Numerical Simulation Of The Change Of Sulphur Deposition And The Impact Of Atmospheric Pollutants On Acidity Of Below-cloud Rain In Fujian Province

Six cities in Fujian Province including Fuzhou, Xiamen, Sanming, Quanzhou, Zhangzhou, Longyan are listed in the national controlling area of acid rain. The formation mechanism of acid rain is very complex relating to emission sources, chemistry, transport and deposition. In this paper the contribution of local and non-local sources to Fujian Province and the acidity change of cloud-water and rainwater in below-cloud area in Xiamen and Fuzhou are discussed.Fujian has low SO2 emissions but its SOx pollution is very serious. This suggests that transport of SOx from neighboring provinces is very significant. Using a 3-D Eulerian transport model with emissions and meteorological data in 1995, 2000, and 2002, the sulphur deposition amounts in Fujian coming from its local emissions and the emissions from its neighboring provinces are simulated. It can be concluded that above 50% of the total sulphur deposition in Fujian is resulted from long-range transport. The change of sulphur deposition in four seasons is further analyzed and explained with changes in meteorological conditions. Comparison of the whole-year and every-season deposition amounts indicates that the contribution of local emissions to SO2 deposition in Fujian Province is very large whereas that to SO42- deposition in this province is small and SO42- deposition is mainly from other provinces, accounting for more than 50% of its total deposition amounts.Simulating also showed that the sulphur deposition amount of 9 cities of Fujian province is decreased year by year except for Xiamen; the sulphur deposition in Xiamen is mainly resulted from local sources; wind plays an important role in SOX transport; sulphur deposition amounts of in-land cities are generally larger than that of coastal cities; smaller area cities receive less sulphur deposition while larger ones receive more.There are in-cloud and below-cloud processes in formation of acid rain, but the relative importance of these two processes is different in various cities. A below-cloud rainwater acidification model is used to simulate the effect of below-cloud gaseous pollutants and aerosol on the acidity of rain in Xiamen and Fuzhou, together considering the process of rainwater absorbing and reacting with below-cloud gaseous pollutants and aerosol collision. The result indicates that the gases and aerosol below-cloud in Xiamen are acidic while those in Fuzhou are alkaline.