The Research On Chemical Characteristics Of The Acidy Precipitation In Nanchang

Great attention has been played on sulfur pollution after a series of ecological damage and economic losses caused by environmental acidification. The chemical composition of precipitation was analyzed on the basis of the result of precipitation collected at two sites in Nanchang during the period from 2007 to 2008, and discussed the chemical feature and pollutant sources. The tow sites located at Qianhu campus and the North campus of Nanchang University, standing for the urban and suburban. To discussed the pollutant characteristics and sources of chemical composition and differences of the toxic trace metal in precipitation at two sites, this study take the method of discounting the effect of sea salt and crust to work out the proportion of anthropogenic activity , combined with mathematical statistics such like the relevance analysis, cluster analysis and principal component analysis. Further more, for the stable sulfur isotopic composition can effectively judge the difference sources of sulfur in the atmospHeric pollution by its "fingerprint" of the characteristics, theδ³⁴S value was taken to analysis the sulfur source of precipitation in Nanchang. Results show that:(1) The weighted rainfall pH value of precipitation in Nanchang less than 5.00, and every precipitation is acid rain, it is lower than previous studies. The volume weighted mean pH value of Qianhu and the north campus are 3.96 and 4.16, respectively. The pH of precipitation at the north campus is higher than it at Qianhu campus while the conductivity is larger, for there are more strong acid buffered by alkaline substances in the atmospHeric environment of the urban area than at suburban. Precipitation is a kind of sulfuric acid and nitric acid mixed acid rain with the value of SO₄^2-/NO₃^- ranging from 0.5 to 3.0∑+/∑- of Qianhu and the north campus are 1.195 and 1.154, shows that it is essential balance between the cation and anion. The pH, conductivity and ions showed a significant seasonal variation. Anthropogenic activity had the greatest impact on the precipitation, Qianhu site was mostly influenced by anthropogenic activity and crust while the north site was mostly influenced by anthropogenic activity and sea salt. A significant correlation between ions of land-based sources, sea salt ions and NO₃^- with SO₄^2-. Principal components analysis and cluster analysis has the same result, shows that the major sources of precipitation are the crust and human activities in Qianhu campus, and human activities and sea salt in the North campus.(2) The concentrations of toxic trace metal elements are much high than other place while close with the concentrations in Guiyang, and show a seasonal fluctuation of high in summer and low in winter. To Cu, Hg and Pb, precipitation is a pollution factor of surface water. There are no correlations between metal elements and pH in the precipitation, but when the pH is less than 4.00, metal concentration increases rapidly. Qianhu site is more influenced by crust and less by sea salt than the north campus. The effect of three sources to the metal concentration is: human＞crust＞sea salt, the impact of human activities to the two campuses is 95.43% and 96.60%, respectively. Cd, Cr, Cu, Mn, Pb and Zn show a good correlation for come from the same sources. The results of principal component analysis are consisted with the cluster analysis. The pollution of trace toxic metals in rainwater is mainly released from human activities, like large smelting, oil-fire furnaces, the wearing tire and automobile exhaust, and so on.(3) Theδ³⁴S in precipitation of Qianhu campus and the North campus in spring and summer precipitation ranged from -3.55 to +3.91‰and from -3.88 to +7.24‰, respectively, which were both in the scope ofδ³⁴S value in precipitation all over the world. There were several sources of sulfur in urban areas, compare with the suburbs areas. It was significantly that the SO₄^2- concentration andδ³⁴S at two sites smaller than the Qianhu and Qingshan Lake, which indicated that the precipitation was not the main source of sulfate in surface water. During the rainy season, the sea salt aerosol was the major source of precipitation with a greaterδ³⁴S value in the rainstorm, while the local land-based sources (anthropogenic and biological sulfur) were the major source of precipitation with a lowerδ³⁴S value. The biological sulfur was the major factor in rainwater of suburban in the spring and summer, and both the anthropogenic and biological sulfur of urban, whereas the sea salt sulfur had less effect to suburban and urban.