Atmospheric Environment (v.124, #PB)

Preface by Hong Liao; Xiaoye Zhang; Maosheng Yao; Yuxuan Wang (95-97).

Particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) is the main air pollutant in Beijing. To have a comprehensive understanding of concentrations, compositions and sources of PM2.5 in Beijing, recent studies reporting ground-based observations and source apportionment results dated from 2000 to 2012 in this typical large city of China are reviewed. Statistical methods were also used to better enable data comparison. During the last decade, annual average concentrations of PM2.5 have decreased and seasonal mean concentrations declined through autumn and winter. Generally, winter is the most polluted season and summer is the least polluted one. Seasonal variance of PM2.5 levels decreased. For diurnal variance, PM2.5 generally increases at night and decreases during the day. On average, organic matters, sulfate, nitrate and ammonium are the major compositions of PM2.5 in Beijing. Fractions of organic matters increased from 2000 to 2004, and decreased afterwards. Fractions of sulfate, nitrate and ammonium decreased in winter and remained largely unchanged in summer. Concentrations of organic carbon and elemental carbon were always higher in winter than in summer and they barely changed during the last decade. Concentrations of sulfate, nitrate and ammonium exhibited significant increasing trend in summer but in reverse in winter. On average they were higher in winter than in summer before 2005, and took a reverse after 2005. Receptor model results show that vehicle, dust, industry, biomass burning, coal combustion and secondary products were major sources and they all increased except coal combustions and secondary products. The growth was decided both changing social and economic activities in Beijing, and most likely growing emissions in neighboring Hebei province. Explicit descriptions of the spatial variations of PM2.5 concentration, better methods to estimate secondary products and ensemble source apportionments models to reduce uncertainties would remain being open questions for future studies.
Keywords: PM2.5; Beijing; Carbonaceous materials; Inorganic ions; Source apportionments;

Seasonal dynamics of coarse atmospheric particulate matter between 2.5 μm and 80 μm in Beijing and the impact of 2008 Olympic Games by Stefan Norra; Yang Yu; Volker Dietze; Nina Schleicher; Mathieu Fricker; Uwe Kaminski; Yuan Chen; Doris Stüben; Kuang Cen (109-118).
Beijing is well known as a megacity facing severe atmospheric pollution problems. One very important kind of pollution is the high amount of particles in Beijing's atmosphere. Numerous studies investigated the dynamics of fine particles smaller 10 μm. Less information is available on the coarse particle fraction larger 10 μm, although geogenic dusts, which often are composed by those coarser particles, frequently affect the air quality in Beijing. Therefore, systematic sampling and analysis of size fractionated particulate matter between 2.5 and 80 μm was performed in Beijing from April 2005 till October 2009. Atmospheric particles were collected in the North-West of Beijing using a cost-effective passive sampling method called Sigma-2. Altogether, 200 weeks could be analysed and assessed. Concentrations and size distribution of atmospheric coarse particles were determined by automated microscopic single particle analysis. Seasonal variability of the total mass of different size fractions was identified as follows: spring > winter > autumn > summer. High concentrations of transparent mineral particles indicate the activity of geogenic sources in spring and winter time, due to asian dust events and resuspension of soil from local bare land during dry and windy periods. The percentage of opaque particle components differs seasonally with relatively high values in winter, confirming combustion of fossil fuels for heating purposes as a predominant pollution source in this season. The influence of meteorological conditions on concentrations and size distribution of atmospheric particulate matter between 2.5 and 80 μm is demonstrated for the whole sampling period. Lowest pollution by coarse aerosols occurred during the period of the 2008 Olympic Summer Games. A general trend of decreasing total coarse particle mass concentrations was observed. Due to frequently observed high total coarse particle mass concentrations of several 100 μg·m³ it is strongly recommended to enhance research and observation regarding these air pollutants to gain a better understanding of their dynamics, health effects, well being impacts on Beijing inhabitants and the effectiveness of mitigation measures.
Keywords: Beijing; Coarse atmospheric particles; Passive sampling; Asian dust; Microscopic particle analysis; Olympic Games;

Impact of synoptic weather patterns and inter-decadal climate variability on air quality in the North China Plain during 1980–2013 by Yang Zhang; Aijun Ding; Huiting Mao; Wei Nie; Derong Zhou; Lixia Liu; Xin Huang; Congbin Fu (119-128).
Potential relationships between air quality, synoptic weather patterns, and the East Asian Monsoon (EAM) over the North China Plain (NCP) were examined during the time period of 1980–2013 using a weather typing technique and ground-based air pollution index (API) data from three cities: Beijing, Tianjin and Shijiazhuang. Using the Kirchhofer method, circulation patterns during the 34-yr study period were classified into 5 categories, which were further used to understand the quantitative relationship between weather and air quality in NCP. The highest API values were associated with a stagnant weather condition when wide-spread stable conditions controlled most part of NCP, while westerly and southerly wind flowed over the northern and eastern part of this region, resulting in both the regional transport and local build-up of air pollutants. Under the continuous control of this weather pattern, API values were found to increase at a rate of 8.5 per day on average. Based on the qualitative and quantitative analysis, a significant correlation was found between the strength of EAM and inter-annual variability of frequencies of the weather patterns. The strengthening of summer/winter monsoon could increase the frequency of occurrence of cyclone/anticyclone related weather patterns. Time series of climate-induced variability in API over the 34 years were reconstructed based on the quantitative relationship between API and predominant weather patterns during 2001–2010. Significant connections between EAM and reconstructed API were found on both the inter-annual and inter-decadal scales. In winter and summer, strengthening/weakening of EAM, which was generally associated with the change of the representative circulation patterns, could improve/worsen air quality in this region.
Keywords: Air quality; North China Plain; Weather typing; East Asia Monsoon; Climate change;

Air quality is significantly influenced by the synoptic, regional and local meteorological conditions. This study aims at elucidating the relation between synoptic flow patterns and low visibility events of haze and fog over the North China Plain (NCP), and the contribution of synoptic flow patterns and boundary layer structure to the severe haze events over the NCP in January 2013. Nine synoptic flow types are statistically identified over the Northern China for autumn and winter of 2004–2014. The flow types with high pressure to the northeast of the NCP (NEH, type 8), weak low pressure band (L-, type 5), high pressure to the southeast (SHE, type 4), and high pressure to the north (NH, type 6) are associated with high occurrence frequencies of low visibility events (48.3%, 42.0%, 37.2%, and 36.7%). The meteorological conditions of these flow patterns reveal synergistic contribution of weak wind and high relative humidity (RH) to low visibility. Quantitative measures for dispersion conditions (recirculation, ventilation, and stagnation) suggest undesirable ventilation and frequent stagnation of the flow types 9 (EH, high pressure to the east), 4, 5, and 8. In January 2013 three regional haze episodes are identified from the distribution of visibility over the NCP, i.e., 10–16 January (EP 1), 22–24 January (EP 2), and 28 January–1 February (EP 3), which were largely associated with the flow types 5, 8, 4, and 9. Coverage of the hazy area exhibited northward expansion in the EP 2 and EP 3 when the RH increased. The abnormally high RH could be attributed to the flow type 6 (NH), which has the highest frequency of precipitation (13.7%) and RH among the nine flow types, and occurred more frequently in that month than in January 2004–2014. The simulation results indicate the evolution of the planetary boundary layer and southerly advection, which was responsible for the high RH and persistent temperature inversion that contributed to the long-lasting haze events.
Keywords: Synoptic flow pattern; Stagnation; Planetary boundary layer; Air pollution; Low visibility;

On-road emission characteristics of VOCs from light-duty gasoline vehicles in Beijing, China by Xinyue Cao; Zhiliang Yao; Xianbao Shen; Yu Ye; Xi Jiang (146-155).
This study is the third in a series of three papers aimed at characterizing the VOC emissions of vehicles in Beijing. In this study, 30 light-duty vehicles fueled with gasoline were evaluated using a portable emission measurement system (PEMS) as they were driven on a predesigned, fixed test route. All of the tested vehicles were rented from private vehicle owners and spanned regulatory compliance guidelines ranging from Pre-China I to China IV. Alkanes, alkenes, aromatics and some additional species in the exhaust were collected in Tedlar bags and analyzed using gas chromatography/mass spectrometry (GC–MS). Carbonyls were collected on 2,4-dinitrophenyhydrazine (DNPH) cartridges and analyzed using high-performance liquid chromatography (HPLC). Overall, 74 VOC species were detected from the tested vehicles, including 22 alkanes, 6 alkenes, 1 alkyne, 16 aromatics, 3 cyclanes, 10 halohydrocarbons, 12 carbonyls and 4 other compounds. Alkanes, aromatics and carbonyls were the dominant VOCs with weight percentages of approximately 36.4%, 33.1% and 17.4%, respectively. The average VOC emission factors and standard deviations of the Pre-China I, China I, China II, China III and China IV vehicles were 469.3 ± 200.1, 80.7 ± 46.1, 56.8 ± 37.4, 25.6 ± 11.7 and 14.9 ± 8.2 mg/km, respectively, which indicated that the VOC emissions significantly decreased under stricter vehicular emission standards. Driving cycles also influenced the VOC emissions from the tested vehicles. The average VOC emission factors based on the travel distances of the tested vehicles under urban driving cycles were greater than those under highway driving cycles. In addition, we calculated the ozone formation potential (OFP) using the maximum incremental reactivity (MIR) method. The results of this study will be helpful for understanding the true emission levels of light-duty gasoline vehicles and will provide information for controlling VOC emissions from vehicles in Beijing, China.
Keywords: VOCs; Light-duty gasoline vehicle; Emission factor; Emission characteristics; PEMS;

Characteristics of ambient volatile organic compounds and the influence of biomass burning at a rural site in Northern China during summer 2013 by Yanhong Zhu; Lingxiao Yang; Jianmin Chen; Xinfeng Wang; Likun Xue; Xiao Sui; Liang Wen; Caihong Xu; Lan Yao; Junmei Zhang; Min Shao; Sihua Lu; Wenxing Wang (156-165).
Volatile organic compounds (VOCs) were measured at a rural site in the North China Plain during summer 2013, which focused on VOCs characteristics and impact of biomass burning. Alkanes and halocarbons made the largest contribution to the sum of the mixing ratio of each VOC compound (total VOCs). Most VOC species mixing ratios had similar day-to-day variability, indicating that the air mass at the sampling site had small local perturbation. Accumulation of pollutants due to biomass burning and advection of plumes from urbanized areas upwind had important impact on diurnal variation patterns of the VOC group. Ethylbenzene/m,p-xylene ratio and its relationship with O3 indicated that sampling site received an aged air parcel. The aromatics and alkenes were the dominant contributors to total ozone formation potential (OFP). The top 5 VOC species based on OFP were toluene, isoprene, ethene, propene and n-Hexane. During the biomass burning period, VOCs had higher OFP values, especially the aromatics and alkynes. The backward trajectories indicated that extensive transport of biomass burning from the Shandong and Hebei provinces had an important effect on VOCs pollution levels.
Keywords: VOCs; Biomass burning; Pollution characteristics; Ozone formation potential; Long-range transport;

Anthropogenic and biogenic organic compounds in summertime fine aerosols (PM2.5) in Beijing, China by Fan Yang; Kimitaka Kawamura; Jing Chen; Kinfai Ho; Shuncheng Lee; Yuan Gao; Long Cui; Tieguan Wang; Pingqing Fu (166-175).
Ambient fine aerosol samples (PM2.5) were collected at an urban site (PKU) in Beijing and its upwind suburban site (Yufa) during the CAREBEIJING-2007 field campaign. Organic molecular compositions of the PM2.5 samples were studied for seven organic compound classes (sugars, lignin/resin acids, hydroxy-/polyacids, aromatic acids, biogenic SOA tracers, fatty acids and phthalates) using capillary GC/MS to better understand the characteristics and sources of organic aerosol pollution in Beijing. More than 60 individual organic species were detected in PM2.5 and were grouped into different compound classes based on their functional groups. Concentrations of total quantified organics at Yufa (469–1410 ng m−3, average 1050 ng m−3) were slightly higher than those at PKU (523–1390 ng m−3, 900 ng m−3). At both sites, phthalates were found as the most abundant compound class. Using a tracer-based method, the contributions of the biogenic secondary organic carbon (SOC) to organic carbon (OC) were 3.1% at PKU and 5.5% at Yufa, among which isoprene-SOC was the dominant contributor. In addition, most of the measured organic compounds were higher at Yufa than those at PKU, indicating a more serious pollution in its upwind region than in urban Beijing.
Keywords: Secondary organic aerosol; Biomass burning; Levoglucosan; 2-Methyltetrols; Phthalates;

Local and distant source contributions to secondary organic aerosol in the Beijing urban area in summer by Jian Lin; Junling An; Yu Qu; Yong Chen; Ying Li; Yujia Tang; Feng Wang; Weiling Xiang (176-185).
Quantification of local and distant source contributions to particulate matter is a key issue to improving air quality in large urban areas, but few studies have focused on secondary organic aerosol (SOA) source contributions in a large area, especially in China. In this study, we extended the Comprehensive Air Quality Model with Extensions (CAMX) version 5.4, replacing the two-product approach by the volatility basis-set (VBS) approach, with updated SOA yields based on smog chamber studies. The modules related to the computationally efficient particulate source apportionment technology (PSAT) used in CAMX v5.4 were extended based on the volatility basis set (VBS) approach. The updated version of the CAMX model was then used to calculate the local and distant source contributions to SOA in Beijing for the first time. The results indicated that the VBS approach substantially improved hourly, daily, and monthly SOA simulations, compared with the two-product approach and the observations. In August 2007, the local source contributions to anthropogenic and biogenic SOA in Beijing were 23.8% and 16.6%, respectively; distant sources dominated for both anthropogenic and biogenic SOA in Beijing: Northern Hebei, Middle Hebei, Northeast China, Inner Mongolia, Shandong, and Tianjin (including Xianghe) contributed 5.1%–18.2% to anthropogenic SOA in Beijing; whereas, Inner Mongolia, Northern Hebei, and Northeast China contributed 12.2%, 18.6%, and 10.1%, respectively, to biogenic SOA in Beijing. Additionally, other areas outside China respectively contributed 5.3% and 10.8% to anthropogenic and biogenic SOA in Beijing: this could be related to strong summer monsoon.
Keywords: SOA; Volatility basis set approach; Particulate source apportionment technology; CAMX;

A volatility basis set approach with chemical aging mechanism has been incorporated into a regional air quality model system (RAQMS) and used to investigate the distribution of organic aerosols (OA) over east China in April 2009, with focus on secondary organic aerosols (SOA) in fine particle and relative contributions from a series of anthropogenic and biogenic VOC precursors. The comparison between the VBS approach prediction and observation at four sites in east China demonstrates a significant improvement in SOA and OA concentrations compared with the traditional two-product model, which predicts very low SOA level. The average value of secondary organic carbon (SOC) for all sites predicted by the VBS approach with chemical aging is 2.8 μgC m−3, quite close to the estimated value of 3.3 μgC m−3. The SOC fraction of organic carbon (OC) also increases from just 5% predicted by the two-product model to 33% by the VBS approach with aging, close to the estimated fraction of 32%, suggesting a more realistic and precise representation of SOA formation by the VBS approach. The enhanced SOC prediction further improve OC prediction, reducing the normalized mean bias from −43% to −18%. The VBS approach with aging predicts SOA concentration in PM2.5 of 5–10 μg m−3 over most parts of east China. The predicted ASOA concentrations vary from 5.0 to 7.5 μg m−3 in the Pearl River Delta, the Yangtze River Delta and the wide areas north of the Yangtze River. BSOA is predicted to be 1.0–2.5 μg m−3 across the regions from southeast China to the middle reaches of the Yangtze River and the Yellow River. Prediction with the VBS approach exhibits that ASOA becomes dominant component of SOA, which is more realistic as compared to the BSOA dominance by the two-product model. The domain-average surface POA and SOA concentrations predicted by the VBS approach with aging over east China are 4.86 μg m−3 and 4.45 μg m−3, with the SOA fraction of total OA and the ASOA fraction of SOA being 48% and 85%, respectively. This indicates the comparable contributions to OA from SOA and POA, and the predominant contribution of ASOA to SOA over east China in springtime. The mean SOA concentrations over east China produced from aromatics, alkanes, alkenes, isoprene, monoterpene and sesquiterpene are predicted to be 2.44, 0.57, 0.8, 0.17, 0.42 and 0.06 μg m−3, respectively, which contribute 55%, 13%, 18%, 4%, 9% and 1% of the total SOA. Aromatics are the dominant contributors to SOA formation.
Keywords: Secondary organic aerosol; Volatility basis-set; Chemical aging; Air quality model; East China;

Comparison of atmospheric nitrous acid during severe haze and clean periods in Beijing, China by Siqi Hou; Shengrui Tong; Maofa Ge; Junling An (199-206).
Continuous measurements were made in Beijing from 22 February to 2 March in 2014, including a severe haze period and a relatively clean period. The concentration of nitrous acid (HONO) ranged from 0.49 to 3.24 ppbv in the severe haze period and from 0.28 to 1.52 ppbv in the clean period. Daytime mean concentrations of SO2, NO, NO2, and NOx in the severe haze period were 58.7 ppbv, 23.2 ppbv, 48.0 ppbv, 71.2 ppbv, respectively, much higher than those in the clean period. The diurnal variations of HONO, NO, NO2, and NOx were weaker in the severe haze period, whereas O3 diurnal variations were opposite with other species in both periods. Moreover, we found better correlations between HONO and NO2 in the clean period than in the severe haze period. Besides, good correlations between HONO and PM2.5, and between PM2.5 and HONO/NO2 ratio were found when PM2.5 concentrations were <350 μg m−3. When PM2.5 concentrations were >350 μg m−3, HONO remained nearly invariable, with a value of 2.95 ppbv. Additionally, very good correlations between HONO and RH (R2 = 0.839), and between HONO/NO2 ratio and RH (R2 = 0.508) were found when RH was ≤65%. The calculated daytime average unknown HONO source rate was 1.85 ppbv h−1 in the severe haze period, higher than 1.26 ppbv h−1 in the clean period.
Keywords: Nitrous acid; Nitrogen oxides; PM2.5; Haze;

Carbonyl compounds over urban Beijing: Concentrations on haze and non-haze days and effects on radical chemistry by Zhihan Rao; Zhongming Chen; Hao Liang; Liubin Huang; Dao Huang (207-216).
Carbonyl compounds play an important role in the formation of secondary aerosols and the cycling of free radicals in the atmosphere. We measured carbonyl compounds over urban Beijing, a megacity in the North China Plain, in summer and winter to investigate the relation of carbonyl compounds with haze and the interaction between carbonyl compounds and atmospheric radical cycling. We also determined carbonyl compounds in summer rainwater. Data of carbonyl compounds were analyzed in four cases, i.e., summer haze days (SHD), summer non-haze days (SND), winter haze days (WHD), and winter non-haze days (WND). Interestingly, the level of carbonyl compounds during WHD approached that of summer days. The results of the principal component analysis showed that there was no obvious source difference between SHD and SND. On WHD, however, more carbonyl compounds originated from the “diesel engine exhaust emission” than those on WND. We evaluated the effect of carbonyl compounds on the free radical cycling and the NO consumption potential for OH formation in the photochemical reactions using a novel ratio method. It was found that the production rate of ROx (the sum of OH, HO2 and RO2 radicals) was highest on SND, while the yield of ROx radicals from the reactions of carbonyl compounds was highest on WHD. Further, carbonyl compounds consumed more NO to produce OH radicals on WHD compared to the other three cases.
Keywords: Carbonyl compound; Haze; Source; Radical cycling;

Effect of ambient humidity on the light absorption amplification of black carbon in Beijing during January 2013 by Yunfei Wu; Renjian Zhang; Ping Tian; Jun Tao; S.-C. Hsu; Peng Yan; Qiyuan Wang; Junji Cao; Xiaoling Zhang; Xiangao Xia (217-223).
Black carbon (BC) and its mixing state were measured with a ground-based single particle soot photometer in urban Beijing during the extremely polluted winter of 2013. Up to 70 ± 14% of the BC-containing particles were thickly-coated during periods of haze, compared to 37 ± 9% on non-hazy days. The thickly-coated number fraction (NFBC-thick) increased with increasing BC, reaching a plateau at ∼80–90% when BC concentrations were ≥15 μg m−3 and visibility was ≤2 km. Regional inflows brought more aged, highly thickly-coated BC to Beijing during haze. The absorption coefficient showed a distinct linear correlation with BC concentration; the mass absorption efficiency (MAE) of BC was acquired, with an overall mean of 4.2 ± 0.01 m2 g−1 at 870 nm. The MAE of BC amplified with increasing ambient relative humidity. This was largely explained by the increase in NFBC-thick, which was likely due to the enhanced production of secondary aerosol under humid conditions.
Keywords: Haze; Black carbon; Light absorption; Ambient humidity;

Approximately 30%–40% of industrial practices and 50% of vehicles in operation were limited in Beijing and its surroundings regions during the Beijing Asia–Pacific Economic Cooperation (APEC) conference in 2014. Compared with values obtained prior to the APEC conference, the atmospheric concentration of submicron aerosol particles (PM1) decreased from 101 to 36.9 μg m−3, or 63%. Of all the inorganic species and black carbon present, the concentrations of nitrate to the total concentration of PM1 decreased the most in terms of both mass concentration, from 25.5 to 7.1 μg m−3, and relative contribution, from 21% to 14%. In addition, both sulfate and ammonium decreased substantially by 9.5 and 8.5 μg m−3, respectively. Accordingly, the relative contributions of ammonium nitrate and ammonium sulfate to light extinction decreased by 10% and 5%, respectively, as a result of the pollution control measures implemented during that period. In addition, polycyclic aromatic hydrocarbons in vehicle emissions were reduced significantly.
Keywords: Submicron aerosol; Asia–Pacific Economic Cooperation; Light extinction; Polycyclic aromatic hydrocarbons;

Numerous previous studies have revealed that statistical models which combine satellite-derived aerosol optical depth (AOD) and PM2.5 measurements acquired at scattered monitoring sites provide an effective method for deriving continuous spatial distributions of ground-level PM2.5 concentrations. Using the national monitoring networks that have recently been established by central and local governments in China, we developed linear mixed-effects (LMEs) models that integrate Moderate Resolution Imaging Spectroradiometer (MODIS) AOD measurements, meteorological parameters, and satellite-derived tropospheric NO2 column density measurements as predictors to estimate PM2.5 concentrations over three major industrialized regions in China, namely, the Beijing–Tianjin–Hebei region (BTH), the Yangtze River Delta region (YRD), and the Pearl River Delta region (PRD). The models developed for these three regions exploited different predictors to account for their varying topographies and meteorological conditions. Considering the importance of unbiased PM2.5 predictions for epidemiological studies, the correction factors calculated from the surface PM2.5 measurements were applied to correct biases in the predicted annual average PM2.5 concentrations introduced by non-stochastic missing AOD measurements. Leave-one-out cross-validation (LOOCV) was used to quantify the accuracy of our models. Cross-validation of the daily predictions yielded R2 values of 0.77, 0.8 and 0.8 and normalized mean error (NME) values of 22.4%, 17.8% and 15.2% for BTH, YRD and PRD, respectively. For the annual average PM2.5 concentrations, the LOOCV R2 values were 0.85, 0.76 and 0.71 for the three regions, respectively, whereas the LOOCV NME values were 8.0%, 6.9% and 8.4%, respectively. We found that the incorporation of satellite-based NO2 column density into the LMEs model contribute to considerable improvements in annual prediction accuracy for both BTH and YRD. The satisfactory performance of our models indicates that constructing LMEs models using various combinations of predictors for different regions would be helpful for predicting PM2.5 concentrations with high accuracy.
Keywords: Ground-level PM2.5 concentrations; Aerosol optical depth; MODIS; Linear mixed-effects model; Satellite-based NO2 column density;

Ground-based remote sensing of aerosol climatology in China: Aerosol optical properties, direct radiative effect and its parameterization by X. Xia; H. Che; J. Zhu; H. Chen; Z. Cong; X. Deng; X. Fan; Y. Fu; P. Goloub; H. Jiang; Q. Liu; B. Mai; P. Wang; Y. Wu; J. Zhang; R. Zhang; X. Zhang (243-251).
Spatio-temporal variation of aerosol optical properties and aerosol direct radiative effects (ADRE) are studied based on high quality aerosol data at 21 sunphotometer stations with at least 4-months worth of measurements in China mainland and Hong Kong. A parameterization is proposed to describe the relationship of ADREs to aerosol optical depth at 550 nm (AOD) and single scattering albedo at 550 nm (SSA). In the middle-east and south China, the maximum AOD is always observed in the burning season, indicating a significant contribution of biomass burning to AOD. Dust aerosols contribute to AOD significantly in spring and their influence decreases from the source regions to the downwind regions. The occurrence frequencies of background level AOD (AOD < 0.10) in the middle-east, south and northwest China are very limited (0.4%, 1.3% and 2.8%, respectively). However, it is 15.7% in north China. Atmosphere is pristine in the Tibetan Plateau where 92.0% of AODs are <0.10. Regional mean SSAs at 550 nm are 0.89–0.90, although SSAs show substantial site and season dependence. ADREs at the top and bottom of the atmosphere for solar zenith angle of 60 ± 5° are −16–−37 W m−2 and –66–−111 W m−2, respectively. ADRE efficiency shows slight regional dependence. AOD and SSA together account for more than 94 and 87% of ADRE variability at the bottom and top of the atmosphere. The overall picture of ADRE in China is that aerosols cool the climate system, reduce surface solar radiation and heat the atmosphere.
Keywords: Aerosol; Optical properties; Aerosol direct radiative effect;

Heavy aerosol loading over the Bohai Bay as revealed by ground and satellite remote sensing by Jinqiang Zhang; Jing Chen; Xiangao Xia; Huizheng Che; Xuehua Fan; Yiyang Xie; Zhiwei Han; Hongbin Chen; Daren Lu (252-261).
Heavy aerosol loading over the Bohai Bay, the innermost gulf of the Yellow Sea, was often recorded by the satellite observations. In order to understand aerosol optical properties and potential causes for the high aerosol loading there, a Cimel sunphotometer station (BH) was established on an offshore platform over the Bay for the first time in June 2012. The aerosol optical properties between July 2012 and July 2013 were employed to validate the satellite retrievals and to characterize temporal variability of aerosol optical properties. In particular, aerosol optical properties at BH were compared with those at Beijing (BJ), an urban station of the North China Plain (NCP), to discuss their potential difference during the same months of the same years. Mean aerosol optical depth at 550 nm (AOD) retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) measurements over the Bohai Bay was 0.79 ± 0.68 during 2004–2013, that even exceeded value over the NCP (0.50 ± 0.57). This fact was supported by the comparison of ground-based remote sensing AODs at BH and BJ. The annual mean Cimel AOD at BH was 0.76 ± 0.62, which was larger than that at BJ (0.64 ± 0.52). The MODIS AOD difference between the Bohai Bay and the NCP was 0.29, being more than two times larger than the Cimel AOD difference between BH and BJ (0.12). This strongly implied that the MODIS retrievals had significant biases over the Bohai Bay that was likely due to sediment in the water and also sea ice in winter. A distinct seasonal variation of AOD was revealed over ocean. The maxima Cimel AOD was observed in summer (1.02 ± 0.75), which was followed by spring (0.86 ± 0.61), autumn (0.54 ± 0.41), and winter (0.39 ± 0.24); this was in good agreement with that over the NCP. High AOD over the Bohai Bay was associated with the heavy exhaust emissions from the ships across the Bay and transport of aerosols from the NCP. Furthermore, a much strong hygroscopic growth of fine mode aerosols over the Sea as a result of humid environment also should contributed to high AOD. This was supported by the observation that the effective radius and fraction of fine mode increased with AOD at the Bay, more importantly, the increasing rate was always larger than that at the NCP. The knowledge of the detailed variations of aerosol optical properties over the polluted ocean region would help to improve satellite aerosol retrieval and to promote our understanding on regional climate change research.
Keywords: Aerosol optical properties; Bohai Bay; North China Plain;

Incorporation of new particle formation and early growth treatments into WRF/Chem: Model improvement, evaluation, and impacts of anthropogenic aerosols over East Asia by Changjie Cai; Xin Zhang; Kai Wang; Yang Zhang; Litao Wang; Qiang Zhang; Fengkui Duan; Kebin He; Shao-Cai Yu (262-284).
New particle formation (NPF) provides an important source of aerosol particles and cloud condensation nuclei, which may result in enhanced cloud droplet number concentration (CDNC) and cloud shortwave albedo. In this work, several nucleation parameterizations and one particle early growth parameterization are implemented into the online-coupled Weather Research and Forecasting model coupled with chemistry (WRF/Chem) to improve the model's capability in simulating NPF and early growth of ultrafine particles over East Asia. The default 8-bin over the size range of 39 nm–10 μm used in the Model for Simulating Aerosol Interactions and Chemistry aerosol module is expanded to the 12-bin over 1 nm–10 μm to explicitly track the formation and evolution of new particles. Although model biases remain in simulating H2SO4, condensation sink, growth rate, and formation rate, the evaluation of July 2008 simulation identifies a combination of three nucleation parameterizations (i.e., COMB) that can best represent the atmospheric nucleation processes in terms of both surface nucleation events and the resulting vertical distribution of ultrafine particle concentrations. COMB consists of a power law of Wang et al. (2011) based on activation theory for urban areas in planetary boundary layer (PBL), a power law of Boy et al. (2008) based on activation theory for non-urban areas in PBL, and the ion-mediated nucleation parameterization of YU10 for above PBL. The application and evaluation of the improved model with 12-bin and the COMB nucleation parameterization in East Asia during January, April, July, and October in 2001 show that the model has an overall reasonably good skill in reproducing most observed meteorological variables and surface and column chemical concentrations. Relatively large biases in simulated precipitation and wind speeds are due to inaccurate surface roughness and limitations in model treatments of cloud formation and aerosol-cloud-precipitation interactions. Large biases in the simulated surface concentrations of PM10, NOx, CO, SO2, and VOCs at some sites are due in part to possible underestimations of emissions and in part to inaccurate meteorological predictions. The simulations of 2001 show that anthropogenic aerosols can increase aerosol optical depth by 64.0–228.3%, CDNC by 40.2–76.4%, and cloud optical thickness by 14.3–25.3%; they can reduce surface net shortwave radiation by up to 42.5–52.8 W m−2, 2-m temperature by up to 0.34–0.83 °C, and PBL height by up to 76.8–125.9 m. Such effects are more significant than those previously reported for the U.S. and Europe.
Keywords: New particle formation; Particle early growth; WRF/Chem; Aerosol direct effects; Aerosol indirect effects; East Asia;

Application of WRF/Chem over East Asia: Part I. Model evaluation and intercomparison with MM5/CMAQ by Yang Zhang; Xin Zhang; Litao Wang; Qiang Zhang; Fengkui Duan; Kebin He (285-300).
In this work, the application of the online-coupled Weather Research and Forecasting model with chemistry (WRF/Chem) version 3.3.1 is evaluated over East Asia for January, April, July, and October 2005 and compared with results from a previous application of an offline model system, i.e., the Mesoscale Model and Community Multiple Air Quality modeling system (MM5/CMAQ). The evaluation of WRF/Chem is performed using multiple observational datasets from satellites and surface networks in mainland China, Hong Kong, Taiwan, and Japan. WRF/Chem simulates well specific humidity (Q2) and downward longwave and shortwave radiation (GLW and GSW) with normalized mean biases (NMBs) within 24%, but shows moderate to large biases for temperature at 2-m (T2) (NMBs of −9.8% to 75.6%) and precipitation (NMBs of 11.4–92.7%) for some months, and wind speed at 10-m (WS10) (NMBs of 66.5–101%), for all months, indicating some limitations in the YSU planetary boundary layer scheme, the Purdue Lin cloud microphysics, and the Grell–Devenyi ensemble scheme. WRF/Chem can simulate the column abundances of gases reasonably well with NMBs within 30% for most months but moderately to significantly underpredicts the surface concentrations of major species at all sites in nearly all months with NMBs of −72% to −53.8% for CO, −99.4% to −61.7% for NOx, −84.2% to −44.5% for SO2, −63.9% to −25.2% for PM2.5, and −68.9% to 33.3% for PM10, and aerosol optical depth in all months except for October with NMBs of −38.7% to −16.2%. The model significantly overpredicts surface concentrations of O3 at most sites in nearly all months with NMBs of up to 160.3% and NO 3 - at the Tsinghua site in all months. Possible reasons for large underpredictions include underestimations in the anthropogenic emissions of CO, SO2, and primary aerosol, inappropriate vertical distributions of emissions of SO2 and NO2, uncertainties in upper boundary conditions (e.g., for O3 and CO), missing or inaccurate model representations (e.g., secondary organic aerosol formation, gas/particle partitioning, dust emissions, dry and wet deposition), and inaccurate meteorological fields (e.g., overpredictions in WS10 and precipitation, but underpredictions in T2), as well as the large uncertainties in satellite retrievals (e.g., for column SO2). Comparing to MM5, WRF generally gives worse performance in meteorological predictions, in particular, T2, WS10, GSW, GLW, and cloud fraction in all months, as well as Q2 and precipitation in January and October, due to limitations in the above physics schemes or parameterizations. Comparing to CMAQ, WRF/Chem performs better for surface CO, O3, and PM10 concentrations at most sites in most months, column CO and SO2 abundances, and AOD. It, however, gives poorer performance for surface NOx concentrations at most sites in most months, surface SO2 concentrations at all sites in all months, and column NO2 abundances in January and April. WRF/Chem also gives lower concentrations of most secondary PM and black carbon. Those differences in results are attributed to differences in simulated meteorology, gas-phase chemistry, aerosol thermodynamic and dynamic treatments, dust and sea salt emissions, and wet and dry deposition treatments in both models.
Keywords: WRF/Chem; MM5/CMAQ; East Asia; Model evaluation; Model intercomparison;

Application of WRF/Chem over East Asia: Part II. Model improvement and sensitivity simulations by Yang Zhang; Xin Zhang; Kai Wang; Qiang Zhang; Fengkui Duan; Kebin He (301-320).
To address the problems and limitations identified through a comprehensive evaluation in Part I paper, several modifications are made in model inputs, treatments, and configurations and sensitivity simulations with improved model inputs and treatments are performed in this Part II paper. The use of reinitialization of meteorological variables reduces the biases and increases the spatial correlations in simulated temperature at 2-m (T2), specific humidity at 2-m (Q2), wind speed at 10-m (WS10), and precipitation (Precip). The use of a revised surface drag parameterization further reduces the biases in simulated WS10. The adjustment of only the magnitudes of anthropogenic emissions in the surface layer does not help improve overall model performance, whereas the adjustment of both the magnitudes and vertical distributions of anthropogenic emissions shows moderate to large improvement in simulated surface concentrations and column mass abundances of species in terms of domain mean performance statistics, hourly and monthly mean concentrations, and vertical profiles of concentrations at individual sites. The revised and more advanced dust emission schemes can help improve PM predictions. Using revised upper boundary conditions for O3 significantly improves the column O3 abundances. Using a simple SOA formation module further improves the predictions of organic carbon and PM2.5. The sensitivity simulation that combines all above model improvements greatly improves the overall model performance. For example, the sensitivity simulation gives the normalized mean biases (NMBs) of −6.1% to 23.8% for T2, 2.7–13.8% for Q2, 22.5–47.6% for WS10, and −9.1% to 15.6% for Precip, comparing to −9.8% to 75.6% for T2, 0.4–23.4% for Q2, 66.5–101.0% for WS10, and 11.4%–92.7% for Precip from the original simulation without those improvements. It also gives the NMBs for surface predictions of −68.2% to −3.7% for SO2, −73.8% to −20.6% for NO2, −8.8%–128.7% for O3, −61.4% to −26.5% for PM2.5, and −64.0% to 7.2% for PM10, comparing to −84.2% to −44.5% for SO2, −88.1% to −44.0% for NO2, −11.0%–160.3% for O3, −63.9% to −25.2% for PM2.5, and −68.9%–33.3% for PM10 from the original simulation. The improved WRF/Chem is applied to estimate the impact of anthropogenic aerosols on regional climate and air quality in East Asia. Anthropogenic aerosols can increase cloud condensation nuclei, aerosol optical depth, cloud droplet number concentrations, and cloud optical depth. They can decrease surface net radiation, temperature at 2-m, wind speed at 10-m, planetary boundary layer height, and precipitation through various direct and indirect effects. These changes in turn lead to changes in chemical predictions in a variety of ways.
Keywords: WRF/Chem; Model improvement; Sensitivity simulation; Aerosol direct effects; Aerosol indirect effects; East Asia;

The online-coupled Weather Research and Forecasting model with Chemistry with the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (referred to as WRF/Chem-MADRID) is applied to simulate meteorological fields, air quality, and the direct and indirect effects of anthropogenic aerosols over East Asia in four months (January, April, July, and October) in 2008. Model evaluation against available surface and satellite measurements shows that despite some model biases, WRF/Chem-MADRID is able to reproduce reasonably well the spatial and seasonal variations of most meteorological fields and chemical concentrations. Large model biases for chemical concentrations are attributed to uncertainties in emissions and their spatial and vertical allocations, simulated meteorological fields, imperfectness of model representations of aerosol formation processes, uncertainties in the observations based on air pollution index, and the use of a coarse grid resolution. The results show that anthropogenic aerosols can reduce net shortwave flux at the surface by up to 40.5–57.2 W m−2, Temperature at 2-m by up to 0.5–0.8 °C, NO2 photolytic rates by up to 0.06–0.1 min−1 and the planetary boundary layer height by up to 83.6–130.4 m. Anthropogenic aerosols contribute to the number concentrations of aerosols by up to 6.2–8.6 × 104 cm−3 and the surface cloud concentration nuclei at a supersaturation of 0.5% by up to 1.0–1.6 × 104 cm−3. They increase the column cloud droplet number concentrations by up to 3.6–11.7 × 108 cm−2 and cloud optical thickness by up to 19.8–33.2. However, anthropogenic aerosols decrease daily precipitation in most areas by up to 3.9–18.6 mm during the 4 months. These results indicate the importance of anthropogenic aerosols in modulating regional climate changes in East Asia through aerosol direct and indirect effects, as well as the need to further improve the performance of online-coupled models.
Keywords: Online-coupled model; WRF/Chem-MADRID; Model evaluation; Aerosol direct effects; Aerosol indirect effects; East Asia;

An extremely severe and persistent haze event occurred over the middle and eastern China in January 2013, with the record-breaking high concentrations of fine particulate matter (PM2.5). In this study, an online-coupled meteorology-air quality model, the Weather Research and Forecasting Model with Chemistry (WRF/Chem), is applied to simulate this pollution episode over East Asia and northern China at 36- and 12-km grid resolutions. A number of simulations are conducted to examine the sensitivities of the model predictions to various physical schemes. The results show that all simulations give similar predictions for temperature, wind speed, wind direction, and humidity, but large variations exist in the prediction for precipitation. The concentrations of PM2.5, particulate matter with aerodynamic diameter of 10 μm or less (PM10), sulfur dioxide (SO2), and nitrogen dioxide (NO2) are overpredicted partially due to the lack of wet scavenging by the chemistry-aerosol option with the 1999 version of the Statewide Air Pollution Research Center (SAPRC-99) mechanism with the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) and the Volatility Basis Set (VBS) for secondary organic aerosol formation. The optimal set of configurations with the best performance is the simulation with the Gorddard shortwave and RRTM longwave radiation schemes, the Purdue Lin microphysics scheme, the Kain-Fritsch cumulus scheme, and a nudging coefficient of 1 × 10−5 for water vapor mixing ratio. The emission sensitivity simulations show that the PM2.5 concentrations are most sensitive to nitrogen oxide (NOx) and SO2 emissions in northern China, but to NOx and ammonia (NH3) emissions in southern China. 30% NOx emission reductions may result in an increase in PM2.5 concentrations in northern China because of the NH3-rich and volatile organic compound (VOC) limited conditions over this area. VOC emission reductions will lead to a decrease in PM2.5 concentrations in eastern China. However, 30% reductions in the emissions of SO2, NOx, NH3, and VOC, individually or collectively, are insufficient to effectively mitigate the severe pollution over northern China. More aggressive emission controls, which needs to be identified in further studies, are needed in this area to reach the objective of 25% PM2.5 concentration reduction in 2017 proposed in the Action Plan for Air Pollution Prevention and Control by the State Council in 2013.
Keywords: WRF/Chem; PM2.5; Regional haze; Northern China; Comparative evaluation; Sensitivity study;

We quantify the contributions from five domestic emission sectors (residential, industry, transportation, energy, and biomass burning) and emissions outside of China (non-China) to concentration and direct radiative forcing (DRF) of black carbon (BC) in China for year 2010 using a nested-grid version of the global chemical transport model (GEOS-Chem) coupled with a radiative transfer model. The Hemispheric Transport of Air Pollution (HTAP) anthropogenic emissions of BC for year 2010 are used in this study. Simulated surface-layer BC concentrations in China have strong seasonal variations, which exceed 9 μg m−3 in winter and are about 1–5 μg m−3 in summer in the North China Plain and the Sichuan Basin. Residential sector is simulated to have the largest contribution to surface BC concentrations, by 5–7 μg m−3 in winter and by 1–3 μg m−3 in summer, reflecting the large emissions from winter heating and the enhanced wet deposition during summer monsoon. The contribution from industry sector is the second largest and shows relatively small seasonal variations; the emissions from industry sector contribute 1–3 μg m−3 to BC concentrations in the North China Plain and the Sichuan Basin. The contribution from transportation sector is the third largest, followed by that from biomass burning and energy sectors. The non-China emissions mainly influence the surface-layer concentrations of BC in western China; about 70% of surface-layer BC concentration in the Tibet Plateau is attributed to transboundary transport. Averaged over all of China, the all-sky DRF of BC at the top of the atmosphere (TOA) is simulated to be 1.22 W m−2. Sensitivity simulations show that the TOA BC direct radiative forcings from the five domestic emission sectors of residential, industry, energy, transportation, biomass burning, and non-China emissions are 0.44, 0.27, 0.01, 0.12, 0.04, and 0.30 W m−2, respectively. The domestic and non-China emissions contribute 75% and 25% to BC DRF in China, respectively. These results have important implications for taking measures to reduce BC emissions to mitigate near-term climate warming and to improve air quality in China.
Keywords: Black carbon; Direct radiative forcing; Sector contribution; Transboundary transport;

Model assessment of atmospheric pollution control schemes for critical emission regions by Shixian Zhai; Xingqin An; Zhao Liu; Zhaobin Sun; Qing Hou (367-377).
In recent years, the atmospheric environment in portions of China has become significantly degraded and the need for emission controls has become urgent. Because more international events are being planned, it is important to implement air quality assurance targeted at significant events held over specific periods of time. This study sets Yanqihu (YQH), Beijing, the location of the 2014 Beijing APEC (Asia–Pacific Economic Cooperation) summit, as the target region. By using the atmospheric inversion model FLEXPART, we determined the sensitive source zones that had the greatest impact on the air quality of the YQH region in November 2012. We then used the air-quality model Models-3/CMAQ and a high-resolution emissions inventory of the Beijing-Tianjian-Hebei region to establish emission reduction tests for the entire source area and for specific sensitive source zones. This was achieved by initiating emission reduction schemes at different ratios and different times. The results showed that initiating a moderate reduction of emissions days prior to a potential event is more beneficial to the air quality of Beijing than initiating a high-strength reduction campaign on the day of the event. The sensitive source zone of Beijing (BJ-Sens) accounts for 54.2% of the total source area of Beijing (BJ), but its reduction effect reaches 89%–100% of the total area, with a reduction efficiency 1.6–1.9 times greater than that of the entire area. The sensitive source zone of Huabei (HuaB-Sens.) only represents 17.6% of the total area of Huabei (HuaB), but its emission reduction effect reaches 59%–97% of the entire area, with a reduction efficiency 4.2–5.5 times greater than that of the total area. The earlier that emission reduction measures are implemented, the greater the effect they have on preventing the transmission of pollutants. In addition, expanding the controlling areas to sensitive provinces and cities around Beijing (HuaB-sens) can significantly accelerate the reduction effects compared to controlling measures only in the Beijing sensitive source zone (BJ-Sens). Therefore, when enacting emission reduction schemes, cooperating with surrounding provinces and cities, as well as narrowing the reduction scope to specific sensitive source zones prior to unfavorable meteorological conditions, can help reduce emissions control costs and improve the efficiency and maneuverability of emission reduction schemes.
Keywords: Critical emission regions; Sensitive source zones; Emission reduction schemes; Numerical model;

The diurnal variations of the water soluble organic and inorganic components as well as six selected metals in PM2.5 around the heating periods of 2013 and 2014 in Beijing were analyzed in this study to investigate the contributions of secondary aerosols and primary pollutants to PM2.5 and the effects of domestic heating and mitigation measures. The before-heating sampling period in 2014 (from Nov. 1st to Nov. 15th) was characterized with reinforced short-term mitigation measures for the 2014 Asia–Pacific Economic Cooperation (APEC) meeting. As a result, the average mass concentrations of PM2.5 and most of the measured species except for Cu, Al, and Ca2+ were greatly reduced during the APEC meeting period. The domestic heating activity alone resulted in a 17.7% increase of PM2.5 in 2013, exerting lesser effects on the increase of PM2.5 than before. Water soluble organic carbon was the most abundant water soluble species in PM2.5, followed by NO 3 − , SO 4 2 − , and NH 4 + . According to the PMF model calculation, secondary aerosols, coal combustion, biomass/waste burning, traffic related pollution, long-range transport, and fugitive soil and sand dust were identified as the main sources of PM2.5 in Beijing, among which secondary formation of aerosols was the dominant source of PM2.5 during the non-APEC period while biomass/waste burning dominated during the APEC period. As a timely feedback on the effects of the mitigation measures adopted by the government, the results of this study provide knowledge necessary for a sustainable urban management.
Keywords: APEC; Heating period; Secondary aerosol; Source apportionment; Air pollution control measures;

Modeled deposition of fine particles in human airway in Beijing, China by Xiaoying Li; Caiqing Yan; Regan F. Patterson; Yujiao Zhu; Xiaohong Yao; Yifang Zhu; Shexia Ma; Xinghua Qiu; Tong Zhu; Mei Zheng (387-395).
This study aims to simulate depositions of size-segregated particles in human airway in Beijing, China during seasons when fine particulate matter concentrations are high (December 2011 and April 2012). Particle size distributions (5.6–560 nm, electrical mobility diameter) near a major road in Beijing were measured by the TSI Fast Mobility Particle Sizer (FMPS). The information of size distributions provided by FMPS was applied in the Multiple-Path Particle Dosimetry model (MPPD) to quantify number and mass depositions of particles in human airway including extrathoracic (ET), tracheobronchial (TB), and pulmonary (PUL) regions of exposed Chinese in Beijing. Our results show that under ambient conditions, particle number concentration (NC) deposition in PUL is the highest in the three major regions of human airway. The total particle NC deposition in human airway in winter is higher than that in spring, especially for ultrafine particles (1.8 times higher) while particle mass concentration (MC) deposition is higher in spring. Although particle MC in clean days are much lower than that in heavily polluted days, total particle NC deposition in human airway in clean days is comparable to that in heavily polluted days. NC deposition for nucleation mode particles (10–20 nm, aerodynamic diameter) in clean days is higher than that in heavily polluted days. MC deposition for accumulation mode particles (100–641 nm, aerodynamic diameter) in heavily polluted days is much higher than that in clean days, while that of nucleation mode is negligible. The temporal variation shows that the arithmetic mean and the median values of particle NC and MC depositions in the evening are both the highest, followed by morning and noon, and it is most likely due to increased contribution from traffic emissions.
Keywords: Fine particle; Ultrafine particle; Deposition; Human airway; MPPD model; Beijing;

Atmospheric particulate mercury in the megacity Beijing: Efficiency of mitigation measures and assessment of health effects by N.J. Schleicher; J. Schäfer; Y. Chen; G. Blanc; Y. Chen; F. Chai; K. Cen; S. Norra (396-403).
Atmospheric particulate mercury (HgP) was studied before, during, and after the Olympic Summer Games in Beijing, China, in August 2008 in order to investigate the efficiency of the emission control measures implemented by the Chinese Government. These source control measures comprised traffic reductions, increase in public transportation, planting of vegetation, establishment of parks, building freeze at construction sites, cleaner production techniques for industries and industry closures in Beijing and also in the surrounding areas. Strictest measures including the “odd-even ban” to halve the vehicle volume were enforced from the 20th of July to the 20th of September 2008. The Olympic period provided the unique opportunity to investigate the efficiency of these comprehensive actions implemented in order to reduce air pollution on a large scale. Therefore, the sampling period covered summer (August, September) and winter (December and January) samples over several years from December 2005 to September 2013. Average HgP concentrations in total suspended particulates (TSP) sampled in August 2008 were 81 ± 39 pg/m3 while TSP mass concentrations were 93 ± 49 μg/m3. This equals a reduction by about 63% for TSP mass and 65% for HgP, respectively, compared to the previous two years demonstrating the short-term success of the measures. However, after the Olympic Games, HgP concentrations increased again to pre-Olympic levels in August 2009 while values in August 2010 decreased again by 30%. Moreover, winter samples, which were 2- to 11-fold higher than corresponding August values, showed decreasing concentrations over the years indicating a long-term improvement of HgP pollution in Beijing. However, regarding adverse health effects, comparisons with soil guideline values and studies from other cities highlighted that HgP concentrations in TSP remained high in Beijing despite respective control measures. Consequently, future mitigation measures need to be tailored more specifically to further reduce HgP concentrations in Beijing.
Keywords: Hg; Particle-bound mercury; Urban aerosols; Adverse health effects; Emission control measures; Olympic Games;

Bioaerosol emissions and detection of airborne antibiotic resistance genes from a wastewater treatment plant by Jing Li; Liantong Zhou; Xiangyu Zhang; Caijia Xu; Liming Dong; Maosheng Yao (404-412).
Air samples from twelve sampling sites (including seven intra-plant sites, one upwind site and four downwind sites) from a wastewater treatment plant (WWTP) in Beijing were collected using a Reuter Centrifugal Sampler High Flow (RCS); and their microbial fractions were studied using culturing and high throughput gene sequence. In addition, the viable (fluorescent) bioaerosol concentrations for 7 intra-plant sites were also monitored for 30 min each using an ultraviolet aerodynamic particle sizer (UV-APS). Both air and water samples collected from the plant were investigated for possible bacterial antibiotic resistance genes and integrons using polymerase chain reaction (PCR) coupled with gel electrophoresis.The results showed that the air near sludge thickening basin was detected to have the highest level of culturable bacterial aerosols (up to 1697 CFU/m3) and fungal aerosols (up to 930 CFU/m3). For most sampling sites, fluorescent peaks were observed at around 3–4 μm, except the office building with a peak at 1.5 μm, with a number concentration level up to 1233–6533 Particles/m3. About 300 unique bacterial species, including human opportunistic pathogens, such as Comamonas Testosteroni and Moraxella Osloensis, were detected from the air samples collected over the biological reaction basin. In addition, we have detected the sul2 gene resistant to cotrimoxazole (also known as septra, bactrim and TMP-SMX) and class 1 integrase gene from the air samples collected from the screen room and the biological reaction basin. Overall, the screen room, sludge thickening basin and biological reaction basin imposed significant microbial exposure risks, including those from airborne antibiotic resistance genes.
Keywords: Wastewater treatment plant; Bioaerosols; Airborne antibiotic resistance genes; Bacterial aerosols; Fungal aerosols; Bacterial pathogens;