| A five-year long term aerosol sampling from 2003-2008 was conducted at seven sampling sites, of which three sites (Shanghai, Beijing and Qingdao) located at urban or coastal areas and the other four sites (Yulin, Duolun, Urumqi and Tazhong) were at or near the major dust sources in China (the Loess Plateau, the Taklimakan Desert and the Gobi Desert).The composition, spatial-temporal variation, size distribution, chemical form, sources and the formation mechanism as well as the mixing of pollutants with dust via the long range transport with its impact on the regional environment were systematically studied by enrichment factors, elemental/ionic tracers, air mass backward trajectory analysis, and multi-statistical analysis including factor analysis and correlation analysis at the metropolitan areas with focus on Shanghai. The main contribution and innovation of this thesis are described as below.The annual haze days at Shanghai exceeded 150 days during 2001-2009. During the past decade, the pH values of rain sharply decreased and the annual acidity of rain increased more than 20 times. The annual concentrations of PM2.5 ranged from 0.050-0.059 mg/m3, which is more than the triple of standard value given by World Health Organization of 0.015 mg/m3. The annual ratio of PM2.5/PM10 in 2004 and 2007 were 0.41 and 0.53, respectively, indicating severe fine particle pollution. 2. The different seasonal formation mechanism of aerosol in ShanghaiSecondary inorganic aerosol(SO42-,NO3-,NH4+), organic aerosol and mineral aerosol were the three most important contributors to aerosol of Shanghai. Significant seasonal variation of aerosol concentrations was observed with the high levels in winter and spring, while the low levels in summer and fall, respectively. The major chemical form of soluble ions in summer and winter were (NH4)2SO4 and NH4NO3, while in winter and spring CaSO4 and Ca(NO3)2 was also found due to the heterogeneous reaction of pollution precursors on the alkaline dust. In summary, the influence of long range transport of dust in spring, the photochemical smog in summer and the severe haze in fall and winter were main formation mechanisms of aerosol in four seasons in Shanghai. The major sources of aerosol in Shanghai included suspended dust, industrial/ vehicle emissions, coal/fossil fuel combustion, metallurgical emission, marine aerosol and secondary aerosol from photochemical reactions. The Ca2+/Al ratio could be used as the tracer for revealing the mixing extent of dust from soil and construction activities. The NO3-/SO42- ratio demonstrated the contributions from mobile sources and stationary sources. The NO3-/SO42- ratio at Shanghai was much higher than other cities in China, which implies that the vehicle emissions has become the major issue of air pollution in Shanghai. The ratio of sea-salt Na+ and non-sea-salt Na+ could be used to estimate the contribution of marine sources and land sources. The average contribution of marine sources to the soluble ions in TSP and PM2.5 was 8.9% and 7.1%, respectively, while the contribution reached as high as 15.4% and 9.9% in summer, respectively.The pollution level, spatial variation and size distribution of Pb were studied. It was found that the concentration of Pb in fine particles range from 50-200 ng m-3 in the past several years and obvious seasonal variation was observed.The ratio of Mg/Al was used to distinguish and estimate the contribution of local and invaded sources to mineral aerosol. During the dust storm in spring, the invaded sources contribute as high as 60% in spring, and about 10% in fall. The composition, sources and transformation mechanism of the ever recorded floating dust in Shanghai as well as the transformation and accumulation of pollutants on dust particles were revealed. The high concentration of pollutants during dust storm may be attributed to the mixing of mineral aerosol with pollution aerosol on the pathway, or the mixing of invaded air mass with local polluted air mass.
|
PDF Full Text Request