Atmospheric Environment (v.60, #C)

The estimated atmospheric lead emissions in China, 1990–2009 by Qian Li; Hongguang Cheng; Tan Zhou; Chunye Lin; Shu Guo (1-8).
Estimates of atmospheric emissions of lead from anthropogenic sources in China from 1990 to 2009 are presented with the information on emissions of both total lead and its spatial distribution in regions. The total emissions during the period 1990–2009 are nearly 200 000 tons. Motor vehicle gasoline combustion was the largest source of anthropogenic emissions. The estimated release of 117 800 t of lead represented 60% of the total emissions. Substantial decline occurred in 2001, when the total emissions were about 81% less than the 2000 value. The reduced lead content of motor vehicle gasoline is the primary reason for the decreased in lead emissions in 2001. After leaded gasoline was phased out, coal combustion became the principal source of emissions. Based on data on emissions from 2005 through 2009, the emissions are concentrated in eastern and central China due to the high level of coal consumption and non-ferrous metal smelting. The five provinces with the largest amounts of lead emissions are Shandong, Hebei, Shanxi, Henan and Jiangsu. These five regions produced nearly 40% of the total.► We provide an inventory of lead emissions from anthropogenic activities in China. ► We provide an analysis of the temporal and spatial variations of lead emissions. ► The emission structure of lead changed in the last 20 years. ► Lead emissions from motor vehicle gasoline combustion declined substantially. ► Coal combustion and non-ferrous metal smelting are important emission sources.
Keywords: Atmospheric lead emission; Emission sources; Motor vehicle gasoline combustion; Coal combustion; Non-ferrous metal smelting;

The hygroscopic behaviors of benzoic acid (BA) particles and internal mixtures of inorganic salts (sodium chloride and ammonium sulfate) and BA are investigated in the 10–90% RH using the hygroscopicity tandem differential mobility analyzer (H-TDMA) system. Different morphology of BA, NaCl–BA, and (NH4)2SO4–BA particles at representative RH is characterized by Transmission Electron Microscopy (TEM). The hygroscopic growth factors (GFs) of BA exhibit a significant reduction in the 75–85% RH, followed by a slight increase at 90% RH. Internally mixed NaCl–BA and (NH4)2SO4–BA particles display deliquescence transitions at 70% RH, followed by apparently hampered hygroscopic growth due to the presence of BA. According to the TEM results, the morphology of BA particles and mixed particles show marked change in humidification, which possibly can be attributed to the strong microstructural rearrangement of BA fraction. This significant restructuring is responsible for the GFs change of BA particles and the hygroscopic behaviors transformation of mixed NaCl–BA and (NH4)2SO4–BA particles. These results demonstrate that atmospheric BA could significantly influence the hygroscopic properties of inorganic aerosols.► The hygroscopicity of benzoic acid (BA) particles is investigated. ► The reason of diameters change of BA particles with the relative humidity is discussed. ► The DRHs of NaCl/BA and (NH4)2SO4/BA mixed particles are lower than those of pure inorganics. ► The internal mixed BA hinders the hygroscopic growth of deliquescent inorganic droplets.
Keywords: Hygroscopicity; Benzoic acid; H-TDMA; Internal mixture; Inorganic salts;

An experimental determination of the H2S overall mass transfer coefficient from quiescent surfaces at wastewater treatment plants by Jane Meri Santos; Virginie Kreim; Jean-Michel Guillot; Neyval Costa Reis; Leandro Melo de Sá; Nigel John Horan (18-24).
This study has investigated overall mass transfer coefficients of hydrogen sulphide from quiescent liquid surfaces under simulated laboratory conditions. Wind flow (friction velocity) has been correlated with the overall mass transfer coefficient (K L ) of hydrogen sulphide in the liquid phase using a wind tunnel study. The experimental values for this coefficient have been compared with predicted K L values obtained from three different emission models that are widely used to determine volatilization rates from the quiescent surfaces of wastewater treatment unit processes. Friction velocity (in a range of 0.11 and 0.27 m s−1) was found to have a negligible influence on the overall mass transfer coefficients for hydrogen sulphide but by contrast two of the models predicted a stronger influence of friction velocity and overestimate the K L values by up to a factor of 12.5, thus risking unnecessary expenditure on odour control measures. However, at low wind speeds or friction velocities, when more odour complaints might be expected due to poor atmospheric dispersion, a better agreement of emission rates with experimental data was found for all the models.► Volatilization of H2S was investigated under different flow conditions. ► Friction velocity does not affect volatilization of H2S at low wind speed. ► WATER9 model provided more realistic estimates of volatilization of H2S. ► Emission models overestimates overall mass transfer coefficient of H2S. ► Volatilization of H2S can be treated as constant for low wind speed conditions.
Keywords: Mass transfer coefficient; Hydrogen sulphide; Volatilization; Odour; Quiescent surface;

In this study, the impact of the rapid rate of urbanization over the Pearl River Delta (PRD) region of China since the 1980s on its seasonal climate is investigated using the Weather Research and Forecasting Model. Two land-cover data are employed to simulate the urbanization effects on the regional climate in both summer (June and August) and winter (December and February) for 26 years from 1984 to 2009. Spatial and temporal features of the urbanization effect on temperature and precipitation are found to be different between summer and winter. Urban warming and modifications of surface variables such as surface latent heat flux and 2-m relatively humidity are more pronounced in summer. Moreover, summer rainfall is enhanced but winter precipitation is reduced. The increase in summer rainfall is mainly contributed by the strong urban heat island effect, which enhances the convective circulation over the urban area. On the other hand, a reduction in winter precipitation is observed. The different behavior during winter time is due to drier northerly winds and increased atmospheric stability. Furthermore, the changes in winter precipitation are associated with the synoptic forcing such as El Niño – Southern Oscillation and monsoon, but no significant correlation can be found between changes in summer rainfall and the synoptic forcing. In other words, the local surface forcing (including radiative fluxes, heat, momentum and water transfer at the air–land interface) dominates over the synoptic forcing in summer but the reverse is true in winter. Under conditions of weak synoptic flow, local thermodynamic effects of urbanization dominates, setting up convergence zone over the urban area and leading to increased precipitation. However, during winter time, under the influence of strong northeasterly synoptic flow, dynamic effects of increased surface roughness urban areas dominate and lead to convergence upwind of the urban region.► Urban warming and modifications of surface variables are more pronounced in summer. ► Summer rainfall is enhanced but winter precipitation is reduced. ► The local forcing dominates over the large-scale forcing in summer but the reverse is true in winter. ► A strong synoptic flow can reduce the urbanization effects over an urban area.
Keywords: Urbanization; Seasonal climate; Urban rainfall;

Assessment and prediction of air quality using fuzzy logic and autoregressive models by José Juan Carbajal-Hernández; Luis P. Sánchez-Fernández; Jesús A. Carrasco-Ochoa; José Fco. Martínez-Trinidad (37-50).
In recent years, artificial intelligence methods have been used for the treatment of environmental problems. This work, presents two models for assessment and prediction of air quality. First, we develop a new computational model for air quality assessment in order to evaluate toxic compounds that can harm sensitive people in urban areas, affecting their normal activities. In this model we propose to use a Sigma operator to statistically asses air quality parameters using their historical data information and determining their negative impact in air quality based on toxicity limits, frequency average and deviations of toxicological tests. We also introduce a fuzzy inference system to perform parameter classification using a reasoning process and integrating them in an air quality index describing the pollution levels in five stages: excellent, good, regular, bad and danger, respectively. The second model proposed in this work predicts air quality concentrations using an autoregressive model, providing a predicted air quality index based on the fuzzy inference system previously developed. Using data from Mexico City Atmospheric Monitoring System, we perform a comparison among air quality indices developed for environmental agencies and similar models. Our results show that our models are an appropriate tool for assessing site pollution and for providing guidance to improve contingency actions in urban areas.► We examine air quality parameter levels using a statistical index (Sigma). ► We model environmental interactions using a reasoning process. ► We predict air quality parameters using historical observations. ► We compare the proposed air quality index with the Mexican and the U.S. indices. ► Our results show a better performance compared against traditional methodologies.
Keywords: Artificial intelligence; Air quality assessment; Pattern processing; Prediction;

European temperate forest soils have been exposed to elevated nitrogen (N) and acid depositions for decades. High nitrous oxide (N2O) and nitric oxide (NO) emissions have been reported from these forests. Since the 1980s, a decline in atmospheric deposition rates has been occurring. Our study addressed the question as to how N oxide fluxes and N turnover processes have changed in response to the declining N depositions in a N-enriched spruce stand (Picea abies (L.) Karst.). Studies were conducted at the Solling roof site under a control-roof with ambient depositions and under a reduced-N-input-roof where N and acid depositions have been reduced to a pre-industrial level for 16–17 years. Open dynamic and closed chamber methods were used to determine NOx and N2O fluxes, respectively, and in situ incubation studies were conducted to measure net N mineralisation. Under the reduced deposition roof, net nitrification and nitrate in soil solution were reduced to undetectable levels causing the soil to change from a net source for NOx (0.62 ± 0.24 kg N ha−1 yr−1) into a net sink (−0.33 ± 0.01 kg N ha−1 yr−1). The uptake of NOx was exclusively controlled by the NOx concentrations of the forest air. Reversal of N enrichment did not affect annual N2O fluxes (0.08 kg N ha−1 yr−1) due to restricted denitrification in the well-aerated organic layer, but the origin of nitrate for denitrification changed from mainly soil-borne N to exclusively deposited N. It was demonstrated that less than two decades of reduced N and acid depositions are sufficient to reduce the surplus N and NOx emissions of this soil.► We investigated long-term reduction of N depositions in a spruce stand. ► Net nitrification and nitrate in soil solution were reduced to undetectable levels. ► The soil changed from a net source for NOx into a net sink. ► NOx uptake was controlled by the NOx concentrations of the forest air. ► N2O fluxes did not change due to limited denitrification in the well-aerated soil.
Keywords: NOx consumption; NOx production; Nitrous oxide; N deposition; Net nitrification; Solling roof project;

The objective of this study is to quantify the relation of aerosol chemical compositions and optical properties, and to assess the impact of relative humidity (RH) on atmospheric visibility and aerosol direct radiative forcing (ADRF). Mass concentration and size distribution of aerosol chemical compositions as well as aerosol optical properties were concurrently measured at Guangzhou urban site during the PRD (Pearl River Delta) campaign from 1 to 31 July, 2006. Gaseous pollutant NO2 and meteorological parameter were simultaneously monitored. Compared with its dry condition, atmospheric ambient extinction coefficient σ ext(RH) averagely increased about 51% and atmospheric visibility deceased about 35%, among which RH played an important role on the optical properties of water soluble inorganic salts. (NH4)2SO4 is the most important component responsible for visibility degradation at Guangzhou. In addition, the asymmetry factor g increased from 0.64 to 0.74 with the up-scatter fraction β decreasing from 0.24 to 0.19 when RH increasing from 40% to 90%. At 80% RH, the ADRF increased about 280% compared to that at dry condition and it averagely increased about 100% during the campaign under ambient conditions. It can be inferred that aerosol water content is a key factor and could not be ignored in assessing the role of aerosols in visibility impairment and radiative forcing, especially in the regions with high RH.► We quantify the relation of aerosol chemical compositions and optical properties. ► We assess the impact of relative humidity on atmospheric visibility and aerosol direct radiative forcing. ► We investigate the influence of relative humidity on aerosol asymmetry factor and up-scatter fraction.
Keywords: Aerosol hygroscopicity; Visibility impairment; Radiative forcing; PRIDE-PRD campaign;

Hygroscopic behavior of wet dispersed and dry deposited NaNO3 particles by HyeKyeong Kim; Mi-Jung Lee; Hae-Jin Jung; Hyo-Jin Eom; Shila Maskey; Kang-Ho Ahn; Chul-Un Ro (68-75).
Previous controversial studies on the hygroscopic behavior of NaNO3 aerosol particles and our frequent observation of crystalline NaNO3-containing ambient particles prompted this hygroscopic study on NaNO3 particles. In this work, the hygroscopic behavior of individual NaNO3 particles of 2.5–4.0 μm in diameter is investigated on a single-particle basis using an optical microscopic technique. Quite different hygroscopic behavior between particles wet dispersed by the nebulization of aqueous NaNO3 solutions and dry deposited powdery particles was observed; i.e., most of wet dispersed particles continuously grew and shrank during humidifying and dehydration processes, respectively, and yet all the dry deposited particles had reproducible deliquescence and efflorescence relative humidities (DRHs and ERHs). The different behavior of the two NaNO3 systems is due to the different nucleation mechanisms. Our hygroscopic study of wet deposited NaNO3 particles indicates that they nucleate via homogeneous nucleation, but the time scale for the nucleation to occur is too long to be atmospherically relevant. And thus no efflorescence of the particles has been observed in the laboratory measurements. However, when chemical species acting as heterogeneous nuclei are present, then efflorescence occurs which can explain the observation of ambient crystalline NaNO3 particles. It is imperative to work with heterogeneous nucleation systems which are more relevant to the real world.► Previous controversial studies on hygroscopic behavior of NaNO3 particles prompted this study. ► Quite different hygroscopic behavior between wet dispersed and dry deposited NaNO3 particles was observed. ► The difference is due to different, i.e. homogeneous and heterogeneous, nucleation mechanisms. ► Similar observations were also made for NaCl, KCl, (NH4)2SO4, Na2SO4, and KNO3.
Keywords: Hygroscopic properties of aerosols; NaNO3; DRH; ERH; Single-particle analysis; Optical microscopy;

Uptake of partially fluorinated alcohols on atmospheric ice surfaces by Elena Moreno; Alfonso Aranda; Yolanda Díaz-de-Mera; Alberto Notario; Diana Rodríguez; Iván Bravo (76-81).
This work provides uptake results of CF3CF2CH2OH and CF3CF2CF2CH2OH on ice over the range temperature 203–223 K using a coated wall flow tube coupled to mass spectrometric detection. The adsorption was fully reversible and the data could be described in terms of the Langmuir isotherm for the range of concentrations and temperatures studied. For this temperature range, ΔH0 ads = −45 ± 11 kJ mol−1 and ΔH0 ads = −46 ± 8 kJ mol−1 were obtained for CF3CF2CH2OH and CF3CF2CF2CH2OH respectively (error is 2σ + 5%). Although ice surfaces do not permanently scavenge the studied partially fluorinated compounds, the partitioning between the gas phase and cirrus or snow-pack surfaces may play a role as a reservoir slowing down other permanent atmospheric sinks.► The study of the uptake of CFCs substitutes on ice surfaces is reported. ► Ice adsorption of partially fluorinated alcohols follows Langmuir-type behavior. ► Cirrus clouds and snow-pack behave as reversible reservoir for fluorinated alcohols.
Keywords: Uptake; Ice; Surface; Fluorinated; Alcohol;

Synthesis, characterization and field evaluation of a new calcium-based CO2 absorbent for radial diffusive sampler by Raffaele Cucciniello; Antonio Proto; Davide Alfano; Oriana Motta (82-87).
In this paper the use of passive sampling as a powerful approach to monitor atmospheric CO2 is assessed. Suitable substrate based on calcium-aluminium oxide was synthetized according to a process which permits to control the particle size of the CaO/Al based sorbent. The study shows that hydration of substrate is an essential part of the process of CO2 absorption and subsequent conversion to carbonate. X-ray diffraction, thermogravimetric analysis, environmental scanning electron microscopic analysis were used in order to characterize the substrate and to establish the best performances both in terms of particle size and CO2 absorption capacity.Passive samplers for CO2 monitoring were prepared and then tested at laboratory level and in the atmospheric environment. Validation was performed by comparison with an infrared continuous detector. Thermogravimetric analysis results, carried out to evaluate the absorbing capability of this new passive device, were in accordance with data collected at the same time by the active continuous analyser.The diffusive sampling rate and the diffusion coefficient of CO2 respect to this new passive device were also evaluated resulting equal to 47 ± 3 ml min−1 and 0.0509 ± 0.005 cm2 s−1, respectively.
Keywords: Radial diffusive samplers; CO2; Diffusion coefficient;

Monitoring and analysis of the chemical composition of air pollutants were conducted over a five-year period (2005–2009) in the sub-urban area of Chiang Mai, Thailand. This study aims to determine the seasonal variation of atmospheric ion species and gases, examine their correlations, identify possible sources and assess major air-flow patterns to the receptor. The dominant gas and particulate pollutants were NH3 (43–58%) and SO 4 2 − (39–48%), respectively. The annual mean concentrations of NH3 (μg m−3) in descending order were 4.08 (2009) > 3.32 (2007) > 2.68 (2008) > 2.47 (2006) and 1.87 (2005), while those of SO 4 2 − (μg m−3) were 2.60 (2007) > 2.20 (2006) > 1.95 (2009) > 1.75 (2008) and 1.26 (2005). Concentrations of particulate ions were analyzed by principle component analysis to find out the possible sources of air pollutants in this area. The first component of each year had a high loading of SO 4 2 − and NH 4 + , which probably came from fuel combustion and agricultural activity, respectively. K+, a tracer of biomass burning, also contributed to the first or the second components of each year. Concentrations of NH 4 + and SO 4 2 − were well correlated (r > 0.777, p < 0.01), which lead to the conclusion that (NH4)2SO4 was a major compound present in this area. The 3-day backward trajectories of air mass arriving at Chiang Mai from 2005 to 2009 were analyzed using the hybrid single particle langrangian integrated trajectory (HYSPLIT) model and grouped by cluster analysis. The air mass data was analyzed for the dry season (n = 18; 100%). The trajectory of air mass in 2005 mainly originated locally (67%). In 2006, the recorded data showed that 56% of air mass was emitted from the western continental region of Thailand. In 2007, the percent ratios from the western and eastern continental areas were equal (39%). In 2008, 67% originated from the western continental area. In 2009, the recorded air mass mainly came from the western continental area (72%). In conclusion, the major trajectories of air mass from 2006 to 2009 originated from the southwest direction of the receptor, but in 2005, the air mass appeared to be locally originated.► 5-year situation of atmospheric pollutants in Chiang Mai, Thailand was analyzed. ► Ammonium from agriculture and sulfate from fuel combustion were the major ions. ► Major air mass approaching Chiang Mai came from southwest direction. ► Long range transport and local emission play important role on air pollution. ► Haze phenomenon in dry season was related with open burning.
Keywords: Ion composition; Air pollution; Pollution sources; Air mass movement;

Data assimilation of surface air pollutants (O3 and NO2) in the regional-scale air quality model AURORA by Ujjwal Kumar; Koen De Ridder; Wouter Lefebvre; Stijn Janssen (99-108).
In the present work, a bias-aware optimal interpolation in conjunction with the Hollingsworth–Lönnberg method to estimate error covariance matrices was applied as data assimilation algorithm in the regional scale air quality model AURORA to assimilate ground level O3 and NO2 concentrations. The study was conducted over the domain Belgium including part of its neighbouring areas with grid resolution of 3 × 3 km2. Data assimilation was carried out for the retrospective simulation in post-processing (offline) mode for a summer and a winter month. Observations were provided by the AIRBASE data archive. Since the air quality model AURORA is presumed to represent background conditions, only the background stations within the domain have been taken into account. The validation of the proposed method was carried out by leaving observations of ten monitoring stations out in one run of the data assimilation process and another ten stations out in the next run and so on (a “leave ten out approach”). The proposed method has been evaluated in both spatial as well temporal domain against various statistical indicators such as correlation coefficient (CORR), root mean square error (RMSE), index of agreement (IOA) and mean fractional bias (MFB). For both the O3 and NO2, the extensive validation results have clearly shown substantial improvement in the data assimilation results over AURORA free run in both the seasons. The results over 70 validation stations show that CORR increased from 0.4 to 0.8 for O3, 0.3 to 0.6 for NO2 while average RMSE reduced from 27.9 to 12.6 for O3 and from 17.4 to 11.0 for NO2 for the month of June. Similar improvements have been observed for the month of Dec as well. Spatial CORR, IOA for monthly means of both the O3 and NO2 concentrations were also increased considerably. The results clearly indicate that the applied bias aware optimal interpolation in conjunction with Hollingsworth–Lönnberg method is a very promising candidate for the statistical correction of regional scale air quality modelling results for the retrospective simulation.► Applied a bias-aware optimal interpolation in the air quality model AURORA in retrospective mode. ► Hollingsworth–Lönnberg method to estimate error covariance matrices. ► The validation was carried out by using “leave ten out approach”. ► The method proves to be very promising especially in retrospective simulation.
Keywords: Data-assimilation; AURORA; Optimal interpolation; Hollingsworth–Lönnberg method;

Effects of light duty gasoline vehicle emission standards in the United States on ozone and particulate matter by Krish Vijayaraghavan; Chris Lindhjem; Allison DenBleyker; Uarporn Nopmongcol; John Grant; Edward Tai; Greg Yarwood (109-120).
More stringent motor vehicle emission standards are being considered in the United States to attain national air quality standards for ozone and PM2.5. We modeled past, present and potential future US emission standards for on-road gasoline-fueled light duty vehicles (including both cars and light trucks) (LDVs) to assess incremental air quality benefits in the eastern US in 2022. The modeling results show that large benefits in ozone and PM2.5 (up to 16 ppb (14%) reductions in daily maximum 8-h ozone, up to 10 ppb (11%) reductions in the monthly mean of daily maximum 8-h ozone, up to 4.5 μg m−3 (9%) reductions in maximum 24-h PM2.5 and up to 2.1 μg m−3 (10%) reductions in the monthly mean PM2.5) accrued from the transition from Tier 1 to Tier 2 standards. However, the implementation of additional nationwide LDV controls similar to draft proposed California LEV III regulations would result in very small additional improvements in air quality by 2022 (up to 0.3 ppb (0.3%) reductions in daily maximum 8-h ozone, up to 0.2 ppb (0.2%) reductions in the monthly mean of daily maximum 8-h ozone, up to 0.1 μg m−3 (0.5%) reductions in maximum 24-h PM2.5 and up to 0.1 μg m−3 (0.5%) reductions in the monthly mean PM2.5). The complete elimination of gasoline-fueled LDV emissions in 2022 is predicted to result in improvements in air quality (up to 7 ppb (8%) reductions in daily maximum 8-h ozone, up to 4 ppb (6%) reductions in the monthly mean of daily maximum 8-h ozone, up to 2.8 μg m−3 (7%) reductions in maximum 24-h PM2.5 and up to 1.8 μg m−3 (8%) reductions in the monthly mean PM2.5) from Tier 2 levels, that are generally smaller than the improvements obtained in switching from Tier 1 to Tier 2.► Simulations of the incremental benefits of successive US LDV emissions standards. ► Tier 1, Tier 2, hypothetical nationwide LEV III standard and zero-out LDV scenario. ► Calculated ozone and PM reductions assuming each standard is prevailing in 2022. ► Tier 2 to LEV III switch offers very small benefit compared to Tier 1 to 2 change. ► Benefit of eliminating LDVs is smaller than the benefit from Tier 1 to 2 transition.
Keywords: LEV; Tier 2; LDV; CAMx; MOVES; Ozone; PM2.5;

Characteristics of aerosols and mass closure study at two WMO GAW regional background stations in eastern China by Peng Yan; Renjian Zhang; Ning Huan; Xiuji Zhou; Yangmei Zhang; Huaigang Zhou; Leiming Zhang (121-131).
In the summer and winter of 2004 and 2005, size-segregated atmospheric aerosols were sampled with modified Andersen KA200 Multi-stage impactor at two regional background stations in the eastern China, the Shangdianzi station (SDZ) in the suburb of Beijing and the Lin'An station (LA) in the Yangtze river delta region, both are WMO Global Atmospheric Watch station, which represent the regional background of air pollutions of the two rapid developing economical zone of China, the Yangtze River Delta region (YRD) and Beijing-Tianjin region. The aerosol mass size distributions, ionic compositions, organic and elemental carbon (OC and EC), and elemental components were analyzed. The mass concentrations for TSP (total suspend particle), PM11 (aerodynamic diameter less than 11 μm), and PM2.1 (aerodynamic diameter less than 2.1 μm) at both sites showed obviously different between the winter and summer, with higher mass concentrations measured in the winter time. All seasonal mean mass concentrations of PM2.1 accounted for over 50% of PM11 at both sites. The aerosol mass closure study indicated that the total mass concentration reconstructed from the aerosol chemical composition agreed well with the measured gravimetric mass at the two stations. The fine aerosol particles at the two stations were composed mainly of sulfate and organic matter. In the summer, more than half of the PM2.1 mass was sulfate, suggesting a dominant contribution of secondary aerosol to the fine particles in these two regions. In the winter, the contribution of nitrate to the fine particles increased significantly due to the lower volatile losses under the cold weather. The proportions of soil type components in the PM2.1 showed similar magnitude in the winter and summer at Lin'An station but significant seasonal differences with higher fractions in the winter at Shangdianzi station. On average EC accounted for about 2%–6% of the fine particle mass (PM2.1) at both sites with proportionally lower EC values in the summer. The percentage of OM (Organic material) in TSP and PM2.1 showed less differences between winter and summer at Lin'An station, about 20%–30% in both TSP and PM2.1, however, the percentage at Shangdianzi station varied greatly from summer to winter, from 11% to 35% in PM2.1 and 12%–28% in TSP. Seasonal and geographical similarities and differences in PM2.1, PM11 and total suspended particles and comparison with previous studies at these regions are also discussed.► Size-segregated aerosols were sampled at two WMO GAW regional background stations in the eastern China. ► The aerosol mass closure was achieved at both sites. ► Sulfate, organic matter and soil type aerosols were the major components in the two regions. ► Sulfate accounted for more than half of the fine particle mass in the summer time. ► The mass concentrations and carbonaceous aerosol at Lin'An station had changed significantly since 1999.
Keywords: Size and chemically resolved aerosols; Aerosol mass closure; Regional background stations;

A comparative study of traffic related air pollution next to a motorway and a motorway flyover by Martine Van Poppel; Luc Int Panis; Eva Govarts; Jeroen Van Houtte; Willy Maenhaut (132-141).
The aim of this study was to investigate the influence of the vertical position of a motorway on the pollutant concentrations in the vicinity of the motorway. Therefore, a near-road monitoring campaign was performed along two adjoining motorway stretches: one motorway at ground level and a motorway flyover. PM2.5 and nitrogen oxides (NO, NO2 and NO x ) were measured at both sides of the motorway on a 30-min resolution. In addition, EC (elemental carbon) was measured on both sides of the road on a daily basis using low volume samplers and thermal–optical transmission (TOT) analysis of filters. PNC (particle number concentration) was measured at one side. The measurement locations on each side of the road were located at 29 m and 102 m from the motorway at ground level and at 60 m and 120 m from the motorway flyover. Pollution roses, showed increased average concentrations in the direction of the road for nitrogen oxides and PM2.5. The impact of road traffic appeared to be higher at ground level compared to the flyover. The difference in concentration between both sides of the road for PM2.5, NO, NO2 and NO x was analysed using linear mixed models. The concentration difference, which can be seen as the contribution of road traffic to the pollutant concentration, was calculated taking into account prevailing wind directions. The results indicate that taking into account confounding parameters (time of day, day of the week, distance to the road and wind speed), the contribution of the motorway traffic to pollutant concentrations is significantly higher when the motorway is at ground level. Furthermore, time of day and day of the week also have a significant effect on the concentration difference. The linear mixed model estimated a reduced road increment at the motorway flyover compared to the ground level motorway of 119 ppb for NO, 29 ppb for NO2 and 3.5 μg m−3 for PM2.5. taking into account confounding parameters.The highest EC and PNC concentrations were measured downwind of the motorway at ground level.► The effect of a flyover on ground level concentrations was measured. ► PM2.5, EC and NO x are compared between a flyover and a motorway at ground level. ► The impact of traffic on ground level concentrations is lower for the flyover.
Keywords: Traffic pollution; Nitrogen oxides; Particulate matter; Elemental carbon; Motorway flyover;

Identifying controlling factors of ground-level ozone levels over southwestern Taiwan using a decision tree by Hone-Jay Chu; Chuan-Yao Lin; Churn-Jung Liau; Yi-Ming Kuo (142-152).
Kaohsiung City and the suburban region of southwestern Taiwan have suffered from severe air pollution since becoming the largest center of heavy industry in Taiwan. The complex process of ozone (O3) formation and its precursor compounds (the volatile organic compounds (VOCs) and nitrogen oxide (NO x ) emissions), accompanied by meteorological conditions, make controlling ozone difficult. Using a decision tree is especially appropriate for analyzing time series data that contain ozone levels and meteorological and explanatory variables for ozone formation. Results show that dominant variables such as temperature, wind speed, VOCs, and NO x can play vital roles in describing ozone variations among observations. That temperature and wind speed are highly correlated with ozone levels indicates that these meteorological conditions largely affect ozone variability. The results also demonstrate that spatial heterogeneity of ozone patterns are in coastal and inland areas caused by sea-land breeze and pollutant sources during high ozone episodes over southwestern Taiwan. This study used a decision tree to obtain quantitative insight into spatial distributions of precursor compound emissions and effects of meteorological conditions on ozone levels that are useful for refining monitoring plans and developing management strategies.► We investigate the temporal variation of O3 using a decision tree approach. ► Temperature, wind speed, VOCs, and NO x mainly affect ozone variations. ► Spatial ozone patterns are caused by sea-land breeze and pollutant sources.
Keywords: Decision tree; Ozone; Volatile organic compounds; Nitrogen oxides; Meteorological conditions;

Aerosol indirect effect during the aberrant Indian Summer Monsoon breaks of 2009 by M.G. Manoj; P.C.S. Devara; Susmitha Joseph; A.K. Sahai (153-163).
The significant role of aerosol–cloud interaction during the large-scale drought producing breaks of 2009 Indian Summer Monsoon is investigated in the present paper. This mega drought had already been attributed to two long breaks, one in June and the other in July-August. While Central India (CI) and northern parts of the country experienced deficient rainfall, the rainfall over the southern Peninsular India (PI) remained close to normal. During the first break in June, which was associated with mid-latitude intrusion of dry air, the Twomey effect (positive aerosol indirect effect – AIE) was a dominant factor inhibiting efficient precipitation over CI region, as compared to that over PI. Moreover, the number of days that experienced significant (at 5% level of significance) positive AIE during the first break was more over CI compared to the same during the second break. The AIE on ice clouds was not as significant as that of the low-clouds. The resulting cloud properties during both break and active phases over CI differ significantly from that over PI for the corresponding periods. The positive AIE mentioned here is attributed to the large-scale deficit of moisture supply to the CI region due to dynamical reasons. However, it is shown that under ample availability of moisture, more aerosols could invigorate deep clouds over specific regions even during the break spells.► Aerosol–cloud interaction catalyses drought producing monsoon breaks in 2009. ► AIE affects Central India much more than Peninsular India in 2009. ► Under adequate moisture availability, aerosols invigorate convection.
Keywords: Aerosol indirect effect; Cloud; Indian summer monsoon; Intraseasonal oscillation; Drought;

Acid rain phenomenon (average WVM pH = 4.9) and a strong association of sulfate scavenging and rain intensity (R 2 = 0.8118) were observed over a seven-month period (October 2010–April 2011) at a densely populated mid-sized Andean city (pop 380,000) that occupies mountain ridge topography (2150 m.a.s.l.). Rain chemistry and PM10 were fairly consistent over four sampling sites representing various scenarios of urban density and topography. All stations exhibited differences in the sulfate content in PM10 between dry and wet periods, further illustrating the sulfate scavenging dynamic. Concentration of major ions evaluated in rain were in order of sulfates (35.2–53.5 μeq L−1) > calcium (14.6–17.3 μeq L−1) > chlorides (3.5–5.1 μeq L−1) > nitrates (2.1–3.1 μeq L−1). Major chemical constituents of PM10 were related with ionic composition of rainwater through scavenging ratios (SRs). High sulfate SRs associated with increased rain intensity reflected higher sulfate ion solubility. Significant contribution of sulfates to total ionic content, higher than 50% at all monitoring stations, suggests important contributions of SO2 emissions, which could come from three principal sources: vehicular emissions due to Colombian fuels with elevated sulfur content, industrial emissions at southeast of the city, and sulfur gas emissions from a nearby active volcano, Nevado del Ruiz, located 27 km southeast of the city.► Urban ridge development of Manizales offers conditions for air pollution studies. ► Acid rain was evenly distributed in the city with a mean VWM pH value of 4.9 units. ► Scavenging rates of sulfates in PM10 increased with increasing rain intensity. ► Sulfates were the predominant ion in rain reflecting a predominance of SO2 emissions. ► Vehicular and volcanic emissions could contribute to high levels of sulfates in rain.
Keywords: Acid precipitation; Scavenging; Rain intensity; Sulfates; Particulate matter; Mid-sized Andean cities; Colombia;

Spatial assessment of air quality patterns in Malaysia using multivariate analysis by Doreena Dominick; Hafizan Juahir; Mohd Talib Latif; Sharifuddin M. Zain; Ahmad Zaharin Aris (172-181).
This study aims to investigate possible sources of air pollutants and the spatial patterns within the eight selected Malaysian air monitoring stations based on a two-year database (2008–2009). The multivariate analysis was applied on the dataset. It incorporated Hierarchical Agglomerative Cluster Analysis (HACA) to access the spatial patterns, Principal Component Analysis (PCA) to determine the major sources of the air pollution and Multiple Linear Regression (MLR) to assess the percentage contribution of each air pollutant. The HACA results grouped the eight monitoring stations into three different clusters, based on the characteristics of the air pollutants and meteorological parameters. The PCA analysis showed that the major sources of air pollution were emissions from motor vehicles, aircraft, industries and areas of high population density. The MLR analysis demonstrated that the main pollutant contributing to variability in the Air Pollutant Index (API) at all stations was particulate matter with a diameter of less than 10 μm (PM10). Further MLR analysis showed that the main air pollutant influencing the high concentration of PM10 was carbon monoxide (CO). This was due to combustion processes, particularly originating from motor vehicles. Meteorological factors such as ambient temperature, wind speed and humidity were also noted to influence the concentration of PM10.► HACA, PCA and MLR are used to assess the sources of atmospheric pollutants at eight stations. ► The stations has been categorized into three different clusters base on locations. ► Motor vehicles are the main sources of air pollutants. ► PM10 is the major air pollutant and has significant correlation with CO.
Keywords: Air pollutants; Multivariate analysis; HACA; PCA; MLR;

Spatial and seasonal variability of water-soluble ions in PM2.5 aerosols in 14 major cities in China by Miao-Ching Cheng; Chen-Feng You; Junji Cao; Zhangdong Jin (182-192).
We analyzed PM2.5 aerosols from 14 major cities in China for concentrations of water-soluble (WS) major and trace elements (Na, Mg, Ca, K, Fe, Mn, Zn, Rb, Sr, Ba, Pb, S and Cl). The main focus was to examine patterns in spatial distribution and seasonal variability. Using principal component analysis, we identified three general sources for WS-elements in aerosols as anthropogenic, seasalts and fine dust particles originating from soils. The spatial patterns identified show that anthropogenic activity is the most important factor influencing the concentration of heavy metals in aerosols. Concentrations of WS-S, Zn and Pb were correlated with the locations of major industrial zones, and regulated by topography and seasonal weather patterns. We found higher WS-metals concentrations during the winter season, probably related to coal combustion in northern China. Moderate correlations of WS-S, Zn, Pb and Cl suggest that coal combustion releases. The seasonal pattern in WS-Fe concentrations shows the importance of acid precipitation events where coal combustion contributes to additional Fe (II) deposition. The findings of this study support the argument that WS-S in fine particles enhanced the production of hydrogen ions act to reduce the pH values of precipitation. Our interpretation of these spatial and seasonal patterns in WS-major and trace elements in aerosols highlights the need for continued research on trends in acidic deposition in major industrial cities in China.► 110 PM2.5 samples in 14 major cities over China and analyze for WS ions in summer and in winter 2003. ► Anthropogenic activities are the main sources for WS ions in PM2.5 particles. ► High concentrations of WS-Zn, Pb and S in winter are mainly due to coal burning. ► Location of industrial zones influence heavy metals of aerosols significantly.
Keywords: Acid precipitation; PM2.5; Water-soluble ions; Anthropogenic sources; Industrial zones;

Health benefit modelling and optimization of vehicular pollution control strategies by Nayan V. Sonawane; Rashmi S. Patil; Virendra Sethi (193-201).
This study asserts that the evaluation of pollution reduction strategies should be approached on the basis of health benefits. The framework presented could be used for decision making on the basis of cost effectiveness when the strategies are applied concurrently. Several vehicular pollution control strategies have been proposed in literature for effective management of urban air pollution. The effectiveness of these strategies has been mostly studied as a one at a time approach on the basis of change in pollution concentration. The adequacy and practicality of such an approach is studied in the present work. Also, the assessment of respective benefits of these strategies has been carried out when they are implemented simultaneously. An integrated model has been developed which can be used as a tool for optimal prioritization of various pollution management strategies. The model estimates health benefits associated with specific control strategies. ISC-AERMOD View has been used to provide the cause–effect relation between control options and change in ambient air quality. BenMAP, developed by U.S. EPA, has been applied for estimation of health and economic benefits associated with various management strategies. Valuation of health benefits has been done for impact indicators of premature mortality, hospital admissions and respiratory syndrome. An optimization model has been developed to maximize overall social benefits with determination of optimized percentage implementations for multiple strategies. The model has been applied for sub-urban region of Mumbai city for vehicular sector. Several control scenarios have been considered like revised emission standards, electric, CNG, LPG and hybrid vehicles. Reduction in concentration and resultant health benefits for the pollutants CO, NO x and particulate matter are estimated for different control scenarios. Finally, an optimization model has been applied to determine optimized percentage implementation of specific control strategies with maximization of social benefits, when these strategies are applied simultaneously.► An integrated air quality decision support system framework has been developed. ► Optimization has been done to maximize the social benefits. ► Model has been applied for Mulund region in Mumbai city. ► Revised emission standards and LPG vehicle strategy found to be most effective.
Keywords: Pollution control strategies; AERMOD; BenMAP; Optimization;

Tracing geogenic and anthropogenic sources in urban dusts: Insights from lead isotopes by R. Del Rio-Salas; J. Ruiz; M. De la O-Villanueva; M. Valencia-Moreno; V. Moreno-Rodríguez; A. Gómez-Alvarez; T. Grijalva; H. Mendivil; F. Paz-Moreno; D. Meza-Figueroa (202-210).
Tracing the source of metals in the environment is critical to understanding their pollution level and fate. Geologic materials are an important source of airborne particulate matter, but the contribution of contaminated soil to concentrations of Pb in airborne dust is not yet widely documented. To examine the potential significance of this mechanism, surface soil samples were collected, as well as wind-transported dust trapped at 1 and 2 m height at seven different locations including residential, industrial, high-traffic and rural sites. Samples of dust deposited on roofs from 24 schools were also obtained and analyzed for Pb isotope ratios.Spatial distribution of Pb of airborne and sedimented dust suggests a process dominated by re-suspension/sedimentation, which was controlled by erosion, traffic and topography of the urban area. Anthropogenic lead input in the city grades outward the urban zone toward geogenic values. Our results shows that Pb-isotopic signatures of leaded gasoline are imprinted in dust sedimented on roofs. Considering that leaded-gasoline has not been in use in Mexico since two decades ago, this signature shows not only a Pb-legacy in soil, but also a re-suspension process affecting air column below 3 m in height. The combination of the 207Pb/206Pb data of the surrounding rocks and urban dust, reveal three well-defined zones with remarkable anthropogenic influence, which correspond to the oldest urban sectors. This work highlights the importance of spatial characterization of metals in particles suspended below a height of 3 m of the airborne column, a fact that should be considered to identify exposure paths to humans and the potential risks. Lead isotope signatures allowed the identification of geogenic and anthropogenic emission sources for dust, a matter that deserves consideration in the efforts to control airborne metal emissions.► Lead isotopes identified geogenic an anthropogenic emission sources for dust. ► Leaded gasoline isotopic signatures are imprinted in sedimented dust from roofs. ► Lead distribution is controlled by erosion, traffic and topography. ► Three impacted areas are identified in oldest urbanized sectors.
Keywords: BSNE; Airborne dust; Lead isotopes; México; Soil resuspension;

The city of São Paulo is located in a subtropical region whose climate exhibits few defined seasons as well as frequent oscillations in temperature and rainfall throughout the year. In addition to interfering with physiological processes, these peculiar climatic dynamics influence the formation of O3 and its influx into leaves, causing species used as bioindicators in temperate climates to be ineffective here. This study evaluated gas exchange variations in CO2 and H2O and leaf injuries induced by O3 in Nicotiana tabacum Bel-W3 in relation to oscillations in environmental conditions. Plants were exposed to an O3-polluted environment for fifteen periods of fourteen days each throughout 2008. Gas exchange and O3 were higher during the summer and winter but were highly variable in all seasons. Severe injuries occurred during the winter and spring, with significant variation in this parameter being observed throughout the year. An analysis of biotic and abiotic variables revealed complex relationships among them, with great importance of meteorological factors in plant responses. We conclude that under unstable climatic conditions, the relationship between O3 flux and injury is weak, and the qualitative character of biomonitoring is further confirmed.► Gas exchange, ozone flux and foliar injury in tobacco Bel-W3 were investigated. ► Biological processes and environmental factors varied greatly throughout the year. ► Meteorological conditions have a great importance in plant responses. ► Under unstable weather conditions, ozone flux and leaf injury had a weak correlation.
Keywords: Nicotiana tabacum Bel-W3; Ozone; Sub-tropical environment; Gas exchange; Leaf injury;

Improving ozone forecasts over Europe by synergistic use of the LOTOS-EUROS chemical transport model and in-situ measurements by R.L. Curier; R. Timmermans; S. Calabretta-Jongen; H. Eskes; A. Segers; D. Swart; M. Schaap (217-226).
In this paper we investigate the added value of assimilation of ozone in-situ measurements for both re-analysis and forecasting purposes. Various simulations were performed using the LOTOS-EUROS chemical transport model and an Ensemble Kalman Filter (EnKF) to assimilate measured ozone surface concentrations over Europe, for spring and summer of 2007. The results for the re-analysis of ozone show a significant improvement in the LOTOS-EUROS performance score when compared to measurements. The average correlation coefficient for the daily maximum ozone concentration improves from 0.72 to 0.83. Similarly, the average Root Mean Square Error (RMSE) for the daily maximum ozone concentration is reduced from 20.8 to 16.9 μg m−3.The free running model performs well in forecast mode and the agreement between in-situ and modeled ozone concentration is good. The average temporal correlation coefficient ranges from 0.62 for the first day forecast to 0.61 for the third day forecast. Based on these results, assimilated fields were used to initialize the forecast. As for the re-analysis a better comparison between model and observation was observed. The mean correlation coefficient increased by 0.07 and the averaged RMSE decreased by 0.65 μg m−3. However, the addition of an inheritance scheme to import additional information from the data assimilation to the forecast did not significantly improve the concentration fields.► Traditional modeling system misses high ozone peak. ► We assess the benefit of the synergistic use of model and measurements. ► The added-value of the data assimilation (DA) of ozone in-situ data is investigated. ► Study of the scaling factors of DA shows that no information can be carried into the forecast. ► In practice, the ozone maxima were better reproduced for both reanalysis and forecasting.
Keywords: Air quality forecasting; Ozone; Chemical transport model; Data assimilation; Ensemble Kalman Filter;

The dry and wet deposition of radionuclides released into the atmosphere can be intercepted by vegetation in terrestrial ecosystems. The aim of this study was to quantify the interception of wet deposited 134Cs and 85Sr by spring oilseed rape (Brassíca napus L.) and spring wheat (Tríticum aestívum L.). The dependency of the intercepted fraction (f) on total above ground plant biomass, growing stage and the Leaf Area Index (LAI) was quantified. A trial was established in Uppsala (east central Sweden), with land management in accordance to common agricultural practices. The field trial was a randomised block design of 1 × 1 m2 parcels with three replicates. During the growing season of 2010, a rainfall simulator deposited 134Cs and 85Sr during six different growth stages. Two to 3 h after deposition, the biomass of the centre 25 × 25 cm2 area of each parcel was sampled and above ground biomass and LAI were measured. The radioactivity concentration and radioactivity of samples were measured by High Purity Germanium (HPGe)-detectors.For 134Cs, there was a correlation between f and LAI (r 2 = 0.55, p < 0.05) for spring wheat, but not for spring oilseed rape (r 2 = 0.28, p > 0.05). For 85Sr, there was a correlation between f and LAI for both crops (r 2 = 0.41, p < 0.05 for spring oilseed rape and r 2 = 0.48 p, <0.05 for spring wheat). There was no correlation between f and above ground plant biomass in spring oilseed rape for either 134Cs (r 2 = 0.01, p > 0.05) or for 85Sr (r 2 = 0.11, p > 0.05). For spring wheat, there was a correlation for both 134Cs (r 2 = 0.36, p < 0.05) and 85Sr (r 2 = 0.32, p < 0.05). For spring oilseed rape, f was highest at growth stage ‘stem elongation’ for 134Cs (0.32 ± 0.22) and 85Sr (0.41 ± 0.29). For spring wheat, f was highest at growth stage ‘ripening’ for both radionuclides (134Cs was 0.36 ± 0.14 and 85Sr was 0.48 ± 0.18). Thus, LAI can be used to quantify interception of both radionuclides for both crops, whereas, above ground plant biomass is a weak measure of interception of wet deposited radiocaesium and radiostrontium.► Deposition of radionuclides by artificial rain. ► Interception was more related to Leaf Area Index than to growth stage. ► Interception was highest at ripening for both crops. ► Interception was related to above ground biomass for spring wheat.
Keywords: Radionuclide; Deposition; Food crops; Biomass; Leaf Area Index; Growth stage;

Emission of oxygenated polycyclic aromatic hydrocarbons from biomass pellet burning in a modern burner for cooking in China by Guofeng Shen; Siye Wei; Yanyan Zhang; Rong Wang; Bin Wang; Wei Li; Huizhong Shen; Ye Huang; Yuanchen Chen; Han Chen; Wen Wei; Shu Tao (234-237).
Biomass pellets are undergoing fast deployment widely in the world, including China. To this stage, there were limited studies on the emissions of various organic pollutants from the burning of those pellets. In addition to parent polycyclic aromatic hydrocarbons, oxygenated PAHs (oPAHs) have been received increased concerns. In this study, emission factors of oPAHs (EFoPAHs) were measured for two types of pellets made from corn straw and pine wood, respectively. Two combustion modes with (mode II) and without (mode I) secondary side air supply in a modern pellet burner were investigated. For the purpose of comparison, EFoPAHs for raw fuels combusted in a traditional cooking stove were also measured. EFoPAHs were 348 ± 305 and 396 ± 387 μg kg−1 in the combustion mode II for pine wood and corn straw pellets, respectively. In mode I, measured EFoPAHs were 77.7 ± 49.4 and 189 ± 118 μg kg−1, respectively. EFs in mode II were higher (2–5 times) than those in mode I mainly due to the decreased combustion temperature under more excess air. Compared to EFoPAHs for raw corn straw and pine wood burned in a traditional cooking stove, total EFoPAHs for the pellets in mode I were significantly lower (p < 0.05), likely due to increased combustion efficiencies and change in fuel properties. However, the difference between raw biomass fuels and the pellets burned in mode II was not statistically significant. Taking both the increased thermal efficiencies and decreased EFs into consideration, substantial reduction in oPAH emission can be expected if the biomass pellets can be extensively used by rural residents.► Oxygenated polycyclic aromatic hydrocarbons emitted from biomass pellets were measured for the first time. ► Two types of pellets and two combustion modes in a modern pellet burner were tested. ► Emission factors of oPAHs for pellets were compared with those for raw biomass fuels burned in a traditional cooking stove. ► Potential emission reduction with efficient deployment of pellets was discussed.
Keywords: Oxygenated PAHs; Biomass pellets; Emission factor; Emission reduction;

Spatiotemporal variations of tropospheric SO2 over China by SCIAMACHY observations during 2004–2009 by Xingying Zhang; Jos van Geffen; Hong Liao; Peng Zhang; Sijia Lou (238-246).
This paper presents results of measurements of tropospheric sulphur dioxide (SO2) from satellite over China during 2004–2009. SCIAMACHY/ENVISAT SO2 data products have been validated by ground based remote sensing instrument MAXDOAS in China, and with predictions of the atmospheric model GEOS–Chem. The spatial and temporal distribution of tropospheric SO2 over China is discussed in this study. The result shows that the SO2 load over East China is decreasing since strong control for pollution emission in 2007 for preparation of 2008 Olympic Games in China, while the SO2 load in West China is increasing all the way during 2004–2009, which might reflect that the anthropogenic activity was added to promote the economy development in west of China.Typical seasonal variation with high pollution levels in winter and low in summer is found in the northwest of China, while the inverse seasonal variation is found for the south of China. The characteristics of tropospheric SO2 over the major cities in China were explored and found that tropospheric SO2 was partly under control from 2007 because of the policy from China government for reduction in SO2 emissions in 2006. And the SO2 value shows remarkably decrease in most of the major cities after 2007 because strong control for the pollution emission for 2008 Olympic games. Guangzhou city shows high SO2 pollution levels in summer time, since most of the coal power plants and thermal power industry are located to the south of Guangzhou city and southerly winds dominate during summer time.► We validate SCIAMACHY SO2 data by MAXDOAS in China. ► Different seasonal variation is found for different energy demand. ► Tropospheric SO2 was partly under control from 2007 for the reduction policy. ► SO2 decrease in several cities for pollution control for the 2008 Olympic Games.
Keywords: Tropospheric SO2; SCIAMACHY; Spatiotemporal variations; China;

Field comparison of cyclonic separator and mass inertial impactor for PM10 monitoring by K.V. George; D.D. Patil; Prashant Kumar; B.J. Alappat (247-252).
Monitoring of ambient PM10 concentrations was carried out using two co-located samplers at 10 different locations over the three seasons (summer, winter and post-monsoon) in Delhi, India. The samplers used for the study were the high volume sampler fitted with a cyclone (commonly known in India as respirable particulate matter sampler or RPM sampler), and a 4-channel speciation sampler (4-SS). The RPM sampler separates the PM10 fraction using centrifugal inertia while the 4-SS separates them using the principle of mass inertial impaction. Comparison of the measured data are made using different graphical techniques and statistical analysis, comprising classical two tailed paired t-test and the criteria recommended by the European Commission working group on particulate matter. The PM10 data monitored by both the samplers showed good overall correlations for the entire data set, with a regression co-efficient value of 0.61. Results indicated that inertial impaction based 4-SS consistently measures higher PM10 concentration compared with the cyclone fitted RPM sampler. Such results were valid for 81% of the total data set and this difference in measured concentrations was ∼66% in the regulatory limit value ranges. Both the samplers have their merits and limitations and hence a conscious choice and appropriate data correction is needed when deploying them for scientific and regulatory monitoring purposes.► PM10 monitored using simultaneous operation of cyclone and impactor based equipments. ► Monitoring conducted at ten different stations in Delhi, India for three seasons. ► PM10 data from two equipments compared using independent and paired t-test. ► Cyclone based equipment measure consistently less PM10 compared to impactor based equipment.
Keywords: Ambient air regulations; Cyclone separator; Mass intertial impactor; Particulate matter; PM10 monitoring;

Polycyclic aromatic hydrocarbons (PAHs) of exhaust emissions were studied in four direct-injection turbocharged four-cylinder diesel engines, with power ratings of 90–136 kW. The engines were operated on biodiesel (B-100), a blend of 30% biodiesel in diesel fuel (B-30), and heated rapeseed oil (RO) in two independent laboratories. Diesel particle filters (DPF) and selective catalytic reduction (SCR) systems were used with B-30 and B-100. Concentrations of individual PAHs sampled in different substrates (quartz, borosilicate fiber and fluorocarbon membrane filters, polyurethane foam) were analyzed using different methods. Benzo[a]pyrene toxic equivalents (BaP TEQ) were calculated using different sets of toxic equivalency factors (TEF). Operation on B-100 without aftertreatment devices, compared to diesel fuel, yielded a mean reduction in PAHs of 73%, consistent across engines and among TEF used. A lower PAH reduction was obtained using B-30. The BaP TEQ reductions on DPF were 91–99% using B-100, for one non-catalyzed DPF, and over 99% in all other cases. The BaP TEQ for heated RO were higher than those for B-100 and one half lower to over twice as high as that of diesel fuel. B-100 and RO samples featured, compared to diesel fuel, a relatively high share of higher molecular weight PAH and a relatively low share of lighter PAHs. Using different sets of TEF or different detection methods did not consistently affect the observed effect of fuels on BaP TEQ. The compilation of multiple tests was helpful for discerning emerging patterns. The collection of milligrams of particulate matter per sample was generally needed for quantification of all individual PAHs.Display Omitted► Emissions of PAHs from four diesel engines examined at different labs. ► Consistent results with different analytical methods and toxic equivalency factors. ► Biodiesel and rapeseed oil reduce lighter PAH, increase heavier carcinogenic PAHs. ► Biodiesel PAH reduction lower on particle filters without catalyst.
Keywords: Diesel engine; Diesel emissions; Particulate matter; Polyaromatic hydrocarbons; PAH; Biofuels; Biodiesel; Rapeseed oil; Exhaust aftertreatment; Diesel particle filter;

Australia's Black Saturday fires – Comparison of techniques for estimating emissions from vegetation fires by Clare Paton-Walsh; Louisa K. Emmons; Christine Wiedinmyer (262-270).
We present a comparison of techniques for estimating atmospheric emissions from fires using Australia's 2009 “Black Saturday” wildfires as a case study. Most of the fires started on Saturday the 7th of February 2009 (a date now known as “Black Saturday”) and then spread rapidly, fanned by gale force winds, creating several firestorms and killing 173 people. The fires continued into early March, when rain and cooler conditions allowed the fires to be extinguished. In this study, we compare two new techniques (and one more established method) to estimate the total emissions of a number of atmospheric trace gases from these fires. One of the new techniques is a “bottom-up” technique that combines existing inventories of fuel loads, combustion efficiencies and emission factors with an estimate of burned area derived from MODIS rapid response daily fire counts. The other new method is a “top-down” approach using MODIS aerosol optical depth as a proxy for total amounts of trace gases emitted by the fires. There are significant differences between the estimates of emissions from these fires using the different methods, highlighting the uncertainties associated with fire emission estimates. These differences are discussed along with their likely causes and used as a vehicle to explore the merits of the different methods, and further constrain fire emissions in the future.► Different methods for estimating emissions from fires are compared. ► Two of the methods agree within expected uncertainties. ► FINNv1 produces a significantly lower estimate than the other methods. ► Missed fires counts in FINNv1 (probably due to cloud cover) cause the low estimate. ► FINNv1 provides a much needed high temporal emissions inventory in near real time.
Keywords: FINNv1; FEEV-AOD; GFEDV3.1; Biomass burning;

We present the results of a PM10 forecasting model that has been applied for air quality management in Santiago, Chile during recent years. The daily operation of this model has served to inform in advance to the population about the air quality they will find in different areas of the city and to help environmental authorities in the decision to take actions on days when concentrations are in ranges considered significantly harmful and to impose restrictions to the activity of the city in advance, when extreme episodes are foreseen. At present, national PM10 standard for 24 h average is 150 μg m 3. According to the range where the concentrations fall, five levels or classes of air quality are defined: good (A), regular (B), bad (C), Critical (D) and Emergency (E). Forecasting is based on the combination of artificial neural networks and a nearest neighbor method. Inputs to the models are concentrations measured at several monitoring stations distributed throughout the city and meteorological information in the region. Outputs are the expected maxima concentrations for the following day at the site of the same monitoring stations. Results for last three years (2009, 2010, 2011) indicate that the model may be considered as an important tool for air pollution control.► The performance of statistical PM10 forecasting models is shown. ► Reasonable accuracy is achieved with a neural network model (ANN). ► Improvement in accuracy of high concentrations forecasting is obtained with a nearest neighbor model (NNM). ► Increase of false alarms episodes is observed with NNM. ► Combination of the ANN and NNM provides a near optimal PM10 operational forecasting system.
Keywords: Air quality forecasting; Particulate matter; PM10; Neural networks; Meteorology forecast;

Effect of plants on methane emissions from a temperate marsh in different seasons by Xiaoxin Sun; Changchun Song; Yuedong Guo; Xianwei Wang; Guisheng Yang; Yingchen Li; Rong Mao; Yongzheng Lu (277-282).
Plants play an important role in CH4 emissions from wetlands. Vascular plants transport CH4 from the anaerobic zone to the atmosphere through their aerenchyma, thereby bypassing the aerobic zone and strongly increasing CH4 emission rates. However, most studies of the effect of plants on wetland CH4 emissions are based on observations made during the growing seasons. The effects in non-growing seasons are still unclear. In this study, we conducted a clipping experiment to investigate the effects of plants on CH4 emissions from a temperate marsh in the growing and non-growing seasons. The results show that the influence of plants on CH4 emissions from the wetland varied among different seasons. Plant-mediated CH4 accounted for 38% of the total fluxes in the plant-growing season. After the growing season, whether the plants transported CH4 from the soil to the atmosphere in situ was determined by the involved environmental conditions. In autumn, the plants did not transport CH4. This is because the CH4 diffused easily in the soil and water, rather than via the plants' organs. In the surface soil freezing period, CH4 diffusion was blocked and accumulated under the frozen surface. The highly concentrated CH4 in the pore water was compelled to enter the organs of the plants and diffused by them. The ‘passive diffusion’ via plants transported 84% of the total CH4 emissions during this period. Nonetheless, the plants did not transport CH4 again in the deep soil freezing season. By synthesizing our data together with previous studies, we suggested that this is because the frozen soil layer was deep enough in this period to exceed the depth horizon of the plants' roots and the CH4 in free water could not enter the plants' organs.► Plants affects on CH4 emissions from a marsh varied across different seasons. ► Plants transported CH4 during the growing season and surface soil freezing period. ► Plants did not transport CH4 in autumn or during the deep soil freezing period. ► Depth of frozen soil controls plant function of CH4 transport during cold seasons.
Keywords: CH4 emission; Plant transportation; Growing season; Cold season; Temperate marsh;

Road traffic is both a major source of ozone precursors (e.g. nitrogen oxides and hydrocarbons) and a potential local sink for ozone in the form of fresh nitric oxide (NO) that depletes ozone. This study investigates the effect of road traffic characteristics on ground level ozone concentration (ppb) applying a quantile regression model (QRM). QRM has certain advantages over other regression methods, including its applicability to non-normal ozone distribution and its ability to handle non-linearities in the relationship of ozone with its covariates. The paper is developed in two parts. In the first part ozone concentrations at urban and rural sites have been compared using data from 80 ozone monitoring sites throughout the UK. The model results in an average urban decrement of about 7 ppb (26%) but indicates variations at various quantiles of the ozone distribution, for instance the difference is 5.25 ppb (25%) and 10.78 ppb (30%) at quantile 0.1 and 0.99, respectively. In the second part the effect of road-traffic characteristics (traffic flow, speed and fleet composition) on urban decrement has been modelled, as a case study in Leeds, UK. The relationship between urban decrement and road traffic characteristics changes at different regimes of ozone distribution indicating a highly non-linear association. Flow of cars, buses and articulated heavy vehicles seem to have the strongest effect on urban decrement; however buses are the only category showing significant effect at all quantiles. The effect of average speed and motorcycles flow was not significant. The results of QRM show that up to 86% ozone variations between rural and urban sites can be explained with the help of traffic characteristics. The effect of various traffic scenarios on urban decrements has been investigated.► This paper describes the effect of road traffic on ground-level ozone. ► On average ozone levels are lower in urban areas by about 26%. ► Urban decrement varies at different quantiles of the ozone concentration. ► Buses flow shows the strongest effect on ozone concentration. ► The effect of several traffic scenarios on urban decrement has been investigated.
Keywords: Tropospheric ozone; Quantile regression model; Road traffic flow; Vehicles speed; Urban decrement; Leeds UK;

Odor and volatile organic compound (VOC) emissions are a concern at animal feeding operations (AFOs). The issue has become more prevalent as human residences move into areas once occupied only by agriculture. Odors near AFOs are generally caused by odorous VOCs emitted from manure, the mixture of feces and urine. Wet distillers grains with solubles (WDGS) are a by-product of the ethanol industry, and WDGS have become a staple in many beef cattle finishing diets. The objective of this research was to determine specific VOC emissions from frozen feces and urine of cattle fed steam-flaked corn (SFC)-based diets containing 0, 15, 30, or 45% WDGS. No differences in flux were detected across dietary treatments for phenol, indole, skatole, or 4-methylphenol (P > 0.23). Dimethyl disulfide and dimethyl trisulfide flux in feces were not different across treatments (P > 0.35) and the flux of volatile fatty acids (VFA) such as acetic, propionic, isobutyric, butyric, isovaleric, and valeric were not different across treatments (P > 0.25). There was a tendency for dimethyl disulfide flux from urine to be greater for cattle consuming an SFC-based diet with 15% WDGS than the other diets (P = 0.10). Furthermore, flux of acetic, propionic, isobutyric, butyric, and isovaleric acid from the urine were not different (P > 0.61) across dietary treatment. There were no significant differences in odor activity value (OAV) across treatments for feces, and only a tendency for dimethyl disulfide in the feces (P = 0.09). Thus, there was no obvious indication that feeding WDGS in conjunction with SFC affects flux of odor or odorous VOC from beef manure. The summed OAV was three times higher in the urine than feces, and a single odorous compound (4-methylphenol) accounted for 97.6%and 67.3% of the OAV in urine and feces, respectively. Therefore, engineering or dietary strategies to reduce odor from beef cattle manure should focus on controlling or reducing 4-methylphenol concentrations in the urine and feces.► We collected manure from cattle fed 0–45% wet distillers grains with solubles. ► We measured VOC flux and odor activity value (OAV) from feces and urine. ► WDGS had little effect on OAV or VOC flux rates. ► VOC emission rates and OAV were higher from urine than feces. ► 4-methylphenol accounted for the majority of OAV in urine and feces.
Keywords: Odor; Cattle; Manure; Volatile organic compound; Air quality;

Polycyclic aromatic hydrocarbons in air particulates and its effect on the Tumen river area, Northeast China by Guangzhu Jin; Linlin Cong; Yingyu Fang; Junlin Li; Miao He; Donghao Li (298-304).
Polycyclic aromatic hydrocarbons (PAHs) were measured in air particulates, ice particulates, snow particulates and river water samples collected during December 2008 to February 2010 in Tumen river area, Northeast China. The total concentration of 15 PAHs in the air particulates, water, water particulates, and particulates in the ice and snow ranged: 3.2–776 ng m−3, 12.9–383 ng L−1, 19.4–2.10 × 103 ng L−1, 62.8–136 ng L−1 and 9.68 × 103–6.96 × 104 ng g−1, respectively. Elevated PAHs were found in winter season, followed by autumn, and lowest in summer. Seasonal variations of air particulate PAHs well reflected by the local residential heating period, which maybe the main contributive factor for high PAH levels in winter. PAH congeners and principal component analysis of 15 PAH congeners in particulate samples of air, water, snow and ice show similar patterns suggesting common sources of PAHs. Fluorene, phenanthrene and pyrene were found to be dominant compounds. PAHs observed in the air particulates appeared to be strongly related to those in other particulate samples, and atmospheric deposition can be an important factor in the environmental quality of the Tumen river area. Additionally, other meteorological factors such as temperature and CO2 levels affecting PAHs distribution in the atmosphere were discussed.► Fifteen PAHs in air particulates, river water, ice and snow were investigated. ► Air particulate and other particulates samples were affected by the common sources. ► Atmospheric deposition is potentially an important factor in the Tumen river.
Keywords: Tumen river; PAHs; Air particulates; Ice; Snow;

Intra-urban spatial variability and uncertainty assessment of PM2.5 sources based on carbonaceous species by Mingjie Xie; Teresa L. Coons; Joshua G. Hemann; Steven J. Dutton; Jana B. Milford; Jennifer L. Peel; Shelly L. Miller; Sun-Young Kim; Sverre Vedal; Lianne Sheppard; Michael P. Hannigan (305-315).
To identify the sources of PM2.5 – bound carbonaceous species and examine the spatial variability of source contributions in the Denver metropolitan area, positive matrix factorization (PMF) was applied to one year of every sixth day ambient PM2.5 compositional data, including elemental carbon (EC), organic carbon (OC), and 32 organic molecular markers, from four sites (two residential and two near-traffic). Statistics (median, inner quantiles and 5th – 95th percentiles range) of factor contributions, expressed as reconstructed carbonaceous mass (EC + OC), were estimated from PMF solutions of replicate datasets generated by using a stationary block bootstrap technique. A seven-factor solution was resolved for a set of data pooled across the four sites, as it gave the most interpretable results and had the highest rate of neural network factor matching (76.9%). Identified factors were primarily associated with high plant wax, summertime emission, diesel vehicle emission, fossil fuel combustion, motor vehicle emission, lubricating oil combustion and wood burning. Pearson correlation coefficients (r) and coefficients of divergence (COD) were used to assess spatial variability of factor contributions. The summertime emission factor exhibited the highest spatial correlation (r = 0.74 – 0.88) and lowest CODs (0.32 – 0.38) among all resolved factors; while the three traffic dominated factors (diesel vehicle emission, motor vehicle emission and lubricating oil combustion) showed lower correlations (r = 0.47 – 0.55) and higher CODs (0.41 – 0.53) on average. Average total EC and OC mass were apportioned to each factor and showed a similar distribution across the four sites. Modeling uncertainties were defined as the 5th – 95th percentile range of the factor contributions derived from valid bootstrap PMF solutions, and were highly correlated with the median factor contribution in each factor (r = 0.77 – 0.98). Source apportionment was also performed on site specific datasets; the results exhibited similar factor profiles and temporal variation in factor contribution as those obtained for the pooled dataset, indicating that the four sites are primarily influenced by similar types of sources. On the other hand, differences were observed in absolute factor contributions between PMF solutions for the pooled versus site-specific datasets, likely due to the large uncertainties in EC and OC factor profiles derived from the site specific datasets with limited numbers of observations.► Sources of carbonaceous PM2.5 were resolved using Positive Matrix Factorization, PMF. ► A 7 factor solution was obtained for a set of data pooled across the 4 urban sites. ► Spatial variability of factor contributions was assessed. ► A bootstrap technique was coupled with PMF model for modeling uncertainty assessment. ► PMF solutions for site-specific datasets were compared with the pooled data solution.
Keywords: Source apportionment; Positive matrix factorization; Bootstrap; Uncertainty; Spatial variability;

Legislative norms developed at the end of the 1970s, structural changes in the economy, and the implementation of filters in both vehicles and industries improved the air quality of North Rhine-Westphalia, the largest western state in Germany in terms of population and economic output. Because these changes occurred unevenly across the state, the main aim of the given study is to analyse the historical development of air pollutants in the various environments (e.g., industrial, traffic or rural background) within the state.NO, NO2 and O3 concentrations observed at six stations (one industrial, two traffic, one urban and two rural background) from 1981 to 2007 have been obtained from the Environmental State Agency for Nature, Environment and Consumer Protection (LANUV NRW). These data have been evaluated to investigate time trends of these pollutants and the impact of weekly cycles on ozone formation in NO x -limited areas (rural background) and VOC-limited areas (urban areas with traffic network). The relationships between ozone production mechanisms and ozone precursors (NO, NO2 and their ratio) have also been taken into account.In contrast to the sharp decrease in NO concentrations (65%), only a moderate, insignificant decrease in NO2 (10%) was observed because catalytic filters in vehicles support emissions of NO2 as a primary pollutant. Changes in NO/NO2 ratio and higher temperature favoured an increase in ozone concentrations (20%), which appears to be the indicator of summer smog. The results showed that, although ozone forming potential is higher at background stations due to higher biogenic VOC and lower NO emissions, time trends were steeper at the industrial stations because of radical changes in NO x concentrations.Examination of the weekly and diurnal cycles of NO and NO2 showed that not only the absolute average values of the pollution levels decreased (with a turning point in 1998) but also the shape of the diurnal cycle (differences between primary and secondary peaks) changed in response to developed legislative norms ().► Long-term pollution data are analysed at different kind of stations in Germany. ► The aim is to evaluate the efficiency of legislation norms for the last 2 decades. ► Analysis of NO x and Ozone data has been carried out in urban and rural areas. ► Weekly cycles of the pollutants are evaluated in NO x - and VOC-limited regimes.
Keywords: Air pollution trends; Ozone formation; Diurnal and weekly cycles; NO x -limited regimes; VOC-limited regimes;

Miscanthus × giganteus and short rotation coppice (SRC) willow (Salix spp.) are increasingly important bioenergy crops. Above-canopy fluxes and mixing ratios of volatile organic compounds (VOCs) were measured in summer for the two crops at a site near Lincoln, UK, by proton transfer reaction mass spectrometry (PTR-MS) and virtual disjunct eddy covariance. The isoprene emission rate above willow peaked around midday at ∼1 mg m−2 h−1, equivalent to 20 μg gdw −1 h−1 normalised to 30 °C and 1000 μmol m−2 s−1 PAR, much greater than for conventional arable crops. Average midday peak isoprene mixing ratio was ∼1.4 ppbv. Acetone and acetic acid also showed small positive daytime fluxes. No measurable fluxes of VOCs were detected above the Miscanthus canopy. Differing isoprene emission rates between different bioenergy crops, and the crops or vegetation cover they may replace, means the impact on regional air quality should be taken into consideration in bioenergy crop selection.► Miscanthus and coppice willow are increasingly important bioenergy crops. ► Above-canopy fluxes were measured using PTR-MS and virtual disjunct eddy covariance. ► Willow isoprene emission peaked at ∼1 mg m−2 h−1, ≡20 μg gdw −1 h−1 standardised. ► Bioenergy crop species choice should consider their impact on regional air quality.
Keywords: VOC; Isoprene; Bioenergy; Miscanthus; Willow; Eddy covariance;

Evaluation of the relaxed eddy accumulation coefficient at various wetland ecosystems by Jeng-Lin Tsai; Ben-Jei Tsuang; Pei-Hsuan Kuo; Chia-Ying Tu; Chi-Ling Chen; Ming-Tung Hsueh; Cheng-Shang Lee; Ming-Hwi Yao; Mei-Li Hsueh (336-347).
Field measurements at various wetland ecosystems were conducted to investigate the coefficients b for different scalars in the relaxed eddy accumulation method. These measurements were performed at paddy, marsh and lagoon fields using the eddy covariance system to collect data with a sampling rate of 10 Hz. Without the application of a wind deadband, the mean median values of b were found to be 0.55 for paddy, 0.57 for marsh and 0.56 for lagoon for all scalar quantities under unstable and near-neutral conditions. However, the median values of b under stable conditions steadily increase with stability. The results of estimated b were well described by proposed relationships as a function of the dimensionless stability parameter z/L. Scalar similarity between carbon dioxide, temperature and water vapor showed a distinct diurnal pattern and change within the day where good scalar correlations were observed at paddy and marsh during daytime, but poor scalar correlations were observed at lagoon. With the application of wind deadband, the reductions of the normalized b factors, b REA, related to the increase of deadband values were evaluated and the results were compared with the reported relationships in the literature. The relative minimal variability of the normalized b REA was found when the wind deadband was equal to 0.8. From the diurnal variation of b REA, the relative maximum values of b REA factors occurred around noon, and lower values were observed in the early morning and late afternoon. Daily median b 0 values for various scalars under unstable and neutral conditions over paddy from the beginning to the end of the study period were used to verify the independence of the variations in surface roughness.► We present the results of REA coefficients at various wetland ecosystems. ► We conclude the better relationship in predicting REA coefficients. ► The relative minimal variability of the b was found when the wind deadband was 0.8. ► We examine the independence of REA coefficients on variations of surface roughness. ► Diurnal patterns of scalar correlations between CO2, H2O and Ta were presented.
Keywords: Relaxed eddy accumulation method; Wind deadband; Wetlands; Trace gas flux; Scalar similarity;

Predicting the soiling of modern glass in urban environments: A new physically-based model by S.C. Alfaro; A. Chabas; T. Lombardo; A. Verney-Carron; P. Ausset (348-357).
This study revisits the measurements of the MULTI-ASSESS and Long Term Soiling programs for understanding physically, and modeling, the processes controlling the soiling of modern glass in polluted conditions. The results show a strong correlation between the size distribution of particles and the evolution of the mass deposited at the surface of the glass. Over observation periods covering more than 2 years, the mass deposition on glass panels sheltered from the rain is observed to accelerate regularly with time at the sites closest to the sources of particulate matter (Roadside sites). At these sites the deposit is also richer in coarse (supermicron) mineral particles than at more distant (Urban Background and Suburban) sites, where the contribution of submicron particles (among which a significant fraction of particulate organic matter) is larger. This size and compositional segregation probably explains that the mass accumulation tends to slow down with time and finally saturate after an estimated duration of more than 10 years at the Suburban sites.The analysis of the correlation between the measured accumulated mass and haze shows that the haze-creating mass efficiency of the deposit decreases progressively as the density of particles increases on the glass panels. This is interpreted as being a consequence of the increasing influence of multiple scattering. A steady-state is eventually obtained when layers of closely packed particles are formed, which occurs for surface masses of the order of a few tens of μg cm−2. After this stage is reached, the haze increases linearly with further mass deposition at a pace conditioned by the size-distribution of the deposit. The parameterization of the evolution of the deposited mass with time, and of the correlation linking this mass to the haze allows proposing a new physically-based model able to predict the development of the haze on sheltered glass. Finally, a comparison of the model predictions with the independent measurements performed at the experimental sites of the AERO program shows that the model is able to simulate correctly the development of the haze at a variety of urban sites ranging from the Suburban to Roadside categories. This predictive tool should help developing conservation strategies adapted to the real environmental conditions of the historical and modern buildings.► We analyze the soiling of glass exposed to a variety of polluted environments. ► Mass deposition and optical impairment do not increase linearly with time. ► A physical model allowing prediction of this increase is proposed and validated. ► In the model, site category (Roadside, Urban Background, or Suburban) is a critical factor.
Keywords: Glass soiling; Haze; Multiple scattering; BC; POM; Deposition rate;

Vertical characteristics of carbonaceous species and their source contributions in a Chinese mega city by Guo-Liang Shi; Ying-Ze Tian; Su-Qin Han; Yu-Fen Zhang; Xiang Li; Yin-Chang Feng; Jian-Hui Wu; Tan Zhu (358-365).
In this work, two new chemical mass balance (CMB) models were applied to estimate the possible source contributions to organic carbon (OC) and the secondary OC (SOC) concentrations in PM10 at 10, 40, 120 and 220 m heights on a meteorological tower in Tianjin. The OC and EC (elemental carbon) were simultaneously measured at the four heights from 24 August to 12 September 2009. The vertical characteristics of OC and EC showed a general decreasing trend with the increasing height. The SOC concentrations were then estimated by the minimum OC/EC ratio method, the NCPCRCMB model and the CMB-Iteration method. The results suggest increasing trends for SOC/TOC and SOC/PM10 up the tower. Additionally, wind rose maps and hourly 72-h back trajectory cluster maps were combined with the source apportionment results to discuss the vertical source contributions to OC, indicating that the percentage contributions of long-range transport sources (such as soil dust and SOC sources) increased with height. SOC formation and transportation by wind affected OC more strongly than each primary source at greater heights. Finally, the levels and sources of the excess OC (the difference between OC concentrations at lower heights to that at 220 m) are discussed. The results suggest that it is more effectively managed for reducing OC to control vehicle and coal sources at the ground level in Tianjin. Information about the more significant sources of excess OC can be used for the development of effective control strategies.► OC and EC in PM10 were measured at four heights on a tower in Tianjin. ► SOC formation and transportation affected OC more strongly at higher heights. ► SOC was estimated by the minimum OC/EC, NCPCRCMB and CMB-Iteration methods. ► It is more effective for excess OC to control the vehicle and coal sources.
Keywords: Vertical characteristics; SOC; CMB-Iteration; Excess OC; NCPCRCMB;

Humic-like Substances (HULIS) comprise a significant fraction of the water-soluble organic aerosol mass and influence the cloud microphysical properties and climate effects of aerosols in the atmosphere. In this work, the most frequently used HULIS isolation and quantification methods including ENVI-18, HLB, XAD-8 and DEAE were comparatively characterized with two model standards, ten interfering compounds, and five ambient aerosol samples. Quantification of HULIS is performed with a TOC analyzer, complemented by an investigation of the chemical structure of the extracted fractions by UV–Vis spectroscopy. The results show that the four isolation methods were all characterized by high reliability, high reproducibility, and low limit of detection (LOD), indicating that each method can be used to efficiently recover Suwannee River Fulvic Acid (SRFA) and be applied to the quantification of the lower amount of HULIS in atmospheric particles. The analytical results of the UV–Vis spectra of HULIS fractions isolated also indicate that they are all favorable for extraction of compounds of high UV absorbance, high MW, and high aromaticity and that the DEAE protocol is the most significant one. Compared with the DEAE method that favors extraction of highly UV-absorbing and more aromatic compounds, SRFA isolated by the ENVI-18, HLB, and XAD-8 protocols were more representative of the global matrix. Each method has its own advantages and disadvantages and is suitable for a particular application. No single method is ideal for both isolation and quantification of HULIS in atmospheric samples.► The four SPE methods are excellent to quantify the lower amount of atmospheric HULIS. ► ENVI-18, HLB, and XAD-8 methods are excellent to isolate HULIS fraction. ► ENVI-18, HLB, and XAD-8 methods favor isolation of the bulk matrix than the DEAE. ► The DEAE method has advantages such as very high selectivity for HULIS.
Keywords: Humic-like substances; Quantification; Isolation; UV–Visible spectroscopy;

Carcinogenic and mutagenic risk associated to airborne particle-phase polycyclic aromatic hydrocarbons: A source apportionment by Mauro Masiol; Angelika Hofer; Stefania Squizzato; Rossano Piazza; Giancarlo Rampazzo; Bruno Pavoni (375-382).
Conventional risk assessment studies provide no detailed information about the role of specific sources determining the total carcinogenic and mutagenic potencies of PAH mixtures on humans health. In this study, the main emission sources of 11 particle-phase PAHs listed as carcinogenic and mutagenic agents by the IARC were identified by a risk apportionment method. The contribution of sources to the total concentration of PAHs in the study area was also quantified. A receptor model based on factor and multiple linear regression analyses was applied to estimate the source-specific risk associated to PAH inhalation in an urban background area of a large city (Venice-Mestre, Northern Italy). The proposed approach has discriminated the sources of mutagenic and carcinogenic congeners and their role in determining a serious hazard for human health. Results, interpreted on the basis of seasonal variations and atmospheric conditions, have shown that even though domestic heating is the main source of total PAHs in winter, a background pollution including traffic mainly accounts for the carcinogenic and mutagenic risk during the whole year. The findings of this work and the approach used can be easily applied to other geographic areas and provide useful information for local and regional air pollution control strategies.► Eleven particle-bound PAHs were monitored for one year in an urban site. ► A receptor model was used to detect the main PM emission sources. ► Sources of carcinogenic and mutagenic effects were also identified. ► A risk assessment was made for each identified source. ► Applicable to other areas, the approach provides information for pollution control.
Keywords: PAHs; Aerosol; Cancer risk assessment; Toxic equivalent factors; Mutagenic equivalent factors;

Comparison of temporal features of sulphate and nitrate at urban and rural sites in Spain and the UK by M.A. Revuelta; R.M. Harrison; L. Núñez; F.J. Gomez-Moreno; M. Pujadas; B. Artíñano (383-391).
A seasonal comparison of aerosol secondary inorganic component (SIC) patterns on annual, weekly and daily timescales has been performed at urban Madrid and London and at rural sites in the central Iberian Peninsula and south-eastern UK alongside data for precursor gases. A database from winter 2004 to summer 2011 has been analysed. Results show the dominant processes affecting the formation and evolution of nitrate ( NO 3 − ) and sulphate ( SO 4 2 − ) in both regions. In Madrid, photochemistry dominates formation of nitrate, which is mostly locally-generated. Strong thermal decomposition results in very low concentrations in summer. In contrast, in London high nocturnal values suggest the importance of heterogeneous formation processes as well as nitrate condensation at lower temperatures. The seasonal nitrate maximum in the UK is found in late winter-early spring, when the region typically receives the highest input of pollutants transported from mainland Europe. Daily evolution of nitrate in both cities is heavily influenced by meteorological factors. Seasonal sulphate patterns show no obvious trend, except at the Spanish rural site in summer where photochemical formation was apparent. In Madrid, daily SO2 and sulphate patterns exhibiting maximum concentrations at noon were found in winter. In previous studies this phenomenon was observed for SO2 in London, where it was explained by the entrainment of pollutants from aloft into the mixing layer. SIC weekend reductions were investigated at the urban background sites of Madrid and London, and in both cities statistically significant fine nitrate reductions of around 20% are found in summer. These values are consistent with the annual reductions observed by researchers in the US. Weekend sulphate reductions occurred in winter, reflecting a clear impact of anthropogenic sulphate in urban environments, in spite of the large reductions in sulphur emissions in Europe in the last decade. Ratios of nitrate and sulphate to oxidant gases and to one another have been calculated for Madrid, and are consistent with a contribution of local formation to sulphate in winter, while in summer a regional background unrelated to urban SO2 is observed. The strong differences in the behaviour seen in London and Madrid (and the rural sites) emphasises the need to study cities individually and not to extrapolate conclusions drawn in one city to others in different climate/topographic situations.► Aerosol nitrate and sulphate patterns are compared seasonally in Madrid and London. ► Results show the dominant processes affecting their formation and evolution. ► Weekly analysis show weekend reductions for nitrate in summer and sulphate in winter. ► Daily evolution of nitrate is heavily influenced by meteorological factors. ► Strong differences seen emphasises the need to study cities individually.
Keywords: Nitrate; Sulphate; Aerosol; Semi-continuous; Timescale;

Experimental results are presented for the shear-driven flushing of a dense fluid from a square street canyon. The flow is both qualitatively and quantitatively influenced by the density of the fluid in the canyon, which is parameterized in terms of the flow Richardson number. A total of 26 experiments were conducted for Richardson numbers ranging from 0.08 to 4.5. For low Richardson numbers the canyon remains well mixed during the flushing process and the density difference decays exponentially (as observed in previous studies flushing a neutrally buoyant tracer). As the Richardson number increases the canyon becomes more stably stratified and the decay rate reduces. For very high Richardson numbers, a two-layer stratification is observed. Over time, for the two-layer case, the lower dense layer gets thinner, indicating that dense fluid is being skimmed from the top of the layer, and less dense, indicating that ambient fluid is being mixed down into the dense layer. Previous studies only observed flushing by skimming. The layer buoyancy decreases linearly over time until the shear layer reaches the bottom of the canyon at which point the rate of layer buoyancy reduction dramatically increases. Results also indicate that the density interface is thinner than the shear layer that is driving the mixing, and that the difference in thicknesses increases with an increasing Richardson number. This result is consistent with previous studies of mixing in stratified shear flows. The initial exponential decay rate was calculated for each experiment and is given by k = 1 / ( 18 + 84 R i ) 1.21 . Following the initial period of exponential decay, the decay rate increases as the stratification weakens.►In flushing process, both, skimming and mixing process were observed. ► The thickness of the interface layer decreased with increasing Ri. ► Layer buoyancy decreases linearly till the shear layer reaches the cavity bottom. ► Density interface is thinner than the shear layer that is driving the mixing. ► The initial exponential decay rate was estimated by an empirical equation.
Keywords: Street canyon; Dense gas; Dispersion;

Impact of different transport mechanisms of Asian dust and anthropogenic pollutants to Taiwan by Chuan-Yao Lin; Charles C.K. Chou; Zifa Wang; Shih-Chun Lung; Chung-Te Lee; Chung-Shin Yuan; Wei-Nai Chen; Shih-Yu Chang; Shih-Chieh Hsu; Wan-Ching Chen; Shaw Chen Liu (403-418).
The impacts of long-range transport of Asian dust and anthropogenic air pollutants to Taiwan are strongly associated with the atmospheric conditions and paths of transport. In this study, we identified 16 significant dust events (daily mean mass concentration ≥ 120 μg m−3) to Taiwan from 2002 to 2008. To investigate transport characteristics associated with long-range transport of Asian dust and anthropogenic air pollutants to Taiwan, significant dust events were further classified into dry (12 cases) and wet (4 cases) types according to atmospheric conditions. We found that the major transport paths for the dry type (DT) dust cases passed through anthropogenic source areas in the low boundary while the major paths for the wet type (WT) dust cases passed over the ocean. After mineral dust, which occupied around 32% of total PM10 mass concentration, anthropogenic ionic pollutants was the second major contributor and occupied 19–22% at three sampling stations in Taiwan for DT cases. In the fine particle, the anthropogenic ionic pollutants contributed from 29 to 36% to PM2.5, making it the major contributor. The two most significant cases, one from the DT and one from the WT cases, were selected to study transport mechanisms with the NAQPMS air quality model. Simulation results also suggest that transport paths and boundary atmospheric conditions play important roles in aerosol compositions.► We identify 16 significant Asian dust events to Taiwan from 2002 to 2008. ► We further classified into dry and wet types according to atmospheric conditions. ► Mean mass fractions of major aerosol species in the PM10 and PM2.5 were discussed. ► Meteorological and air quality models were employed to study the transport mechanism.
Keywords: Asian dust; Anthropogenic pollutants; Long-range transport; Modeling;

Collocated and simultaneous measurements of aerosols near the ground were conducted using a lidar and aerosol sampler at Tsukuba, Japan, to clarify the relationship between lidar-derived optical properties and in-situ microphysical properties. The total linear particle depolarization ratio (δ p) ranged from 14% to 18% when nonspherical mineral dust particles were predominant in the supermicrometer range on May 7–8, 2008, whereas it ranged from 6% to 7% when spherical sea-salt particles were predominant in that range on September 3–4, 2008. Sulfates and nitrates were predominant in the submicrometer range for these two periods. Water-dialysis analysis on May 6–7 indicated that 29% of the coarse particles were water insoluble, whereas 70% were water soluble or nearly soluble on September 3–4. The ratio of dry mass concentration to the backscattering coefficient (M/β p) was 34–39 g m−2 sr on May 7–8 and 6.2–6.3 g m−2 sr on September 3–4. Our results provide evidence that lidar-derived β p and δ p capture the aerosol mass concentration and relative abundance of the spherical and nonspherical particles although the microphysical properties vary significantly for individual particles.Display Omitted► Collocated and simultaneous measurements of the aerosol were made using a lidar and aerosol sampler. ► The depolarization ratio was 14–18% when nonspherical mineral dust was present. ► The depolarization ratio was 6–7% when spherical sea salt droplets were present. ► The dry mass concentration-to-backscattering coefficient ratios were obtained.
Keywords: Aerosol; Lidar; Backscatter; Depolarization; Mass concentration; Particle shape;

Ground based comparison of solar UV index in Kathmandu, Pokhara and Biratnagar by Niranjan P. Sharma; Binod K. Bhattarai; Balkrishna Sapkota; Berit Kjeldstad (428-435).
This paper presents the ground based comparison of solar UV index at three major cities in Nepal (Kathmandu, Pokhara and Biratnagar). Kathmandu (27.72° N, 85.32° E), Pokhara (28.22° N, 83.22° E) and Biratnagar (26.45° N, 87.27° E) are located at an elevation of 1350 m, 800 m and 72 m respectively from the sea level. This comparison was performed from January to December 2009 for Kathmandu (KTM) and Pokhara (PKR) and from February to December 2009 for Biratnagar (BRT). The measurement instruments used are the NILU-UV irradiance meter and the Moderate Resolution Imaging Spectroradiometer (MODIS). The NILU-UV irradiance meter records the UV radiation whereas the MODIS estimates AOD. During this study, the monthly mean UV Index (UVI) in July were found to be 7.5 ± 2.5 in KTM, 8.6 ± 3.5 in PKR and 7.2 ± 3.1 in BRT. Meanwhile, the hourly mean UVI during monsoon at 7UT was found to be 5.7 ± 2.5 in KTM, 6.4 ± 2.6 in PKR and 5.8 ± 2.5 in BRT. The highest values of these hourly mean UVI was found at or around noon. The UVI values between KTM and PKR was slightly more correlated with its correlation coefficient being 0.73 than that between KTM and BRT whose correlation coefficient was 0.65. Similarly, the mean bias difference for KTM, BRT and KTM, PKR was found to be 4.8% and −38.1% respectively. This higher and lower mean bias difference indicates large and small deviation in UV data. The study also showed that besides solar elevation, the fluctuation in UVI was also influenced by the variation in ozone, aerosols and clouds. Furthermore, a year long comparison of UVI indicated that the UVI in Pokhara was higher than that in Kathmandu and Biratnagar. This analysis also showed that the extreme values of UVI were not found during the study period.► UVI at PKR was found to be higher than the UVI at KTM and BRT. ► In an average, extreme values of UVI were not found during study. ► MODIS estimated monthly mean AOD at BRT was found higher than that at KTM and PKR.
Keywords: UV radiation; Spectrum; Solar Zenith Angle; CIE; UV index;

Penetration of fine particles through rough cracks by Alvin C.K. Lai; Joanna L.S. Fung; M. Li; K.Y. Leung (436-443).
Many building materials have random roughness protrusion scales of up to hundreds of micrometers. A scaled down experimental facility was designed to investigate fine particles' penetration through a straight, smooth and rough crack under four different pressures ranging from 2 to 8 Pa. Sandpapers with three different roughness scales were used to create 10 to 100 micron rough surfaces. Particle concentration for sizes ranging from 20 to 500 nm was measured to determine the penetration. Contrary to expectations, the results are not sensitive to roughness scales. Besides, it is also noticed that under low differential pressure scenario, deposition for rough cracks for small particles is higher than that of smooth crack which will offer better protection for indoor exposure. A simple mathematical model was also developed to predict particle deposition on rough surfaces by diffusion mechanism on extended surfaces. The experimental results match well with the model prediction.► We measured particle penetration of smooth and rough crack experimentally. ► Fine particles concentration of 30 nm–500 nm were measured. ► At low pressure rough crack gives lower penetration than smooth crack. ► The results show that penetration is not sensitive to the roughness scales. ► A simple mathematical model accounting diffusion was developed for rough surfaces.
Keywords: Building crack; Penetration; Rough surfaces; Model; Fine aerosols;

Saharan dust impact in central Italy: An overview on three years elemental data records by S. Nava; S. Becagli; G. Calzolai; M. Chiari; F. Lucarelli; P. Prati; R. Traversi; R. Udisti; G. Valli; R. Vecchi (444-452).
In southern European countries, Saharan dust may episodically produce significant increases of PM10, which may also cause the exceedance of the PM10 daily limit value established by the European Directive (2008/50/EC). The detection with very high sensitivity of all the elements that constitute mineral dust makes PIXE technique a very effective tool to assess the actual impact of these episodes.In this work, a review of long-term series of elemental concentrations obtained by PIXE has been accomplished with the aim of identifying the occurrence of Saharan dust transport episodes over long periods in Tuscany and characterising them in terms of composition and impact on PM concentration, tracing back their contribution to the exceedances of the PM10 limit value.The impact of the different Saharan intrusions on PM10 showed a very high variability. During the most intense episodes (which occurred with a frequency of few times per year) the calculated soil dust concentration reached values as high as 25–30 μg m−3, to be compared with background values of the order of 5 μg m−3. The Saharan dust contribution was decisive to cause the exceedance of the PM10 daily limit value in the 1–2% of the days considered in the present work.► PIXE is very effective to quantify the actual mineral dust contribution to PM. ► The impact of Saharan intrusions on PM10 is extremely variable from case to case. ► Desert dust concentrations up to 20–25 μg m−3 during the most intense episodes. ► Saharan dust determinant for PM10 daily limit exceedance in 2% of analysed samples.
Keywords: Desert dust; PIXE; Elemental composition; Long-range transport; PM10;

Radon (222Rn) found in uranium mine shaft ventilation exhaust gases could pose hazards to the surrounding environment and the public by virtue of its progeny. Radon migration under complex terrain is complicated by pollution source characteristics, geographical features of the dispersion region, meteorological conditions and precipitation. Fluid dynamics computations of 222Rn dispersion are performed for uranium mine shaft exhausts for complex models of the actual physical terrain corresponding to a mine in the Jiangxi Province of China. The eight cases studied included a ventilation shaft source, four downwind velocities (0.5, 1.0, 2.0, 4.0 m s−1) and two underlying surface roughness characteristics (0.1 m, 1.0 m). 222Rn distributions in the vicinity of uranium mine ventilation shaft are computed and compared with field measurements.► Computational fluid dynamics can account for complex meteorology and geography. ► Modeling of radon dispersion from uranium mine shafts. ► Increasing surface roughness causes Rn accumulation for small wind speeds. ► Increasing wind speeds increases radon dispersion. ► Field measurements agree closely with the numerical investigations.
Keywords: Uranium mine shaft ventilation; Radon (222Rn); Atmospheric dispersion; Modeling; Field measurements;

Mechanism and kinetic study on the gas-phase reactions of OH radical with carbamate insecticide isoprocarb by Chenxi Zhang; Wenbo Yang; Jing Bai; Yuyang Zhao; Chen Gong; Xiaomin Sun; Qingzhu Zhang; Wenxing Wang (460-466).
As one of the most important carbamate insecticides, isoprocarb [2-(1-methylethyl) phenyl methylcarbamate, MIPC] is widely used in agricultural and cotton spraying. The atmospheric chemical reaction mechanism and kinetics of MIPC with OH radical have been researched using the density functional theory in this paper. The study shows that OH radical is more easily added to the C atoms of aromatic ring than to carbon-oxygen double bond, while the H atom is abstracted more difficulty from –CONH– group and aromatic ring than from the –CH3– group and the –CH– group. At room temperature, the total rate constant of MIPC with OH radical is about 5.1 × 1012 cm3 molecule−l s−l. OH radical addition reaction and H atom abstraction reaction are both important for the OH-initiated reaction of MIPC. The energy-rich adducts (MIPC-OH) and the MIPC's radical isomers are open-shell activated radicals and can be further oxidized in the atmosphere.► OH radicals are more easily added to aromatic ring than to C=O bond. ► The rate constant of the MIPC with OH is about 5.1 × 10−12 cm3 molecule−l s−l. ► The OH addition reactions decreases with the temperature increasing. ► The H abstraction reactions increases with the temperature increasing.
Keywords: Isoprocarb; OH radical; Microscopic mechanism; Kinetic study;

Characterization of cloud water chemistry at Mount Tai, China: Seasonal variation, anthropogenic impact, and cloud processing by Jia Guo; Yan Wang; Xinhua Shen; Zhe Wang; Taehyoung Lee; Xinfeng Wang; Penghui Li; Minghu Sun; Jeffrey L. Collett; Wenxing Wang; Tao Wang (467-476).
To investigate cloud chemistry in the fast developing region of north China, five intensive observation campaigns were performed at the summit of Mount Tai (Mt. Tai) during 2007–2008. A total of 482 cloud water samples were collected using single-stage and two-stage cloud collectors. Inorganic ions, organic acids and species associated with S(IV) oxidation in cloud water were analyzed. The results showed that 80% of the cloud samples were acidic (pH < 5.6), and 55% of the samples were strongly acidified (pH < 4.5). The clouds at Mt. Tai contained much higher anthropogenic and crustal ion concentrations than observed at many other rural sites; the most abundant ions in the cloud water were NH4 + (volume weighted mean concentration of 1215 μeq L−1), SO4 2− (1064 μeq L−1), NO3 (407 μeq L−1) and Ca2+ (193 μeq L−1), suggesting large influences of anthropogenic emissions on cloud water. Seasonal variations of cloud composition were observed, showing high fractions of NH4 + and SO4 2− in summer and more soil/crustal ions in spring and winter. Backward trajectory analysis showed that the cloud water pH in air masses arriving from the south was typically much lower than when air was transported from the north. Higher nitrate fraction and low pH were found in air masses from the industrialized coastal regions of China, indicating an increased contribution of HNO3 to cloud acidification due to higher NO x emissions. The drop size dependence of cloud chemical composition was examined. Smaller droplets were more acidified than larger ones. The drop size dependence tendency of ion concentrations varied with cloud evolution. SO4 2−, NH4 + and NO3 were more enriched in larger droplets in the initial stages of the clouds, and tended to be higher in smaller drops with cloud development. In-cloud aqueous sulfate formation was estimated using a selenium tracer method. In-cloud aqueous production on average accounted for 27% of the measured cloud water sulfate, with a range from 5% to 62% for individual cloud events.► A comprehensive study of cloud water was conducted at Mt Tai in China in 2007–2008. ► Cloud water composition at Mt. Tai is strongly influenced by anthropogenic emissions. ► Cloud water has low pH values and is more acidic for air masses from southern China. ► Drop-size dependence of cloud ionic composition varies with cloud evolution. ► In-cloud S(IV) oxidation on average accounts for 27% of the total cloud sulfate.
Keywords: Cloud composition; Drop size dependence; In-cloud produced sulfate; Cloud scavenging; Mount Tai;

Influence of tree provenance on biogenic VOC emissions of Scots pine (Pinus sylvestris) stumps by Minna Kivimäenpää; Narantsetseg Magsarjav; Rajendra Ghimire; Juha-Matti Markkanen; Juha Heijari; Martti Vuorinen; Jarmo K. Holopainen (477-485).
Resin-storing plant species such as conifer trees can release substantial amounts of volatile organic compounds (VOCs) into the atmosphere under stress circumstances that cause resin flow. Wounding can be induced by animals, pathogens, wind or direct mechanical damage e.g. during harvesting. In atmospheric modelling of biogenic VOCs, actively growing vegetation has been mostly considered as the source of emissions. Root systems and stumps of resin-storing conifer trees could constitute a significant store of resin after tree cutting. Therefore, we assessed the VOC emission rates from the cut surface of Scots pine stumps and estimated the average emission rates for an area with a density of 2000 stumps per ha. The experiment was conducted with trees of one Estonian and three Finnish Scots pine provenances covering a 1200 km gradient at a common garden established in central Finland in 1991.VOC emissions were dominated by monoterpenes and less than 0.1% of the total emission was sesquiterpenes. α-Pinene (7–92% of the total emissions) and 3-carene (0–76% of the total emissions) were the dominant monoterpenes. Proportions of α-pinene and camphene were significantly lower and proportions of 3-carene, sabinene, γ-terpinene and terpinolene higher in the southernmost Saaremaa provenance compared to the other provenances. Total terpene emission rates (standardised to +20 °C) from stumps varied from 27 to 1582 mg h−1 m−2 when measured within 2–3 h after tree cutting. Emission rates decreased rapidly to between 2 and 79 mg h−1 m−2 at 50 days after cutting. The estimated daily terpene emission rates on a hectare basis from freshly cut stumps at a cut tree density of 2000 per ha varied depending on provenance. Estimated emission ranges were 100–710 g ha−1 d−1 and 137–970 g ha−1 d−1 in 40 and in 60 year-old forest stands, respectively. Our result suggests that emission directly from stump surfaces could be a significant source of monoterpene emissions for a few weeks after logging in a Scots pine stand, but provenance properties strongly affect resin flow from root to stump surface.► Emissions of volatile organic compounds (VOC) from Scots pine stumps were measured. ► Emission rates relative to stump area were 27–1582 mg h−1 m−2 after cutting. ► Tree provenance affected the VOC composition. ► Emission rates were estimated for different aged pine stands. ► Fresh stump surface is a significant source of monoterpene emissions.
Keywords: Pinus sylvestris; Stump; VOC; Monoterpene; Logging;

Intra-urban spatial variability of PM2.5-bound carbonaceous components by Mingjie Xie; Teresa L. Coons; Steven J. Dutton; Jana B. Milford; Shelly L. Miller; Jennifer L. Peel; Sverre Vedal; Michael P. Hannigan (486-494).
The Denver Aerosol Sources and Health (DASH) study was designed to evaluate associations between PM2.5 species and sources and adverse human health effects. The DASH study generated a five-year (2003–2007) time series of daily speciated PM2.5 concentration measurements from a single, special-purpose monitoring site in Denver, CO. To evaluate the ability of this site to adequately represent the short term temporal variability of PM2.5 concentrations in the five county Denver metropolitan area, a one year supplemental set of PM2.5 samples was collected every sixth day at the original DASH monitoring site and concurrently at three additional sites. Two of the four sites, including the original DASH site, were located in residential areas at least 1.9 km from interstate highways. The other two sites were located within 0.3 km of interstate highways. Concentrations of elemental carbon (EC), organic carbon (OC), and 58 organic molecular markers were measured at each site. To assess spatial variability, site pairs were compared using the Pearson correlation coefficient (r) and coefficient of divergence (COD), a statistic that provides information on the degree of uniformity between monitoring sites. Bi-weekly co-located samples collected from July 2004 to September 2005 were also analyzed and used to estimate the uncertainty associated with sampling and analytical measurement for each species. In general, the two near-highway sites exhibited higher concentrations of EC, OC, polycyclic aromatic hydrocarbons (PAHs), and steranes than did the more residential sites. Lower spatial heterogeneity based on r and COD was inferred for all carbonaceous species after considering their divergence and lack of perfect correlations in co-located samples. Ratio–ratio plots combined with available gasoline- and diesel-powered motor vehicle emissions profiles for the region suggested a greater impact to high molecular weight (HMW) PAHs from diesel-powered vehicles at the near-highway sites and a more uniformly distributed impact to ambient hopanes from gasoline-powered motor vehicles at all four sites.► Concentrations of PM2.5 associated carbonaceous species were measured from 4 urban sites in Denver. ► Spatial variability was assessed using the Pearson correlation coefficient (r) and coefficient of divergence (COD). ► Near-highway sites exhibited higher concentrations of EC, OC, PAHs, and steranes than residential sites. ► Large uncertainties associated with sampling and species quantification will bias the estimation of r and CODs. ► CODs derived from co-located samples are useful points of reference to analyze spatial variability of PM2.5 species.
Keywords: Particulate matter; PM2.5; Organic molecular marker; Spatial variability; Co-located samples; Motor vehicle influence;

There is evidence of adverse health impacts from human exposure to traffic-related ultrafine particulate matter pollution. As more commuters are spending a significant portion of their daily routine inside vehicles, it is increasingly relevant to study exposure levels to harmful pollutants inside the vehicle microenvironment. This study is one of the first research efforts to combine detailed freeway traffic data (at 20 s intervals) and in-vehicle ultrafine particulate (UFP) exposure data under varying vehicle ventilation conditions. Results show that due to negative correlation between traffic speed and density, traffic states have a small but significant impact on in-vehicle UFP concentrations, highest in high traffic flow-high speed conditions or in high traffic density-low speed conditions. Vehicle cabin barrier effects are the primary determinant of in-vehicle exposure concentrations, providing 15% protection with the windows down, 47% protection with the windows up and the vent open, and 83–90% protection with the windows up and the vent closed (more with the air conditioning on). Unique results from this study include the dominance of ventilation over traffic effects on UFP and the non-linear relationships between traffic variables and UFP concentrations. The results of this research have important implications for exposure modeling and potential exposure mitigation strategies.► Vehicle ventilation is the dominant influence on in-vehicle UFP. ► Traffic states have a small but significant impact on in-vehicle UFP. ► Traffic impacts vary by vehicle ventilation and can be non-linear or lagged. ► Individual high-emitters eclipse aggregate traffic flow effects on UFP. ► Congestion per se does not increase in-vehicle UFP exposure concentrations.
Keywords: In-vehicle exposure; Roadway concentrations; Ultrafine particles; Detailed traffic data; Traffic congestion;

Particulate matter (PM) is a complex, heterogeneous mixture that changes in time and space. It encompasses many different chemical components and physical characteristics, many of which have been cited as potential contributors to toxicity. Each component has multiple sources, and each source generates multiple components. Identifying and quantifying the influences of specific components or source-related mixtures on measures of health-related impacts, especially when particles interact with other co-pollutants, therefore represents one of the most challenging areas of environmental health research. Current knowledge does not allow precise quantification or definitive ranking of the health effects of PM emissions from different sources or of individual PM components and indeed, associations may be the result of multiple components acting on different physiological mechanisms. Some results do suggest a degree of differential toxicity, namely more consistent associations with traffic-related PM emissions, fine and ultrafine particles, specific metals and elemental carbon and a range of serious health effects, including increased morbidity and mortality from cardiovascular and respiratory conditions. A carefully targeted programme of contemporary toxicological and epidemiological research, incorporating more refined approaches (e.g. greater speciation data, more refined modelling techniques, accurate exposure assessment and better definition of individual susceptibility) and optimal collaboration amongst multidisciplinary teams, is now needed to advance our understanding of the relative toxicity of particles from various sources, especially the components and reactions products of traffic. This will facilitate targeted abatement policies, more effective pollution control measures and ultimately, a reduction in the burden of disease attributable to ambient PM pollution.► Identifying toxic component(s) of particulate matter is a major challenge. ► Evidence suggesting differential toxicity of components and sources are discussed. ► Targeted and contemporary studies are needed to further understand relative toxicity of particles. ► Goals of refined research are abatement policies, pollution control measures and improved health.
Keywords: Particulate matter; Differential toxicity; Source-related mixtures; Chemical components;

Contributions of biogenic volatile organic compounds to net ecosystem carbon flux in a ponderosa pine plantation by Nicole C. Bouvier-Brown; Gunnar W. Schade; Laurent Misson; Anita Lee; Megan McKay; Allen H. Goldstein (527-533).
When assessing net ecosystem exchange (NEE) and net ecosystem carbon balance (NECB), respiration is generally assumed to be the only significant loss of carbon to the atmosphere. However, carbon is also emitted from ecosystems in the form of biogenic volatile organic compounds (BVOCs). Here we consider the magnitude of systematic difference caused by omitting this additional carbon loss from the net ecosystem carbon balance, as compared to the NEE term, of the ponderosa pine plantation at Blodgett Forest. We find that 9.4 (range 6.2–12.5) g C m−2 yr−1 were emitted from this ecosystem as BVOCs. This is 4.0 (2.0–7.9) % of annual NEE, and neglecting this additional loss of carbon causes an overestimation of carbon storage for this rapidly growing commercial forest plantation. For ecosystems that are not storing carbon as rapidly, where photosynthesis and respiration are more closely balanced, ignoring BVOC emission may cause a larger error in the estimation of NECB.► We quantified the carbon lost as BVOCs from a ponderosa pine plantation. ► We found that BVOCs contribute to 4.0 (2.0–7.9) % of annual NEE. ► Neglecting BVOC carbon loss causes an overestimation of carbon storage.
Keywords: Biogenic volatile organic compounds; Net ecosystem exchange; Carbon balance;

A Bioaerosol sensing instrument referred to as WIBS-4, designed to continuously monitor ambient bioaerosols on-line, has been used to record a multiparameter “signature” from each of a number of Primary Biological Aerosol Particulate (PBAP) samples found in air. These signatures were obtained in a controlled laboratory environment and are based on the size, asymmetry (“shape”) and auto-fluorescence of the particles.Fifteen samples from two separate taxonomic ranks (kingdoms), Plantae (×8) and Fungi (×7) were individually introduced to the WIBS-4 for measurement along with two non-fluorescing chemical solids, common salt and chalk. Over 2000 individual-particle measurements were recorded for each sample type and the ability of the WIBS spectroscopic technique to distinguish between chemicals, pollen and fungal spore material was examined by identifying individual PBAP signatures. The results obtained show that WIBS-4 could potentially be a very useful analytical tool for distinguishing between natural airborne PBAP samples, such as the fungal spores and may potentially play an important role in detecting and discriminating the toxic fungal spore, Aspergillus fumigatus, from others in real-time.If the sizing range of the commercial instrument was customarily increased and permitted to operate simultaneously in its two sizing ranges, pollen and spores could potentially be discriminated between. The data also suggest that the gain setting sensitivity on the detector would also have to be reduced by a factor >5, to routinely detect, in-range fluorescence measurements for pollen samples.► A laboratory assessment of the WIBS-4 bioaerosol sensor for PBAP discrimination. ► Multiparameter optical signatures of in-flight pollen and fungal spore are measured. ► Aspergillus fumigatus gives a signature which could be used for field detection.
Keywords: Single particle fluorescence; Primary Biological Aerosol Particles; WIBS;

Sensitivity of predicted pollutant levels to urbanization in China by Man Yu; Gregory R. Carmichael; Tong Zhu; Yafang Cheng (544-554).
Urbanization in China accompanies economic development and population growth. Changes in land use leads to changes in both meteorological and chemical fields. In this study, the impact of land use change in Jing-Jin-Ji (JJJ, indicating Beijing–Tianjin–Hebei) and Yangtze River Delta (YRD) areas on meteorology and ozone concentrations are studied using the WRF–Chem model. Land use change is represented by two different land cover data sets: USGS and MODIS. Monthly-average simulations show that urbanization causes an increase in 2-m temperature by maximum 2.4 °C and 3.2 °C in these two areas, respectively. Wind speed simulations suggest a decrease (average 1.2 m s−1) in daytime for YRD, and in nighttime for JJJ. Dew point differences show a dry effect over both areas, with maximum −3 °C in JJJ and −2.4 °C in YRD. Planetary Boundary Layer (PBL) height increases by 400 m (maximum in JJJ) and 600 m (maximum in YRD) for daytime, and nighttime increases are less than 100 m. Daytime ozone concentrations in JJJ increase by 20 ppb due to urbanization, while in YRD the difference is around 5 ppb. Compared to observations, mean errors in urban areas was improved when using updated land use information by 14.2% and 35.6%, and in suburban areas by 5.8% and 10.7%. Updating land use data set in air quality modeling is important in application to regions with rapid urbanization such as China. The effects due to land use change can be as large as those due to 20% increase in emissions.► We model urbanization impact on air quality in JJJ and YRD areas. ► Urbanization increases T-2, decreases wind speeds and dew points, and enhances PBL heights. ► Ozone simulations rise after urbanization, but with different diurnal pattern in two areas. ► After updating land cover data, mean errors between simulations and observations are reduced in both urban and base points.
Keywords: Urbanization; WRF–Chem; Ozone; Meteorology; USGS; MODIS;

Stable isotope techniques may be a suitable tool for tracing industrial emissions in the atmosphere and the environment provided that the isotopic compositions of industrial emissions are distinct. We determined the isotopic compositions of nitrate, ammonium and sulfate in PM2.5 emitted from two industrial stacks at a large upgrader site in the Athabasca oil sands region (AOSR), northeastern Alberta, Canada, and compared them to the nitrogen and sulfur isotopic compositions of source materials and upgrading by-products. We found distinct isotopic compositions of nitrate and ammonium in PM2.5 compared to those reported for atmospheric nitrate and ammonium in the literature. Nitrate in PM2.5 had δ15N values of 9.4‰ (Stack A) and 16.1 ± 1.2‰ (Stack B) that were significantly enriched in 15N compared to the feedstock materials (∼2.5‰), by-products of upgrading (−0.3–1.3‰), and atmospheric N2 (0‰). δ15N of ammonium in PM2.5 showed a large range with values between − 4.5 to +20.1‰ (Stack B). We report the first measurements of the triple oxygen isotopic composition of industrial emitted nitrate. Nitrate emitted as PM2.5 is not mass-independently enriched in 17O resulting in Δ17O = 0.5 ± 0.9‰ (Stack B) and is therefore distinct from atmospheric nitrate, constituting an excellent indicator of industrial derived nitrate. δ18O values of nitrate in PM2.5 (36.0 and 17.6 ± 1.8‰ for Stack A and B, respectively) were also significantly lower than δ18O values of atmospheric nitrates and hence isotopically distinct. δ34S values of sulfate in PM2.5 were with 7.3 ± 0.3‰ (Stack A) and 9.4 ± 2.0‰ (Stack B) slightly enriched in 34S compared to δ34S in bitumen (4.3 ± 0.3‰) and coke (3.9 ± 0.2‰). δ18O values of sulfate in PM2.5 were 18.9 ± 2.9‰ and 14.2 ± 2.8‰ for Stack A and Stack B, respectively. The isotopic composition of sulfate in PM2.5 was not sufficiently different from δ34S and δ18O values of sulfate in long-range atmospheric deposition in industrial countries to serve as a quantitative indicator for industrial emitted PM2.5. We conclude that δ18O and Δ17O values of nitrate in stack-emitted PM2.5 are excellent, and δ15N values of nitrate and ammonium are suitable indicators for identifying and tracing of PM2.5 nitrate and ammonium emitted from two stacks in the AOSR in the surrounding terrestrial and aquatic ecosystems.► Stack-emitted PM2.5 in the Athabasca oil sands region is isotopically distinct. ► Nitrate in PM2.5 has unique δ18O and Δ17O values suitable for tracing emissions. ► Emitted nitrate in PM2.5 is not mass-independently enriched in 17O. ► Nitrate and ammonium in PM2.5 are often enriched in 15N. ► δ15N of NO3 and NH4 in PM2.5 are suitable tracers for industrial stack emissions.
Keywords: Nitrate; Ammonium; Sulfate; Industrial emissions; Athabasca oil sands; Alberta;

This paper presents measurements of electrical charges on ultrafine particles (UFPs) of different electrical mobility diameters (30, 50, 80, and 100 nm) in on- and near-freeway environments. Using a tandem Differential Mobility Analyzer (DMA) system, we first examined the fraction of UFPs carrying different number of charges on two distinctive freeways: a gasoline-vehicle dominated freeway (I-405) and a heavy-duty diesel truck dominated freeway (I-710). The fractions of UFPs of a given size carrying one or more charges were significantly higher on the freeways than in the background. The background UFPs only carried up to two charges but freeway UFPs could have up to three charges. The total fraction of charged particles was higher on the I-710 than I-405 across the studied electrical mobility diameters. Near the I-405 freeway, we observed a strong decay of charged particles on the downwind side of the freeway. We also found fractional decay of the charged particles was faster than total particle number concentrations, but slower than total ion concentrations downwind from the freeway I-405. Among charged particles, the highest decay rate was observed for particles carrying three charges. Near the I-710 freeway, we found strong net positive charges on nucleation mode particles, suggesting that UFPs were not at steady-state charge equilibrium near freeways.► Electrical charges on ultrafine particles (UFPs) were measured on- and near-freeways. ► The fractions of charged UFPs were significantly higher on the freeways than in the background. ► Charged particles decayed faster than total particles but slower than ion downwind from the freeway. ► Strong net positive charges were found on nucleation mode particles near freeways.
Keywords: Ultrafine particle; Freeway; Charge;

Stability of organic nitrogen in NADP wet deposition samples by John T. Walker; Tracy L. Dombek; Lee A. Green; Nina Gartman; Christopher M.B. Lehmann (573-582).
Organic compounds represent an important yet largely uncharacterized component of atmospheric nitrogen deposition. Rapid progress in understanding the sources and spatiotemporal patterns of organic nitrogen (ON) deposition will require the use of existing large-scale monitoring infrastructure, such as the National Atmospheric Deposition Program's National Trends Network (NADP/NTN). The purpose of this study is to investigate the analytical and sampling requirements for adding ON measurements to the NTN, with specific interest in examining ON stability during sampling and storage. The analytical technique for total nitrogen (TN) used by the NADP's Central Analytical Laboratory (CAL) and associated quality assurance data are described. We then compare TN, inorganic nitrogen (IN = NH4 + + NO3 ), and ON (ON = TN − IN) concentrations in a field study between standard weekly NADP/NTN samples (unrefrigerated during sampling and storage), daily event samples collected using the Atmospheric Integrated Research Monitoring Network protocol (AIRMoN, unrefrigerated during sampling but refrigerated during storage), and daily event samples that were preserved via refrigeration in the field upon collection (AIRMoN_Ref, refrigerated during sampling and storage). Using AIRMoN_Ref as the reference for comparison, total loss of ON in weekly NTN samples in the field and during laboratory storage is approximately 40%. This bias is likely dominated by losses of ON in the collection bucket. However, additional loss may occur during laboratory storage at room temperature prior to analysis. Loss of ON was also observed in AIRMoN samples, though differences relative to AIRMoN_Ref (10.8%) were less than weekly NTN samples. Biases in ON are more consistently negative at higher ambient temperatures. Storage experiments indicated that refrigeration at 4 °C at the CAL was sufficient to stabilize ON concentrations. We conclude that weekly sampling for ON is feasible if precipitation is refrigerated or frozen immediately upon collection. Samples should be kept refrigerated or frozen prior to analysis. Preliminary results indicate that NO2 , an additional inorganic species not currently measured by the CAL, makes a small contribution to TN (<1%), but if neglected may cause significant negative bias in ON determined as TN − IN. We recommend that CAL include NO2 quantification as a component of IN for bulk ON determination.► Wet deposition measurement of organic nitrogen (ON) requires chilling of samples upon collection. ► ON loss in NADP AIRMoN daily wet deposition samples is ≈11% as compared to refrigerated collector. ► ON loss in unfiltered NADP NTN weekly wet deposition samples is ≈40%. ► Biases in ON are more consistently negative at higher ambient temperatures.
Keywords: Organic nitrogen; Wet deposition; Nitrogen deposition; NADP; Critical loads;

Chemical characteristics of PM2.5 aerosol in Incheon, Korea by Jong-Kyu Choi; Jong-Bae Heo; Soo-Jin Ban; Seung-Muk Yi; Kyung-Duk Zoh (583-592).
We examined the characteristics, sources, and distribution of PM2.5 and carbonaceous species in particulate samples collected from June 2009 to May 2010 in Incheon, Korea. The average PM2.5 concentration (41.9 ± 9.0 μg m−3) exceeded the annual level set by the United States' National Ambient Air Quality Standards (15 μg m−3). The major fraction of PM2.5 consisted of ionic species (accounting for 38.9 ± 8.8%), such as NO3 , SO4 2−, and NH4 +, as well as organic carbon (OC) (accounting for 18.9 ± 5.1%). We also analyzed the seasonal variation in PM2.5 and secondary aerosols such as NO3 and SO4 2− in PM2.5. While SO4 2− concentrations were higher in spring and summer, the concentration of PM2.5 and NO3 were the highest in winter. SO4 2− concentrations were higher during the spring and summer, but PM2.5 and NO3  were highest during the winter. As an important aerosol indicator, water-soluble organic carbon (WSOC) (mean 4.7 ± 0.8 μg m−3, 58.9 ± 10.7% of total OC) showed a strong relationship with NO3 , SO4 2−, and SOC (R 2 = 0.56, 0.67, and 0.65, respectively), which was indicative of favorable conditions for SOC formation during the sampling period. Among the individual organic aerosols measured, n-alkanes, n-alkanoic acids, levoglucosan, and phthalates were major components, whereas PAHs (polycyclic aromatic hydrocarbons), oxy-PAHs, hopanes, and cholestanes were minor components. The concentration of organic compounds during smoggy periods was higher than during non-event periods. The n-alkane and n-alkanoic acid species during the smoggy periods were 10–14 times higher than during the normal period. Using principal component analysis coupled with multiple linear regression analysis, we identified the primary sources of PM2.5 to be motor vehicle/sea salt, secondary organic aerosols, combustion, biogenic/meat cooking, and soil sources.► We examined the characteristics, sources, distributions of PM2.5 and carbonaceous species in Incheon, Korea. ► The variation and difference of all the measured compounds were compared and evaluated by each season and daily episode. ► Organic compounds in PM2.5 samples were measured using GC × GC–TOFMS. ► We identified the source/contribution of the aerosol components in the site using PCA–MLRA analysis.
Keywords: PM2.5; Primary organic aerosol (POA); Secondary organic aerosol (SOA); Water-soluble organic carbon (WSOC); Principal component analysis (PCA); GC × GC–TOFMS;

Volcanic air pollution, known as vog (volcanic smog) has recently become a major issue in the Hawaiian islands. Vog is caused when volcanic gases react with oxygen and water vapor. It consists of a mixture of gases and aerosols, which include sulfur dioxide and other sulfates. The source of the volcanic gases is the continuing eruption of Mount Kilauea. This paper studies predicting vog using statistical methods. The data sets include time series for SO2 and SO4, over locations spanning the west, south and southeast coasts of Hawaii, and the city of Hilo. The forecasting models include regressions and neural networks, and a frequency domain algorithm. The most typical pattern for the SO2 data is for the frequency domain method to yield the most accurate forecasts over the first few hours, and at the 24 h horizon. The neural net places second. For the SO4 data, the results are less consistent. At two sites, the neural net generally yields the most accurate forecasts, except at the 1 and 24 h horizons, where the frequency domain technique wins narrowly. At one site, the neural net and the frequency domain algorithm yield comparable errors over the first 5 h, after which the neural net dominates. At the remaining site, the frequency domain method is more accurate over the first 4 h, after which the neural net achieves smaller errors. For all the series, the average errors are well within one standard deviation of the actual data at all the horizons. However, the errors also show irregular outliers. In essence, the models capture the central tendency of the data, but are less effective in predicting the extreme events.► This paper studies forecasting volcanic air pollution. ► The techniques include regressions, neural networks, and frequency domain methods. ► The frequency domain method yields the most accurate predictions. ► The neural network places second.
Keywords: Volcanic air pollution; Vog; Sulfates; Forecasting; Time series models; Frequency domain methods;

We assess the mesoscale climatology of dust storm events affecting Salt Lake City, Utah (SLC) since the 1930s, and document the ascendant controls on atmospheric dust generation and transport in the semi-arid Great Basin. Records indicate a seasonal and diurnal pattern, with dust storms typically occurring in spring months during the afternoon. Since 1930, SLC had 379 dust event days (DEDs), averaging 4.7 per year. Air quality station data from populated regions in Utah indicate that dust events produced elevated PM10 exceeding NAAQS on 16 days since 1993, or 0.9 per year. Analysis of DEDs over the period 1948–2010 (n = 331) indicates that approaching mid-level troughs caused 68% of these dust outbreaks and storms. We analyzed two significant DEDs occurring on 19 April 2008 and 4 March 2009, both of which produced elevated particulate matter (PM) levels in the populated region surrounding SLC. Strengthening cyclonic systems are the primary producer of dust outbreaks and storms; the Great Basin Confluence Zone (GBCZ) in the lee of the Sierra Nevada is a known region of cyclogenesis. These cyclonic systems produce strong southwesterly winds in the eastern Great Basin of Utah - termed “hatu winds” – that exceed threshold friction velocities, entrain sediments and loft them into the atmosphere. Plumes identified in MODIS satellite imagery on case study DEDs indicate specific dust source areas, not widespread sediment mobilization. These “hotspots” include playa surfaces at Sevier Dry Lake, Tule Dry Lake, and the Great Salt Lake Desert, as well as Milford Flat, an area burned by Utah's largest wildfire in 2007. The characteristic mountain-valley topography in the Basin & Range physiographic province creates terrain channeling that enhances deflation and funnels dust-bearing winds toward SLC, a growing urban center.► We examined meteorological controls on dust events affecting air quality in Salt Lake City, Utah. ► The cyclonic systems develop in the Great Basin Confluence Zone, leeward of the Sierra Nevada. ► Dust is transported by strong southerly winds and terrain channeling by Basin & Range topography. ► MODIS images depict plumes from source hotspots including playa lakes and fire-disturbed areas.
Keywords: Pre-frontal winds; Dust; PM10; PM2.5; Regional air quality;

A new stepwise regression method was proposed in this study to develop a high-resolution emission inventory. Utilizing PM10 emission inventory as an example, a group of regression models for various industrial and non-industrial sectors were developed based on an emission case study of Handan region in northern China. The main data requirements of the regression models for industrial sectors were coal consumption, electricity consumption, other solid fuel consumption, and annual operating cost of exhaust gas control devices. The data requirements for non-industrial sector emission estimations were the area of construction sites, the length of transportation routes, the vehicle population, and the cultivated land area. The models were then applied to Tangshan region in northern China, and the results revealed that the developed regression models had relatively satisfactory performance. Modeling error at the regional level and county level was 17.0% and 30.4%, respectively. The regression models were also applied to other regions in northern China. The results indicated that the new method could generate emission estimations with significantly lower error than found in previous emission inventory studies. The modeling uncertainty due to the allocation of modeling input parameter value, from regional level to county level, was also discussed in this study. It was concluded that the new statistical method presented is a promising technique for the development and updating of high-resolution emission inventories based on easily obtained statistical data. It can be performed with data available from the current statistical reporting system in China. It does not require a detailed data investigation and survey, as is necessary by conventional “bottom-up” emission inventory investigation approach.► A regression method is proposed to develop a county-level PM10 emission inventory. ► The method does not require a detailed data investigation. ► The results indicated that the new method had relatively satisfactory performance. ► Modeling errors of case study at regional and county levels were 17.0% and 30.4%.
Keywords: County level resolution; PM10 emission inventory; Regression models (RMS); Uncertainty;

An integrated air quality simulation and optimization approach was proposed to improve the accuracy of the high-resolution PM10 emission inventories developed through regression models. A case study of Tangshan region in northern China was presented as an example. A linear programming optimization model was developed to minimize the mean error between simulated and monitored PM10 concentrations in different counties. A transfer coefficient matrix was used to represent source–receptor relationships and was developed through running a MM5-CMAQ air quality model. The results revealed that the proposed simulation–optimization approach could decrease the error of the PM10 emission inventory from 17.0 to 7.9% at the regional level, and from 31.44 to 14.17% at the county level. Accuracy improvement ranged from 0.39 to 61.44% for the study counties in Tangshan. The correlation coefficient between the estimated PM10 emissions and the monitored PM10 concentration in various counties was also increased from 0.82 to 0.91. Together with the regression models, the simulation–optimization method provides a promising and effective framework for developing high-accuracy and high-resolution air pollutant emission inventories.► A simulation and optimization approach was used to improve PM10 emission inventory. ► A transfer coefficient matrix was used to represent source–receptor relationships. ► The emission inventory error was reduced from 17.0 to 7.9% at the regional level. ► The emission inventory error was reduced from 31.44 to 14.17% at the county level. ► The method framework is effective for developing high-accuracy emission inventory.
Keywords: Air pollution; CMAQ model; Emission inventory; Linear programming; Optimization; Transfer coefficient;

Real-time air quality forecasting, part I: History, techniques, and current status by Yang Zhang; Marc Bocquet; Vivien Mallet; Christian Seigneur; Alexander Baklanov (632-655).
Real-time air quality forecasting (RT-AQF), a new discipline of the atmospheric sciences, represents one of the most far-reaching development and practical applications of science and engineering, poses unprecedented scientific, technical, and computational challenges, and generates significant opportunities for science dissemination and community participations. This two-part review provides a comprehensive assessment of the history, current status, major research and outreach challenges, and future directions of RT-AQF, with a focus on the application and improvement of three-dimensional (3-D) deterministic RT-AQF models. In Part I, major milestones in the history of RT-AQF are reviewed. The fundamentals of RT-AQF are introduced. Various RT-AQF techniques with varying degrees of sophistication and skills are described comparatively. Among all techniques, 3-D RT-AQF models with online-coupled meteorology–chemistry and their transitions from mesoscale to unified model systems across scales represent a significant advancement and would greatly enhance understanding of the underlying complex interplay of meteorology, emission, and chemistry from global to urban scales in the real atmosphere. Current major 3-D global and regional RT-AQF models in the world are reviewed in terms of model systems, component models, application scales, model inputs, forecast products, horizontal grid resolutions, and model treatments of chemistry and aerosol processes. An important trend of such models is their coupling with an urban model or a computational fluid dynamic model for urban/local scale applications at 1 km or less and with an exposure model to provide real-time public health assessment and exposure predictions. Evaluation protocols are described along with examinations of current forecasting skills and areas with large biases of major RT-AQF models.► A comprehensive review for real-time air quality forecasting (RT-AQF). ► Major milestones in the history of RT-AQF. ► Assessment of major RT-AQF techniques. ► A detailed review of 3-D RT-AQF models. ► Evaluation protocols and review of current forecasting skills of RT-AQF models.
Keywords: Air quality forecasting; Historic milestone; Techniques and tools; Evaluation methods;

Real-time air quality forecasting, part II: State of the science, current research needs, and future prospects by Yang Zhang; Marc Bocquet; Vivien Mallet; Christian Seigneur; Alexander Baklanov (656-676).
The review of major 3-D global and regional real-time air quality forecasting (RT-AQF) models in Part I identifies several areas of improvement in meteorological forecasts, chemical inputs, and model treatments of atmospheric physical, dynamic, and chemical processes. Part II highlights several recent scientific advances in some of these areas that can be incorporated into RT-AQF models to address model deficiencies and improve forecast accuracies. Current major numerical, statistical, and computational techniques to improve forecasting skills are assessed. These include bias adjustment techniques to correct biases in forecast products, chemical data assimilation techniques for improving chemical initial and boundary conditions as well as emissions, and ensemble forecasting approaches to quantify the uncertainties of the forecasts. Several case applications of current 3-D RT-AQF models with the state-of-the-science model treatments, a detailed urban process module, and an advanced combined ensemble/data assimilation technique are presented to illustrate current model skills and capabilities. Major technical challenges and research priorities are provided. A new generation of comprehensive RT-AQF model systems, to emerge in the coming decades, will be based on state-of-the-science 3-D RT-AQF models, supplemented with efficient data assimilation techniques and sophisticated statistical models, and supported with modern numerical/computational technologies and a suite of real-time observational data from all platforms.► A comprehensive review for real-time air quality forecasting (RT-AQF). ► Recent scientific advances of RT-AQF for potential model improvements. ► Review of major numerical & computational techniques to improve AQF skills. ► Detailed review of chemical data assimilation and ensemble forecasting techniques. ► Recommendations on major technical challenges and research priorities.
Keywords: Air quality forecasting; Scientific improvement; Chemical data assimilation; Ensemble forecasting;

‘Corrigendum to “A literature review of concentrations and size distributions of ambient airborne Pb-containing particulate matter” [Atmos. Environ. 45 (28) (2011) 5005–5015]’ by Seung-Hyun Cho; Jennifer Richmond-Bryant; Jonathan Thornburg; Jeff Portzer; Robert Vanderpool; Kevin Cavender; Joann Rice (680-681).