of coarse particles, especially on a local scale. An extensive sampling program for the coarse particles was conducted using University of North Carolina (UNC) passive aerosol samplers. The samplers were deployed for 4–5 week periods during four seasons, fall, winter, spring, and summer at 25 different sites across Syracuse, a small city located in central New York. The substrates from the UNC passive samplers were analyzed with computer-controlled scanning electron microscopy (CCSEM) providing size, shape, and elemental composition in the form of fluoresced X-ray spectra. Adaptive resonance theory (ART-2a) based neural network algorithm was applied with processed X-ray data to identify homogenous particles classes of 25,437 coarse particles from all four seasons. Thirty-four particle classes were identified with similar chemical characteristics. The mass fractions of particles in each identified class were then used to assess the homogeneity of composition and concentration across the measurement domain for each season. Road/soil dust, carbonaceous dust, biological materials, and deicing road salt were identified as the major sources of the urban coarse particles. Spatial and seasonal variations in both composition and concentration were observed and a noticeable heterogeneity between adjacent sites is indicated by the coefficient of divergence and correlation coefficient analysis.► UNC Passive Sampler deployed at 25 locations in 4 seasons in Syracuse, NY. ► Coarse particles characterized using computer-controlled scanning electron microscopy. ► Particle classes identified using an adaptive theory resonance neural network. ► Spatial and temporal patterns of coarse particle mass and composition were determined. ► Heterogeneity of particle data was assessed using coefficient of divergence analysis.
Keywords: Coarse particles; Passive sampler; Computer-controlled scanning electron microscopy; Heterogeneity; Adaptive resonance theory (ART-2a);

Long-term exposure models for traffic related NO2 across geographically diverse areas over separate years by L.-J. Sally Liu; Ming-Yi Tsai; Dirk Keidel; Armin Gemperli; Alex Ineichen; Marianne Hazenkamp-von Arx; Lucy Bayer-Oglesby; Thierry Rochat; Nino Künzli; Ursula Ackermann-Liebrich; Peter Straehl; Joel Schwartz; Christian Schindler (460-471).
Although recent air pollution epidemiologic studies have embraced land-use regression models for estimating outdoor traffic exposure, few have examined the spatio-temporal variability of traffic related pollution over a long term period and the optimal methods to take these factors into account for exposure estimates. We used home outdoor NO2 measurements taken from eight geographically diverse areas to examine spatio-temporal variations, construct, and evaluate models that could best predict the within-city contrasts in observations. Passive NO2 measurements were taken outside of up to 100 residences per area over three seasons in 1993 and 2003 as part of the Swiss cohort study on air pollution and lung and heart disease in adults (SAPALDIA). The spatio-temporal variation of NO2 differed by area and year. Regression models constructed using the annual NO2 means from central monitoring stations and geographic parameters predicted home outdoor NO2 levels better than a dispersion model. However, both the regression and dispersion models underestimated the within-city contrasts of NO2 levels. Our results indicated that the best models should be constructed for individual areas and years, and would use the dispersion estimates as the urban background, geographic information system (GIS) parameters to enhance local characteristics, and temporal and meteorological variables to capture changing local dynamics. Such models would be powerful tools for assessing health effects from long-term exposure to air pollution in a large cohort.► Long-term exposure models developed for 8 different areas in Switzerland. ► Unique comparison of LUR models using seasonal NO2 measurements made a decade apart. ► Best LUR models used land-use, dispersion, meteorological, and temporal predictors. ► Individual local area models by year best captured NO2 spatial distribution. ► Implications on the generalizability of LUR models for air pollution health studies.
Keywords: Air pollution; Geographic information systems (GIS); Land use regression (LUR); NO2; Exposure assessment; Meteorology;

There is a global concern about adverse health effects of particulate matter (PM) originating from diesel engine exhaust. In the current study, parametric investigations were carried out using a CRDI (Common Rail Direct Injection) diesel engine operated at different loads at two different engine speeds (1800 and 2400 rpm), employing diesel and 20% biodiesel blends (B20) produced from Karanja oil. A partial flow dilution tunnel was employed to collect and measure the mass of the primary particulates from diesel and biodiesel blend collected on a 47 mm quartz substrate. The collected PM (particulate matter) was subjected to chemical analyses in order to assess the amount of Benzene Soluble Organic Fraction (BSOF) and trace metals using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). For both diesel and biodiesel, BSOF results showed decreasing levels with increasing engine load. B20 showed higher BSOF as compared to those measured with diesel. The concentration of different trace metals analyzed also showed decreasing trends with increasing engine loads. In addition, real-time measurements for Organic Carbon (OC), Elemental Carbon (EC) and total particle-bound Polycyclic Aromatic Hydrocarbons (PAHs) were carried out on the primary engine exhaust coming out of the partial flow dilution tunnel. Analysis of OC/EC data suggested that the ratio of OC to EC decreases with corresponding increase in engine load for both fuels. A peak in PAH concentration was observed at 60% engine load at 1800 rpm and 20% engine load at 2400 rpm engine speeds almost identical for both kinds of fuels. Comparison of chemical components of PM emitted from this CRDI engine provides new insight in terms of PM toxicity for B20 vis-a-vis diesel.► PM of B20 & diesel were analysed for BSOF, trace metals, real-time OC, EC & PAHs. ► B20 showed lower particulate mass emission at all engine operating conditions. ► BSOF was higher for B20 PM, indicating higher toxic potential of biodiesel. ► OC was higher for B20. With increasing engine load, (i) OC/EC & (ii) PAHs decreased. ► Metals in the PM showed a decreasing trend with increasing engine load.
Keywords: Biodiesel; Particulates; Trace Metals; Elemental carbon/ organic carbon; PAHs;

Changes in OMI tropospheric NO2 columns over Europe from 2004 to 2009 and the influence of meteorological variability by Yipin Zhou; Dominik Brunner; Christoph Hueglin; Stephan Henne; Johannes Staehelin (482-495).
This study analyzes the changes of NO2 vertical tropospheric columns (VTCs) over Europe during the period 2004–2009 using a statistical model, based on a homogeneous high-quality data set of observations of the Ozone Monitoring Instrument OMI. At each point of a regular grid, a Generalized Additive regression Model (GAM) with non-parametric model terms was fitted to the observed columns to describe the most relevant factors contributing to the observed variability in NO2 VTCs. These factors include annual cycle, day of week, wind, precipitation, retrieved cloud radiance fraction, and trend. Significant negative changes are found in areas with large anthropogenic sources over Western Europe (mostly from −4 to −8% year−1). The overall negative changes are consistent with EMEP/CEIP (European Monitoring and Evaluation Programme/Center on Emission Inventories and Projections) emission estimations and previous trend studies. However, we found remarkably large spatial variations in NO2 column changes within individual regions. Our analysis shows that in particular the NO x emissions from Spanish power plants (from −10 to approx. −20% year−1) and over the center of England (up to approx. −12% year−1) have been strongly reduced in the past few years, at a rate exceeding the reported emission changes averaged over the individual country. A number of other features of the temporal behavior of the time series of tropospheric NO2 distributions over Europe were quantified, including clear annual and weekly cycles. Modeling the influence of wind considering both wind direction and wind speed not only improves the accuracy of the trend results, but can be particularly interesting for identifying the sources of the NO2 VTCs and the transport pathways of air pollutants. The effects of precipitation are observed to vary obviously during warm and cold months, due to the strong seasonal dependence of soil NO x emissions.► Analysis of changes in OMI satellite NO2 columns over Europe from 2004 to 2009. ► Significant negative trends in many densely populated areas in Western Europe. ► Largest decline in northwestern Spain in a region with large power plant emissions. ► Large decline also in industrial area in central England. ► Wind speed and direction are shown to have a pronounced impact on NO2 columns.
Keywords: NO2 trends; Generalized additive model; Remote sensing; Air pollution; Emissions;

Wind tunnel investigation of the downwash effect of a rooftop structure on plume dispersion by Amit Gupta; Ted Stathopoulos; Patrick Saathoff (496-507).
This paper investigates the downwash effect of a rooftop structure (RTS) representing a typical RTS on plume dispersion. The effect of wind direction, exhaust speed, stack location, stack height, and RTS crosswind width on the severity of the downwash effect on the plume is assessed. Wind tunnel experiments were conducted to obtain plume centerline concentrations on the roof of typical low-rise and high-rise buildings. Measurements were obtained downwind of an RTS with height h = 4 m, along-wind length l = 8 m for 3 crosswind widths w = 10 m, 20 m and 30 m. Flow visualization was also conducted to obtain a qualitative assessment of the flow downwind of the RTS. The downwash produced by the RTS caused a significant increase in roof level concentration depending on building height, stack location, stack height, exhaust speed, wind direction and RTS crosswind width. An attempt is made to provide design guidance for determining stack height required to avoid the downwash effect for an exhaust placed downwind of the RTS.► Downwash due to a rooftop structure (RTS) on plume increased re-entrainment. ► Downwash effect depends on stack, RTS and building characteristics. ► Downwash effect decreases with increase in stack height and exhaust speed. ► Downwash leads to enhanced dilution and plume bending. ► Downwash effect of RTS is negligible for tall buildings.
Keywords: Re-entrainment building; Dispersion; Rooftop structure; Dilution; Wind tunnel;

Empirical model derived from dispersion calculations to determine separation distances between livestock buildings and residential areas to avoid odour nuisance by Günther Schauberger; Rainer Schmitzer; Martin Kamp; Andreas Sowa; Roman Koch; Wilfried Eckhof; Franziska Eichler; Ewald Grimm; Joachim Kypke; Eberhard Hartung (508-515).
A new VDI guideline is under development in Germany to calculate the separation distance S (m) required between livestock and residential areas to avoid odour annoyance by an empirical model. On the basis of model calculations for 23 sites by a Lagrangian dispersion model (AUSTAL2000) a regression model was developed, using a power function S = aEb . The power function is defined by three input parameters which were restricted for an improved fit of the regression model. The basis of the power function is the odour emission flow rate E (ouE s−1) in the range between 500 ouE s−1 ≤ E ≤ 50,000 ouE s−1. The two other predictors are the relative frequency of the wind direction F (‰) of a 10° sector (10‰ ≤ F ≤ 60‰) and the odour exceedance probability P (%) (7% ≤ P ≤ 40%) of the odour impact criterion, which define the exponent b and the multiplicative factor a of the power function. One of the requirements for this empirical model was a conservative assessment, which results in only a 12% underestimation of the separation distance compared to the dispersion model. The model can be used in a “paper and pencil” mode, which enabling a simple and straightforward first evaluation of a planned livestock building. For a more detailed assessment, a dispersion model can be applied with the entire meteorological information available (e.g. stability of the atmosphere, wind velocity), the geometry of the emission source, a time dependant odour emission rate, as well as the orography of the site.Display Omitted► Odour is one of the major nuisances in the environment, often caused by livestock. ► In rural areas odour annoyance is handled by a separation distances. ► This distances were calculated by empirical models. ► A new empirical model was developed by using a Lagrangian dispersion model. ► The features of this new guideline are presented.
Keywords: Separation distance; Nuisances; Livestock; Odour; Residential area; Dispersion model;

Formation of secondary organic carbon and cloud impact on carbonaceous aerosols at Mount Tai, North China by Zhe Wang; Tao Wang; Jia Guo; Rui Gao; Likun Xue; Jiamin Zhang; Yang Zhou; Xuehua Zhou; Qingzhu Zhang; Wenxing Wang (516-527).
Carbonaceous aerosols measured at Mount Tai in north China in 2007 were further examined to study the formation of secondary organic carbon (SOC) and the impact of clouds on carbonaceous species. A constrained EC-tracer method and a multiple regression model showed excellent agreement in estimating SOC concentration. The average concentrations of non-volatile and semi-volatile SOC (SOCNV and SOCSV) were 2.61, 5.58 μg m−3 in spring and 2.81, 10.44 μg m−3 in summer. The total SOC accounted for 57.3% and 71.2% of total organic carbon in spring and summer, respectively, indicating the presence of high loading of secondary organic aerosol (SOA) in the North China Plain. The fraction of SOCNV increased with photochemical age (as indicated by NOx/NOy ratios) of air mass, whereas SOCSV was also influenced by the dynamic equilibrium between formation and sink. Significant scavenging by clouds of non-volatile organic carbon (OCNV) and elemental carbon (EC) was observed, whereas semi-volatile organic carbon (OCSV) concentrations increased during clouds, suggesting substantial SOA formation through aqueous-phase reactions in clouds. A mass balance model was proposed to quantify the scavenging coefficients for OCNV, EC and formation rates of OCSV in clouds. The scavenging coefficient constant of EC (K EC) varied from 0.11 to 0.90 h−1, and was higher than that of OCNV (K NV-OC: 0.07–0.55 h−1), implying internal mixing of EC with more hygroscopic species. The formation rate constant (J SV-OC) and sink constant (S SV-OC) of OCSV ranged from 0.09 to 1.39 h−1 and 0.001 to 1.07 h−1, respectively. These field derived parameters could be incorporated into atmospheric models to help close the gap between predicted and observed SOA loadings in the atmosphere.► Constrained EC-tracer and multiple regression methods for SOC estimation agree well. ► Strong SOA formation at Mt. Tai and high SOA loading in the North China Plain. ► Different dependence of non-volatile and semi-volatile SOC on photochemical age. ► Significant scavenging of non-volatile OC and EC by clouds at Mt. Tai. ► Semi-volatile SOC formation through aqueous-phase reactions in cloud processing.
Keywords: Secondary organic aerosol (SOA); In-cloud SOA formation; Cloud scavenging; Carbonaceous aerosol; Mount Tai (Mt. Tai); Multiple linear regression;

Effect of ambient air pollution on daily mortality rates in Guangzhou, China by Ignatius Tak Sun Yu; Yong hui Zhang; Wilson Wai San Tam; Qing Hua Yan; Yan jun Xu; Xiao jun Xun; Wei Wu; Wen Jun Ma; Lin Wei Tian; Lap Ah Tse; Xiang Qian Lao (528-535).
We aimed to investigate the effects of ambient air pollutants on daily mortality in a relatively stable and homogeneous population in Guangzhou, China. Daily mortality, air pollution, and weather data between 2006 and 2009 were collected. The generalized additive model with poison regression was used to estimate the excessive risks (ERs) of air pollutants (PM10, SO2, and NO2) on total, cardiovascular and respiratory mortality. The effects of lag0–1 were the greatest for total non-accidental and cardiovascular deaths. The increments of 10 μg m−3 in SO2, NO2, and PM10 were associated with ERs of 1.54% (95%CI: 1.03–2.06%), 1.42% (95%CI: 1.06–1.78%), and 1.26% (95%CI: 0.86–1.66%) respectively for total non-accidental deaths, and 2.28% (95%CI: 1.40–3.16%), 1.81% (95%CI: 1.20–2.41%), and 1.79% (95%CI: 1.11–2.47%) respectively for cardiovascular deaths. For persons who died from respiratory disease, however, the maximum effects occurred at lag0. The ERs for SO2, NO2, and PM10 were 1.36% (95%CI: 0.23–2.50%), 1.47% (95%CI: 0.66–2.29%) and 0.93% (95%CI: 0.03–1.83%), respectively. The effects of the three air pollutants on mortality were stronger in elderly and in women. The ERs in the present study were higher than those reported in Europe, the U.S., and most other Asian cities. Our findings show relatively higher ERs of daily mortality by ambient air pollutants in the center of Guangzhou, China, compared with estimates in other cities. Further studies with accurate exposure measurement among homogeneous population are needed to evaluate the precise magnitudes of the effects of the air pollutants.► The magnitudes of the excess risk of mortality by air pollution varied in different cities and countries. ► The excess risk of daily mortality by air pollutants was higher among homogeneous population in city central areas. ► Further studies with accurate exposure measurement among homogeneous populations are needed.
Keywords: Ambient air pollution; Daily mortality; Chinese;

Impact of the 2009 Attica wild fires on the air quality in urban Athens by V. Amiridis; C. Zerefos; S. Kazadzis; E. Gerasopoulos; K. Eleftheratos; M. Vrekoussis; A. Stohl; R.E. Mamouri; P. Kokkalis; A. Papayannis; K. Eleftheriadis; E. Diapouli; I. Keramitsoglou; C. Kontoes; V. Kotroni; K. Lagouvardos; E. Marinou; E. Giannakaki; E. Kostopoulou; C. Giannakopoulos; A. Richter; J.P. Burrows; N. Mihalopoulos (536-544).
At the end of August 2009, wild fires ravaged the north-eastern fringes of Athens destroying invaluable forest wealth of the Greek capital. In this work, the impact of these fires on the air quality of Athens and surface radiation levels is examined. Satellite imagery, smoke dispersion modeling and meteorological data confirm the advection of smoke under cloud-free conditions over the city of Athens. Lidar measurements showed that the smoke plume dispersed in the free troposphere and lofted over the city reaching heights between 2 and 4 km. Ground-based sunphotometric measurements showed extreme aerosol optical depth, reaching nearly 6 in the UV wavelength range, accompanied by a reduction up to 70% of solar irradiance at ground. The intensive aerosol optical properties, namely the Ångström exponent, the lidar ratio, and the single scattering albedo, showed typical values for highly absorbing fresh smoke particles. In-situ air quality measurements revealed the impact of the smoke plume down to the surface with a slight delay on both the particulate and gaseous phase. Surface aerosols increase was encountered mainly in the fine mode with prominent elevation of OC and EC levels. Photochemical processes, studied via NO x titration of O3, were also shown to be different compared to typical urban photochemistry.► Burnt scar mapping reveal 13,045 ha of forest destructed by the fires in Athens. ► Sunphotometric measurements showed extreme AODs (up to 6 in UV). ► Solar irradiance levels at ground decreased up to 70%. ► In-situ measurements show smoke impacts on particulate matter and photochemistry.
Keywords: Pollution; Biomass burning; Aerosol; Photochemistry; Radiation;

We use a general circulation model (NASA Goddard Institute for Space Studies GCM 3) to investigate the regional climate response to removal of aerosols over the United States. We perform a pair of transient 2010–2050 climate simulations following a scenario of increasing greenhouse gas concentrations, with and without aerosols over the United States and with present-day aerosols elsewhere. We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4–0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1–2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.► We perform two 2010–2050 climate simulations to examine the climate response to US aerosol removal. ► Removing US aerosols causes surface temperatures to increase by 0.4–0.6 K in the eastern US. ► Temperatures during summertime heat waves in the Northeast rise by as much as 1–2 K. ► The warming in the Northeast is amplified by feedbacks involving cloud cover and soil moisture. ► Reducing US aerosol sources to achieve air quality goals may lead to unintended regional warming.
Keywords: Regional climate change; Pollution; Short-lived species; Air quality; Particulate matter;

The numerical modeling the sensitivity of coastal wind and ozone concentration to different SST forcing by Hyun-Jung Choi; Hwa Woon Lee; Won-Bae Jeon; Soon-Hwan Lee (554-567).
This study evaluated an atmospheric and air quality model of the spatial variability in low-level coastal winds and ozone concentration, which are affected by sea surface temperature (SST) forcing with different thermal gradients. Several numerical experiments examined the effect of sea surface SST forcing on the coastal atmosphere and air quality. In this study, the RAMS-CAMx model was used to estimate the sensitivity to two different resolutions of SST forcing during the episode day as well as to simulate the low-level coastal winds and ozone concentration over a complex coastal area. The regional model reproduced the qualitative effect of SST forcing and thermal gradients on the coastal flow. The high-resolution SST derived from NGSST-O (New Generation Sea Surface Temperature Open Ocean) forcing to resolve the warm SST appeared to enhance the mean response of low-level winds to coastal regions. These wind variations have important implications for coastal air quality. A higher ozone concentration was forecasted when SST data with a high resolution was used with the appropriate limitation of temperature, regional wind circulation, vertical mixing height and nocturnal boundary layer (NBL) near coastal areas.► This study attempted to simulate the air quality with the new fine SST data. ► Near the coastal regions, the NGSST-O has more increased temperatures. ► The intensified NBL in NGSST-O is shown. ► Predicting the ozone concentrations was improved by applying the NGSST-O.
Keywords: NGSST-O; NOSST; RAMS-CAMx; Coastal wind; NBL; Ozone concentration;

We investigated suspended particulate matter (SPM, particles with a 100% cut-off aerodynamic diameter of 10 μm) and PM2.5 (particles with a 50% cut-off aerodynamic diameter of 2.5 μm) concentrations in aerosols sampled in Akita Prefecture, Japan, from April 2008 to January 2010, and the carbon isotope ratios (δ13C) of elemental carbon (EC) in both SPM and PM2.5 and in samples from possible sources. We also determined the ion contents of SPM and estimated the back trajectories of air masses arriving at Akita Prefecture during the study period. The SPM concentration was very low (annual average, 15.2 μg m−3), and it tended to be higher in spring and lower in winter. We attributed the higher SPM in spring to dust storms brought from the Asian continent. The average annual PM2.5 concentration was 8.6 μg m−3. δ13C of source samples (gasoline and diesel vehicle exhaust, fireplace soot, open biomass burning emissions, street dust, soil, charcoal, and coal) ranged from −34.7‰ to −1.8‰. δ13C values of soot from gasoline light-duty (−24.4 ± 0.7‰) and passenger vehicles (−24.1 ± 0.6‰) were very similar to that of soot from all diesel vehicles (−24.3 ± 0.3‰). δ13C was enriched in SPM in winter compared with summer values, moreover, only a slight seasonal trend was detected in δ13C in PM2.5. From these data and the source results, we hypothesized that the enrichment of δ13C of SPM and PM2.5 in winter was a long-range effect of overseas combustion processes such as coal combustion. In addition, δ13C of SPM was correlated with Cl and Mg2+ contents in SPM, suggesting the influence of sea salt. We verified this hypothesis by back trajectory analyses. The results indicated a continental influence effects on EC of SPM and PM2.5 in winter.► We investigated EC source in SPM and PM2.5 to use δ13C. ► The δ13C of ambient and many sources were analyzed. ► The EC in winter were affected by coal heating in the Eurasian continent.
Keywords: Stable carbon isotope ratio; IRMS; Particulate matter; Elemental carbon; SPM; PM2.5; Source apportionment;

Utilizing state estimation to determine the source location for a contaminant by Andrew J. Annunzio; George S. Young; Sue Ellen Haupt (580-589).
In the event of an atmospheric contaminant release, it is crucial to ascertain the source information for the contaminant, both for mitigation purposes and to predict subsequent transport and dispersion. Here, obtaining part of this information, namely the contaminant source location, is accomplished by adopting a state estimation approach for instantaneous and continuous contaminant releases. The relevant state components that we exploit here are the contaminant cloud’s axis and spread. For an instantaneous release, we can adopt a Lagrangian approach to obtain the source location by extrapolating state observations back to the initial state. In contrast, the formulation for a continuous release cannot adopt this strictly Lagrangian approach because a steady flow of contaminants implies that the contaminant cloud is statistically stationary with respect to the sensor grid. Therefore, the concentration data are averaged in time and a hybrid Lagrangian/Eulerian framework is used to determine the average state. It is shown that with these frameworks it is possible to ascertain the contaminant source location for both dense and sparse sensor grids. An advantage of these algorithms is that no meteorological input is required. The algorithms in the form presented here, are relevant for short-range transport and dispersion. However, the source term estimation method presented here can be extended to longer-range applications by relaxing assumptions on the contaminant atmospheric transport and dispersion.► Lagrangian approach improves efficiency for contaminant source location estimation. ► Instantaneous sources can be handled with a purely Lagrangian approach. ► Continuous sources require a combined Lagrangian/Eulerian approach. ► An advantage of these algorithms is that no meteorological input is required.
Keywords: Source term estimation; Atmospheric transport and dispersion; FUSION field trial 2007; Contaminant spread; State estimation;

Analysis of acid rain patterns in northeastern China using a decision tree method by Xiuying Zhang; Hong Jiang; Jiaxin Jin; Xiaohua Xu; Qingxin Zhang (590-596).
Acid rain is a major regional-scale environmental problem in China. To control acid rain pollution and to protect the ecological environment, it is urgent to document acid rain patterns in various regions of China. Taking Liaoning Province as the study area, the present work focused on the spatial and temporal variations of acid rains in northeastern China. It presents a means for predicting the occurrence of acid rain using geographic position, terrain characteristics, routinely monitored meteorological factors and column concentrations of atmospheric SO2 and NO2. The analysis applies a decision tree approach to the foregoing observation data. Results showed that: (1) acid rain occurred at 17 stations among the 81 monitoring stations in Liaoning Province, with the frequency of acid rain from 0 to 84.38%; (2) summer had the most acid rain occurrences followed by spring and autumn, and the winter had the least; (3) the total accuracy for the simulation of precipitation pH (pH ≤ 4.5, 4.5 < pH ≤ 5.6, and pH > 5.6) was 98.04% using the decision tree method known as C5. The simulation results also indicated that the distance to coastline, elevation, wind direction, wind speed, rainfall amount, atmospheric pressure, and the precursors of acid rain all have a strong influence on the occurrence of acid rains in northeastern China.► A decision tree method is used to predicate the acid rain in northeastern China. ► Acid rain occurred at 17 stations among the 81 monitoring stations. ► Summer has the most acid rain occurrences followed by spring, autumn, and winter. ► Total accuracy for the simulation of precipitation pH is 98.04%. ► Geography, elevation, and atmospheric factors affect the occurrence of acid rains.
Keywords: Acid rain; Decision tree; Geographical position; Terrain characteristics; Meteorological data; Column SO2 and NO2; Northeast China;

There have been very few studies carried out in Indonesia on the atmospheric aerosol optical properties and their impact on the earth climate. This study utilized solar radiation and aerosol measurement results of Indonesian GAW station Bukit Kototabang in Sumatra. The radiation data of nine years were used as input to a radiation simulation code for retrieving optically equivalent parameters of aerosols, i.e., aerosol optical thickness (AOT), coarse particle to fine particle ratio (γ-ratio), and soot fraction. Retrieval of aerosol properties shows that coarse particles dominated at the station due to high relative humidity (RH) reaching more than 80% throughout the year. AOT time series showed a distinct two peak structure with peaks in MJJ and NDJ periods. The second peak corresponds to the period of high RH suggesting it was formed by active particle growth with large RH near 90%. On the other hand the time series of hot spot number, though it is only for the year of 2004, suggests the first peak was strongly contributed by biomass burning aerosols. The γ-ratio took a value near 10 throughout the year except for November and December when it took a larger value. The soot fraction varies in close relation with the γ-ratio, i.e. low values when γ was large, as consistent with our proposal of active particle growth in the high relative periods.► The study shows radiative properties of aerosols thus obtained at Bukit Kototabang station undergo a characteristic seasonal variation and large temporal change particularly related with the tropical atmospheric condition. ► Retrieval of aerosol properties shows that coarse particles dominated at the station due to high relative humidity (RH) reaching more than 80% throughout the year. AOT time series showed a distinct two peak structure with peaks in MJJ and NDJ periods. ► Results of the study showed large contribution of biomass burning aerosols to the AOT500 in dry season period. ► It was found from the study that direct and diffuse radiation fluxes were useful to retrieve particle size γ and soot fraction f soot, while NIR flux was useful for estimate optical aerosol thickness AOT500.
Keywords: AOT (aerosol optical thickness); Coarse particle to fine particle ratio (γ-ratio); Soot fraction; f soot; γ-ratio;

Concentrated human activity and limited atmospheric mixing create a high potential for airborne pollutant impacts to alpine lakes developed as mountain resorts. Lake Tahoe is a major alpine resort straddling the California–Nevada border, receiving more than two million visitors each year. The lake’s clarity has declined substantially since the inception of intense development in the Tahoe basin in the 1970s. The 2002–2004 Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted as part of a multi-agency effort to develop a water quality management plan for the lake. Estimating aerosol deposition to the lake requires detailed knowledge of the spatial and temporal patterns of aerosol concentration, size distribution, and chemical composition over the entire basin – and developing a management plan requires also that the sources of the aerosols be known with considerable specificity. In lieu of the intensive measurement network implied by this level of detail, we hypothesized that a set of measurements to characterized the temporal, spatial, and size distribution patterns of particles in ambient air and in local emissions in the vicinity of Lake Tahoe could be used to extrapolate long time series of simple measurements to an annual aerosol deposition computation. Here we report the results of our detailed aerosol measurement campaign. Our results show that there are strong systematic and repeating gradients in aerosol loading that occur as functions of location, land use, traffic activity, and time of day, and that road dust is a major source of aerosols around the lake. In addition, we observed strong consistency of particle size distributions as a function of source type, largely independent of particle concentrations. Finally, we demonstrated the use of particle counters to directly observe downwind dispersion and deposition of particles. Together, these findings support the use of imputed location- and time-specific size distributions in annual aerosol deposition calculations, even though particle size distributions were not directly measured in the LTADS baseline monitoring program, and that program was conducted at only a limited set of sites in the Tahoe basin.Two companion articles in this journal issue describe the overall findings of the LTADS study (Dolislager et al., “Overview of the Lake Tahoe Atmospheric Deposition Study”) and the results of measurements taken on the lake itself (VanCuren et al., “Air Pollution in the Shore Zone of a Large Alpine Lake – 2 – Local and Regional Pollutant Distribution over Lake Tahoe California–Nevada”).
Keywords: Lake Tahoe; Aerosol; Size distributions; Emissions; Road dust; Deposition; Water quality; Alpine lake;

A summary of the Lake Tahoe Atmospheric Deposition Study (LTADS) by Leon J. Dolislager; Richard VanCuren; James R. Pederson; Ash Lashgari; Eileen McCauley (618-630).
The Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted by the California Air Resources Board (CARB) primarily to generate refined estimates of the atmospheric deposition of nitrogen (N), phosphorous (P), and particulate matter (PM) directly to Lake Tahoe, which straddles the boundary between the states of California and Nevada in the United States of America. LTADS estimated that approximately 185, 3, and 755 metric tons respectively of N, P, and PM being directly deposited to the lake from the atmosphere. Various measurements of emissions, meteorology, and air quality were made within and west (typically upwind) of the Lake Tahoe Air Basin to better understand the pollutant sources contributing to the atmospheric deposition. The data indicate that ammonia (NH3) contributes the bulk of the N loading. Aerosols with diameters greater than 2.5 μm contribute the bulk of the P and PM mass loadings. The emission sources of P and PM appear to be primarily local and associated with motor vehicles. However, construction, fires, and natural sources also contribute to the pollutant loadings. LTADS was part of a much larger research program to guide efforts to restore the remarkable water clarity of Lake Tahoe.
Keywords: LTADS; Lake Tahoe; Atmospheric deposition; Air quality; Meteorology;

The temporal, spatial, and size-distribution patterns of particles in ambient air over the surface of Lake Tahoe (Nevada and California) were studied as part of the 2003–2004 Lake Tahoe atmospheric deposition study (LTADS). The concentration of population along the shoreline of Lake Tahoe makes accurate characterization of local aerosol generation and transport especially important in estimation of annual particle flux to the surface of the lake. Measurements taken while cruising on the lake show that aerosol concentrations in near shore areas are primarily controlled by a combination of diurnal cycling of land- and lake- breezes and particle emissions driven by cycles of human activity near the shore. These effects were observed to be highly localized. Highest concentrations were found just offshore from urbanized areas, especially shoreline centers of activity; lowest concentrations were found along undeveloped shoreline; low-to-intermediate concentrations were measured over the middle areas of the lake. The on-lake data reported here indicate that aerosols over the lake, and thus dry deposition to the lake, are dominated by the same processes that control onshore emissions, and that the impact is strongest in the near shore areas of the lake.
Keywords: Lake Tahoe; Aerosol; Size distributions; Road dust; Deposition; Water quality;

An assessment of ozone concentrations within and near the Lake Tahoe Air Basin by Leon J. Dolislager; Richard VanCuren; James R. Pederson; Ash Lashgari; Eileen McCauley (645-654).
The Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted by the Air Resources Board of the State of California (CARB) primarily to generate refined estimates of the atmospheric deposition of nitrogen, phosphorous, and particulate matter directly to Lake Tahoe, which straddles the border between the states of California and Nevada near Reno, Nevada. The enhanced air quality monitoring during LTADS also included ozone measurements, which yielded additional insights into atmospheric processes and the role of transport in determining ozone concentrations within the Lake Tahoe Air Basin.The Lake Tahoe Air Basin is located generally downwind of air basins with major emissions of ozone precursors (e.g., VOCs, NOx), capable of generating significant ozone concentrations. Furthermore, vegetation on the western slope of the Sierra Nevada contribute biogenic organic compounds to the air mass. Ozone concentrations within the Tahoe Basin infrequently exceed the local 1-h threshold set to protect forest health (0.08 ppm) and the California 8-h ambient air quality standard (0.070 ppm). A concern then is the potential contribution of regional emission sources to the ozone concentrations observed in the Tahoe Basin. The ozone data collected during LTADS helped to better characterize the relative contribution of local and regional pollution sources to ozone air quality within the Tahoe Basin.The data indicate potential 1- or 2-day intact transport on rare occasions but generally the mixing of the atmosphere over the Sierra Nevada disperses the anthropogenic ozone throughout the boundary layer, which is generally more than a kilometer or two deep during the day. The data analysis indicates that emissions from upwind air basins add to the atmospheric burden of ozone concentrations, raising the regional concentrations in the Sierra Nevada. Given the large background and upwind enhancements relative to the ambient air quality standards, the local contribution does not need to be large to contribute to exceedances of an ozone air quality standard.This information can be used to refine hypotheses about the relative role of local and regional sources of air pollution impacting the Tahoe Basin. Ultimately, the improved understanding of air quality within the Tahoe Basin will guide actions in pollution control plans designed to protect public health and welfare (e.g., visibility, forest health) within this unique alpine setting.
Keywords: LTADS; Lake Tahoe; Sierra Nevada; Ozone; Transport;

A survey of NO2:SO2 emission ratios measured in marine vessel plumes in the Strait of Georgia by Robert McLaren; Patryk Wojtal; Jamie D. Halla; Cris Mihele; Jeffrey R. Brook (655-658).
We report nocturnal measurements of NO2 and SO2 by DOAS within marine vessel plumes that impact an island site close to Vancouver during the summer of 2005. The median NO2/SO2 molar ratio from 17 ship plumes (2.86) is marginally higher than the molar NOx/SOx emissions ratio for both: marine vessel emissions (2.39–2.66) in a 2005 inventory for the region and, “underway” emissions of major ocean going vessels (2.04–2.12) in a related marine inventory. Due to the limited nature of our survey, we conclude that the difference between observations and inventories is not unreasonable. The generally low NO2/SO2 ratios we observe are a direct result of the high sulfur content of marine fuels. Measurement of NO2/SO2 ratios is one way to monitor future changes that will occur when new regulations come into force in the Emissions Control Area (ECA) for North American waters, with restrictions on the sulfur content of marine fuel by 2012.
Keywords: Marine vessel emissions; Emissions control; Emissions inventory; NO2; SO2; DOAS;

Ammonia biofiltration and nitrous oxide generation during the start-up of gas-phase compost biofilters by Guilherme D.N. Maia; George B. Day V; Richard S. Gates; Joseph L. Taraba (659-664).
Gas-Phase Biofiltration technology is widely utilized for treating ammonia gas (NH3) with one of its potential detrimental by-products being nitrous oxide (N2O), a potent greenhouse gas (100-y radiative forcing 298 times greater than carbon dioxide). The present work was conducted to investigate the relation between NH3 removal during biofiltration and N2O generation as a product of incomplete denitrification during the start-up of gas-phase compost biofilters. Four laboratory scale tubular biofilters in up flow mode (20 s residence-time) were studied for 21 days: 3 replicates were subjected to 16 ppmv (0.78 g m−2 h−1) of NH3 and a statistical control not subjected to NH3. Ammonia concentration differences between biofilter inlet (Bottom = 16 ppmv) and outlet (Top) and N2O concentration differences between biofilter outlet (Top) and biofilter inlet (background concentrations at the bottom) were used to determine the extent of the correlation between NH3 removal and N2O generation. Correlations with CH4 and CO2 were also reported. The high Spearman correlation coefficients for the three replicates (ρ = −0.845, −0.820, and −0.841, with P ≤ 0.0001 for replications A, B and C, respectively) suggested that availability of nitrate/nitrite owing to NH3 nitrification favored conditions for N2O generation as a sub-product of denitrification. The statistical control received no NH3 inputs and did not generate N2O. Therefore, the results indicated that the process of NH3 removal was a trigger for N2O production. Carbon dioxide and N2O were moderately correlated. Methane and N2O were weakly correlated and only for replicate C. No significant correlation was found for the Statistical Control between N2O and CH4.
Keywords: Ammonia biofiltration; Gas-phase biofilters; Greenhouse gases; Livestock; Nitrous oxide; Nitrification; Denitrification;

Generation of reactive oxygen species (ROS) – including superoxide (O2 ), hydrogen peroxide (HOOH), and hydroxyl radical (OH) – has been suggested as one mechanism underlying the adverse health effects caused by ambient particulate matter (PM). In this study we compare HOOH and OH production from fine and coarse PM collected at an urban (Fresno) and rural (Westside) site in the San Joaquin Valley (SJV) of California, as well as from laboratory solutions containing dissolved copper or iron. Samples were extracted in a cell-free, phosphate-buffered saline (PBS) solution containing 50 μM ascorbate (Asc). In our laboratory solutions we find that Cu is a potent source of both HOOH and OH, with approximately 90% of the electrons that can be donated from Asc ending up in HOOH and OH after 4 h. In contrast, in Fe solutions there is no measurable HOOH and only a modest production of OH. Soluble Cu in the SJV PM samples is also a dominant source of HOOH and OH. In both laboratory copper solutions and extracts of ambient particles we find much more production of HOOH compared to OH: e.g., HOOH generation is approximately 30–60 times faster than OH generation. The formation of HOOH and OH are positively correlated, with roughly 3% and 8% of HOOH converted to OH after 4 and 24 h of extraction, respectively. Although the SJV PM produce much more HOOH than OH, since OH is a much stronger oxidant it is unclear which species might be more important for oxidant-mediated toxicity from PM inhalation.
Keywords: Particulate matter (PM); Reactive oxygen species (ROS); Transition metals; Copper; Iron;

Wind tunnel measurements of pollutant turbulent fluxes in urban intersections by Matteo Carpentieri; Paul Hayden; Alan G. Robins (669-674).
Wind tunnel experiments have been carried out at the EnFlo laboratory to measure mean and turbulent tracer fluxes in geometries of real street canyon intersections. The work was part of the major DAPPLE project, focussing on the area surrounding the intersection between Marylebone Road and Gloucester Place in Central London, UK. Understanding flow and dispersion in urban streets is a very important issue for air quality management and planning, and turbulent mass exchange processes are important phenomena that are very often neglected in urban modelling studies. The adopted methodology involved the combined use of laser Doppler anemometry and tracer concentration measurements. This methodology was applied to quantify the mean and turbulent flow and dispersion fields within several street canyon intersections. Vertical profiles of turbulent tracer flux were also measured. The technique, despite a number of limitations, proved reliable and allowed tracer balance calculations to be undertaken in the selected street canyon intersections. The experience gained in this work will enable much more precise studies in the future as issues affecting the accuracy of the experimental technique have been identified and resolved.
Keywords: Urban canopy; Concentration measurements; Pollutant exchanges; Laser Doppler anemometry; Vertical exchanges;

Particulate matter exposure of bicycle path users in a high-altitude city by Oscar A. Fajardo; Nestor Y. Rojas (675-679).
It is necessary to evaluate cyclists’ exposure to particulate matter and if they are at a higher risk due to their increased breathing rate and their exposure to freshly emitted pollutants. The aim of this pilot study was to determine cyclists’ exposure to PM10 in a highly-polluted, high-altitude city such as Bogotá, and comment on the appropriateness of building bicycle paths alongside roads with heavy traffic in third world cities. A total of 29 particulate matter (PM10) measurements, taken at two sampling sites using Harvard impactors, were used for estimating the exposure of users of the 80th street bicycle path to this pollutant. PM10 dose could be considered as being high, especially due to high concentrations and cyclists’ increased inhalation rates. A random survey was conducted over 73 bicycle path users to determine cyclists’ time, distance and speed on the bicycle path on a daily and weekly basis, their level of effort when cycling and general characteristics, such as this population’s gender and age. Based on this information, the PM10 average daily dose (ADDc) for different bicycle path users and the ratio between ADDc and a reference ADD for people at rest exposed to an indoor concentration of 25 μg m−3 were estimated. The average increase in ADD was 6%–9% when riding with light effort and by 12%–18% when riding with moderate effort. The most enthusiastic bicycle path users showed ADDc/ADDr ratios as high as 1.30 when riding with light effort and 1.64 when riding with moderate effort, thereby significantly increasing their PM10 exposure-associated health risks.► Users of bicycle paths alongside main roads in Bogotá are exposed to high PM10 levels. ► Cycling on such bicycle paths may increase the PM10 average daily dose (ADD) up to 64%. ► The ADD depends strongly on the level of effort and the cycling time.
Keywords: Bicycle path; PM10; Exposure; Average daily dose; Cycling; Cyclist;

Corrigendum to “Intra-urban correlation and spatial variability of air toxics across an international airshed in Detroit, Michigan (USA) and Windsor, Ontario (Canada)” [Atmos. Environ. 44 (2010) 1162–1174] by Lindsay Miller; Lawrence D. Lemke; Xiaohong Xu; Shannon M. Molaroni; Hongyu You; Amanda J. Wheeler; Jason Booza; Alice Grgicak-Mannion; Richard Krajenta; Phillip Graniero; Helene Krouse; Lois Lamerato; Delbert Raymond; John Reiners; Linda Weglicki (683-686).