| 1. Three Asian dust sources, i.e., the western high-Ca-dust in the Taklimakan Desert, the northwestern high-Ca-dust and the northeastern low-Ca-dust in Mongolia Gobi, were identified based on the air mass trajectories plus the elemental tracer analysis (e.g., SO42-/S, Ca2+/Ca, Na+/Na and Ca/Al). The transport pathways of dust, concentrations of pollutant precursors and meteorological conditions were the main factors affecting the mixing extent of pollutants with dust. The western dust source was least polluted in comparison to the other two dust sources, and it mainly derived from the Taklimakan Desert, a paleo-marine source. Anyway, it was still found that the dust could have already mixed with pollution aerosol even near dust source regions. The northwestern dust had a considerable mixing and chemical reaction with sulfur precursors from the coal mines on the pathway of the long-range transport. The amount of SO42-, NO3- and NH4+ increased 2-3 times in the relatively polluted transport pathway of 2006 Beijing dust storm compared to the non-dust periods. Typical pollution elements, such as Zn, As, Pb, S and Cd were also more enriched. Additionally, the mixing of biomass burning aerosol with dust was verified. The northeastern dust reached Shanghai with high acidity, and it became the mixed aerosol with the interaction among dust, local pollutants, and sea-salts. The mixing mechanisms of the dust with the pollution aerosol on the local, medium-range, and long-range scale revealed from this study would improve the understanding of the impacts of Asian dust on regional/global climate change.2. The chemical and optical characteristics of dust aerosol and the relation between each other were evaluated to understand the effect of dust and anthropogenic aerosol on the regional climate. The single scattering albedo of dust aerosol in the wavelength of 657,870 and 1020nm was mainly determined by the percentage of black carbon in particles, while the strong light absorbing at 439nm was probably due to the significant proportion of iron oxides in the dust aerosol other than black carbon. Linear relationship between aerosol optical properties and aerosol chemical compositions was found. The results indicated that soluble ions, i.e. SO42-, NO3-, NH4+ and K+, were the main contributors to the light extinction of fine particles while mineral aerosol contributed more to that of coarse particles. Black carbon, as a strong light absorbing species, was found contributing to the light extinction of both fine and 3. The air quality degradation and formation mechanism of haze in big cities of China was elucidated by comprehensive research of atmospheric aerosol and trace gases in Shanghai. The morning and evening rush hours were the two main pollution episodes in one day, which was due to the vehicle emission and meteorological conditions. The single scattering albedo of winter aerosol was as low as 0.79, reflecting the high fraction of the strong light absorbing substance, black carbon in the particles. Major contributors to the aerosol in Shanghai were soluble inorganic ions, organic aerosol and mineral aerosol. SO42-, NH4+, NO3- and K+ were main species of soluble inorganic ions, which derived from photochemical reactions, in-cloud aqueous formation and biomass burning. Organic aerosol contributed 28.8% to PM2.5, of which secondary organic aerosol contributed about 30% to total organic aerosol. The enrichment degree of Se and S was the most significant in all elements, which was attributed to the widely used coal in China. Organic aerosol, sulfate, nitrate and element carbon were the major contributors to light extinction, which accounted for an average of 47%, 22%,14% and 12%, respectively. The major sources of organic and elemental carbon were vehicle emission, thus control measures on the growing vehicle numbers have been urgent need on the improvement of air quality of Shanghai and other big cities in China.4. A synergy of satellite observation, lidar measurement and ground-based aerosol sampling was conducted to monitor the biomass burning in the Yangtze River Delta (YRD), China. Regional biomass burning was indicated by the satellite signal, i.e., fire spots, column carbon monoxide, and aerosol optical depth. K+, EC, OC, and OC/EC were significantly enhanced in the biomass burning episode. Organic aerosol contributed-50% to PM10 and biomass derived CO contributed-25-35% of total CO. No significant increase of O3 was observed, which was attributed to depletion due to the oxidation formation of sulfate and nitrate. Vertical profile showed low mixing height and extremely high aerosol extinction coefficient (532nm) of 740±280 Mm-1 near the ground with average of 320±250 Mm-1 within the boundary layer. Mass extinction efficiency of PM10 was 3.8±0.5 m2/g. The air pollution in YRD during the biomass burning episode not only derived from the local agricultural burning, but also affected by the transport of smoke aerosol from far regions, such as Shandong and Anhui provinces. It is suggested that effective controls on biomass burning emission caused by the post-harvest anthropogenic activities could have positive effect on air quality in YRD, and will be an efficient way on the meet of air quality in the forthcoming 2010 Shanghai World Expo.5. The different formation mechanisms of haze in three pollution episodes during April to June,2009 in Shanghai were elaborated. Three types of haze, i.e., secondary inorganic pollution, dust, and biomass burning were confirmed by using the typical aerosol chemical species, air mass backward trajectory and chemical tracers analysis. SO2, NOx and CO were significantly elevated in the secondary inorganic pollution episode, while CO increased obviously in the biomass burning episode. The ratio of CO/NOx (-14) could be used as the tracer to indicate the possible influence of biomass burning, as it is distinctly distinguished from the other periods (CO/NOx: 9-10). Linear regression analysis suggested the significant correlation between SO2, NOx, CO and PM2.5 in the secondary inorganic pollution episode, respectively, indicating the sources from coal burning, vehicle emission and power plants. While it was found that PM2.5 only correlated with CO in the biomass burning episode, indicating the dominance of organic aerosol. Vertical structure of aerosol by LIDAR suggested distinct differences of mixing height, depolarization ratio, vertical distribution of aerosol optical parameters in different episodes. The impact of long-range and regional transport on the air quality of Shanghai was evaluated by satellite observations.6. The acidity level of the precipitation in Shanghai was considerably high with the annual mean pH value of 4.49 and the frequency of acid rain was 71%. In 2005 the acidity of rain in Shanghai increased more than 15 times in the past 8 years compared to 1997. The concentration of SO42- was higher than the most polluted cities abroad, indicating Shanghai has been a severe polluted city over the world. The high coal/fuel consumption from urbanization and the rapid increasing amount of motor vehicles from motorization resulted in the high emission of SO2 and NOx, the precussors of the high concentration of acidic ions, SO42- and NO3-, which were the main reason of the severe acid rain in Shanghai. SO42- and NO3- existed mainly in the form of CaSO4 and Ca(NO3)2, indicating the neutralization capability of Ca2+ dominated over NH4+. The principal component analysis indicated that SO42-, NO3-, NH4+ and partial Ca2+ derived from anthropogenic sources, K+, Mg2+ and Ca2+ mostly originated from mineral sources, and almost all the Cl- and Na+ derived from the sea. The chemistry of precipitation in Shanghai was under the influence of local pollution sources and the long-and moderate-range transport through back trajectory analysis.
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