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.