Atmospheric Environment (v.54, #C)

Spatiotemporal modeling with temporal-invariant variogram subgroups to estimate fine particulate matter PM2.5 concentrations by Chu-Chih Chen; Chang-Fu Wu; Hwa-Lung Yu; Chang-Chuan Chan; Tsun-Jen Cheng (1-8).
Short-term exposure estimation of daily air pollution levels incorporating geographic information system (GIS) into spatiotemporal modeling remains a great challenge for assessing corresponding acute adverse health effects. Due to daily meteorological effects on the dispersion of pollutants, explanatory spatial covariables and their coefficients may not be the same as in classical land-use regression (LUR) modeling for long-term exposure. In this paper, we propose a two-stage spatiotemporal model for daily fine particulate matter (PM2.5) concentration prediction: first, daily nonlinear temporal trends are estimated through a generalized additive model, and second, GIS covariates are used to predict spatial variation in the temporal trend-removed residuals. To account for spatial dependence on meteorological conditions, the dates of the study period are divided by the sill of the daily empirical variogram into approximately temporal-invariant subgroups. Within each subgroup, daily PM2.5 estimations are obtained by combining the temporal and spatial parts of the estimations from the two stages. The proposed method is applied to the modeling of spatiotemporal PM2.5 concentrations observed at 18 ambient air monitoring stations in Taipei metropolitan area during 2006–2008. The results showed that the PM2.5 concentrations decreased whereas the relative humidity and wind speed increased with the sill subgroups, which may be due to the effects of daily meteorological conditions on the dispersions of the particles. Also, the covariates and their coefficients of the LUR models varied with subgroups and had in general higher adjusted R-squares and smaller root mean square errors in prediction than those of a single overall LUR model.► Separate LUR models are needed to better predict daily PM2.5 concentration. ► Dates need to be grouped for temporal-invariant homogeneous spatial association. ► Subgroup mean PM2.5 concentration decreased with relative humidity and wind speed. ► The subgroup cross-validation adjusted R-squares ranged from 0.39 to 0.59.
Keywords: Empirical variogram; Geographic information system; Kriging; Land-use regression; Temporal trend;

Evaluation of ginkgo as a biomonitor of airborne polycyclic aromatic hydrocarbons by Michio Murakami; Maho Abe; Yoriko Kakumoto; Hiromi Kawano; Hiroko Fukasawa; Mahua Saha; Hideshige Takada (9-17).
The utility of ginkgo leaves as biomonitors of airborne polycyclic aromatic hydrocarbons (PAHs) was evaluated. We investigated PAH concentrations among tree species, the effect of variations in leaf position in a tree, tissue distributions, correlations between ginkgo leaves and air, and seasonal variations. Among the five species examined (Ginkgo biloba L., Zelkova serrata Makino, Liriodendron tulipifera L., Prunus yedoensis Matsum, and Magnolia kobus DC.), ginkgo accumulated the greatest amount of PAHs from roadside air. Most PAHs (∼80%) were accumulated in the wax fraction, and most of the remainder (17%) penetrated the inner tissues of the leaves. PAH concentrations in ginkgo leaves decreased with increasing height and distance from the road, reflecting the derivation of PAHs from vehicle emissions. Seasonal time-series sampling showed that PAH concentrations in ginkgo leaves increased with time, attributable to the effects of temperature and accumulation through long-term exposure. Concentrations in ginkgo leaves collected from various roads showed a strong and significant correlation with those in air collected by a high-volume air sampler (r 2  = 0.68, P  < 0.01). Ginkgo leaf data clearly showed a dramatic decrease in the ratio of low-molecular-weight (LMW) PAHs to high-molecular-weight PAHs from 2001 or 2002 to 2006, indicating that on-road diesel emission regulations effectively reduced LMW PAH concentrations in air.►We evaluated the utility of ginkgo as a tool for biomonitoring PAHs in air. ► PAH concentrations in ginkgo were strongly correlated with those in air. ► PAHs in ginkgo were affected by temperature and long-term accumulation. ► Ginkgo accumulated PAHs derived from vehicle emissions. ► The data showed that diesel emission regulations reduced low molecular weight PAHs.
Keywords: Diesel emission; PAHs; Roadside; Temporal variation; Tissue distribution; Tokyo;

The paper presents the results of a field test carried out in Gdańsk region between 01-01-2010 and 31-12-2010 in order to demonstrate equivalence of the Eberline FH 62-1 sampler to the reference gravimetric method of suspended PM10 dust measurement. The differences in PM10 dust concentration provided by both methods have been discussed for different seasons of the year. A method of estimation of the correction factors/correction equations has been described based on the European Union guide “Demonstration of Equivalence of Ambient Air Monitoring Methods. EC Working Group on Guidance for the Demonstration of Equivalence”. The results obtained from Eberline sampler are equivalent to the ones from gravimetric method, but after application of data correction. The investigation revealed different correction factors/correction equations for winter and summer season. The winter season is characterized by higher PM10 concentration and bigger discrepancies between both methods. A lack of equivalence has been found for PM10 dust concentration higher than 30 μg m−3.► The results obtained via the Eberline sampler are equivalent reference method, but after using correction data. ► There was not a single correction factor/correction equation for the entire measurement period. ► For the dust concentration higher than 30 μg m−3 the equivalence conditions are not fulfilled.
Keywords: PM10 dust; Field test; Correction factors; Eberline sampler;

The latest SAPRC photochemical mechanism SAPRC07 (S07), an update from SAPRC99 (S99), is implemented into the Community Multi-scale Air Quality (CMAQ) model and applied to simulate a high ozone episode during the Texas Air Quality Study 2000 (TexAQS 2000). The results from the S07 mechanism are compared with those from the S99 mechanism. In general, the predicted O3 concentrations by S07 are lower than those of S99 with maximum difference as high as 20%. The two mechanisms also show significant differences in the predicted OH, HNO3, PAN and HCHO concentrations. S99 predicts higher OH concentration by 7–20%, higher PAN by approximately 20–25% and higher HCHO by approximately 15% than S07. OH budget analysis suggests that OH propagation factor (POH) is higher in urban and industrial areas but lower in rural areas. Although S07 generally predicts similar or higher POH, S99 predicts higher new OH formation rate from H2O + O(1D) and leads to higher OH and thus higher O3 in most part of the domain. OH reactions with VOCs and CO accounts for a majority part of reacted OH. Secondary VOCs photolysis is not a main path of regenerated OH. New OH mainly comes from H2O + O(1D) reaction. Although the two mechanisms predict different ozone concentrations, the relative response factor (RRF) of ozone at rural, urban and industrial sites under emission controls of anthropogenic NOx and VOC controls by factors 0.6–1.4 predicted by the two mechanisms are very similar. This suggests that although the absolute predictions are different, both models will provide nearly identical attainment assessment in regulatory applications.► In southeast Texas, SAPRC07 predicts 8–20% lower O3 than SAPRC99. ► Difference in OH and O3 is mainly due to NO2 + OH and H2O + O(1D) rate constants. ► There are significant differences in OH budget between urban and rural sites. ► The two mechanisms predict similar relative response factor of 8-h O3.
Keywords: SAPRC07; SAPRC99; CMAQ; TexAQS 2000; Relative response factor; Hydroxyl radical;

Thermal stability of inorganic and organic compounds in atmospheric particulate matter by Cinzia Perrino; Elisabetta Marconi; Luca Tofful; Carmela Farao; Stefano Materazzi; Silvia Canepari (36-43).
The thermal behaviour of atmospheric particulate matter (PM) has been investigated by using different analytical approaches to explore the added value offered by these technique in environmental studies. The thermogravimetric analysis (TGA), carried out on both certified material and real PM samples, has shown that several mass losses can be detected starting from 80 °C up to above 500 °C, when pyrolysis occur.Thermo-optical analysis of PM and ion chromatographic analysis of the residual have shown that the mass losses in the temperature range 80–180 °C are not justified by the release of either organic or inorganic compounds; it can be thus attributed to the release of weakly and strongly bound water. Release of water has also been evidenced in the temperature range 225–275 °C.The release of ammonium chloride and nitrate has been detected only above 80 °C. This indicates that the release of nitric acid, hydrochloric acid and ammonia, which is observed downstream of the filters during the sampling of atmospheric PM at ambient temperature, cannot be reproduced off-line, after the end of the sampling. We successfully explored one of the possible explanations, that is the desorption of HNO3, HCl and NH3 adsorbed on collected particles.NH4NO3 and NH4Cl, which can be thermally released by the filter, exhibit a different thermal behaviour from NaNO3 and NaCl, which are thermally stable up to 370 °C. This different behaviour can be used to discriminate between natural and secondary sources of atmospheric inorganic salts, as the interconversion that is observed when heating mixtures of pure salts resulted to be not relevant when heating real PM samples.► We studied the thermal behaviour of inorganic ions and organic matter in PM. ► TGA weight loss at temperatures below 150 °C can be mainly attributed to water. ► After the end of the sampling, ammonium salts on filters are stable up to about 80 °C. ► Thermal analysis helps in detecting natural/secondary contribution to Cl and NO3 .
Keywords: Atmospheric particulate matter; Thermogravimetric analysis; Ammonium salts; Thermo-optical analysis; Water; Sampling artefact;

Evaluation of the uncertainty in the ozone flux effect modelling: From the experiments to the dose–response relationships by Giacomo Gerosa; Angelo Finco; Riccardo Marzuoli; Juha-Pekka Tuovinen (44-52).
The paper is an attempt to assess the uncertainty involved in the modelling process of deriving the flux–effects relationships from the experimental evidences of a network of coordinated experiments on ozone and vegetation (the LRTAP Convention's ICP Vegetation).Ten modelling steps have been described and analysed. Even if some steps were more critical than others in introducing uncertainty, the whole modelling process seems to be quite robust.The stomatal dose calculation is precise enough when performed on long time periods (e.g. growing season). The main sources of inaccuracy for the stomatal dose calculation can be ascribed to the adoption of different schemes for the calculation of ozone concentration at leaf level (7–10%). The estimation of the ozone effects on vegetation, and particularly the derivation of the plant's response at the theoretical zero-ozone dose, proves to be the main source of uncertainty of the whole process (up to 17%). In order to improve the precision of this step an increased number of ozone treatments and replicates in the experiments is recommended, while a harmonization/standardization of the calculation algorithm is required to improve the accuracy of the dose calculation.► Uncertainty involved in the ozone flux-vegetation response modelling process has been assessed. ► Ten modelling steps have been described and analysed. ► Some steps resulted critical but the whole modelling process appears to be quite robust. ► The uncertainty of the dose is due to the different leaf-level O3 calculation schemes adopted. ► The estimation of the effects on vegetation revealed to be the main source of uncertainty.
Keywords: Ozone dose; Ozone effects; Vegetation; OTC; Flux–effects relationship; Uncertainty;

The effects of operating conditions on semivolatile organic compounds emitted from light-duty, gasoline-powered motor vehicles by Jason S. Herrington; Michael D. Hays; Barbara J. George; Richard W. Baldauf (53-59).
A thermal extraction-gas chromatography-mass spectrometry (TE-GC-MS) method was utilized to quantitatively examine semivolatile organic compounds (SVOCs) in fine particulate matter (PM2.5) collected from light-duty, gasoline-powered vehicle (LDGV) exhaust. Emissions were analyzed from a subset of 18 vehicles tested in the Kansas City Light-Duty Vehicle Emissions Study (KCVES). The KCVES applied the LA92 Unified Driving Cycle (UDC), consisting of “cold start”, “hot stabilized running”, and “warm start” phases. The sensitivity of the TE-GC-MS analysis provided the opportunity to examine the emission rates and proportions of SVOCs (including polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes) in PM2.5 on an individual vehicle basis for each UDC phase. Mean target SVOC emissions rates of 5.01 μg km−1, 0.28 μg km−1, and 0.63 μg km−1 were reported for the cold start, hot stabilized running, and warm start phases, respectively. Operating conditions as depicted by each UDC phase significantly affected SVOC emission rates and proportions in PM2.5. The cold start phase emission rates were significantly higher than the hot stabilized running and warm start phases for 89% of the target SVOCs. An increase in SVOC proportions in PM2.5 was observed during the warm start phase compared with the cold start and hot stabilized running phase. This observation was significant for 31% of the target compounds, including chrysene, benzo[a]anthracene, and pyrene. Vehicles tested in both summer and winter provided emissions data describing ambient temperature effects. Emission rates were significantly higher in the winter for 92% of the target SVOCs. Until now, observations of specific SVOCs in motor vehicle emissions produced under changing operating conditions were scant. Such emissions data may be useful for emissions modeling, source apportionment studies, and human exposure assessments.► The LA92 Unified Driving Cycle (UDC) was employed. ► Collected PM2.5 from light-duty, gasoline-powered vehicle (LDGV) exhaust. ► Utilized thermal extraction-gas chromatography-mass spectrometry (TE-GC-MS). ► Emission rates and proportions of semivolatiles were quantitatively determined. ► Operating conditions significantly affected emission rates and proportions.
Keywords: Particulate matter; Motor vehicle emissions; Thermal extraction; Organic PM; Vehicle operating conditions;

Urban sprawl is altering the landscape, with current trends pointing to further changes in land use that will, in turn, lead to changes in population, energy consumption, atmospheric emissions and air quality. Urban planners have debated on the most sustainable urban structure, with arguments in favour and against urban compaction and dispersion. However, it is clear that other areas of expertise have to be involved. Urban air quality and human exposure to atmospheric pollutants as indicators of urban sustainability can contribute to the discussion, namely through the study of the relation between urban structure and air quality. This paper addresses the issue by analysing the impacts of alternative urban growth patterns on the air quality of Porto urban region in Portugal, through a 1-year simulation with the MM5-CAMx modelling system. This region has been experiencing one of the highest European rates of urban sprawl, and at the same time presents a poor air quality. As part of the modelling system setup, a sensitivity study was conducted regarding different land use datasets and spatial distribution of emissions. Two urban development scenarios were defined, SPRAWL and COMPACT, together with their new land use and emission datasets; then meteorological and air quality simulations were performed. Results reveal that SPRAWL land use changes resulted in an average temperature increase of 0.4 °C, with local increases reaching as high as 1.5 °C. SPRAWL results also show an aggravation of PM10 annual average values and an increase in the exceedances to the daily limit value. For ozone, differences between scenarios were smaller, with SPRAWL presenting larger concentration differences than COMPACT. Finally, despite the higher concentrations found in SPRAWL, population exposure to the pollutants is higher for COMPACT because more inhabitants are found in areas of highest concentration levels.► The impacts of alternative urban growth patterns on air quality are evaluated. ► Numerical modelling using MM5-CAMx is applied. ► Urban sprawl results in higher PM10 and O3 concentrations. ► Population exposure to the pollutants is higher for compact urban areas.
Keywords: Air quality modelling; Urban structure; Land use; Atmospheric emissions;

Ambient protein concentration in PM10 in Hefei, central China by Hui Kang; Zhouqing Xie; Qihou Hu (73-79).
The total protein associated with bioaerosol particulate matter (PM) is generally measured as an all-inclusive indicator of airborne biological material, which may enhance the effects of allergens, allergic and asthmatic responses. To investigate the level and seasonal variations of biological loading, PM10 were collected in a metropolitan area of Hefei, central China from June 2008 to February 2009 and analyzed for total protein mass, trace elements, and water-soluble ions. The protein concentration in PM10 ranged from 2.08 to 36.71 μg m−3 with an average of 11.42 μg m−3. This was the highest value reported so far in the literature. The total protein was found to have a significant correlation with the air pollution index (API) and mean visibility (VV), indicating the potential influence of anthropogenic sources and/or crustal sources. The protein content displayed an obvious seasonal variation with respect to weather conditions. In the rainy season the level of protein was low, while in the dry season and foggy weather the level of protein was relatively high. A correlation analysis revealed that the relationship between total protein concentration and water-soluble ions K+ and NO 3 − in PM10 during the dry season is 0.92 and 0.66 (P < 0.05), respectively, suggesting that anthropogenic pollution and biomass burning are main contributors during this period.► Ambient protein concentration in PM10 in Hefei, Central China was investigated. ► The protein level was very high in comparison with the literature reports elsewhere. ► The protein content displayed obviously seasonal variation with respect to rainy and dry season. ► The anthropogenic pollution and biomass burning were mainly contributions during dry season.
Keywords: Protein; PM10; Bioaerosol; China;

Significant emissions of 210Po by coal burning into the urban atmosphere of Seoul, Korea by Ge Yan; Hyung-Mi Cho; Insung Lee; Guebuem Kim (80-85).
We conducted a year-round survey of precipitation samples to investigate the sources of excess 210Po in the urban atmosphere of Seoul, Korea. The dominant fraction of 210Po in our samples, independent of the in-situ decay of tropospheric 210Pb, was linked with anthropogenic processes. Using vanadium and potassium as tracers, the excess 210Po was mainly attributed to combustion of coal, with minor contributions from biomass burning. The annual integrated amount of 210Po deposited over the Seoul area via precipitation was estimated to be 1.75 × 1010 Bq yr−1, which might represent a potential public health risk in the vicinity of major point sources, due to its highly adverse biological effects. Since the world coal consumption is growing, the magnitude of coal burning derived 210Po is expected to increase in the following decades, which should be carefully monitored.► We investigated precipitation samples for excess atmospheric 210Po source in Seoul. ► Coal burning is the dominant source. ► Biomass burning is an important secondary source. ► The anthropogenic 210Po can be a potential health hazard.
Keywords: Po-210; Source; Seoul; Wet deposition; Health risk; Coal burning;

Performance assessment of retrospective meteorological inputs for use in air quality modeling during TexAQS 2006 by Fong Ngan; Daewon Byun; Hyuncheol Kim; Daegyun Lee; Bernhard Rappenglück; Arastoo Pour-Biazar (86-96).
To achieve more accurate meteorological inputs than was used in the daily forecast for studying the TexAQS 2006 air quality, retrospective simulations were conducted using objective analysis and 3D/surface analysis nudging with surface and upper observations. Model ozone using the assimilated meteorological fields with improved wind fields shows better agreement with the observation compared to the forecasting results. In the post-frontal conditions, important factors for ozone modeling in terms of wind patterns are the weak easterlies in the morning for bringing in industrial emissions to the city and the subsequent clockwise turning of the wind direction induced by the Coriolis force superimposing the sea breeze, which keeps pollutants in the urban area. Objective analysis and nudging employed in the retrospective simulation minimize the wind bias but are not able to compensate for the general flow pattern biases inherited from large scale inputs. By using an alternative analyses data for initializing the meteorological simulation, the model can re-produce the flow pattern and generate the ozone peak location closer to the reality. The inaccurate simulation of precipitation and cloudiness cause over-prediction of ozone occasionally. Since there are limitations in the meteorological model to simulate precipitation and cloudiness in the fine scale domain (less than 4-km grid), the satellite-based cloud is an alternative way to provide necessary inputs for the retrospective study of air quality.► Weather conditions during TexAQS 2006 were assimilated with conventional observations. ► Model ozone biases were reduced when assimilated meteorological inputs were used. ► Weak easterlies and turning of wind are key factors for ozone modeling in the post-frontal conditions. ► Assimilation reduces the wind bias but cannot compensate for the biases inherited from large scale inputs. ► Satellite-based cloud is an alternative way to provide accurate inputs for air quality modeling.
Keywords: TexAQS 2006; Sea-breeze; Houston ozone; MM5; CMAQ; Nudging; Objective analysis;

Chemical composition of PM10 in Switzerland: An analysis for 2008/2009 and changes since 1998/1999 by M.F.D. Gianini; R. Gehrig; A. Fischer; A. Ulrich; A. Wichser; C. Hueglin (97-106).
In this study, the chemical composition of PM10 at various sites in Switzerland during a one year period in 2008/2009 and changes since the time of a similar characterisation campaign in 1998/1999 are investigated. The concentrations of main components of PM10 were found to be similar at different site types north of the Alps (i.e. urban background, suburban and rural sites). Secondary inorganic PM10 components (nitrate, sulphate and ammonium) constituted the largest PM10 mass fraction, followed by carbonaceous matter (OM and EC), while the abundance of mineral dust and trace elements was small (both <10%). At a rural site south of the Alps the concentrations of secondary inorganic components were much lower and the concentrations of OM and EC clearly higher than north of the Alps. Enhanced concentrations of EC, trace elements and to a lesser extent of OM and mineral dust were found at an urban roadside site. At this site, typical traffic related trace elements like Cu, Fe, Mo, Sb and Ba were highly enriched.This paper indicates clear positive effects of emission reduction strategies for PM10 and precursors implemented during the past ten and more years. The concentrations of sulphate and EC declined during the considered time period, EC reductions were especially strong at the urban roadside site (−2.4 μg m−3). In contrast, the concentration of nitrate slightly increased at all of the considered sites (0.2–0.5 μg m−3). Large reductions in the concentrations of many trace elements in PM10 during the past ten years are evident. As an example, the observed relative decrease of Pb is about −80%, which is a success of the ban of leaded gasoline in Switzerland and in the EU.► Chemical composition of PM10 at different site types in Switzerland is investigated. ► The results are compared with data from ten years before. ► Sulphate, elemental carbon and various trace elements declined during past ten years. ► In contrast, nitrate concentrations slightly increased. ► The observed changes allow an assessment of implemented emission control measures.
Keywords: PM10; Elemental composition; Reduction measures; Long-term changes; Trace metals;

Trends in NOx and NO2 emissions from road traffic in Great Britain by Sean D. Beevers; Emily Westmoreland; Mark C. de Jong; Martin L. Williams; David C. Carslaw (107-116).
In this paper we have compared detailed road traffic NOx emissions with the equivalent trends in ambient roadside NOx measurements. This was undertaken separately in Great Britain and London, for all of the major roads, and by road type and location. The emissions trends were created using different emissions factors, those used in UK emissions inventories (Base case), the Swiss-German handbook (HBEFA), and those created from recent remote sensing measurements in the UK (RSD). An alternative assumption for use of Selective Catalytic Reduction (SCR) in the articulated Heavy Goods Vehicle (HGV) fleet was also tested. For all scenarios traffic flows, speeds and vehicle age were kept constant. Comparison between the emissions scenarios in Great Britain showed that by 2009, NOx emissions estimates from road traffic could be as much as 25% greater than current UK estimates and 31% greater in London. The RSD emissions inventory gave the smallest downward trend in NOx emissions, from 2004 to 2009, of between 3 and 4%/year and this compared with a reduction of ∼6%/year from the Base Case and HBEFA scenarios. All scenarios compared poorly with roadside NOx measurement trends from UK sites, which typically reduce by between 1% and 2%/year. We have shown that the differences in NOx emissions trends were driven, partially at least, by the relative contribution from light duty diesel vehicles. An analysis from 2700 NOx measurement sites throughout Europe has shown that this problem is unlikely to be limited to the UK, and identifies a difficulty in meeting EU limit values for NO2, obligations under the National Emission Ceilings Directive () and the Gothenburg Protocol () and for forecasting future changes in PM2.5.► We compared road traffic NOX emissions with NOX measurements in Great Britain. ► We used UK emissions factors, the Swiss-German handbook, and vehicle remote sensing. ► Emissions could be as much as 31% greater than current UK estimates. ► The largest differences were in urban areas. ► Between 2004 and 2009 the best performing inventory used remote sensing measurements.
Keywords: Emissions inventory; NOx; NO2; Remote sensing; Emissions trends;

A 3D Lagrangian micromixing dispersion model LAGFLUM and its validation with a wind tunnel experiment by Giovanni Leuzzi; Andrea Amicarelli; Paolo Monti; David J. Thomson (117-126).
A stochastic numerical model, LAGFLUM (LAGrangian FLUctuation Model), is developed to determine the mean and the fluctuation statistics of scalar fields generated in 3D turbulent flows from continuous sources. The model couples a macromixing scheme with a micromixing scheme. The macromixing scheme, based on the so called “well-mixed” criterion, is utilized to evaluate the mean concentration, while the micromixing IECM (Interaction by Exchange with the Conditional Mean) scheme is integrated to calculate the higher statistical moments of the concentration. The model LAGFLUM is tested by comparison with the MUST (Mock Urban Setting Test) wind tunnel experiment, which is the laboratory counterpart of the original (real-atmosphere) MUST experiment. In both these experiments the dispersion of a passive tracer in a 3D flow field, in the presence of obstacles, is measured. Using a flow field reconstructed from the experimental flow measurements, the ensemble mean, standard deviation, intensity of fluctuations and skewness of the concentration predicted by LAGFLUM are compared with the available measurements. The results show a generally good agreement between the observations and the simulation, in particular for the mean and the standard deviation of the concentration. Predictions obtained with the flow field replaced by a flow field calculated using a numerical model and with the IECM model replaced by the IEM (Interaction by Exchange with the Mean) model are also compared with the measurements.► A 3D Lagrangian model is developed to determine the concentration fluctuations. ► The model is tested by comparison with the MUST wind tunnel experiment. ► The micromixing IECM scheme is coupled with a macromixing scheme. ► The concentration variances agree well with observations.
Keywords: Concentration fluctuations; IECM; IEM; MUST experiment; Turbulent dispersion; Canopy turbulence;

A chemometric approach to determine local and regional sources of PM10 and its geochemical composition in a coastal area by Mauro Masiol; Stefania Squizzato; Daniele Ceccato; Giancarlo Rampazzo; Bruno Pavoni (127-133).
The present study aims at estimating the local and external sources of PM10 in a coastal semi-rural background site of Po Valley (Italy) using experimental data and different chemometric approaches. An improved application of the factor–cluster analysis (FCA) is here presented. A factor analysis on the elemental and water soluble inorganic ions composition of PM10 was first performed, to detect the most probable sources, then the application of the multi-linear regression analysis pointed out the most important: sea-spray contributed most to PM10 mass (24%), then secondary aerosol (21%), anthropogenic local pollution (13%) and combustions (8%). Samples with similar source profiles were then grouped using cluster analysis on the source contributions. Clusters interpreted on the basis of wind data and back-trajectory frequencies indicated the most probable origins, by discriminating local generation and long-range transport processes. An indirect estimation of the influence of local and external contributions to PM10 evidenced that PM10 regulatory limits are exceeded because of local weather conditions and external transport. A discriminant analysis was also carried out to check the performance of FCA in grouping samples and extracting further information on PM10 sources.► An approach is proposed to assess local and external contributions to PM10. ► Sample elemental and ionic compositions were source apportioned. ► Groups of samples with similar source patterns were sorted by cluster analysis. ► The group composition was interpreted according to wind roses and back-trajectories. ► The background composition, local and regional-scale contributions were quantified.
Keywords: Elemental composition; Ionic species; Long-range transport; Local sources; PM10; Venice;

A mass transfer model for VOC emission from silage by Sasha D. Hafner; Felipe Montes; C. Alan Rotz (134-140).
Silage has been shown to be an important source of emissions of volatile organic compounds (VOCs), which contribute to the formation of ground-level ozone. Measurements have shown that environmental conditions and silage properties strongly influence emission rates, making it difficult to assess the contribution of silage in VOC emission inventories. In this work, we present an analytical convection-diffusion-dispersion model for predicting emission of VOCs from silage. It was necessary to incorporate empirical relationships from wind tunnel trials for the response of mass transfer parameters to surface air velocity and silage porosity. The resulting model was able to accurately predict the effect of temperature on ethanol emission in wind tunnel trials, but it over-predicted alcohol and aldehyde emission measured using a mass balance approach from corn silage samples outdoors and within barns. Mass balance results confirmed that emission is related to gas-phase porosity, but the response to air speed was not clear, which was contrary to wind tunnel results. Mass balance results indicate that alcohol emission from loose silage on farms may approach 50% of the initial mass over six hours, while relative losses of acetaldehyde will be greater.► We developed an analytical model for predicting VOC emission from silage. ► The model was accurate for wind tunnel emission of ethanol from corn silage. ► The model generally over-predicted VOC emission measured with a mass balance method.
Keywords: Dairy farms; Silage; Volatile organic compounds; Emission; Model;

Soiling results from the deposition of pollutants on materials. On glass, it leads to an alteration of its intrinsic optical properties. The nature and intensity of this phenomenon mirrors the pollution of an environment. This paper proposes a new statistical model in order to predict the evolution of haze (H) (i.e. diffuse/direct transmitted light ratio) as a function of time and major pollutant concentrations in the atmosphere (SO2, NO2, and PM10 (Particulate Matter < 10 μm)). The model was parameterized by using a large set of data collected in European cities (especially, Paris and its suburbs, Athens, Krakow, Prague, and Rome) during field exposure campaigns (French, European, and international programs). This statistical model, called NEUROPT-Glass, comes from an artificial neural network with two hidden layers and uses a non-linear parametric regression named Multilayer Perceptron (MLP). The results display a high determination coefficient (R 2  = 0.88) between the measured and the predicted hazes and minimizes the dispersion of data compared to existing multilinear dose–response functions. Therefore, this model can be used with a great confidence in order to predict the soiling of glass as a function of time in world cities with different levels of pollution or to assess the effect of pollution reduction policies on glass soiling problems in urban environments.► Glass optical properties (haze) are impaired by the atmospheric pollution. ► We modeled the haze as a function of time and main pollutants (NO2, SO2, PM10). ► A neural network model gives better results than previous existing models. ► Soiling in cities and benefits of pollution reduction policies can be assessed.
Keywords: Soiling; Glass; Neural network; Atmospheric pollution; Dose–response function;

Comparative source apportionment of PM10 in Switzerland for 2008/2009 and 1998/1999 by Positive Matrix Factorisation by M.F.D. Gianini; A. Fischer; R. Gehrig; A. Ulrich; A. Wichser; C. Piot; J.-L. Besombes; C. Hueglin (149-158).
PM10 speciation data from various sites in Switzerland for two time periods (January 1998–March 1999 and August 2008–July 2009) have been analysed for major sources by receptor modelling using Positive Matrix Factorisation (PMF). For the 2008/2009 period, it was found that secondary aerosols (sulphate- and nitrate-rich secondary aerosols, SSA and NSA) are the most abundant components of PM10 at sites north of the Alps. Road traffic and wood combustion were found to be the largest sources of PM10 at these sites. Except at the urban roadside site where road traffic is dominating (40% of PM10 -- including road salt), the annual average contribution of these two sources is of similar importance (17% and 14% of PM10, respectively). At a rural site south of the Alps wood combustion and road traffic contributions to PM10 were higher (31% and 24%, respectively), and the fraction of secondary aerosols lower (29%) than at similar site types north of the Alps.Comparison of PMF analyses for the two time periods (1998/1999 and 2008/2009) revealed decreasing average contributions of road traffic and SSA to PM10 at all sites. This indicates that the measures that were implemented in Switzerland and in neighbouring countries to reduce emissions of sulphur dioxide and PM10 from road traffic were successful. On the other hand, contributions of wood combustion did not change during this ten year period, and the contribution of nitrate-rich secondary aerosols has even increased. It is shown that PMF can be a helpful tool for the assessment of long-term changes of source contributions to ambient particulate matter.► Road traffic and wood combustion are the largest sources of PM10 in Switzerland. ► Road traffic related PM10 clearly declined during past ten years. ► In contrast, contribution of wood combustion remained about constant. ► Receptor modelling can be very useful for assessment of long-term changes.
Keywords: Trend analysis; Factor analysis; Receptor modelling; Road traffic emissions; Wood combustion emissions;

On-board measurements of emissions from diesel trucks in five cities in China by Hong Huo; Zhiliang Yao; Yingzhi Zhang; Xianbao Shen; Qiang Zhang; Kebin He (159-167).
This paper, which focuses on diesel trucks, is the third in a series of three papers published in Atmospheric Environment to understand vehicle emissions in China by conducting on-board emission measurements. Diesel trucks are a significant source of emissions in ambient air, especially for NOx. Recently, China announces an aggressive target to reduce national NOx emissions by 10% from 2010 to 2015 in the “Twelfth Five-Year Plan (2011–2015)” and diesel vehicles are identified as a key target for NOx control. However, the understanding of the real-world emissions of diesel trucks is limited. In this study, we measured HC, CO, NOx, and PM2.5 emissions from 175 diesel trucks of different sizes and technologies in five Chinese cities during 2007 and 2011, and generated emission factors on the basis of the measurements. The results show that the HC, CO, and PM2.5 emission factors have been reduced significantly as the emission standards become more stringent from Euro 0 to Euro IV, but the NOx emission factors change differently. Euro II trucks have 3–6% higher NOx emission levels than Euro I technologies and Euro III trucks fail to show a reduction as regulated by the standards. More stringent NOx requirements (e.g. Euro IV) for diesel vehicles need to be enforced. The comparison with the emission factors used in recent emission inventory studies shows that these inventories may have overestimated or underestimated diesel emissions for the years after 2006. This study emphasizes the importance of conducting local measurement research to improve the accuracy of the estimates of mobile emissions in China.► We measured HC, CO, NOx, and PM2.5 emissions from 175 diesel trucks in China. ► HC, CO, and PM emission factors (EF) are reduced as emission standards get stricter. ► NOx emissions of Euro II and Euro III trucks failed to show a reduction as regulated. ► Stricter requirement is needed for the target of reducing NOx by 10% in five years. ► Inventory studies for China need to improve EFs on the basis of local measurements.
Keywords: Emission factors; Diesel trucks; On-board emission measurement; Mobile emission inventory;

Impact of HONO sources on the performance of mesoscale air quality models by M. Gonçalves; D. Dabdub; W.L. Chang; O. Jorba; J.M. Baldasano (168-176).
Nitrous acid (HONO) photolysis constitutes a primary source of OH in the early morning, which leads to changes in model gas-phase and particulate matter concentrations. However, state-of-the-art models of chemical mechanisms share a common representation of gas-phase chemistry leading to HONO that fails in reproducing the observed profiles. Hence, there is a growing interest in improving the definition of additional HONO sources within air quality models, i.e. direct emissions or heterogeneous reactions. In order to test their feasibility under atmospheric conditions, the WRF-ARW/HERMES/CMAQ modeling system is applied with high horizontal resolution (4 × 4 km2) to Spain for November 24–27, 2008. HONO modeled sources include: (1) direct emissions from on-road transport; NO2 hydrolysis on aerosol and ground surfaces, the latter with (2) kinetics depending exclusively on available surfaces for reaction and (3) refined kinetics considering also relative humidity dependence; and (4) photoenhanced NO2 reduction on ground surfaces. The DOMINO measurement campaign performed in El Arenosillo (Southern Spain) provides valuable HONO observations. Modeled HONO results are consistently below observations, even when the most effective scenario is assessed, corresponding to contributions of direct emissions and NO2 hydrolysis with the simplest kinetics parameterization. With the additional sources of HONO, PM2.5 predictions can be up to 14% larger in urban areas. Quantified impacts on secondary pollutants have to be taken as a low threshold, due to the proven underestimation of HONO levels. It is fundamental to improve HONO sources definition within air quality models, both for the scientific community and decision makers.► Air quality models should include HONO sources other than gas-phase chemistry. ► HONO direct emissions have noticeable influence in polluted urban areas. ► Heterogeneous chemistry parameterizations need to be improved. ► HONO sources introduction significantly impacts secondary pollutant predictions.
Keywords: Tropospheric chemistry; Hydroxyl radical; Nitrous acid sources; Secondary pollutants formation; Air quality modeling;

Atmospheric fate of a series of furanaldehydes by their NO3 reactions by I. Colmenar; B. Cabañas; E. Martínez; M.S. Salgado; P. Martín (177-184).
The kinetics of the reactions of the NO3 radical with 2-furanaldehyde, 3-furanaldehyde and 5-methyl-2-furanaldehyde have been measured at 298 ± 2 K and 760 Torr of total pressure using a relative kinetic method. The simultaneous losses of furanaldehydes and a reference compound were followed by FTIR spectroscopy. The rate constants obtained for the NO3 reactions are (in cm3 molecule−1  s−1): (1.20 ± 0.28) × 10−12 for 2-furanaldehyde, (3.41 ± 0.79) × 10−12 for 3-furanaldehyde and (5.51 ± 1.27) × 10−12 for 5-methyl-2-furanaldehyde. This study is the first determination of the rate constants for the reaction of NO3 radicals with furanaldehydes. The results are presented and discussed in terms of structure-reactivity relationships. Calculated atmospheric lifetimes reveal that the night-time reaction with the nitrate radical is the most important loss process for these kinds of compounds.► Rate coefficients for reactions of NO3 with furanaldehydes have been determined. ► A relative method with FTIR technique has been used as detection. ► Nitrate radical, is the major sink for the furanaldehydes in the atmosphere.
Keywords: Furanaldehydes; Rate coefficients; NO3 radical; Relative method; Atmospheric implications;

In situ measurements of mercury (Hg) exchange fluxes between natural surfaces and atmosphere were carried out at 14 sampling sites in Guangdong province, southern China, which is the most populated and industrialized area in China. It is found Hg fluxes varied significantly from different landscapes. The average fluxes of Hg from agricultural bare soils, dry paddy soils, and wet paddy fields were in the ranges of 18.2–135, 2.7–14.2, and 1.4–22.8 ng m−2 h−1, respectively. Average fluxes for bare soil and forest soil were 135 and 6.6 ng m−2 h−1, respectively. We did not observe significant correlations between Hg fluxes and soil Hg concentrations for all the sampling sites, and this is probably due to the different soil utilizations at the sampling sites. Dry paddy soils and wet paddy fields exhibited relatively lower Hg fluxes than other agricultural soils. Dry paddy soils had low soil porosity which might minimize the interface of soil to the atmosphere. Besides, low penetrations of solar radiation and relevant biotic activities in dry paddy soils might also result in low air Hg concentrations in soil pool which in turn result in minimal diffusions of Hg to the atmosphere. Hg fluxes from wet paddy fields were mainly controlled by soil Hg concentrations, which affected the Hg contents of above water layer and could also release Hg0 through the water layer to the atmosphere. It was also found that sites close to large anthropogenic point sources exhibited relatively higher emission fluxes, indicating potential of Hg reemissions from historical deposited Hg from anthropogenic sources.►Mercury emissions from natural surfaces of Guangdong province were elevated. ► Utilizations of soil was an important factor in affecting soil flux. ► Areas close to anthropogenic sources present relatively higher emission fluxes.
Keywords: Mercury flux; Natural source; Re-emission; Southern China;

Size distributions of thirteen polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), and organic carbon (OC) in the range of 0.01–18 μm were measured using a nano Micro-Orifice Uniform Deposit Impactor (nano-MOUDI) in an urban location in Guangzhou, China in July 2006. PAH size distributions were fit with five modes and the respective mass median aerodynamic diameters (MMAD) are: Aitken mode (MMAD: ∼0.05 μm), three accumulation modes AMI, AMII, AMIII (MMAD: 0.13–0.17 μm, 0.4–0.45 μm, and 0.9–1.2 μm, respectively), and coarse mode (MMAD: 4–6 μm). Seven-ring PAH was mainly in AMII and AMIII. Five- and six-ring PAHs were found to be abundant in all the three AM. Three- and four-ring PAHs had a significant presence in the coarse mode in addition to the three AM. Size-resolved gas-particle partition coefficients of PAHs (K p ) were estimated using measured EC and OC data. The K p values of a given PAH could differ by a factor of up to ∼7 on particles in different size modes, with the highest K p associated with the AMI particles and the lowest K p associated with the coarse mode particles. Comparison of calculated overall K p with measured K p values in Guangzhou by shows that adsorption on EC appeared to be the dominant mechanism driving the gas-particle partitioning of three- and four-ring PAHs while absorption in OM played a dominant role for five- and six-ring PAHs. The calculated equilibrium timescales of repartitioning indicate that five- to seven-ring PAHs could not achieve equilibrium partitioning within their typical residence time in urban atmospheres, while three- and four-ring PAHs could readily reach new equilibrium states in particles of all sizes. A partitioning flux is therefore proposed to replace the equilibrium assumption in modeling PAH transport and fate.► We report the abundances and size distributions of thirteen PAHs in urban aerosols. ► K p is calculated based on EC and OC measurement and compared with measured K p values. ► Partitioning equilibrium timescale is calculated for PAHs with various volatilities.
Keywords: Polycyclic aromatic hydrocarbons; Size distribution; Gas/particle partitioning; Urban aerosol;

Who controls the monthly variations of NH4 + nitrogen isotope composition in precipitation? by Hong-Wei Xiao; Hua-Yun Xiao; Ai-min Long; Yan-Li Wang (201-206).
Nitrogen isotopes of ammonium (δ15N–NH4 +) in precipitation have been analyzed, to study their monthly variations, from Oct. 2008 to Sep. 2009 at Guiyang, Southwest China. δ15N–NH4 + values were higher in winter and lower in summer showing a strong sine curve. In summer (rainy season), raindrop may remove more light ammonia by washout process, because raindrop incorporated 15NH3 preferentially while left the 14N in the atmosphere. At the same time, longer sunshine times imply more hv for producing H2SO4 of SO2 to H2SO4, which accelerates gaseous to particle conversion of NH3 to (NH4)2SO4 by unidirectional reactions for isotopic enriched 14N. The above two aspects can somewhat cause the seasonal variation of nitrogen isotopic composition, but are not the main or direct reasons. The temperature has an opposite trend with seasonal variation of δ15N values. The temperature not only causes seasonal variation of δ15N values, but also increases the volatilization rate of NH3 and microbial activities. And there is a robust linear relationship between temperature and δ15N, showing that the temperature is the main factor to decide the monthly variation of δ15N–NH4 +.► There is a strong sine curve relationship between δ15N–NH4 + and seasons. ► Precipitation, sunshine and temperature cause the monthly variations of δ15N–NH4 + values. ► Temperature is the most important reason to control the seasonal variation of δ15N–NH4 +.
Keywords: Ammonium; δ15N; Isotopic fractionation; Unidirectional reaction; Exchange reaction; Seasonal variation;

Household, stairs and entryway dust samples were collected from 16 houses distributed across Greater Cairo by using vacuum cleaner and sweeping methods during summer season of 2009. Lead (Pb), nickel (Ni), cadmium (Cd), aluminum (Al), iron (Fe), zinc (Zn), cobalt (Co), chromium (Cr) and copper (Cu) were measured in different dust particle sizes: <38 μm, >38–45 μm and >45–63 μm. The highest average concentrations of Pb, Ni, Cd, Co, Cu, and Cr in different particle sizes were found in entryway followed by household and stairs. Al, Fe and Zn concentrations followed the pattern of entryway > stairs > household. Pb, Ni, Cd, Zn, Co and Cr were found in significantly (p < 0.01) higher concentrations in dust of the small particle size (<38 μm), whereas Al, Fe and Cu were detected in significantly (p < 0.01) higher concentrations in dust of the large particle size (>45–63 μm). The average concentrations of the individual metals in dust of the small particle size (<38 μm) were 268, 196.4 and 254.49 μg gm−1 for Pb, 49.6, 43.5 and 46.66 μg gm−1 for Ni, 2.86, 2.15 and 2.71 μg gm−1 for Cd, 4340, 3796 and 2602 μg gm−1 for Al, 2860, 2200 and 2004 μg gm−1 for Fe, 209.25, 152.3 and 103.26 μg gm−1 for Zn, 4.1, 2.88 and 1.96 μg gm−1 for Co, 85.99, 74.06 and 83.17 μg gm−1 for Cr and 168.2, 156.5 and 122.02 μg gm−1 for Cu in entryway, stairs and household, respectively. The mean concentrations of Cu and Pb in the entryway, stairs and household dust exceeded the maximum permissible limit 100 μg gm−1 for Cu and Pb in soil. The highest concentrations of Pb, Cd, Co and Ni were found in urban areas, Al and Fe in the residential areas, and Cu, Zn and Cr in the residential near to industrial area. Significant positive correlation (p < 0.001) were found between the metal concentrations in household and entryway dust, indicating that the metals in household dust may be derived from outdoor sources in addition to dust generated within the house itself. The contribution of anthropogenic sources, especially traffic emission, to metal levels in household, entryway and stairs dust was reflected by the high values of enrichment factors for Pb, Cd, Zn and Cu and Ni and Cr in fine dust particle compared to the average crustal composition. Insignificant positive correlation coefficients were found between the concentrations of Pb and other metals in household dust. However, the correlation coefficients between the concentrations of Cd, Ni, Cr, Cu, Zn and Fe were statistically significant.► In this study, household, stairs and entryway dusts were sampled from from some houses in Cairo. ► The concentration and distribution of heavy metal in dusts were investigated. ► The relationships between measured heavy metal were studied. ► Major sources of measured heavy metals were identified.
Keywords: Household dust; Stairs; Entryway; Metals; Distribution; EF; Urban; Residential area; Greater Cairo;

Quantifying the contribution of environmental factors to isoprene flux interannual variability by Ahmed B. Tawfik; Reto Stöckli; Allen Goldstein; Shelley Pressley; Allison L. Steiner (216-224).
Terrestrial isoprene emissions directly respond to leaf temperature, photosynthetically active radiation (PAR), soil moisture, and plant characteristics such as leaf area index (LAI). Prior work has estimated isoprene interannual variability at 5–25%, however the relative contributions of individual environmental factors have not been delineated. A biogenic isoprene emissions model (MEGAN) is coupled to a regional climate model (RegCM4-CLM) to evaluate variations in monthly isoprene emissions. We use a novel approach to estimate the contribution of environmental factors to monthly averaged isoprene flux variability and analyze regional differences over the contiguous U.S. for summers spanning 1994–2008. Consistent with earlier studies, isoprene flux varies 8–18% interannually with the greatest variability occurring in July. Yearly changes in isoprene flux are poorly described by any single environmental factor, yet temperature and soil moisture together account for at least 80% of the total isoprene flux variations for all regions during the summer. Soil moisture plays the most significant role in controlling variability over the Northeast and Southeast, but only exceeds temperature in importance during August in the Northeast and July in the Southeast. PAR and LAI are nearly negligible contributors to summer interannual variability. Uncertainty in climate model soil moisture parameterizations can drive large variability in isoprene fluxes when including the isoprene soil moisture dependency factor, suggesting a need for further validation.► A regional climate model is coupled with a widely used isoprene emissions model. ► Control of environmental factors on isoprene flux variations is quantified. ► No single environmental factor can explain yearly variations in isoprene flux. ► Temperature and soil water factors jointly account for >80% of variations. ► Light and leaf area index variations are negligible contributors to variability.
Keywords: Isoprene flux; Interannual variability; Soil moisture; Environmental factors; United States; Biogenic emissions;

Positive sampling artifacts of organic carbon fractions for fine particles and nanoparticles in a tunnel environment by Chong-Shu Zhu; Chuen-Jinn Tsai; Sheng-Chieh Chen; Jun-Ji Cao; Gwo-Dong Roam (225-230).
The positive artifacts in particulate organic carbon fractions for fine particles (PM2.5) and nanoparticles (PM0.1) were characterized in a tunnel environment by using the QBQ (a quartz filter behind a quartz filter) method. The OC concentrations of the backup quartz filters ranged from 3.56 to 11.38 μg m−3 with the average of 6.70 μg m−3 for PM2.5, and from 2.62 to 7.27 μg m−3 with the average of 4.64 μg m−3 for PM0.1. The most abundant species on the backup quartz filters was OC1 for both PM2.5 and PM0.1, accounting for 56.9% and 41.1% of the measured organic carbon, respectively. Most of EC fractions (EC1–EC3) on the backup filters for PM2.5 and PM0.1 were below the minimum detection limit. Therefore, only OC contributed to positive artifacts distinctly with the average percentage of 21.7% and 48.0% for PM2.5 and PM0.1, respectively. The artifacts for four organic carbon fractions ranged from 36.1% (OC1) to 4.4% (OC4) for PM2.5 and from 68.0% (OC1) to 31.9% (OC4) for PM0.1. The uncorrected OC/EC ratios on the front quartz filters were higher by as much as 30% and 107% for PM2.5 and PM0.1 than those corrected for positive organic artifacts, respectively. That is, much higher percentage of positive artifacts was found for PM0.1 OC fractions on the front filters. The comparison of the present and previous studies shows that OC positive artifacts vary widely among various PM fractions and sampling sites attributing to many factors that are worth investigating in the future.► OC artifacts for four organic carbon fractions in a tunnel environment were severe. ► OC positive artifacts vary widely among various PM fractions and sampling sites. ► More positive artifacts were found for PM0.1 OC than PM2.5 OC.
Keywords: Positive artifacts; Organic carbon; PM2.5; PM0.1; Tunnel;

Dust, biomass burning smoke, and anthropogenic aerosol detected by polarization-sensitive Mie lidar measurements in Mongolia by Dulam Jugder; Nobuo Sugimoto; Masato Shinoda; Reiji Kimura; Ichiro Matsui; Masataka Nishikawa (231-241).
Polarization-sensitive Mie-scattering lidars were installed for dust storm monitoring at Sainshand and Zamyn-Uud in the Gobi Desert and at the Mongolian capital city of Ulaanbaatar in 2007. We studied the temporal and spatial distributions and transportation of dust, elevated dust, biomass burning smoke, and anthropogenic aerosol by using lidar measurements from the end of 2007 to the first half of 2010. The study results show that the maximum height of dust layers over the Gobi Desert of Mongolia during dust event periods varied from 0.5 to 5.5 km above the ground level (AGL). The 95th percentile level of dust vertical distribution was found at 4 and 4.5 km for Zamyn-Uud and Sainshand, respectively. The averaged maximum height of dust layers during dust events was 2.0–2.2 km AGL at those Gobi sites. The lidar measurements also revealed transport of dust layers elevated in the atmosphere. Base heights of elevated dust layers varied from 0.5 to 2.5 km AGL, while maximum heights from 2.5 to 4.5 km AGL. Backward air trajectory analyses suggested source areas of the elevated dust that transported from other source regions to southeastern Mongolia. A detail study was conducted of the dust event in 19–20 May 2008. Hourly maximum dust concentrations of PM10 (PM2.5) reached 1139–1409 (384–404) μg m−3 during the dust event episode. Dust concentration of PM10 had high correlations with visibilities. Threshold winds for dust emission were determined at Sainshand and Zamyn-Uud. The lidar measurements at the three sites detected vertical profiles of biomass burning smoke and anthropogenic aerosol with top heights of 3–4 km AGL.► Top heights of dust vertical profiles were 0.5–5.5 km over the Gobi by lidars. ► Elevated dust layers had base heights of 0.5–2.5 km and top heights of 2.5–4.5 km. ► Averaged heights of dust layers were 2.0–2.2 km at the two Gobi sites. ► Transported air pollution and biomass burning smoke were extending up to 3–4 km. ► Threshold winds for dust emission were determined for the two Gobi sites.
Keywords: Dust storm; Dust event; Threshold wind; Dust vertical profile; Dust concentration; Particulate matter; PM10; PM2.5; Dust layer; Elevated dust transport; Gobi Desert; Biomass burning smoke; Anthropogenic aerosol; Mie lidar extinction coefficient;

Reduction of black carbon aerosols in Tokyo: Comparison of real-time observations with emission estimates by Y. Kondo; K. Ram; N. Takegawa; L. Sahu; Y. Morino; X. Liu; T. Ohara (242-249).
Black carbon (BC) aerosols alter the radiation budget both directly (by absorbing solar visible radiation) and indirectly (by acting as cloud condensation nuclei) and cause adverse health effects. The absorbing efficiency and direct radiative effect of BC strongly depend on its mass concentration (M BC) and type of emission source. In the present study, we report measurements of M BC at the Research Center for Advanced Science and Technology (RCAST), located at the center of the urban boundary of Tokyo, using an EC-OC analyzer from 2003 to 2005 and a filter-based Continuous Soot Monitoring System (COSMOS) during 2007–2010. The results indicate that M BC have decreased significantly from 2.6 μg m−3 to 0.5 μg m−3 (∼80% reduction) between 2003 and 2010. Vehicular emissions are the dominant source of BC in Tokyo, and the observed reduction in M BC is mainly attributed to the stringent regulations of particulate matter exhaust from vehicles imposed by the Japanese government. In addition, this observation is also supported from emission estimates using diurnal-weekly variations of M BC in Tokyo and explains the observed reduction to within about 20%. This is the first clear evidence of a significant reduction in BC emissions in Tokyo and shows that measures taken to reduce BC emissions from traffic sources have a strong effect on air quality in a mega-city and also reduce the climate impact of traffic emissions. We highlight the importance of long-term and reliable measurements in detecting BC trends and for the validation and regulation of emission control measures in mega-cities.► We measured black carbon (BC) accurately in Tokyo from 2003 to 2010. ► We show the first clear evidence of a large reduction in BC (∼80%) in Tokyo. ► Vehicular emissions were a dominant source of BC in Tokyo. ► BC reduction was caused by regulations of PM emissions set up by the Japanese government.
Keywords: Black carbon; Mega-cities; Vehicular emission; Diurnal variability;

Elemental characterization and source identification of size resolved atmospheric particles in French classrooms by Dinh Trinh Tran; Laurent Y. Alleman; Patrice Coddeville; Jean-Claude Galloo (250-259).
Indoor airborne particles were chemically characterized to identify their major sources in 3 elementary schools presenting different site typologies (rural, urban, and industrial) in the North of France. The sampling campaigns were conducted simultaneously indoors and outdoors during 2 weekly periods successively in each school, in presence and absence of pupils.The indoor weekly mean PM10 mass concentrations in presence of pupils varied from 72.7 to 85.3 μg m−3, generally exceeding the WHO guidelines. The presence/absence PM10 ratios confirm the PM10 concentrations raise during children’s activities. Their presence leads to an increase of elemental concentration (ng m−3) but does not influence the elemental distribution in the different particulate fractions.Crustal elements represent an important portion (7–10%) of the indoor PM10 mass, mostly driven by the Ca content (4.4–7.2%) due to the use of chalk. The trace elements (As, Cd, Cu, Pb, Sb, …) are enriched in the fine fractions (70–100%) compared to the coarse ones. Crustal elements (Al, Ca, Ti, Sr, …) present higher concentrations in the coarse fractions (40–60%).Elemental ratios and Cluster Analysis confirmed different particulate metal sources from the school surroundings. Among these sources, re-suspension dust, traffic, and marine aerosols were observed in all schools. Mixed anthropogenic sources were identified in urban and industrial sites, and petro-chemistry was only evidenced in the school near the industrial zone. Indoors, these outdoor anthropogenic particles represent the only sources of trace elements evidenced during this study.► Children's activities in classroom increase mainly the PM2.5–10 mass fraction. ► Their activities clearly impact major elements due to chalk dusts. ► The presence of children impact the elemental content, not the elemental distribution. ► Indoor trace elements originate essentially from outdoor sources.
Keywords: Indoor; Outdoor; Particles; Trace metals; Elemental distribution; Source origin;

Computer-controlled scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to obtain ambient PM mass concentrations, elemental size distributions, morphologies, and particle types during four Bermuda grass burn events in Imperial Valley, California. Passive PM samplers were deployed to three to six locations surrounding each burn for durations of 24–120 h. Average PM2.5 and PM10 levels were modestly but significantly higher at locations less than 3.2 km (two miles) from the nearest burn (n = 37). During one monitored burn, higher winds caused an intense ground-level plume to envelop two samplers mounted on telephone poles very close to the field. For this event, 24-h PM2.5 exposures downwind were up to 17 times higher than that measured upwind. Particles were classified into five distinct chemical types consistent with local area sources. Burn-related particle types, primarily submicron carbonaceous particles, contributed 95% of the PM2.5 in the location directly impacted by the ground-level plume, compared to only 12% in the upwind location. Downwind PM10–2.5 particles were enriched in potassium, phosphorus, chlorine, calcium, silicon, and sulfur, consistent with analyses of bulk and partially-burned Bermuda grass. The accuracy and precision of passive sampler PM measurements were all within 4 μg m−3, though low median values caused high percent differences for PM2.5. The use of electron microscopy and passive sampling in this study enabled detailed PM characterizations, spatial comparisons, and rapid deployment in often dynamic sampling scenarios.Display Omitted► Passive PM samplers deployed to 4 burn events, 3–6 locations each, for 24–120 h. ► Locations less than 3.2 km from nearest burn had significantly higher PM2.5 and PM10. ► For 1 burn with ground-level plume, PM2.5 downwind was17 times higher than upwind. ► 95% of PM2.5 downwind of plume were burn-related, compared to only 12% upwind. ► Inorganic species in downwind coarse PM same as bulk Bermuda grass sample.
Keywords: PM2.5; PM10; Agricultural burning; Passive samplers; Electron microscopy; Exposure assessment;

Particle emission from laser printers with different printing speeds by Jeong Hoon Byeon; Jang-Woo Kim (272-276).
The present work investigated particle emissions for 10 min operating time for commercial color laser printers having different printing speeds (5, 24, 38 prints per minute (ppm)) in an experimental chamber (5 m3) under 1 h−1 of air exchange rate. Number and mass concentrations of the emission particles were measured, and a correlation between emission and printing speed is discussed. The average mobility equivalent particle diameter (50–244 nm) of the emission was proportional to the printing speed (5–38 ppm) but the average particle number concentration (5.3–1.2 × 104 particles cm−3) was inversely proportional to the speed. From morphology analyses of the particles, it could be estimated that the number decrease (or diameter increase) rates of the primary particles due to coagulation were 3.25 (0.17), 3.40 (0.44), and 9.31 × 103 (0.96) particles cm−3 s−1 (nm s−1) for 5, 24, and 38 ppm, respectively. Corresponding particle mass emission rates (or mass emission per print) were 0.007 (0.23), 0.039 (0.27), and 0.449 (1.97) mg h−1 (×10−4 mg print−1) for 5, 24, and 38 ppm, respectively.
Keywords: Particle emission; Laser printers; Printing speed; Coagulation;

Dark aerobic methane emission associated to leaf factors of two Acacia and five Eucalyptus species by Makoto Watanabe; Yoko Watanabe; Yong Suk Kim; Takayoshi Koike (277-281).
We sought the biological factors determining variations in the methane emission rates from leaves of different plant species under aerobic conditions. Accordingly, we studied relations between the methane emission rate and leaf traits of two Acacia and five Eucalyptus species. We grew seedlings of each species in a glasshouse and measured the methane emission rate of the detached leaves under dark conditions at 30 °C. At the same time we measured the leaf mass per area (LMA), water content, and concentrations of carbon and nitrogen. There was no correlation between the leaf nitrogen concentration and the methane emission rate. This is consistent with previous findings that enzymatic processes do not influence methane emission. We found a significant negative correlation between LMA and the methane emission rate. Our results suggest that leaf structure is primarily responsible for differences in the rates of aerobic methane emission from leaves of different species.► Factors explaining variations between species in leaf methane emission were studied. ► We measured the rate of methane emission by detached leaves under dark conditions. ► There was a negative correlation between LMA and the methane emission rate. ► Leaf structure is an important in variations of methane emission rate between species.
Keywords: Aerobic methane emission; Correlation analysis; Evergreen tree species; Greenhouse gas; Leaf mass per area; Leaf structural trait;

Dry and wet deposition of elemental carbon on a tropical forest in Thailand by Kazuhide Matsuda; Hiroyuki Sase; Naoto Murao; Tatsuya Fukazawa; Kan Khoomsub; Phuvasa Chanonmuang; Thiti Visaratana; Pojanie Khummongkol (282-287).
In order to further understand atmospheric deposition of elemental carbon (EC) with respect to climate and plant impacts, dry and wet deposition of EC was investigated in a tropical deciduous forest, Sakaerat, Thailand. Micro-meteorological measurements and monthly sampling of PM2.5 aerosols were carried out continuously over one year in 2010 at the top of an experimental tower 38 m above the ground established in the forest. The dry deposition was estimated by the inferential method by using an empirical parameterization of aerosol deposition velocity. For measurement of wet deposition, biweekly sampling of EC directly filtrated from rainwater was carried out continuously over one year in 2010. EC concentration significantly increased during the period from January to March due to heavy biomass burning, and decreased during the period from June to September due to less biomass burning and the washout effect by rainfall. High deposition velocities were caused by high wind speed in February to April and also by both large displacement height and medium wind speed in May to July. Dry deposition increased during the period from February to April when the concentration and deposition velocity were both high, and decreased during the period from June to December when the concentration or deposition velocity was low. Wet deposition peaked in March because of the washout effect of high EC in the atmosphere of the late dry season. Wet deposition was somewhat high from August to October with increased rainfall. Both dry and wet deposition increased in the leafless season and decreased in the leafy season, respectively. The annual dry and wet depositions were estimated as 0.58 and 0.05 mg m−2 day−1, respectively. Taking the uncertainties of estimations into account, dry deposition was still significantly higher than wet deposition.► We characterized the dry and wet deposition of elemental carbon in a tropical forest. ► The majority of elemental carbon deposition is due to the dry disposition process. ► Both dry and wet depositions of elemental carbon are high in the leafless season.
Keywords: Aerosols; Elemental carbon; Dry deposition; Wet deposition; Southeast Asia;

Accurate description of atmospheric reactions of a series of low-molecular-weight (LMW) aldehydes (C1–C4) with NO2 has been modeled using a direct dynamic approach. The profiles of the potential energy surface were constructed at the BMC-CCSD//MPWB1K/6-311G(d,p) level of theory, and two different pathways have been found: H-abstraction and NO2-addition. The modeling results found that the contribution of NO2-addition reaction pathway to the total rate constant is very small and thus this kind of pathway is insignificant in atmospheric conditions. The predicted H-abstraction products are mainly reactive acyl radical and nitrous acid (HONO) which is very mutagenic and carcinogenic pollutant as well as the precursor of acid deposition. The rate constants of both pathways were also deduced by using canonical variational transition state theory incorporating with the small curvature tunneling correction within 200–360 and 360–2000 K. Theoretical overall rate constants are in good agreement with the available experimental values, whose increase in the order of k formaldehyde < k acetaldehyde < k propanal < k butanal, implying that relative long-chain LMW aldehydes are more reactive toward NO2 than those short-chain LMW aldehydes in the atmospheric condition. At 298 K, the total rate constants of LMW aldehydes (C1–C4) with NO2 are obtained as 1.65 × 10−25, 1.43 × 10−24, 3.39 × 10−24 and 1.83 × 10−23 cm3 molecule−1 s−1, respectively.Display Omitted► Atmospheric reaction mechanism of aldehydes (C1–C4) with NO2. ► Major H-abstraction from and minor NO2-addition onto aldehydes (C1–C4). ► Atmospheric reaction kinetics of aldehydes (C1–C4) with NO2. ► Theoretical prediction model. ► Theoretical rate constants are in good agreement with available experimental values.
Keywords: Low-molecule-weight aldehydes; NO2; Atmospheric chemical reaction; Theoretical calculation model; Rate constant;

Influence of extensive compressed natural gas (CNG) usage on air quality by Jeeranut Suthawaree; Helena Akhter Sikder; Charlotte Emily Jones; Shungo Kato; Hitoshi Kunimi; Abu Naser Mohammed Hamidul Kabir; Yoshizumi Kajii (296-307).
Compressed Natural Gas (CNG) is an inexpensive, indigenous energy resource which currently accounts for the majority of automobile and domestic energy consumption in Bangladesh. This extensive CNG usage, particularly within the capital city, Dhaka, heavily influences the atmospheric composition (and hence air quality), yet to date measurements of trace gases in regions dominated by CNG emissions are relatively limited. Here we report continuous observations of the atmospherically important trace gases O3, CO, SO2, NO x and volatile organic compounds (VOC), in ambient air in Dhaka City, Bangladesh, during May 2011. The average mixing ratios of O3, CO, SO2, and NO x for the measurement period were 18.9, 520.9, 7.6 and 21.5 ppbv, respectively. The ratios of CO to NO reveal that emissions from gasoline and CNG-fuelled vehicles were dominant during the daytime (slope of ∼26), while in contrast, owing to restrictions imposed on diesel fuelled vehicles entering Dhaka City, emissions from these vehicles only became significant during the night (slope of ∼10). The total VOC mixing ratio in Dhaka was ∼5–10 times higher than the levels reported in more developed Asian cities such as Tokyo and Bangkok, which consequently gives rise to a higher ozone formation potential (OFP). However, the most abundant VOC in Dhaka were the relatively long-lived ethane and propane (with mean mixing ratios of ∼115 and ∼30 ppbv, respectively), and as a consequence, the ozone formation potential per ppb carbon (ppbC) was lower in Dhaka than in Tokyo and Bangkok. Thus the atmospheric composition of air influenced by extensive CNG combustion may be characterized by high VOC mixing ratios, yet mixing ratios of the photochemical pollutant ozone do not drastically exceed the levels typical of Asian cities with considerably lower VOC levels.► Compressed Natural Gas (CNG) has become a common energy source for Bangladesh. ► Ambient levels of O3, CO, SO2, NOx, and VOC in Dhaka are reported during May 2011. ► Comparison of pollutant levels of pre- and post-CNG suggested an improvement of air quality. ► Influence of emission of different types of vehicle during daytime and nighttime. ► Relatively lower OFP/ppbC in Dhaka than that of Tokyo.
Keywords: Compressed natural gas; Air quality; Dhaka city; Bangladesh; Ozone formation potential;

Monoterpene emissions from an understory species, Pteridium aquilinum by Monica B. Madronich; James P. Greenberg; Carol A. Wessman; Alex B. Guenther (308-312).
Monoterpene emissions from the dominant understory species Pteridium aquilinum (Bracken fern) in a mixed temperate forest were measured in the field during the summers of 2006, 2007 and 2008. The results showed that Bracken fern emitted monoterpenes at different rates depending if the plants were located in the understory or in open areas. Understory plants emitted monoterpene levels ranging from 0.002 to 13 μgC gdw −1 h−1. Open area plants emitted monoterpene levels ranging from 0.005 to 2.21 μgC gdw −1 h−1. During the summer of 2008 greenhouse studies were performed to complement the field studies. Only 3% of the greenhouse Bracken fern plants emitted substantial amounts of monoterpenes. The average emission, 0.15 μgC gdw −1 h−1 ± 0.9 μgC gdw −1 h−1, was much lower than that observed in the field. The factors controlling monoterpene emissions are not clear, but this study provides evidence of the potential importance of understory vegetation to ecosystem total hydrocarbon emissions and emphasizes the need for longer-term field studies.
Keywords: Monoterpenes; Emissions; Understory; Photosynthetically active radiation; Temperature; Bracken fern;

Application of an oxidation catalyst mainly by diesel-fuelled passenger cars reduces harmful exhaust emissions of particulate matter (PM). As a side effect, the primary NO2/NOx emission ratio by these vehicles increased from 10% in 2000 (before the introduction of the oxidation catalyst) to between 55% and 70% in 2010. The impact of this evolution in traffic emissions was studied from both a health and a regulatory perspective. Primary NO2 emissions from road traffic in the Netherlands is expected to increase from 8 kt in 2000 to 15 kt by 2015 and subsequently to decrease to 9 kt by 2020. Meanwhile, exhaust PM emissions from road traffic in the Netherlands will decrease from 7 kt in 2000 to 3 kt by 2020. The impact of exhaust PM on air quality and health was assessed according to the mass concentrations of elemental carbon (EC) in ambient air, as EC is a more sensitive indicator than PM. Monitoring data on the NO2/EC concentration ratios near road traffic between 2000 and 2010 indicate no significant change in ambient air quality. This indicates that health effects in epidemiological studies associated with long-term exposure to NO2 concentrations are still valid. The health impact from the introduction of the oxidation catalyst was assessed by comparing the relatively higher NO2 (“cost”) and lower EC (“benefit”) concentrations at street locations. “Relative” refers to traffic emissions in situations “with” and “without” the oxidation catalyst being introduced. The cost–benefit ratio in 2010 was in balance, but benefits are expected to outweigh costs by 2015 and 2020. It is concluded that the application of oxidation catalysts is beneficial from a health perspective, but from a regulatory perspective it complicates compliance with the average annual limit value of NO2. This indicates that additional local measures may be required in order to meet air quality standards at locations with high traffic intensities.► Increasing primary NO2 in NOx emissions hampers compliance with NO2 limit value. ► Positive health effects of decreasing exhaust PM versus increasing NO2 in 2010–2020. ► Relative risk of long-term exposure to NO2 expected to decrease the coming years.
Keywords: Air quality; NO2; Road traffic emissions; Health impact;

Dispersion of particle numbers and elemental carbon from road traffic, a harbour and an airstrip in the Netherlands by M.P. Keuken; J.S. Henzing; P. Zandveld; S. van den Elshout; M. Karl (320-327).
Emissions of combustion aerosol by transport activities near residential areas are associated with adverse health effects. The composition of combustion aerosol from road traffic, a harbour and an airstrip has been investigated by measurements of PM2.5, elemental carbon (EC), organic carbon (OC) and size-resolved particle number concentrations (PNC). PM2.5 concentrations are not significantly increased downwind of transport activities. Combustion aerosol from road traffic is identified by EC, OC and PNC and an airstrip by OC and a large number of nucleation particles (i.e. particles smaller than 25 nm). Combustion emissions from a harbour have not been distinguished from background concentrations probable due to the height of these emissions and their large temporal variability. EC is suggested (over OC and PNC) as an indicator for the mass of combustion emissions by road traffic. EC is more stable during dispersion, has a higher contrast against background concentrations and is relatively easy to monitor. From our study on size-resolved PNC downwind of a motorway, it is concluded that dispersion of PNC from road traffic may be modelled as a conservative parameter on a medium city scale. The modelled spatial distribution of EC and PNC in the city of Rotterdam shows that EC is elevated both near urban and motorway traffic, while PNC has the highest relative values near motorway traffic. This illustrates that the urban population is exposed to different levels and composition of combustion aerosol which may result in different health impacts.► PNC, PM2.5, EC and OC in combustion aerosol from road traffic, a harbour and an airstrip. ► Dispersion modelling of size-resolved PNC near a motorway. ► Spatial distribution of PNC and EC in the city of Rotterdam, the Netherlands.
Keywords: Urban air quality; Combustion aerosol; PNC; EC; Dispersion modelling;

The eruption of the Icelandic volcano Eyjafjallajökull in April 2010 resulted in an unprecedented flight-ban at many European airports for many days. While much of the scientific interest in the eruption was related to the chemical and physical properties of the ash cloud and how it dispersed, a secondary effect was the reduction in aviation emissions at airports around Europe and elsewhere. In this study we aim to quantify the impact the flight-ban had on concentrations of nitrogen oxides at measurement sites close to London Heathrow Airport. A technique based on boosted regression trees is used to build an explanatory model of NO x and NO2 concentrations based on hourly meteorological and aircraft emissions data in the 3-years preceding the flight-ban. We show that the airport closure resulted in an unambiguous effect on NO x and NO2 concentrations close to the airport, even though the ban only lasted six days. Furthermore, we estimate the annual impact airport emissions have on mean concentrations of NO x and NO2 for different years and compare these estimates with a detailed dispersion modelling study and previous work that was based on the analysis of monitoring site data. For the receptor most affected by the flight-ban approximately 200 m south of the airport we estimate the airport contributes about 13.5 μg m−3 NO x (≈23% of the total measured NO x concentration), which is similar in magnitude to detailed dispersion modelling estimates of 12.0 μg m−3, but approximately twice that of other estimates based on the analysis of ambient measurements. Other measurement sites showed more mixed results due to the prevailing meteorology at the time of the ban, which affected the extent to which these sites were affected by the flight-ban. The techniques developed and applied in this paper would have application to other short-term interventions that affect air quality.► Methods developed to detect and quantify short-term interventions. ► Airport closure can be unambiguously detected. ► Airport contribution similar to dispersion modelling, but higher than previous estimates. ► Methods suitable for assessing other short-term interventions.
Keywords: Aviation; Emissions; Change detection; Intervention; Aircraft; Nitrogen oxides; Nitrogen dioxide;

Levels, sources and seasonality of coarse particles (PM10–PM2.5) in three European capitals – Implications for particulate pollution control by P. Kassomenos; S. Vardoulakis; A. Chaloulakou; G. Grivas; R. Borge; J. Lumbreras (337-347).
Coarse particles of aerodynamic diameter between 2.5 and 10 μm (PMc) are produced by a range of natural (windblown dust and sea sprays) and anthropogenic processes (non-exhaust vehicle emissions, industrial, agriculture, construction and quarrying activities). Although current ambient air quality regulations focus on PM2.5 and PM10, coarse particles are of interest from a public health point of view as they have been associated with certain mortality and morbidity outcomes.In this paper, an analysis of coarse particle levels in three European capitals (London, Madrid and Athens) is presented and discussed. For all three cities we analysed data from both traffic and urban background monitoring sites. The results showed that the levels of coarse particles present significant seasonal, weekly and daily variability. Their wind driven and non-wind driven resuspension as well as their roadside increment due to traffic were estimated. Both the local meteorological conditions and the air mass history indicating long-range atmospheric transport of particles of natural origin are significant parameters that influence the levels of coarse particles in the three cities especially during episodic events.► Coarse particle levels in Athens, Madrid and London. ► Wind driven and non-wind driven resuspension of coarse particles. ► Long-range atmospheric transport and roadside increment of coarse particles.
Keywords: Particulate matter; Coarse particles; Resuspension; Urban atmosphere; Vehicle emissions;

Ozone is a major pollutant of indoor air. Many studies have demonstrated the adverse health effect of ozone and the byproducts generated as a result of ozone-initiated reactive chemistry in an indoor environment. This study developed a Computational Fluid Dynamics (CFD) model to predict the ozone distribution in an aircraft cabin. The model was used to simulate the distribution of ozone in an aircraft cabin mockup for the following cases: (1) empty cabin; (2) cabin with seats; (3) cabin with soiled T-shirts; (4) occupied cabin with simple human geometry; and (5) occupied cabin with detailed human geometry. The agreement was generally good between the CFD results and the available experimental data. The ozone removal rate, deposition velocity, retention ratio, and breathing zone levels were well predicted in those cases. The CFD model predicted breathing zone ozone concentration to be 77–99% of the average cabin ozone concentration depending on the seat location. The ozone concentration at the breathing zone in the cabin environment can better assess the health risk to passengers and can be used to develop strategies for a healthier cabin environment.► A CFD model was developed to study the influence of surface reactions on the ozone distributions in an aircraft cabin. ► The CFD model showed reasonable agreement with available experimental data. ► Breathing-zone ozone concentration varies amongst passengers and ranges from 77 to 99% of the bulk air concentration.
Keywords: Ozone; Aircraft cabin; Air quality; CFD; Surface chemistry; Breathing zone;

Comparative assessment of a real-time particle monitor against the reference gravimetric method for PM10 and PM2.5 in indoor air by Viša Tasić; Milena Jovašević-Stojanović; Sotiris Vardoulakis; Novica Milošević; Renata Kovačević; Jelena Petrović (358-364).
Accurate monitoring of indoor mass concentrations of particulate matter is very important for health risk assessment as people in developed countries spend approximately 90% of their time indoors. The direct reading, aerosol monitoring device, Turnkey, OSIRIS Particle Monitor (Model 2315) and the European reference low volume sampler, LVS3 (Sven/Leckel LVS3) with size-selective inlets for PM10 and PM2.5 fractions were used to assess the comparability of available optical and gravimetric methods for particulate matter characterization in indoor air. Simultaneous 24-hour samples were collected in an indoor environment for 60 sampling periods in the town of Bor, Serbia. The 24-hour mean PM10 levels from the OSIRIS monitor were well correlated with the LVS3 levels (R 2  = 0.87) and did not show statistically significant bias. The 24-hour mean PM2.5 levels from the OSIRIS monitor were moderately correlated with the LVS3 levels (R 2  = 0.71), but show statistically significant bias. The results suggest that the OSIRIS monitor provides sufficiently accurate measurements for PM10. The OSIRIS monitor underestimated the indoor PM10 concentrations by approximately 12%, relative to the reference LVS3 sampler. The accuracy of PM10 measurements could be further improved through empirical adjustment. For the fine fraction of particulate matter, PM2.5, it was found that the OSIRIS monitor underestimated indoor concentrations by approximately 63%, relative to the reference LVS3 sampler. This could lead to exposure misclassification in health effects studies relying on PM2.5 measurements collected with this instrument in indoor environments.► We compare real-time particle monitor readings against the reference gravimetric method. ► Real-time PM10 measurements are of high accuracy compared to the reference method. ► Strong correlation between PM10 measurements (R 2  = 0.87) obtained with the two methods. ► Real-time monitor underestimated indoor concentrations of PM10 by approximately 12%. ► Real-time monitor underestimated indoor concentrations of PM2.5 by approximately 63%.
Keywords: Particulate matter; Optical monitor; Indoor air pollution; Aerosol monitoring; Exposure assessment;

Wooden building products indoors are known to be able to affect the perceived air quality depending on their emission strength. The indoor application of modern ecological lacquer systems (eco-lacquers or ‘green’ lacquers) may be a much stronger source than the substrates itself. Especially with regard to the formation of ultrafine particles by gas-to-particle conversion in the presence of ozone or other reactive species the impact of the applied building products on the indoor air quality has to be addressed. The present study reports a two concentration step ozonation of OSB panels, painted beech boards, and a number of solid ‘exotic’ wood types in a 1 m³ emission test chamber. The emission of volatile organic compounds (VOC) was recorded as well as the formation of ultrafine particles in the range 7–300 nm. The products are characterized on the basis of their ozone deposition velocity; the obtained values of 0.008–0.381 cm s−1 are comparable with previously published data. Within the samples of the present study one eco-lacquer was the strongest source of VOC (total VOC ∼ 60 mg m−3) while the wooden building products (OSB) were of intermediate emission strength. The lowest emission was found for the solid (exotic) wood samples. The VOC release of the samples corresponded roughly to the particle formation potential. However, the strongest UFP formation was measured for one solid wood sample (‘Garapa’) which showed a strong surface reaction in the presence of ozone and formed a large number of particles <40 nm. Overall, the experiments demonstrated the necessity of real-life samples for the estimation of UFP indoor air pollution from the ozone chemistry of terpenes.► We measured the VOC emission from several wood species in a test chamber. ► Solid wood species were found to be weak emission sources compared to wood products. ► When adding ozone we characterized formation of particles and ozone deposition velocity. ► The application of ‘green’ lacquers increased VOC emission and particle formation.
Keywords: Exotic wood emission; Ozone–terpene reaction; Emission test chambers; Ultrafine particles;

A backward-time stochastic Lagrangian air quality model by Deyong Wen; John C. Lin; Dylan B. Millet; Ariel F. Stein; Roland R. Draxler (373-386).
We describe a backward-time Lagrangian air quality model based on time-reversed, stochastic particle trajectories. The model simulates the transport of air parcels backward in time using ensembles of fictitious particles with stochastic motions generated from the Stochastic Time-Inverted Lagrangian Transport model (STILT). Due to the fact that STILT was originally developed out of the HYSPLIT lineage, the model leverages previous work () that implemented within HYSPLIT a chemical scheme (CB4). Chemical transformations according to the CB4 scheme are calculated along trajectories identified by the backward-time simulations. This approach opens up several key advantages: 1) exclusive focus upon air parcels that affect the receptor's air quality; 2) the separation of transport processes—elucidated by backward-time trajectories—from chemical reactions that enables implications of multiple emission scenarios to be probed; 3) the potential to incorporate detailed sub-gridscale mixing and transport phenomena that are not tied to Eulerian gridcells.The model was used to simulate concentrations of air quality-relevant species (O3 and NO x ) at eight measurement sites in the Canadian province of Ontario. The model-predicted concentrations were compared with observations, and comparisons show that simulated O3 concentrations usually agree well with observations across sites in rural areas, small towns, and big urban regions. Furthermore, the backward-time model showed improved performance over the previous approach involving forward-time particle trajectories, especially for O3. However, the model under-estimated NO x at sites away from the big cities, possibly due to the inability of the coarsely gridded emission grids to resolve fine-scale NO x sources.Influences of cross-border transport of U.S. emission sources on the test sites were investigated using the model by turning off anthropogenic and natural U.S. emission sources. The model results suggest that total U.S. emissions contributed more than 30% of O3 concentrations at the target sites and that over half of all hours during the simulation period were affected either by anthropogenic or natural emissions from the U.S. sources, indicating the importance of U.S. sources for air quality across Ontario.► A backward-time stochastic Lagrangian air quality model was developed. ► The new model can simulate a variety of gaseous species that affect air quality. ► The model demonstrated a satisfactory performance of ozone simulations. ► U.S. emissions have significant influences on ozone levels across Ontario.
Keywords: Air quality; Lagrangian model; Cross-border pollutant transport; Tropospheric ozone;

Ambient mixing ratios of chlorofluorocarbons, hydrochlorofluorocarbons and hydrofluorocarbons in 46 Chinese cities by Xuekun Fang; Jing Wu; Jianhua Xu; Daikuan Huang; Yehong Shi; Dan Wan; Hai Wu; Min Shao; Jianxin Hu (387-392).
Air samples in 46 cities all over China were collected in October and November 2010, and the levels of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were measured and are discussed in this work. In most cities, the ambient mixing ratios of CFCs were within 20% enhancements of the background values, while the levels of HCFCs and HFCs were significantly higher than the background values (P  < 0.01). Compared with the results of previous research conducted in 2001 and other single-city studies, the levels of CFC-11, CFC-12 and CFC-113 have decreased since then, while the levels of HCFCs and HFCs have increased rapidly. The results are consistent with the fact that CFCs have been replaced by the interim replacements (HCFCs and HFCs) in compliance with the Montreal Protocol.
Keywords: Halocarbons; Chlorofluorocarbons (CFCs); Hydrochlorofluorocarbons (HCFCs); Hydrofluorocarbons (HFCs); Mixing ratios; Urban; China;

Influence of building insulation on outdoor concentrations of regional air-pollutants by Ulrik Smith Korsholm; Bjarne Amstrup; Thomas Boermans; Jens Havskov Sørensen; Shiyu Zhuang (393-399).
The effects of building insulation on ground-level concentration levels of air pollutants are considered. We have estimated regionally averaged reductions in energy consumption between 2005 and 2020 by comparing a business as usual with a very low energy building scenario for the EU-25. The corresponding reductions in air pollutant emissions were calculated using emission factors. Annual simulations with an air-quality model, where only the emission reductions due to insulation was accounted for, were compared for the scenarios, and statistically significant changes in ground-level mass concentration of main air pollutants were found. Emission reductions of up to 9% in particulate matter and 6.3% for sulphur dioxide were found in north-western Europe. Emission changes were negligible for volatile organic compounds, and carbon monoxide decreased by 0.6% over southern Europe while nitrogen oxides changed by up to 2.5% in the Baltic region. Seasonally and regionally averaged changes in ground-level mass concentrations showed that sulphur dioxide decreased by up to 6.2% and particulate matter by up to 3.6% in north-western Europe. Nitrogen oxide concentrations decreased by 1.7% in Poland and increases of up to 0.6% were found for ozone. Carbon monoxide changes were negligible throughout the modelling domain.► Estimation of pollutant emission reductions due to increased building insulation. ► Comparison of annual simulations with an air-quality model with and without emission reductions. ► Emission reductions up to 9% for PM and 6.3% for SO2 in western Europe. ► Seasonally and regionally averaged mass concentration reductions up to 6.2% for SO2 and 3.6% for PM. ► Winter-time increase in ozone mass concentration.
Keywords: Air pollutants; Building insulation; Emission factor;

Indoor air quality in typical temperate zone Australian dwellings by S.B. Molloy; M. Cheng; I.E. Galbally; M.D. Keywood; S.J. Lawson; J.C. Powell; R. Gillett; E. Dunne; P.W. Selleck (400-407).
We report the results of a comprehensive study of indoor air quality in typical temperate zone Australian dwellings. Forty dwellings located over an 800 km2 area in the south-east of Melbourne with a range of ages, materials and structures representative of Australian dwellings were selected. A range of indoor air quality pollutants were sampled both inside and outside for one week each in Winter/Spring 2008 and Summer/Autumn 2009. Information was collected on house characteristics, the surrounding areas and occupant activities during the sampling.Weekly indoor averaged CO2 (536 ± 121 ppm), CO (0.3 ± 0.2 ppm), PM2.5 (8.4 ± 4.0 μg m−3), temperatures (21.2 ± 2.0 °C), water vapour mixing ratios (7.9 ± 1.3 g kg−1), benzene (1.3 ± 1.1 μg m−3), toluene (8.8 ± 7.9 μg m−3) and xylenes (6.2 ± 6.7 μg m−3) varied from 1.1 to approximately three times higher compared to the equivalent outdoors concentrations. Formaldehyde (12.2 ± 4.7 ppb), other carbonyls (7.9 ± 2.6 ppb) and total volatile organic compounds (181.1 ± 89.5 μg m−3) had indoor concentrations of factors between eight and 12 times higher compared to outdoor concentrations. Weekly averaged indoor ozone (0.7 ± 0.7 ppb), NO2 (8.4 ± 3.9 ppb) and PM10 (20.4 ± 8.1 μg m−3) were significantly lower than outdoors.Correlations and factor analysis showed the major influences on this indoor air quality were (a) dwelling age, whereby dwellings constructed in recent decades compared to older buildings were found to have increased concentrations of the highly elevated species formaldehyde, other carbonyls and total volatile organic compounds, and (b) combustion and cooking activities that increased the concentrations of multiple species including CO, CO2, NO2, H2O and particles. The indoor pollutant concentrations from this study were in general comparable with or lower than other Australian or overseas studies.► Concentrations of common indoor pollutants measured in 40 Australian dwellings. ► Pollutants include CO2, NO2, CO, O3, particulates, formaldehyde and other carbonyls. ► Dwelling age, combustion and cooking activities found to have influence on air quality. ► Results are comparable to or lower than other Australian and overseas studies.
Keywords: Indoor air quality; Particulates; Nitrogen dioxide; Formaldehyde; Carbonyls; VOCs;

Air contaminants emitted from stored animal wastewater affect human health and the environment. Measurements of gaseous emissions from undisturbed animal wastewater are abundant in the literature. However, in-barn wastewater management is characterized by the frequent occurrence of surface liquid disturbances. Information about emissions during and after wastewater disturbances is scarce. This study evaluates emissions of NH3, CO2 and H2S under transient conditions after wastewater disturbances (caused by slurry addition, water addition and mixing), and describes the mechanisms involved until reaching steady-state conditions. All three disturbances modified the gas emission patterns. Emissions of NH3 immediately decreased after the disturbances (−61% after slurry and water addition and by −91% after mixing), and then gradually increased during 90–200 min. Emissions of CO2 increased during the disturbances (40% during slurry and water addition and 1515% during mixing), and then decreased during up to 30 min after the disturbance. H2S emissions sharply increased during all three disturbances and then decreased for 2 min to 20 min. Emissions under transient conditions were related to the formation of a pH profile. Transient emissions should be considered in gas emission studies as they may represent an important part of the cumulative gas emissions during slurry storage.► Animal slurry in farms is frequently disturbed. ► Ammonia emissions immediately after disturbances are minimum. ► Then ammonia emissions increase until they reach a steady condition. ► Carbon dioxide and hydrogen sulfide emissions are very high during disturbances. ► Emissions under transient conditions are an important part of the total storage time.
Keywords: Slurry; Gas; pH; Mixing; Pig;

Measured extinction spectra of six different components of desert dust have been used as input for a mineral dust retrieval algorithm for the Infrared Atmospheric Sounding Interferometer IASI based on Singular Vector Decomposition. The use of measured dust component extinction spectra rather than dust sample-based optical properties widely used in thermal infrared applications improves retrieval results significantly. Correlation between IASI derived dust optical depth (at 0.5 μm) and AERONET sun-photometer observations from six months over Northern Africa, the Arabian Peninsula and Asia improved from formerly 0.623 to now 0.757 while the root-mean-square difference decreased from 0.322 to now 0.174 and the bias decreased (in terms of its absolute value) from −0.181 to 0.003. The dynamically adjusted e−1 envelope of the deviation histogram between AERONET and IASI dust AOD at 0.5 μm is at 0.160 while 80% of all IASI observations are within AOD0.5 μm ± 0.2 of respective AERONET values.Spatial patterns of dust observations with the retrieval based on dust components compare very well with known features in terms of monthly mean gridded Aerosol Optical Depth. Although originally being developed for Northern Africa, the Arabian Peninsula and adjacent Oceans, the retrieval method performs equally well in Asian dust source regions and downwind areas. As a further strength it provides observations at day and night overpasses of the Metop spacecraft, thus twice daily.► Mineral component extinction spectra for dust aerosol characterization in IASI retrieval. ► Good coverage of temporal evolution of dust events above AERONET stations. ► Validation against AERONET: ρ = 0.757, RMSD = 0.174. ► Successful Application over Northern Africa, Arabian Peninsula and Central and East Asia.
Keywords: Mineral dust; Remote sensing; Thermal infrared; IASI;

Air pollutant emission factors produced by open burning of rice straw were estimated using the residual mass method which incorporated ambient air-quality and meteorological data of measured stations. The residual mass method regarded the residual mass of air pollutants as emissions caused by the open burning of rice straw. Lasting from November 27–28, 2002, the selected episode resulted in the most serious air pollution in the recent decade in terms of open burning of rice straw, significantly degrading air quality in central-south Taiwan. Emission factors from open burning of rice straw, as modeled by the residual mass method, were 30.3 ± 1.45, 5.14 ± 0.13, 3.44 ± 0.09, 6.28 ± 0.34, and 0.058 ± 0.003 g kg−1 for CO, NMHCs, NOx, PM10 and SO2, respectively. The maximum daily emissions of CO and PM10 were 1000 kg km−2 and located at central-south Taiwan. Additionally, emissions of CO and PM10 in EPS were 7.67 and 9.33 times higher than MON during the rice straw burning episode. The spatial emission of EPS and MON were also presented with the residual mass method. Comparing our results with those of other studies revealed that calculated emission factors in this study were in an acceptable range.► Calculate emissions and emission factors for air pollutants from open burning of rice straw. ► Estimate emission factor with residual mass approach incorporating ambient air quality data and meteorological data. ► Compare emission factors of this study with other four studies.
Keywords: Air pollution episode; Agricultural fire; SO2; NO2; NMHC; CO; PM10;

Statistical characterisation of bio-aerosol background in an urban environment by M. Jamriska; T.C. DuBois; A. Skvortsov (439-448).
In this paper we statistically characterise the bio-aerosol background in an urban environment. To do this we measure concentration levels of naturally occurring microbiological material in the atmosphere over several days. Naturally occurring bio-aerosols can be considered as noise, as they mask the presence of signals coming from biological material of interest (such as an intentionally released biological agent). Analysis of this ‘biobackground’ was undertaken in the 1–10 μm size range and a 3–9% contribution was found to be biological in origin – values which are in good agreement with other studies reported in the literature. A model based on the physics of turbulent mixing and dispersion was developed and validated against this analysis. The Gamma distribution (the basis of our model) is shown to comply with the scaling laws of the concentration moments of our data, which enables us to universally characterise both biological and non-biological material in the atmosphere. An application of this model is proposed to build a framework for the development of novel algorithms for bio-aerosol detection and rapid characterisation.► We measured and characterised bio-aerosol background in an urban environment. ► Biological aerosol of size 1–10 micron contributed 3–9% to total number concentration. ► We developed statistical model based on the physics of turbulent mixing & dispersion. ► The Gamma distribution complies with the scaling laws of the concentration moments. ► The model can be used for development of rapid algorithms for bio-aerosols detection.
Keywords: Aerosol; Biobackground; Biodetection; Model; Algorithm; Turbulent mixing; 47.27.nb; 47.27.eb; 05.45.Tp; 92.60.Fm; 92.60.Mt;

Every year during the winter and pre-monsoon periods most of the Indian peninsula, Bay of Bengal and the adjoining Indian Ocean are affected by a polluted regional haze, known as the South Asian Winter Haze (SAWH). This article is the first of a series of three papers collectively anticipated at the central idea of retrieving aerosol component type and effective radius of the SAWH by incorporating experimental data of ground-based solar radiometer into Mie theory, and validation by collocated in-situ measurements. The work presented in this paper provides an approach to retrieve optical depths and their spectral curvature for SAWH at a tropical coastal station, Visakhapatnam (17.7°N, 83.3°E). A dataset comprised of 92 wintertime atmospheric optical depths are obtained from spectral extinction measurements of direct solar flux by means of a Multi-Wavelength Solar Radiometer during the period of October 2002 to February 2004. The inter-channel correlations established a linear relation and the airmass conditions specific to this dataset suggested a two-component linear model; the stable and variable components of which are analysed to obtain the mentioned optical parameters. Results indicate that the spectral curvature is best represented by a Lorentz model with a central wavelength of 0.40425 ± 0.02945 μm, a width of 0.40382 ± 0.10253 μm, a constant of 0.92623 ± 0.33793, and a wavelength independent component of 0.95778 ± 0.15678. Resonance-like structure of the obtained spectral curvature resembles wavelength dependent extinction characteristic of absorbing soot particles; thereby supports the key findings from INDOEX campaign.Display Omitted► The first of a three article series anticipated at ground-based remote sensing of regional haze. ► Formulates an alternate retrieval of AOD and spectral curvature of the South Asian Winter Haze. ► Resulted spectral curvature is best represented by a Lorentz model. ► Brings out an alternative to Angstrom turbidity parameters. ► Results support the key findings from INDOEX campaign.
Keywords: South Asian winter haze; Aerosol optical depth; Spectral curvature; Ground-based remote sensing; Solar radiometry;

A large-eddy simulation is performed on a turbulent dispersion of chemically reactive air pollutants in a two-dimensional urban street canyon with an aspect ratio of 1.0. Nitrogen monoxide emitted from a line-source set on the bottom of the street canyon disperses and reacts with Ozone included in a free stream. The reactions have significant influences on the concentrations of pollutants in the canyon space, and they increase the concentrations of the reaction products relative to of the concentrations of the reactants. The transport of air pollutants through a free shear layer above the canyon is closely related to the structure of the turbulence. Gases in the canyon are mainly exhausted when low-speed regions appear above the canyon. In contrast, pollutants in the free stream flow into the canyon with high-speed fluid bodies. Consequently, the correlation between the time fluctuations of the reactants' concentrations strongly affects the reaction rates in the region near the free shear layer. In this calculation, the correlation term reaches to a value of 20% of the mean reaction rate at a maximum there.► The dispersion of reactive air pollutants in a street canyon was investigated. ► NO–O3 reaction made the concentration of product higher than those of reactants. ► The turbulent concentration field highly affected the mean reaction rate. ► The correlation of concentrations accounted for 20% of the rate at a maximum.
Keywords: LES; Urban street canyon; Turbulent dispersion; Bimolecular chemical reaction;

Variation of PM2.5 concentrations in relation to street washing activities by Angeliki Karanasiou; Teresa Moreno; Fulvio Amato; Aurelio Tobías; Elena Boldo; Cristina Linares; Julio Lumbreras; Rafael Borge; Andrés Alastuey; Xavier Querol (465-469).
Several studies conducted in urban areas have pointed out that road dust resuspension contributes significantly to PM concentration levels. Street washing is one of the methods proposed to reduce resuspended road dust contributions to ambient PM concentrations. As resuspended particles are mainly found in the coarse mode, published studies investigating the effects of street washing have focused on PM10 size fraction. As the PM2.5 mass fraction of particles originating from mechanical abrasion processes may still be significant we conducted a study in order to evaluate the effects of street washing on the mitigation of resuspension of fine particles. The PM2.5 mass concentration data were examined and integrated with the occurrence of street washing activities. In addition, the effect of the meteorological variability, traffic flow and street washing activities, on ambient PM2.5 levels was evaluated by means of a multivariate regression model. The results revealed that traffic flow is the most important factor that controls PM2.5 hourly concentrations while street washing activities did not influence fine particle mass levels.
Keywords: PM2.5; Road dust; Resuspension; Wind speed; Wind direction; Traffic; Madrid; Spain;

Transboundary movement of polycyclic aromatic hydrocarbons (PAHs) in the Kuroshio Sphere of the western Pacific Ocean by Hu-Ching Huang; Chon-Lin Lee; Chin-Hsing Lai; Meng-Der Fang; I.-Chien Lai (470-479).
Atmospheric PAHs in the Kuroshio Sphere of southern Taiwan were measured and characterized using samples collected simultaneously at four sites from February to October in 2007. Higher PAH concentrations occurred in winter (range 2.41 ± 1.85 to 40.8 ± 6.97 ng m−3) and autumn (range 1.21 ± 0.32 to 65.1 ± 57.4 ng m−3) than in summer (range 0.87 ± 0.36 to 17.7 ± 2.88 ng m−3). Comparison of the total PAH concentrations from the four sampling sites showed that the total PAH concentrations from the Kaohsiung urban site (KHU) were 1.7–4.4 times higher than those from the Kaohsiung coastal site (KHC), 3.6–26 times those from a rural coastal site (Kenting, KT), and 16.9–53.8 times those from an offshore island site (Lanyu, LY). The PAH compositional pattern, diagnostic ratios and principal component analysis indicated that the major sources of PAHs in the study area can be classified into three categories. The first is vehicular sources from local traffic, the second is natural soils, and the third is industrial activities including coke ovens and incinerator emissions. The results from back trajectories also demonstrated that atmospheric PAHs were produced by local sources but were also influenced by transboundary movement of terrestrial pollutants. The characteristics and sources of atmospheric PAHs identified in this study provide useful information for estimating the effects and transportation of PAHs in the Kuroshio Sphere.► The concentrations of PAHs in the winter and autumn were much higher than those in summer. ► Distinct sources of the study area in different seasons were identified. ► The major sources of PAHs in the study area can be characterized as traffic, natural soils, and industrial activities. ► Polluted air from southwestern Taiwan might contribute significantly to the Kuroshio main stream. ► An event of a transboundary movement of PAHs was illustrated by back trajectories, fingerprinting and PCA.
Keywords: PAHs; Seasonal variation; Back trajectories; Kuroshio;

Real-time sampling of particulate matter smaller than 2.5 μm from Amazon forest biomass combustion by M.A.M. Costa; J.A. Carvalho; T.G. Soares Neto; E. Anselmo; B.A. Lima; L.T.U. Kura; J.C. Santos (480-489).
Particle size distribution from forest biomass combustion is an important parameter as it affects air quality, global climate and human health. There have been several studies that relate emission of 2.5–10 μm particulates and their effects on human health. The objective of this study was to sample particulates smaller than 2.5 μm from Amazon forest biomass burning in laboratory and field experiments. Sampling was carried out using three instruments: two DataRAM 4 (model DR 4000) and a Cascade Impactor. Isokinetic probes were used for sampling in the stacks, and an omnidirectional instrument was used for field sampling. The field experiment was conducted in a 4 ha Amazon forest test site in the state of Acre, in Brazil. Ignition, flaming and smoldering combustion phases were analyzed. Results were obtained in terms of particle size distribution and concentration. Comparison of laboratory and field experiments showed that particle size distributions were similar in both cases. Particle sizes obtained in the laboratory ranged from 0.05 to 0.8 μm; in the field experiment, sizes varied from 0.03 to 0.3 μm. Average concentrations in the laboratory and in the field were 185 mg m−3 and 350 mg m−3, respectively. It is important to emphasize that those results were obtained throughout the burning process and the diameters sampled were smaller than 2.5 μm.► Real-time sampling of PM2.5 from Amazon biomass combustion. ► Determination of PM2.5 concentration in laboratory and open field fires. ► Combustion behavior under flaming and smoldering was analyzed. ► Laboratory results agreed with field results.
Keywords: Ultra-fine particulate matter; Real-time sampling; Amazon forest fires;

Surface tension depression by low-solubility organic material in aqueous aerosol mimics by Allison Schwier; Dhruv Mitroo; V. Faye McNeill (490-495).
Surface-active material, including long-chain fatty acids (LCFAs), comprises a significant fraction of organic aerosol mass. Surface-active species are thought to form a film at the gas–aerosol interface, with implications for aerosol heterogeneous chemistry and cloud formation. However, LCFA phase behavior and surface-bulk partitioning has not been characterized under most conditions typical of tropospheric aerosol water (i.e. acidic, high ionic content), making it challenging to predict surface film formation in aerosols. In this study, we present measurements of the surface tension of aqueous solutions containing the slightly soluble LCFAs oleic and stearic acid. The effect of varying pH, organic concentration, and inorganic salt content was tested for each system. We observe surface tension depression compared to water of up to ∼30 and 45% for aqueous solutions containing stearic or oleic acid at pH 0–8 and high inorganic salt concentrations (NaCl and (NH4)2SO4). This suggests that surface film formation is favorable for these species in atmospheric aerosols.► Surface tension was measured for fatty acids in aqueous solutions with varying pH and salt content. ► Oleic and stearic acid depress surface tension at conditions typical of atmospheric aerosols. ► This suggests surface film formation is favorable for atmospheric aerosols.
Keywords: Long-chain fatty acids; Surface tension; Aerosols;

This study investigates the environmental exposure of residents of a community in southwest Virginia to respirable concentrations of dust (PM-10 i.e. PM10) generated by trucks hauling coal from surface coal mining operations. The study site is representative of communities in southwest Virginia and other parts of Appalachia that are located in narrow hollows where homes are placed directly along roads that experience heavy coal truck traffic.Preliminary air sampling (Particulate Matter i.e. PM10) was conducted for a period of approximately two weeks during early August 2008 in the unincorporated community of Roda, Virginia, at two locations (about a mile apart along Roda Road (Route 685) in Wise County, Virginia). For the purposes of this study (a combination of logistics, resource, and characterization of PM) we sited the PM samplers near the road to ascertain the micro exposure from the road. The results revealed high levels of PM10 (the mean adjusted 24-h concentration at the Campbell Site = 250.2 μg m−3 (±135.0 μg m−3); and at the Willis Site = 144.8 ± 60.0 μg m−3). The U.S. 24-h national ambient air quality standard for PM10 is 150 μg m−3. Elemental analysis for samples (blank-corrected) collected on Quartz filter paper (on one randomly selected day) at both the sites revealed the presence of antimony, arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, mercury, nickel, selenium. Electron micrographs reveal the morphology and habit (shapes and aggregates) of the particulate matter collected.
Keywords: Surface coal mining; PM10; Elemental analysis; Electron microscopy; Air toxic;

Role of traffic in atmospheric accumulation of heavy metals and polycyclic aromatic hydrocarbons by Janaka Gunawardena; Prasanna Egodawatta; Godwin A. Ayoko; Ashantha Goonetilleke (502-510).
Traffic related emissions have been recognised as one of the main sources of air pollutants. In the research study discussed in this paper, variability of atmospheric total suspended particulate matter (TSP), polycyclic aromatic hydrocarbons (PAH) and heavy metal (HM) concentrations with traffic and land use characteristics during weekdays and weekends were investigated. Data required for the study were collected from a range of sampling sites to ensure a wide mix of traffic and land use characteristics.The analysis undertaken confirmed that zinc has the highest concentration in the atmospheric phase during weekends as well as weekdays. Although the use of leaded gasoline was discontinued a decade ago, lead was the second most commonly detected heavy metal. This is attributed to the association of previously generated lead with roadside soil and re-suspension to the atmosphere. Soil related particles are the primary source of TSP and manganese to the atmosphere. The analysis further revealed that traffic sources are dominant in gas phase PAHs compared to the other sources during weekdays. Land use related sources become important contributors to atmospheric PAHs during weekends when traffic sources are at their minimal levels.► Role of traffic in atmospheric accumulation of heavy metals and PAHs investigated. ► Zinc has the highest concentration during weekends as well as weekdays. ► Re-suspension of roadside soil result in lead being second commonly detected metal. ► Soil particles are the primary source of TSP and manganese to the atmosphere. ► Traffic sources are dominant in gas phase PAHs during weekdays.
Keywords: Air pollutants; Air quality; Heavy metals; Polycyclic aromatic hydrocarbons; Total suspended particulate matter; Traffic emissions;

Characterization of urban aerosol using aerosol mass spectrometry and proton nuclear magnetic resonance spectroscopy by M.J. Cleveland; L.D. Ziemba; R.J. Griffin; J.E. Dibb; C.H. Anderson; B. Lefer; B. Rappenglück (511-518).
Particulate matter was measured during August and September of 2006 in Houston as part of the Texas Air Quality Study II Radical and Aerosol Measurement Project. Aerosol size and composition were determined using an Aerodyne quadrupole aerosol mass spectrometer. Aerosol was dominated by sulfate (4.1 ± 2.6 μg m−3) and organic material (5.5 ± 4.0 μg m−3), with contributions of organic material from both primary (∼32%) and secondary (∼68%) sources. Secondary organic aerosol appears to be formed locally. In addition, 29 aerosol filter samples were analyzed using proton nuclear magnetic resonance (1H NMR) spectroscopy to determine relative concentrations of organic functional groups. Houston aerosols are less oxidized than those observed elsewhere, with smaller relative contributions of carbon-oxygen double bonds. These particles do not fit 1H NMR source apportionment fingerprints for identification of secondary, marine, and biomass burning organic aerosol, suggesting that a new fingerprint for highly urbanized and industrially influenced locations be established.► SOA constitutes approximately 2/3 of organic aerosol loadings in Houston. ► Data indicate a water insoluble fraction of oxidized organic aerosol. ► Aerosol WSOC is less oxidized and does not fit previously identified 1H NMR source fingerprints.
Keywords: Aerosol mass spectrometer; Houston; Nuclear magnetic resonance spectroscopy; Organic aerosol; Oxidation;

Topographic Target Light scattering Differential Optical Absorption Spectroscopy (ToTaL-DOAS) measurements were performed in a street canyon in Gwangju, Korea (35°10′51.43″N, 126°52′53.74″E) during a period of 10 days in October 2010. NO2 slant volume mixing ratios (VMRs) at the lowest elevation angle (EL) of 1°, as obtained from ToTaL-DOAS measurements, were validated via comparisons with collocated in situ ground data, showing good agreement within a scatter range of 20% during the entire measurement period, and within a scatter range of 15% when cloudy days were excluded. For the first time, based on inversion calculations using ToTaL-DOAS data, we retrieved NO2 vertical distributions that consist of five layers (from 6 to 118 m) for three measurement days. We obtained generally decreasing NO2 VMRs with altitude, whereas increased NO2 VMRs at two elevated layers (6–19 m and 19–33 m) were observed on 26 and 27 October. We obtained a coefficient of determination (R 2) of 0.87 (0.61) between slant VMRs at 1° EL (retrieved NO2 VMRs in the layer from 6 m to 19 m) and in situ data, with the scatter of the correlation being within the 15% (10%) range. The relation between retrieved NO2 VMRs at 6–19 m and slant VMRs at 1° EL yielded an R 2 value of 0.97, with the scatter of the correlation being within the 5% range. The results demonstrate that the ToTaL-DOAS technique is a useful tool in identifying the temporal and vertical characteristics of NO2 VMRs in an urban street canyon with a complex geometry.► It is difficult to identify vertical distributions of trace gases in an urban street canyon. ► The ToTaL-DOAS technique has been used to derive NO2 vertical distributions in a street canyon. ► A retrieval procedure is introduced for determining NO2 vertical profiles using ToTaL-DOAS data. ► Hourly variations in NO2 vertical distributions from 6 to 118 m in height were successfully obtained. ► Retrieved NO2 VMRs at the lowest layer (6–19 m) were compared with the in situ data.
Keywords: NO2 vertical distribution; Street canyon; ToTaL-DOAS; DOAS; Gas remote sensing;

Real time black carbon measurements in West and Central Africa urban sites by El Hadji Thierno Doumbia; Catherine Liousse; Corinne Galy-Lacaux; Seydi Ababacar Ndiaye; Babacar Diop; Marie Ouafo; Eric Michel Assamoi; Eric Gardrat; Pierre Castera; Robert Rosset; Aristide Akpo; Luc Sigha (529-537).
Real time measurements of Black Carbon (BC) in PM2.5 aerosols were performed during AMMA and POLCA programs, between 2005 and 2010 in Cotonou (Benin), Dakar (Senegal), Bamako (Mali), and Yaounde (Cameroon). Indeed, BC was chosen as a metric because of its interest as an urban pollutant. The instrumented sites are representative of the traffic source. At Dakar, BC concentrations are high from November to April (13,000 ± 3500 ng m−3) and lower from May to September (8000 ± 3200 ng m−3). In dry season (November–April), high BC concentrations occurred as a result of northeasterly long-range transport of polluted air masses over West Africa, in addition to local emissions. However, during wet season (May–September) reduced traffic levels, school vacations and wet deposition processes contribute to lower BC concentration levels. Measured diurnal BC peak concentrations, at all sites, mainly occur during morning and evening rush-hour periods, indicating the paramount role of traffic. Highest values are observed between 5–9 a.m. and from 5 p.m. to 9 p.m. depending on the site, while lowest are occurred at night time and middle afternoon when activities of the population are reduced. BC source apportionment from absorption measurements also confirmed the relative importance of traffic (88%) versus biomass burning (12%). Also, BC measurements were functions of days of the week, with highest values occurring on Fridays and lowest ones on Sundays. Spatial variations associated to BC levels are very different from one site to another, revealing different types of sources with strong variations at the regional scale. It appears that mean BC concentrations in Dakar are lower by a factor of two, compared to those observed in Bamako, but remain higher than in some other West African sites (e.g. Cotonou, Yaounde). Overall, BC concentrations in our different sites are comparable to reported European and Asian megacity levels. Finally, using measured BC/PM2.5 ratios, we have estimated PM2.5 mass concentrations in Dakar from June 2008 to June 2009 to be 44.4 ± 14.3 μg m−3, well above the threshold of 10 μg m−3. This paper clearly highlights high pollution levels in West African large cities, with potential important impacts on the health of the regional population.► We examined black carbon concentrations and sources in West and Central African cities. ► Traffic is major source of BC in these regions. ► BC levels are high, in the same order of those from European or Asian mega cities. ► Annual PM2.5 levels in Dakar are four times higher than the WHO threshold.
Keywords: Atmospheric pollution; Black carbon; PM2.5; Urban site; Traffic;

The black carbon (BC) component of ambient particulate matter is an important marker for combustion sources and for its impact on human health and radiative forcing. Extensive data archives exist for the black smoke metric, the historic measure of ambient particle darkness. An expression presented in earlier publications () for estimating BC concentrations from traditional black smoke measurements is shown to have limitations that can be addressed by using a more systematic approach to the issue of corrections for increasing darkening of the filter. The form of the more general relationship is shown to be an off-axis parabola rather than the on-axis parabola of the earlier work. Existing data from co-located black smoke and aethalometer measurements at 5 UK sites are reanalysed in this context. At very low concentrations of dark particles (British Black Smoke index < ∼10 μg m−3) a simple linear relationship BC (/μg m−3) ≈ 0.27·BSIBRITISH will suffice. A parabolic relationship, [ BC / μg m − 3 ] = 5.2 − 1.1 + 1.5 × BSI BRITISH + 62 − 13 + 19 − 7.9 − 0.9 + 1.1 , quantitatively similar to the previously published relationship will be more reliable for BSIBRITISH values up to 20–25 μg m−3. The full set of data available was fitted empirically to the off-axis parabola over the range 0–80 μg m−3 as the quadratic: [BC/μg m−3] = (0.27 ± 0.03) · BSIBRITISH  − (4.0 ± 0.2) × 10−4(BSIBRITISH)2, but this curve is highly dependent on the variations between the individual data sets. Adding the extra complexity of the full off-axis parabolic relationship is unlikely to be justified in practical situations. All expressions apply also to the OECD definition of black smoke with the substitution BSIBRITISH  = 0.85·BSIOECD. However, in common with the previous approach, they apply only to black smoke values obtained from standard black smoke samplers with 25 mm diameter filters and ∼2 m3  day−1 volumetric flow rate, and presume a value 16.6 m2  g−1 for the specific absorption of BC in ambient particulate matter measured by aethalometry. Fitting uncertainties correspond to imprecision in estimated BC of ±5%, ±12% and ±18% at BSIBRITISH of 5, 20 and 80 μg m−3, respectively. Spatial and temporal variation in particle ensemble optical properties contributes to uncertainty in BC quantification.► The aim is to derive black carbon concentrations from ‘black smoke’ measurements. ► Shortcomings in a previous expression at higher blackness values are highlighted. ► New semi-empirical expressions are given, from numerical fitting to aethalometer BC. ► Aspects of the relationship between a reflectance metric and BC are discussed.
Keywords: Black smoke; Black carbon; Aethalometer; BS1747 standard; ISO 9835 standard; Air quality;

Physicochemical characteristics of aerosols measured in the spring time in the Mediterranean coastal zone by J. Piazzola; K. Sellegri; L. Bourcier; M. Mallet; G. Tedeschi; T. Missamou (545-556).
Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterization of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high NO 3 − and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea-breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm−1 and 3.6 Mm−1, respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences.► We present a physicochemical analysis of aerosols sampled along Mediterranean coast. ► We study the effects of land and sea breezes, the fetch on the aerosol properties. ► We study the impact of marine aerosols by anthropogenic activities. ► A strong contribution of nitrate in the super micron mode for marine air mass periods. ► A dominant signature of sea-salts for strong offshore wind conditions.
Keywords: Coastal aerosols; Anthropogenic compounds;

Potential of the International Monitoring System radionuclide network for inverse modelling by Mohammad Reza Koohkan; Marc Bocquet; Lin Wu; Monika Krysta (557-567).
The International Monitoring System (IMS) radionuclide network enforces the Comprehensive Nuclear-Test-Ban Treaty which bans nuclear explosions. We have evaluated the potential of the IMS radionuclide network for inverse modelling of the source, whereas it is usually assessed by its detection capability. To do so, we have chosen the degrees of freedom for the signal (DFS), a well established criterion in remote sensing, in order to assess the performance of an inverse modelling system. Using a recent multiscale data assimilation technique, we have computed optimal adaptive grids of the source parameter space by maximising the DFS. This optimisation takes into account the monitoring network, the meteorology over one year (2009) and the relationship between the source parameters and the observations derived from the FLEXPART Lagrangian transport model. Areas of the domain where the grid-cells of the optimal adaptive grid are large emphasise zones where the retrieval is more uncertain, whereas areas where the grid-cells are smaller and denser stress regions where more source variables can be resolved.The observability of the globe through inverse modelling is studied in strong, realistic and small model error cases. The strong error and realistic error cases yield heterogeneous adaptive grids, indicating that information does not propagate far from the monitoring stations, whereas in the small error case, the grid is much more homogeneous. In all cases, several specific continental regions remain poorly observed such as Africa as well as the tropics, because of the trade winds. The northern hemisphere is better observed through inverse modelling (more than 60% of the total DFS) mostly because it contains more IMS stations. This unbalance leads to a better performance of inverse modelling in the northern hemisphere winter. The methodology is also applied to the subnetwork composed of the stations of the IMS network which measure noble gases.► Assesses the potential of the CTBTO/IMS radionuclide network for inverse modelling. ► We determine how the information from observation is propagated in space and time. ► Poorly observed zones are identified: mainly tropical zones and Africa. ► The results could be used for potential network station reallocations.
Keywords: Inverse modelling; Atmospheric dispersion; Comprehensive Nuclear-Test-Ban Treaty; Radionuclides; Multiscale data assimilation; Network design;

Energy Dispersive X-ray Fluorescence (EDXRF) was compared to Inductively Coupled Plasma Mass Spectrometer (ICP-MS) for the measurements of elements (Mg, Al, Si, S, Cl, K, Ca, Ti, V, Cr, Fe, Co, Ni, Mn, Cu, Zn, As, Br, Sr, Pb, Mo, Cd, Sn and Sb) in particulate matter (PM10) collected on Teflon and two types of quartz filters at different sites. Two different methods of EDXRF analysis, linear calibration and standardless analysis, were studied. For the linear calibration, Pb, Mn, Fe, Cu, Ti and Zn were found to be site and filter type independent whereas Ca was only site independent. The site effect was evidenced for K, As, Ni, and V for quartz filter. The standardless EDXRF analysis showed better results than linear calibrations except for As, Co and V for Teflon filters and Cr and V for quartz filters. The measurement uncertainty of standardless EDXRF analysis was estimated by establishing a model equation. The measurement uncertainty estimated with this model equation was confirmed by field experiments provided that elemental masses exceeded observed thresholds. It was found that standardless EDXRF analysis is able to quantify most of the elements studied, particularly on Teflon filters rather than quartz filters. The standardless EDXRF analysis complies with the data quality objectives (DQO) of European Directives to measure Pb in PM10 for three types of filters, even at concentrations lower than limit values (LV). The detection limits (MDL) of standardless EDXRF analysis for measuring As and Cd were found to be insufficient to meet the legislative requirements. The MDL of Ni was sufficiently low for measurements; however, measurement uncertainties remained higher than the DQO at the lower concentrations than LV.► We study on the efficiency of standardless EDXRF to measure elements in PM10. ► We estimate the measurement uncertainties. ► EDXRF enables to measure Pb, Mn, Fe, Cu, Ti and Zn for whatever filter and matrix. ► Teflon filter is more appropriate for EDXRF measurements than quartz filter. ► The data quality objectives of legislations were met for Pb, Zn and Cu.
Keywords: Heavy metals; EDXRF; Uncertainty; Standardless analysis; PM10; ICP-MS;

Activation of “synthetic ambient” aerosols – Relation to chemical composition of particles <100 nm by J. Burkart; R. Hitzenberger; G. Reischl; H. Bauer; K. Leder; H. Puxbaum (583-591).
Cloud condensation nuclei (CCN) are an important fraction of atmospheric aerosols because of their role in cloud formation. Experimental studies focus either on direct field measurements of complex ambient aerosols or laboratory investigations on well defined aerosols produced from single substances or substance mixtures. In this study, we focussed on the ultrafine aerosol because in terms of number concentration, the majority of the CCN are expected to have sizes in this range. A field study was performed from July 2007 to October 2008 to investigate the activation behaviour of the atmospheric aerosol in Vienna (). Filter samples of the aerosol <0.1 μm aerodynamic equivalent diameter were collected, elutriated and used to generate “synthetic ambient” aerosol in a nebulizer. Chemical analyses of the ultrafine water soluble material were also performed. The CCN properties of the “synthetic ambient” aerosol were obtained using the University of Vienna CCN counter () at a nominal supersaturation (SS) of 0.5%. Activation diameters d act ranged from 54.5 nm to 66 nm, were larger than d act of typical single inorganic salts and showed no seasonal pattern in contrast to the fraction of water soluble organic carbon (WSOC), which ranged from 44% in spring to 15% in winter. The average hygroscopicity parameter κ () obtained from the activation curves ranged from 0.20 to 0.30 (average 0.24), which was significantly lower than κ chem calculated from the chemical composition (0.43 ± 0.07).► The activation diameters of the water soluble aerosol <100 nm are larger than those for typical single inorganic salts. ► κ  = 0.24 ± 0.09 for the water soluble aerosol <100 nm. ► Neither the activation diameters nor κ show seasonal variations even though the WSOC clearly does. ► The WSOC ranges from 44% in spring to 15% in winter.
Keywords: CCN activation; Ultrafine aerosol;

Evidence from firn air for recent decreases in non-methane hydrocarbons and a 20th century increase in nitrogen oxides in the northern hemisphere by David R. Worton; William T. Sturges; Claire E. Reeves; Mike J. Newland; Stuart A. Penkett; Elliot Atlas; Verity Stroud; Kristen Johnson; Norbert Schmidbauer; Sverre Solberg; Jakob Schwander; Jean-Marc Barnola (592-602).
The atmospheric evolution of eight non-methane hydrocarbons (ethane, acetylene, propane, n-butane, isobutane, n-pentane, isopentane and benzene) and five alkyl nitrates (2-propyl, 2-butyl, 3-methyl-2-butyl and the sum of 2+3-pentyl nitrates) are reconstructed for the latter half of the 20th century based on Arctic firn air measurements. The reconstructed trends of the non-methane hydrocarbons (NMHCs) show increasing concentrations from 1950 to a maximum in 1980 before declining towards the end of last century. These observations provide direct evidence that NMHCs in the northern hemisphere have declined substantially during the period 1980–2001. Benzene concentrations show a smaller increase between 1950 and 1980 than the other NMHCs indicating that additional sources of benzene, other than fossil fuel combustion, were likely important contributors to the benzene budget prior to and during this period. The declining benzene concentrations from 1980 to 2001 would suggest that biomass burning is unlikely to be important in the benzene budget as biomass burning emissions were reportedly increasing over the same period. Methyl and ethyl nitrate show growth patterns in the firn that suggested perturbation by in-situ production from an unidentified mechanism. However, the higher alkyl nitrates show evidence for increasing concentrations from 1950 to maxima in the mid 1990s before decreasing slightly toward the end of the last century. The differing atmospheric evolution of the alkyl nitrates relative to their parent hydrocarbons indicate an increase in their production efficiency per hydrocarbon molecule. Using a steady state analysis of hydrocarbon oxidation and alkyl nitrate production and loss we show that reactive nitrogen oxide (NOx) concentrations in the northern hemisphere have likely increased considerably between 1950 and 2001.► NMHC abundances increased from 1950 to 1980 followed by notable declines. ► Alkyl nitrate abundances increased from 1950 to mid 1990s followed by small declines. ► Overall increase in alkyl nitrates greater than NHMCs indicating importance of additional factor, i.e., NOx. ► Alkyl nitrate to hydrocarbon relationships showed evidence for 20th century increase in NOx.
Keywords: Alkyl nitrates; Hydrocarbons; Benzene; Firn air; Atmospheric trends; Nitrogen oxides;

Cloud rise model for radiological dispersal devices events by Avi Sharon; Itzhak Halevy; Daniel Sattinger; Ilan Yaar (603-610).
As a part of the preparedness and response to possible radiological terror events, it is important to model the evolution of the radioactive cloud immediately after its formation, as a function of time, explosive quantity and local meteorological conditions. One of the major outputs of a cloud rise models is the evaluation of cloud top height, which is an essential input for most of the succeeding atmospheric dispersion models. This parameter strongly affects the radiological consequences of the event. Most of the cloud rise models used today, have been developed according to experiments were large quantities of explosives were used, within the range of hundreds of kilograms of TNT. The majority of these models, however, fail to address Radiological Dispersion Devices (RDD) events, which are typically characterized by smaller amounts of TNT. In this paper, a new, semi-empirical model that describes the vertical evolution of the cloud up to its effective height as a function of time, explosive quantity, atmospheric stability and horizontal wind speed, is presented. The database for this model is taken from five sets of experiments done in Israel during 2006–2009 under the “Green Field” (GF) project, using 0.25–100 kg of TNT.► We present a new model for the explosion cloud rise creating following a RDD event. ► The new model predicts the final cloud top height (“the effective height”). ► Model parameters are: explosive amount, time, atmospheric stability and horizontal wind intensity. ► The predicted cloud top heights are different than those predicted by others. ► The new predictions have radiological consequences for both, first and later responders.
Keywords: Cloud rise model; RDD; CBRN; Risk assessment; Atmospheric dispersion models;

Estimating the height of the nocturnal urban boundary layer for dispersion applications by Sam Pournazeri; Akula Venkatram; Marko Princevac; Si Tan; Nico Schulte (611-623).
We analyzed three data sets to examine methods to estimate the height of the stable boundary layer (SBL) in the complex setting of an urban area. We focused on a data set from a field study that we conducted in Riverside, California, in 2011 in which surface micrometeorological variables were measured using a sonic anemometer. In addition, profiles of temperature and relative humidity were measured with a tethersonde up to a height of 500 m. These measurements, supplemented with data from other field studies, were used to evaluate representative diagnostic and prognostic models for the SBL height. As expected, these models performed poorly in the spatially inhomogeneous setting of the urban area. The time integrated friction velocity (u *), with time starting at sunset, provided the best estimate of the height. This formulation is useful because we show that the surface friction velocity can be estimated with a measurement of wind speed at one height, and an estimate of the surface roughness length.► Structure of the urban nocturnal boundary layer was investigated through a field study. ► Different models for the stable boundary layer heights (SBL) were evaluated. ► These models performed poorly in the spatially inhomogeneous setting of the urban area. ► Observed SBL heights, correlated well with the time integral of friction velocity. ► Surface friction velocity can be estimated using the measured wind speed at one level.
Keywords: Stable boundary layer height; Urban micrometeorology; Urban dispersion; Friction velocity;

Concept to assess the human perception of odour by estimating short-time peak concentrations from one-hour mean values. Reply to a comment by Janicke et al. by Günther Schauberger; Martin Piringer; Rainer Schmitzer; Martin Kamp; Andreas Sowa; Roman Koch; Wilfried Eckhof; Ewald Grimm; Joachim Kypke; Eberhard Hartung (624-628).
Biologically relevant exposure to environmental pollutants often shows a non-linear relationship. For their assessment, as a rule short term concentrations have to be determined instead of long term mean values. This is also the case for the perception of odour. Regulatory dispersion models like AUSTAL2000 calculate long term mean concentration values (one-hour), but provide no information on the fluctuation from this mean. The ratio between a short term mean value (relevant for odour perception) and the long term mean value (calculated by the dispersion model), called the peak-to-mean value, is usually used to describe these fluctuations. In general, this ratio can be defined in different ways. , in a comment to which includes a statement that AUSTAL2000 uses a constant factor of 4, argue that AUSTAL2000 does not apply a peak-to-mean factor and does not calculate odour exceedance probabilities. Instead it calculates the frequency of so-called odour-hours by applying the relation between the 90-percentile of the instantaneous concentration and the hourly mean (), not between some peak value and the mean. According to , the 90-percentile of the instantaneous concentration can in practice be estimated with sufficient accuracy from the hourly mean by using a factor of 4.Having so far replied to we take additionally the opportunity to elaborate a little more on the peak-to-mean concept, especially pointing out that a constant factor independent of the stability of the atmosphere, the distance from and the geometry of the source, is not appropriate. On the contrary it shows a sophisticated structure which cannot be described by only one single value.
Keywords: Annoyance; Peak to mean; Separation distance; Nuisances; Livestock; Odour; Dispersion model;

A diffusive sampling device for measurement of ammonia in air by Tomomi Yamada; Shigehisa Uchiyama; Yohei Inaba; Naoki Kunugita; Hideki Nakagome; Hiroshi Seto (629-633).
A diffusive sampling device, the DSD-NH3, has been developed for measurement of ammonia in air. The DSD-NH3 comprises silica gel impregnated with phosphoric acid as the absorbent, a porous sintered polyethylene tube that acts as a diffusive membrane, and a small polypropylene syringe that is used for the elution of analytes from the absorbent. Silica gel impregnated with phosphoric acid is used as absorbent for the DSD-NH3; basic gases in ambient air, including ammonia, are trapped in the DSD-NH3 device by their reaction with phosphoric acid in the sampler to form their corresponding phosphoric acid salts. After collection, the DSD-NH3 samplers are eluted by water. Cations in the eluate, including ammonium ions, are analyzed by ion chromatography. A side-by-side comparison was made with active samplers, demonstrating good correlation (r 2 = 0.996). The sampling rate (94.5 ml min−1) was determined from comparison with an active sampling method and sampling rates. The sampling rate is also calculated from the respective molecular weights according to a rule based on Graham’s law. The theoretical sampling rate with the DSD-NH3 is 95.4 ml min−1 and agrees with the experimental value (94.5 ml min−1). Little influence of wind velocity on the sampler was observed. The relative standard deviations for ammonia concentrations were 4.7% with face velocity ranging 0–5.0 m/s.
Keywords: Diffusive sampling device; Ammonia; Sampling rate; Graham’s law;

Effect of the number of measurement sites on land use regression models in estimating local air pollution by Xavier Basagaña; Marcela Rivera; Inmaculada Aguilera; David Agis; Laura Bouso; Roberto Elosua; Maria Foraster; Audrey de Nazelle; Mark Nieuwenhuijsen; Joan Vila; Nino Künzli (634-642).
Land use regression (LUR) models are often used in epidemiologic studies to predict the air pollution exposure of health study participants. Such models are often based on a small to moderate number of air pollution measurement sites across the study area, and on a set of variables characterizing factors such as traffic patterns and surrounding land uses that are used as potential predictors. We used resampling techniques on a set of 148 measurement sites of NO2 in the urban area of Girona (Spain) to investigate the effect of the number of measurement sites on the LUR model performance, in particular on predictive ability and on the variables being chosen in the final model. In addition, we investigated the effect of the number of potential predictors and the variable selection algorithm used, and the consequences of the use of LUR predictions in regression models for a health outcome. Our results showed that, especially in small samples, both the adjusted within-sample R 2 and the leave-one-out cross-validation R 2 tended to give highly inflated values when compared to their prediction ability in a validation dataset. When the number of potential predictors was high, LUR models developed with a small number of measurement sites tended to give higher within-sample and cross-validated R 2 than those developed with more sites. Validation dataset R 2 showed a poor performance of models developed with a small number of sites that improved as the number of sites increased. Models developed with a small number of sites tended to select a different set of variables every time, were very sensitive to the number of potential predictors offered and resulted in stronger attenuation of coefficients when air pollution predictions were used in a health model. Our results suggest that LUR models aimed at characterizing local air pollution levels in complex urban settings should be based on a large number of measurement sites (>80 in our setting) and that the set of potential predictors should be restricted.► The prediction ability of LUR models developed with few sites is often inflated. ► >100 sites may be needed to characterize NO2 levels in complex urban settings. ► Air pollution models based on few sites difficult the detection of health effects.
Keywords: Land use regression; Measurement error; Modeling; NO2; Residential exposure; Spain;

Radioactivity in smoke particulates from prescribed burns at the Savannah River Site and at selected southeastern United States forests by Adwoa A. Commodore; G. Timothy Jannik; Teresa P. Eddy; Stephen L. Rathbun; Anna M. Hejl; John L. Pearce; Elizabeth A. Irvin-Barnwell; Luke P. Naeher (643-656).
In this study we compare airborne radionuclide concentrations during prescribed burns at the Savannah River Site (SRS) and a sample of forests in the Southeastern United States. The spatial trends of airborne radionuclide concentrations from prescribed burn areas at SRS are also characterized. Total suspended particulate (TSP) samples were taken at three settings (subsequently termed burn sample populations): during prescribed burns at SRS (n = 34), on nonburn days at SRS (n = 12) and during prescribed burns at five offsite locations in the Southeastern United States (n = 2 per location). Mass concentrations of TSP were calculated and alpha, beta and gamma spectroscopy was performed to determine radionuclide activity concentrations. Spatial correlation in radionuclide concentration was assessed and ordinary kriging was used to create continuous surface maps across our study area. Median activity concentrations of natural radionuclides including 40K, thorium and uranium isotopes (n = 34) were higher in samples from SRS prescribed fires (p < 0.02) compared to offsite locations (n = 10) and nonburn days (n = 12). Median gross beta activity was also higher at SRS (p < 0.0001). Median concentrations of anthropogenic radionuclides did not significantly differ among burn sample populations except for 238Pu (p = 0.0022) and 239, 240Pu (p = 0.014) with median concentrations of 8.41 × 10−4 and 6.72 × 10−5 pCi m−3 at SRS compared to 1.55 × 10−4 and −7.07 × 10−6 pCi m−3 (nonburn days) and 1.46 × 10−4 and 2.78 × 10−6 pCi m−3 (offsite burns) respectively. Results from our spatial analysis found that only 40K demonstrated significant spatial correlation (X 2  = 15.48, p = 0.0004) and spatial trends do not appear to directly link areas with higher activity concentrations with SRS facilities.► Radionuclide concentrations in smoke at SRS and a sample of forests are compared. ► Gross beta, 40K and isotopes of uranium, thorium and plutonium were higher at SRS. ► Results suggest no added radiation exposure is introduced from SRS prescribed burns.
Keywords: Total suspended particulates; Prescribed burns; Radionuclides; Spatial analysis;

Spatial distribution of ultrafine particles in urban settings: A land use regression model by Marcela Rivera; Xavier Basagaña; Inmaculada Aguilera; David Agis; Laura Bouso; Maria Foraster; Mercedes Medina-Ramón; Jorge Pey; Nino Künzli; Gerard Hoek (657-666).
The toxic effects of ultrafine particles (UFP) are a public health concern. However, epidemiological studies on the long term effects of UFP are limited due to lacking exposure models. Given the high spatial variation of UFP, the assignment of exposure levels in epidemiological studies requires a fine spatial scale. The aim of this study was to assess the performance of a short-term measurement protocol used at a large number of locations to derive a land use regression (LUR) model of the spatial variation of UFP in Girona, Spain.We measured UFP for 15 min on the sidewalk of 644 participants’ homes in 12 towns of Girona province (Spain). The measurements were done during non-rush traffic hours 9:15–12:45 and 15:15–16:45 during 32 days between June 15 and July 31, 2009. In parallel, we counted the number of vehicles driving in both directions. Measurements were repeated on a different day for a subset of 25 sites in Girona city. Potential predictor variables such as building density, distance to bus lines and land cover were derived using geographic information systems. We adjusted for temporal variation using daily mean NOx concentrations at a central monitor. Land use regression models for the entire area (Core model) and for individual towns were derived using a supervised forward selection algorithm.The best predictors of UFP were traffic intensity, distance to nearest major crossroad, area of high density residential land and household density. The LUR Core model explained 36% of UFP total variation. Adding sampling date and hour of the day to the Core model increased the R 2 to 51% without changing the regression slopes. Local models included predictor variables similar to those in the Core model, but performed better with an R 2 of 50% in Girona city.Independent LUR models for the first and second measurements at the subset of sites with repetitions had R 2’s of about 47%. When the mean of the two measurements was used R 2 improved to 72%.LUR models for UFP were developed, based on a highly cost-effective short-term monitoring campaign at a large number of sites, with fair performance. Complementing the approach with further strategies to address sources of temporal variation of UFP is likely to result in improved models as indicated by the good performance of the model based on the subset of sites with one repeated measurement. Our approach is promising for UFP and possibly for other PM components requiring active sampling.► Short-term monitoring of UFP is feasible and cost-effective for deriving LUR models. ► Traffic intensity, distance to nearest major crossroad are the main predictors of UFP. ► Using the mean of repeated measurements at each site improves LUR’s R 2 considerably.
Keywords: Particle number concentration; PM0.1; LUR; Exposure assessment; Monitoring; Outdoor home; Traffic; Girona; Spain;

Particle number concentration (PNC) and transition metal content are implicated in the health effects of airborne particulate matter (PM) but they are difficult to measure so consequently their temporal and spatial variations are not well characterized. Daily concentrations of PNC and particle-bound water-soluble metals (V, Cr, Mn, Fe, Ni, Cu, As, Cd and Pb) were measured at background and kerbside sites in Glasgow and London to examine if other metrics of air pollution such as optical darkness (absorbance) of collected filter samples of PM, gravimetric PM, and NO, NO2 and CO gas concentrations, can be used as surrogates for the temporal and spatial variations of the former. NO2 and NOx exhibited a high degree of within-site correlation and with PNC and water-soluble metals (Fe, Cu, As, Cd, Pb) at background sites in both cities. There is therefore potential to use NO2 and NOx as surrogates for PNC and water-soluble metal at background sites. However, correlation was weaker in complex street canyon environments where pollutant concentrations are strongly affected by local sources and the small-scale variations in pollutant dispersion induced by the wind regimes within street canyons. The corollary of the high correlation between NO2 and PNC and water-soluble metals at the background sites is that the latter pollutants may act as confounders for health effects attributed to NO2 from such sites. Concentrations of CO cannot be used as a surrogate for PNC. Increments in daily NOx and NO2 concentrations between trafficked and background sites were shown to be a simple and novel surrogate for daily spatial variation of PNC; for example, increments in NOx explained 78–79% of the variance in PNC at the paired sites in both Glasgow and London, but relationships were city specific. The increments in NOx also explained 70% of the spatial variation in Cu and Ni in Glasgow but not in London. Weekly NO2 measurements derived from passive diffusion tubes were also shown to correlate well with increments in PNC. A high temporal correlation between PNC and 1,3-butadiene and benzene (which can also be measured by passive sampler) implies that passive sampler measurements may be a straightforward tool for deriving long-term spatial patterns in PNC.► Particle number concentration (PNC) and transition metals in particulate matter have been associated with health outcomes. ► PNC and metals are difficult and expensive to measure, so they are not routinely monitored. ► NO2 and NOx can be used as surrogates for PNC and water-soluble metal at background sites but not at street canyons. ► Weekly NO2 measurements derived from passive diffusion tubes could be used as metrics for long-term exposure to PNC.
Keywords: Particle number concentration; Nitrogen oxides; Transition metals; Air pollution; Glasgow; London;

A new sensor for the assessment of personal exposure to volatile organic compounds by Cheng Chen; Katherine Driggs Campbell; Indira Negi; Rodrigo A. Iglesias; Patrick Owens; Nongjian Tao; Francis Tsow; Erica S. Forzani (679-687).
To improve our understanding of indoor and outdoor personal exposures to common environmental toxicants released into the environment, new technologies that can monitor and quantify the toxicants anytime anywhere are needed. This paper presents a wearable sensor to provide such capabilities. The sensor can communicate with a common smart phone and provides accurate measurement of volatile organic compound concentration at a personal level in real-time, providing environmental toxicants data every three minutes. The sensor has high specificity and sensitivity to aromatic, alkyl, and chlorinated hydrocarbons with a resolution as low as 4 parts-per-billion (ppb), with a detection range of 4 ppb–1000 ppm (parts-per-million). The sensor’s performance was validated using Gas Chromatography and Selected Ion Flow Tube – Mass Spectrometry reference methods in a variety of environments and activities with overall accuracy higher than 81% (r 2 > 0.9). Field tests examined personal exposure in various scenarios including: indoor and outdoor environments, traffic exposure in different cities which vary from 0 to 50 ppmC (part-per-million carbon from hydrocarbons), and pollutants near the 2010 Deepwater Horizon’s oil spill. These field tests not only validated the performance but also demonstrated unprecedented high temporal and spatial toxicant information provided by the new technology.► A VOC sensor for optimal sensitivity, selectivity, portability, and usability. ► Sensor demonstrated accurate and reliable results in validation and field tests. ► Elevated hydrocarbons detected in traffic, remodeled rooms, and kerosene lamps. ► Sensor is wearable and offers real-time results without false alarms. ► Sensor is suitable for indoor/outdoor environmental personal exposure studies.
Keywords: Air monitoring; Environmental health; Indoor air quality; Real-time sensor; Personal exposure assessment; Wireless and wearable integrated sensor;

A new online coupled regional climate-chemistry-aerosol model (RIEMS-Chemaero) has been developed and applied to investigate direct radiative effects of dust aerosol and mixed aerosols over East Asia in March 2010, when an extremely intense dust storm on 19–22 March swept across almost the entire east China including the Pearl River Delta of south China, where little dust storm was observed before. The model results are evaluated against ground observation of PM10 concentration, aerosol optical depth (AOD) from both AERONET measurement and satellite retrieval (MODIS). The comparison demonstrates a good ability of RIEMS-Chemaero in reproducing major features of aerosol spatial distribution and temporal variation, as well as dust evolution during the dust storm period. However, the model tends to generally underpredict AOD at AERONET sites, with larger biases at urban sites than that at rural sites. Dust aerosols exerted a significant impact on radiation energy budget during the dust storm period, with the 4-day mean values of shortwave and longwave radiative forcings at the surface up to −90 W m−2 and +40 W m−2, respectively, over the Gobi desert. The monthly mean net dust radiative forcings at the surface ranged from −9 to −24 W m−2 over the dust source regions, and from −6 to −21 W m−2 over wide downwind areas including the middle and lower reaches of the Yellow River and the Yangtze River and the Yellow Sea. The net dust radiative forcing at TOA varied from near zero to +6.0 W m−2 in large areas of the continent. The monthly mean values of the net direct radiative forcings due to dust, non-dust aerosols and all aerosols (dust + sea salt + anthropogenic aerosols) averaged over the whole domain are estimated to be −3.9 W m−2, −5.6 W m−2 and −9.3 W m−2, respectively, at the surface, and to be +0.9 W m−2, −3.0 W m−2 and −2.0 W m−2, respectively, at TOA, indicating a light dust warming effect and an overall aerosol cooling effect in the springtime over East Asia. In east China, the net radiative forcings due to dust, non-dust aerosols and all aerosols at the surface are enhanced to −8.4 W m−2, −10.2 W m−2 and −18.0 W m−2, respectively, due to both the frequent dust influence and the intensive anthropogenic emissions in this region. The dust forcing accounts for about 42% of the total aerosol forcing at the surface in the domain, implying a potentially important role of mineral dust in radiation budget and regional climate. The semi-direct effect of dust aerosol tends to reduce cloud cover throughout the domain and it is partly responsible for the direct radiative forcings because of the feedbacks among aerosol, radiation, cloud and dynamics.► An online coupled model with aerosol feedbacks, namely RIEMS-Chemaero, is developed. ► The model is able to predict PM10 level and aerosol optical depth reasonably well. ► Dust storms in March 2010 exerted great impacts on radiation budget over East Asia. ► The net dust direct radiative forcings were −3.9 W m−2 at the surface and +0.9 W m−2 at TOA. ► The net direct radiative forcings by all aerosols are −9.3 W m−2 at the surface and −2.0 W m−2 at TOA.
Keywords: Mineral dust; Anthropogenic aerosols; Direct radiative forcing; Semi-direct effect; Regional climate model; Aerosol–climate interactions;

An improved correction method was established using passive air samplers to assess the distributions of polychlorinated naphthalenes (PCNs) in the eastern Pearl River Delta, South China. This method was based on a joint correction that used the active air sampling rate and the addition of depuration compounds. As a correction factor, the depuration compounds’ properties do not need to be similar to the target compounds. The total PCN air concentrations ranged from 6.4 to 832, with an average of 148 ± 201 pg m−3 in the study area, while the TEQ of the PCNs ranged from 1.2 × 10−4 to 2.6 × 10−2  pg m−3. High concentrations of PCNs were mostly observed in the highly industrialized areas. The PCN air levels were remarkably increased in winter compared with summer. Tri-CNs was the most dominant homologue group, while CN 24 was the most dominant congener. The high proportion of combustion-related PCNs suggests that the contribution of combustion sources to the PCN air burden has been significant recently in comparison with historical emissions.► An improved correction method for passive air sampler was established. ► Air distributions of PCNs in the PRD were assessed using this method. ► High concentrations of PCNs were mostly observed in the highly developed areas. ► The contribution of combustion PCN sources has been increasing recently.
Keywords: Improved correction method; Passive air sampling; Polychlorinated naphthalene; Pearl River Delta; South China;

Numerical calculations are performed to reproduce the transport and dispersion of the continuous release of dense gases over flat homogeneous surfaces with and without the mitigating influence of a downwind water curtain. Frequently such plumes are released as a result of a chemical manufacturing, storage or gas transportation accident resulting in a ground-level hazard due to gas flammability or toxicity. A field situation in which cold carbon dioxide was released upwind of water curtains () was simulated using the open-source software FDS (Fire Dynamic Simulator) a full 3-d CFD model. Only water-spray enhancement of dispersion was considered; hence, no chemical removal or reactions were present or simulated. Wind-tunnel measurements for a 1:28.9 scale replication of the Moodie experiments are also compared with the 3-d CFD results. Concentration distributions, percent dilution and forced diffusion parameters were compared in scatter diagrams. Concentration field contours with and without active spray curtains are also presented.► Model replicated dense gas dispersing with water-spray curtain mitigation devices. ► Cold carbon dioxide released upwind of water curtains was simulated using CFD. ► Wind-tunnel measurements were compared with the 3-d CFD results. ► Concentration, percent dilution and forced dilution were compared in diagrams.
Keywords: Computational fluid dynamics; Dense gas clouds; Water sprays; Dispersion; Mitigation;

Adequate air quality modeling is reliant on accurate meteorological simulations especially in the planetary boundary layer (PBL). To understand how the boundary layer processes affect the mixing and transport of air pollutants, the sensitivity of Weather Research Forecasting (WRF) model with different PBL schemes (YSU and MYJ) is utilized. Community Multiscale Air Quality (CMAQ) modeling system is performed subsequently to study the effects of the PBL physical processes on the meteorological and air quality simulations. A comparison is made of two distinct atmospheric conditions. Case 1 considers the influence of the Asian continental outflow where air pollutants carried by long-range transport (LRT) to Taiwan. The variation in ozone (O3) concentration between the two sensitivity runs is mainly caused by the PBL height difference with WRF–MYJ predicts much deeper PBL height near the frontal low-pressure region than does the WRF–YSU. Case 2 is associated with the land-sea breeze flow. In this situation O3 is locally produced from the western side of the country where major metropolitan cities and highways are located. Distinctions in O3 are caused by difference in the strength of the land-sea breeze flow between the two runs. At night the WRF–YSU predicts a weaker offshore land breeze than does the WRF–MYJ near the western coastline. During the day, the WRF–YSU predicts a stronger sea breeze near the offshore area than does the WRF–MYJ, while over the landside, the WRF–YSU predicts a lower wind speed than does the WRF–MYJ.► We modeled two WRF and CMAQ simulations using YSU and MYJ PBL schemes. ► For long-range transported O3, difference between two runs is caused by PBL height. ► For local produced O3, land-sea breeze flow dominates redistribution of O3.
Keywords: Yonsei University (YSU) PBL scheme; Mellor–Yamada–Janjic (MYJ) PBL scheme; Air quality modeling; Land-sea breeze; Long-range transport;

Atmospheric particulate matter (PM) exhibits a high correlation with public health. The mixture distributions of PM in Taiwan derive mainly from anthropogenic (industrial) and natural (rural) air pollutants. This study determines the mixture distribution of monthly PM2.5 and PM10 data of a dust storm occurred in Taiwan in March 2008 using a finite mixture distribution model (FMDM). The probabilities of a contaminated area are mapped using sequential Gaussian simulation (SGS) with the FMDM cut-off values of PM2.5 and PM10. Results show that PM2.5 and PM10 can be individually fitted using the FMDM. Using the SGS with FMDM cut-off values can delineate high and low concentration areas. Spatial patterns of PM2.5 and PM10 concentrations show seasonal variations caused by dust storms and meteorological conditions. The difference of the mixture distribution of high and low PM concentrations during the dust storm is significant. The area with high PM concentration is delineated in the industrial and urban areas of Taiwan (southwestern, west central, and northern Taiwan). This information can define the boundaries of the PM hotspot areas to control pollutants and reduce public exposure.► The probabilities of contaminated area of particulate matter are mapped. ► Dust storm and meteorological conditions cause variations of spatial patterns of PM. ► The area with high PM concentration is delineated in the industrial and urban areas. ► PM2.5 and PM10 can be individually fitted by finite mixture distribution models.
Keywords: Finite mixture distribution; Particulate matter; PM2.5; PM10; Sequential Gaussian simulation; Dust storm; Meteorological condition;

Aerosol absorption over Bay of Bengal during winter: Variability and sources by Sumita Kedia; S. Ramachandran; T.A. Rajesh; Rohit Srivastava (738-745).
Measurements of black carbon (BC) mass concentration were made over the Bay of Bengal (BoB) during the period of 27 December 2008–29 January 2009. BC mass concentration is highest over the Coastal-BoB (5.1 ± 3.0 μg m−3) and is more than a factor of two higher than the South-BoB (2.5 ± 1.4 μg m−3). The source regions of BC over the study region is identified using the Total Potential Source Contribution Function (TPSCF) analysis. The probable source regions over the Coastal-BoB and North-BoB (India, Indo-Gangetic plain, Pakistan, Afghanistan) are found to be distinctly different than that over the East-BoB and South-BoB (mostly from southeast Asia). The spectral distribution of absorption coefficients suggested similar source types of BC present over the entire BoB, with significant contribution of absorbing aerosols from the sources other than fossil fuel burning. Our results suggest that the entire BoB remains dominantly influenced by aerosols emitted from biomass/biofuel burning during winter. Single scattering albedo (SSA) is found to vary in the range of 0.63–0.70 over different parts of BoB with the lowest value over Coastal-BoB and the highest value over South-BoB. SSA values observed in the present study are the lowest ever reported over the BoB in the last decade indicating highest concentration of absorbing aerosols over the BoB during winter. The present work and the results obtained will have strong implications while investigating the effect of anthropogenic aerosols over marine environment, and in estimating the spatiotemporal variation of aerosol radiative impact.► Absorption coefficients calculated from BC mass measured over BoB in winter. ► BC comes from IGP to N-BoB and from southeast Asia to S-BoB in winter. ► >90% BC originate from biomass/biofuel combustion over BoB. ► Spectral dependence of BC aerosols is similar over North and South-BoB. ► SSA varies from 0.63 (Coastal-BoB) to 0.70 (South-BoB) in winter.
Keywords: Black carbon; Absorption; Bay of Bengal; PSCF; Source region; Variability;

An air pollution episode and its formation mechanism during the tropical cyclone Nuri's landfall in a coastal city of south China by John Xun Yang; Alexis Kai Hon Lau; Jimmy Chi Hung Fung; Wen Zhou; Mark Wenig (746-753).
In this work we investigated an air pollution episode during the landfall process of a tropical cyclone (TC) in Hong Kong. TCs affect air condition and account for most air pollution episodes in summer of this region. In August 2008, TC Nuri made direct landfall in Hong Kong. Before its landfall, an air pollution episode occurred, where major pollutants like SO2 and PM10 increased eight and six times higher respectively. Rather than using single measurement method, we combined ground air sampling, lidar, sunphotometer and satellite lidar CALIPSO with focus on aerosol to study the episode mechanism, and some new phenomena were found. During the episode, it was found that heavy inland aerosol plumes existed in areas larger than urbanized regions and were elevated vertically and transported southward. During episode, planetary boundary layer (PBL) expansion and height increase were observed, which is different from previous reported PBL compression and height decrease. While vertical subsidence and horizontal stagnation and consequently local aerosol accumulation were attributed as the main episode cause in previous cases, our observation showed that transported aerosols dominated in this TC landfall event. This can be further confirmed by examining aerosol chemical composition, size distribution and single scattering albedo, where transported related species showed significantly change and local indicators remained relatively stable. Invigorated cloud droplets were found on the boundary layer top upon aerosol elevation. The results indicate that site difference and TC tracks should be considered for analyzing episode formation mechanism. They can cause difference in the strength of vertical subsidence and horizontal advection and affect pollution flow direction, which subsequently results in different pollution formation processes.► We studied an air pollution episode caused by a tropical cyclone (TC) landfall. ► Extensive aerosol elevation and transport and invigorated clouds were found. ► Boundary layer showed expansion rather than previously reported compressing. ► Transport indicators of aerosol species showed significantly change.
Keywords: Air pollution; Aerosol; Tropical cyclone; Remote sensing;

Corrigendum to “Predicting wetland contamination from atmospheric deposition measurements of pesticides in the Canadian Prairie Pothole region” [Atmos. Environ. 45 (2011) 7227–7234] by Paul G. Messing; Annemieke Farenhorst; Don T. Waite; D.A. Ross McQueen; James F. Sproull; David A. Humphries; Laura L. Thompson (754).