Different emission inventories were applied to investigate the spatial distribution and temporal variation of anthropogenic emission in China during the period from 2000 to 2010. The analysis results indicate that the total anthropogenic emission generally increased during the past 10 years. NO_x emission increased continuouslly and it exceeded SO₂ emission in 2010. From 2006 to 2010, PM₁₀ and SO₂ emissions decreased by 76% and 10%, respectively. From 2000 to 2010, the emissions of SO₂, NO_x, and BC increased by 5.6 Tg (25%), 13.1 Tg (85%), and 0.3 Tg (20%), respectively, but OC emission decreased by about 0.7 Tg (17%), PM₁₀ emission largely decreased by 12.4 Tg (74%), and there was no obvious change in NMVOC emission. There are quite large differences in the temporal variations of emissions among different regions of China.

The daily averages of the aerosol radiative forcing (ARF) at the surface and the top of the atmosphere (TOA) were calculated in several years in China. A radiative transfer model (SBDART) was utilized to simulate the solar irradiance values at the surface and TOA by using as input aerosol properties retrieved from AERONET sun photometer measurements. At the AERONET stations at SACOL, Xianghe, and Taihu, the daily mean ARF values were (-7.2±7.1), (-11.7±9.5), and (-14.9±8.3) W/m² at the TOA; (-21.9±12.2),(-36.5±29.5), and (-42.2±21.0) W/m² at the surface; and (14.7±9.7), (24.8±23.0), and (27.3±16.5) W/m² in the atmosphere, respectively. The surface cooling and the atmosphere warming caused by aerosol at Xianghe and Tiahu stations were greater than at SACOL. The daily ARF of the desert dust aerosol was significantly greater than the total average of aerosol, especially at the surface and in the atmosphere, showing that dust can produce more obvious surface cooling and atmosphere warming.

As the collision theory for raindrop and aerosol particle is important in below-cloud scavenging, collision efficiency as a function of raindrop diameter (D_p) and aerosol diameter (d_p) is discussed. The scavenging coefficient (SC) under thundercloud is 5 to 6 times higher than those under non-thundercloud when d_p is less than 1 μm. Field measurements of aerosol number concentration at bottom and top of Huangshan mountain from June to August of 2011 were used to analyze the variation characteristics of observed and theoretical SCs. The results show that observed SC variation for ultrafine-sized particle is in reasonable agreement with the theoretical one, and the observed SC is 5 to 6 times higher than the theoretical SC. Submicron-sized particle SC is higher under thundercloud than that under non thundercloud. Based on the observations, exponential relationship between the hour-averaged SC and rainfall intensity is derived, in which the correlation coefficient is 0.81.

Both the mumber of slight rain(defined as 0~1 mm per day)days and the rainfall mount of slight rain decreased distinctly in the most regions of eastern China during the past 50 years,except in some regions in the northern part of eastern China.The positive correlation between the visibilty during dry and sunny days and the variation of slight rain were found in the regions of the Beijing-Tianjin-Tangshan district,the middle and low reaches of the Yangtze River, and the coast of southern China. At the same time, the increase of AOD(aerosol optical depth), the decrease of visibility, and the reduction of cloud droplet radius were found in the above-mentioned regions, and it is inferred that the reduction of slight rain in these regions is related to the radiative effects of aerosol.

By using HTDMA (hygroscopic tandem differential mobility analyzer) system, hygroscopicity of ambient aerosols was observed during 8-20 December 2009 in Beijing. It was found that the aerosol hygroscopic growth factor value varied between 1.01 and 1.40 in winter, showing weak hygroscopicity and nearly hydrophobicity. Daily variation of aerosol growth factor showed a bimodal mode (two peaks at midnight and noon and two valleys in the morning and evening rush hour) or a single-peak mode (a peak at midnight and a valley at noon). One of the major factors influencing aerosol hygroscopicity was the content of weak hygroscopic and nearly hydrophobic components in the ambient aerosol.

Ninety-nine volatile organic compounds (VOCs) species were measured in autumn in Beijing. The average concentration of VOCs was 54.6 ppb. The average concentiations of NMHCs and oxygenated VOCs were 38.0 ppb and 10.04 ppb, respectively. The pollution status of VOCs was evaluated based on the diurnal variation and ratio between typical VOCs species(E/E and B/T). The air masses observed were characterized to photochemical-aged and supposed to be affected mainly by traffic emission sources. The same conclusion was reached by the co-analysis of air mass backward trajectory and B/T value at noon.

We analyzed the weather situation, boundary layer structure, and PM_2.5 concentration during the haze-fog event of 27 to 31 Jan 2013 occurred in the North China plain(NCP). The weather conditions indicated that latitudinal circulation and weak pressure system controlled the NCP area during that period. There were continuous inversion layer and stable structure within the boundary layer. The surface and lower level wind was usually less 2 m/s, and relative humidity was higher. Such stable weather situation and high emissions were favorable to pollutant accumulation and fine aerosol's formation. Then, the high PM_2.5 concentration directly leaded to low visibility and heavy fog-haze. Real-time WRF-Chem model made a good forecast for the PM_2.5 concentration and the haze spatio-temporal distribution and evolution in the NCP area. The wind convergence and pollutant accumulation usually occurred along the mountain edge and in the NCP area.

We used a nephelometer to monitor scattering coefficients on the top of a laboratory building in East China University of Science and Engineering from April to December in 2009. PM_2.5 was simultaneously sampled every day to obtain its mass concentrations and its chemical components. We studied characteristics of diurnal variation in scattering coefficients in different seasons, correlations between scattering coefficient and PM_2.5, and power correlation between visibility and chemical components of PM_2.5. Results indicated that scattering coefficients were higher in autumn and winter and lower in summer. The diurnal variation of scattering coefficient indicated two peaks observed at 6:00 and 18:00,respectively. The peak value was higher in autumn and winter but the diurnal variation changed little in summer. The seasonal comparison indicated that scattering coefficients had strong linear correlations with PM_2.5 in all the seasons. It was found that visibility had power function correlations with secondary ions in spring, with EC in summer, and with both organic components and secondary ions in fall. Due to the complexity of components, sources, and formation mechanisms, no obvious correlations between visibility and components were found for winter.

Dust emission has significant influences on the air quality of Nanjing. Annual emissions of soil, paved road, and construction dusts in 2010 were estimated by using AP-42 methods and their spatial distributions with a 3 km×3 km grid resolution are given. Results showed that the emissions of PM₁₀ in Nanjing were 261, 67 270, and 7 540 tons, respectively. The largest dust emission was from the paved road, and the emission value gradually decreased from downtown to suburban area. Overall, the dust emission of PM₁₀ in Nanjing was less than that in Shanghai and was about 67.3% of the local industry emission.

Using the visibility formula of IMPROVE, the data of atmospheric complex pollution monitoring system in Hangzhou from July 2011 to June 2012 was analysed. The primary extinction material was determined. The results showed that the ratio of pollutant extinction coefficient to atmospheric total extinction coefficient decreased when the visibility decreased, and the ratio decreased from 85% at 10 km to 22% at below 2 km. The extinction coefficients of nitrate and sulfate at below 2 km were 4.43 and 3.15 times of those at 10 km, respectively. The extinction coefficients of main pollutants in Hangzhou showed very significant seasonal variation and daily variation. The extinction coefficient of nitrate was lower in summer and autumn and higher in winter and spring, while the extinction coefficient of sulfate was higher in autumn and lower in the other seasons.

Samples of ambient fine particulate matter were collected using Andersen cascade sampler. The contributions of secondary organic carbon (SOC) to particulate matter in different sizes were determined by the "OC/EC minimum ratio" technique. The sources of size-resolved fine particulate matter in Hangzhou were analyzed using the CMB model. The results showed that secondary aerosol and vehicle exhaust were the major sources in small-size segment. The contribution of suspended dust, cement dust, and fly ash gradually increased in coarse segment, and the contribution of secondary particles and vehicle exhaust dropped to about 50%.

Ammonia samples were collected at 193 sites in Hangzhou in September 2010 and in March 2011 using Italy Kerry Ring passive sampling device. The concentrations of NH₄⁺ were measured by ion chromatography. Temporal and spatial distributions of ammonia were calculated by ARCGIS interpolation. The results show that the average concentration of ammonia was 7 μg/m³ in Hangzhou, which did not exceed the health standards for the design of Chinese industrial enterprise of 200 μg/m³. Ammonia concentration was higher in the east part of the city than in the west and was higher in September than in March. Meteorological factors and source strength of ammonia are the main factors affecting atmospheric ammonia distribution.

An air pollution episode over the Yangtze River Delta (YRD) during the period from 8 to 16 Dec 2011 was investigated using MM5-CMAQ model system. There were high NO₂ concentrations in Shanghai and Hangzhou. Ozone concentrations were greater than 40 ppb in the southeast of Hangzhou and on the borders between Anhui, Zhejiang, and Jiangxi provinces. The SO₂ concentrations in Shanghai and Nanjing were high. The pollution episode occurred when SO₂ from emission and NO₂ from chemical and emission processes accumulated under weak diffusion conditions. NO also accumulated consuming ozone and resulting in a decrease of O₃ concentration.

PM_2.5 samples were collected during the four seasons of 2011 in Jinan using a sampler of medium-flow capacity, and 16 kinds of polycyclic aromatic hydrocarbons (PAHs) bounded to PM_2.5 were analyzed by GC-MS to investigate their seasonal variations and sources. The results indicated that annual total PAHs concentration in PM_2.5 ranged from 1.94 to 92.19 ng·m^-3, showing obvious seasonal variations, and it apparently increased during the haze periods in autumn and winter. Diagnostic ratio (DR) and principal component analysis (PCA) results suggested that the PAHs in PM_2.5 were mainly derived from vehicle emission, coal combustion, and biomass burning. The mean values of BEQ and CR observed during the haze periods were higher than those during the clean periods. During the haze periods in autumn and winter, the mean values of BEQ (5.32 ng·m^-3, 8.65 ng·m^-3) and CR(5.85×10^-6, 8.88×10^-6) were higher than the BEQ values (3.31 ng·m^-3, 3.64×10^-6) and the CR values (2.63 ng·m^-3, 2.89×10^-6) in spring and summer, respectively. BEQ and CR values indicated that haze pollution in autumn and winter would seriously impair human health in Jinan.

On the basis of long-term dataset (including aerosol mass concentration,black carbon concentration, scattering coefficient, visibility and extinction coefficient), the study gives the following three conclusions. First, visibility is negatively correlated with aerosol mass concentration. When the PM₁ mass concentration is greater than 60 μg/m³ visibility does not change significantly as the PM₁ mass concentration decreases, and when the PM₁ concentration is less than 60 μg/m³ visibility increases rapidly as the PM₁ mass concentration decreases. Secondly, the relative humidity has a major influence on the visibility. Thirdly, in Guangzhou aerosol hygroscopic growth factor and relative humidity has the following relationship: f(RH)=0.6+0.133×(1－RH/100)^－1.633. The local f(RH) is comparable to the growth curve of the IMPROVE with in the relative humidity range between 50% and 80%.

On the basis of the operational forecasting data of PM_2.5 output by CMAQ model run in Guangzhou Institute of Tropical and Marine Meteorology, China Meteorological Administration, and by using the HYSPLIT4 model, the regional transported effect of PM_2.5 at Guangzhou Panyu Atmospheric Composition Station from Dec 2012 to Mar 2013 was analyzed. The transported intension was defined according to Poirot's transport probability. The results are the following.The variation tendency of transport intension was consistent with the variation tendency of the observed data of PM_2.5. The calculation results for transport intension are relatively reasonable. The concentration of PM_2.5 in Panyu of Guangzhou was mainly influenced by the external sources. The local pollution contribution of PM_2.5 was only 31%, and contributions from the Pearl River Delta(PRD, including Guangzhou) and the outside of the PRD were 73% and 27%, respectively. There were three transport channels of PM_2.5, the north, northeast, and coastal paths.

Atmospheric concentration of Pb from MSW incineration plants in the studied city was estimated by using CALPUFF model, and then inhalational health risk was assessed. The results indicate that, affected by local meteorological conditions and terrain, the concentration distribution shows significant seasonal variations and topography-dependent characteristics. In autumn and winter, Pb diffuses widely and spreads mainly in the southwest part of the city, with the maximal concentrations of 7.9 × 10^-3 and 7.0 × 10^-3 μg/m³, respectively. The diffusion area is relatively small in spring and summer, with the maximum values of 5.4 × 10^-3 and 7.5 × 10^-3 μg/m³, respectively, in the central region. The inhalational risk distribution is consistent with Pb concentration distribution. Children's exposure risk is nearly 2 times of the risk of adults, and males have slightly higher risk than females. The risk is negligible, compared with the risk reference recommended by USEPA, and it is even less than 4% of the background risk..

On the basis of the 50-year (1961-2010) data observed at 122 meteorological stations in Sichuan basin, we studied the monthly, seasonal, and annual distributions of visibility in the basin as well as the interannual variations. The relations of the interannual variations of visibility with the meteorological factors (wind and air temperature), energy consumption, and increasing population were analyzed to explore the factors causing the visibility changes. The results showed that 1)the annual average of dry visibility in Sichuan basin was 18.8 km with four centers of low visibility (about 11 km) in association with the climate, population, industry, and urbanization; 2)over the 50 years, 87 sites (about 71%) in the basin were found to have negative trends in dry visibility with the change rates of-4.5~-0.07 km/10a, while 35 sites (about 29%) in the basin mostly located in the northern edge had positive trends in visibility with the change rates of 3.3~0.08 km/10a; 3)the visibility had significant seasonal variations with the highest in summer and the lowest in winter; and 4)the reduction of atmospheric visibility in the basin is closely related to the declining wind, warming air, increasing energy consumption, and population.

Daily PM_2.5 samples were collected during the typical month of each season of 2011 at an urban site of Chengdu. 32 elements were detected in PM_2.5 by ICP-MS, among which there were 9 hazardous elements. The concentrations, enrichment factors, and possible sources of the 9 elements were analyzed in this study. The annual average concentrations of Pb,Mn,As,Cr,Sb,Cd,Se,Ni, and Co were (171.7±86.2), (66.4±36.7), (19.8±11.1), (9.2±5.0), (6.5±4.2), (3.5±1.9), (2.7±1.2), (2.5±1.6), and (0.5±0.3) ng·m^-3, respectively. The As concentrations in most of the collected samples exceeded the guideline values provided by WHO and Chinese ambient air quality standards. High enrichment factors of Se,Cd,Sb,Pb, and As were found, ranging from 492 to 5340. Relatively low enrichment factors were observed for all the hazardous elements during spring, since the ambient aerosol was significantly affected by soil dust. The results of the factor analysis further revealed that these hazardous elements were mainly contributed by anthropogenic sources such as motor vehicle emissions, coal combustion, and metal smelting.

Vertical profiles of aerosol data and meteorological factor at Dunhunang in China were obtained by using observation instruments loaded in a remote-controlled airplane. The observations suggest that convective mixing of aerosols accumulated in the vicinity of the ground at nighttime is the main factor of diurnal variation of aerosol vertical distribution. Monthly-mean vertical distributions suggest that concentrations of fine particles and water vapor are higher in summer than in spring while those of coarse particles are lower in spring than in summer. During dust storms, number mixing ratio of coarse particles increased, while that of fine particles slightly decreased. The size distributions had two peaks. In the retreat periods of dust storms, the decreasing rates and speeds of number mixing ratios for the coarse and fine particles were different. These differences imply the different origins of the dust storms.

For studying the concentration characteristics and sources of carbonaceous aerosols during winter in Lanzhou, daily PM_2.5 samples were collected during the period from 5 Dec to 12 Dec in 2011. Elemental carbon(EC) and organic carbon(OC) were measured by the thermal/optical method using DRI-2001A. The results indicated that the average mass concentrations of EC and OC were 7.48 and 22.71 μg/m³, respectively, during winter in Lanzhou.Snow had significant effect on the ambient concentrations of EC and OC. The correlation coefficient between EC and OC was 0.98,which revealed that the emission sources of carbonaceous aerosol were relatively simple during winter in Lanzhou and EC and OC had the same sources. Mass concentration of SOC was 3.26 μg/m³, and it was only 14.4% of the concentration of OC in PM_2.5. Factor analysis on the eight carbon fractions of carbonaceous aerosol indicated that coal combustion and vehicle emissions were the major sources for carbonaceous aerosol in PM_2.5.