[Geochemical character of precipitation in summer of Shanghai 2008-2009]

The chemical compositions of the rainwater collected in Shanghai in Summer of 2008-2009 were investigated. The chemical character and pollutant source of rainwater were evaluated depended on HYSPLIT model, ions tracer techniques, correlation and principal component analysis. The results showed that: (1) the mean pH in rain was 4.72 and 4.68; (2) the frequency of acid rain was 53.30% and 63.30%, respectively, in 2008 and 2009; (3) ionic concentration was SO4(2-) > NH4+ > NO3- > Cl- > Ca2+ > Na+ > Mg2+ > K+, in which the secondary components like SO4(2-), NO3- and NH4+ contributed significantly to total ions of rainwater and they accounted for 55.01% and 65.97% of total ions in 2008 and 2009, respectively, which indicate the severe secondary pollution in Shanghai; (4) the ratio of SO4(2-) to NO3- in Summer precipitation in 2008 and 2009 was 3.19 and 2.13, respectively, which implies sulfuric-nitrous mixed type of precipitation; (5) the content of DOC varied from 1.36 mg/L to 10.69 mg/L and average value was 2.44 mg/L in rainwater; (6) SO4(2-) and NO3- were mainly in the form of (NH4) 2SO4 and NH4NO3, which showed the dominant neutralization effect of NH4+ over Ca2+ in Summer. Source identification indicated that SO4(2-), NH4+, NO3-, K+ and most Ca2+ derived from anthropogenic sources, while Mg2+ and Cl- derived from both marine and non-marine but non-marine was over marine. The chemistry of precipitation in Shanghai was impacted by local pollutants and the long-and moderate-range transport by Southwest monsoon according to backward trajectory analysis.