| The city of Shanghai, as China's economic and financial trade and shipping center, with the accelerated process of urbanization, population expansion and the continued increase in car ownership, was faced with the increasingly serious problem of acid rain pollution. The precipitation changes in concentrations of toxic and hazardous substances monitoring and source apportionment of research should be strengthened and deepened, in order to avoiding acid rain pollution causing the urban ecology, population and economic development more damage. In this study we report the severe acid rain over Shanghai, based on the continuing sampling the precipitation samples throughout the whole year and the chemical composition of atmospheric precipitation in Shanghai to study the cause of acidification of precipitation in Shanghai, heavy metal pollution, organic carbon and nitrogen content and the seasonal variations of wet deposition, and Be and Pb concentrations in precipitation and wet deposition fluxes of seasonal variation, and using correlation analysis, principal component analysis, sea salt tracer, air mass back trajectory model and the natural radionuclide tracers 7Be and 210Pb to judge the source of major ions in precipitation of Shanghai.Through the above study, draw the following conclusions:1. The pH value of precipitation in Shanghai has significant seasonal variations, with winter and spring low, summer and autumn high and the overall low pH value. The annual average pH of precipitation only was 4.35, well below the standard acid rain value of pH<5.6, indicating acid rain pollution is particularly serious.2. The concentrations of major soluble ions were in the order of SO42->NH4+> Ca2+>NO3->Cl->Na+>Mg2+>K+>F-.The annual average ion concentrations of SO42-,NO3-, Cl- were 109.46,44.76, and 36.23μeq/L in rainwater, respectively; The annual average ion concentrations of NH4+, Ca2+ and Na+ were 90.02,87.84 and 25.71μeq/L in rainwater, respectively. During 2009 to 2010 the average annual precipitation in Shanghai, the equivalence ratio of SO42-/NO3- was 2.45, indicating that Shanghai acid rain was sulfuric acid and nitric acid compound; from 1999 to 2009, the ratio of SO42-/NO3- in precipitation of Shanghai has been a downward trend, and the ratio has declined from 6.44 in 1999 to 2.45 in 2009, indicating that in recent years atmospheric NOx pollution in relation to SO2 pollution was more serious in Shanghai; 1999～2009 the equivalent ratio of (Ca2++NH4+)/(SO42-+NO3-) in precipitation of Shanghai first increased and then showed a downward trend, indicating that in recent years, the severe acid precipitation was closely related to the reduction of alkaline substances in the urban atmosphere of Shanghai.3. The volume-weighted average (VWM) concentrations of heavy metals in atmospheric precipitation in Shanghai, Al, Zn, Fe, Mn, Pb and Cu were 69.75, 58.16,38.38,11.57,11.10 and 4.28μg/L, respectively. The concentrations of Pb and Zn in precipitation were over the standard of Class I surface water limits for heavy metals and other heavy metals were not exceeded, indicating in Shanghai Pb and Zn pollution in precipitation were relatively serious.4. The concentration range of dissolved organic carbon (DOC) in rainwater samples were 1.36～12.52 mg/L, with the annual average concentration of 2.80mg/ L. The average content of total soluble nitrogen 3.31 mg/L; the average content of nitric nitrogen were 0.56 mg/L; the annual average concentration of ammonium nitrogen were 1.07 mg/L; the annual average content of organic nitrogen were 1.68 mg/L.The annual average content in precipitation of total nitrogen were 3.31 mg/L significantly higher than the surface water of the total nitrogen content of V class quality standards required, indicating that total nitrogen content in atmospheric precipitation of Shanghai were seriously overweight and became an pollution source of the surface drinking water in Shanghai.5. The concentration of 'Be in Shanghai precipitation was in the range of 0.47～5.99 Bq/L, and the volume-weighted annual average concentration was 1.46 Bq/L; the concentration of 210Pb in Shanghai precipitation was in the range of 0.06～0.90 Bq/L, and the volume-weighted annual average concentration was 0.26 Bq/L. The concentrations of 7Be and 210Pb in Shanghai precipitation had the same seasonal variation:with higher concentrations in winter and spring, with the lowest concentrations in summer, and between the concentration of the middle in autumn. The annual wet deposition flux of 7Be was 1834.24 Bq·m-2·yr-1; the annual wet deposition flux of 210Pb was 295.98 Bq·m-2·yr-1. The wet deposition flux of 7Be and 210Pb accounted for the total atmospheric deposition flux 89% and 62%, while dry deposition accounted for only 11% and 38% of the total deposition flux, indicating 7Be mainly through wet deposition landed to the ground surface,210Pb not only through wet deposition to the surface, but also by dry deposition to the surface deposition, and wet deposition is greater than the contribution of dry deposition. The concentrations ratio value of 7Be/210Pb ranged from 2.61 to 25.77, with the annual average value of 6.72, and the ratio value of 7Be/210Pb in spring precipitation were significantly higher than the other three seasons. It can be concluded in the spring of Shanghai, there were the transport of rich 'Be air mass from the upper atmosphere to near-surface called "Spring leakage" phenomenon.6. The source identification with several different methods indicated that Mn, Zn, Sr, Cu, Cd, Ni mainly derived from soil dust; Fe, Al, and Pb mainly derived from industrial activities or the direct emissions of coal-fired emissions; SO42-, NO3-, Ca2+ were mainly anthropogenic contribution, Mg2+, K+ were mainly crustal source contributions, Na+, Cl- were mainly marine source contribution. The concentrations of NO3-, SO42-, NH4+ in northwest air mass sources of precipitation were highest during all the directions of air mass sources of precipitation; the ion concentrations in precipitation with the air masses from ocean origin were overall lower than that in precipitation with the continental air mass origin, indicating that the chemistry of precipitation in Shanghai, was under the influence of not only local pollution sources, but also the long-and moderate-range transport of pollutants from northwest and southwest direction over the continent.7. The correlations between 7Be and NO3-, SO42-, NH4+ is higher, and the correlations between 210Pb and SO42-,NH4+ is relatively high. The highest concentration of 7Be and 210Pb concentrations in the winter, indicating that one importation reason of severe acid precipitation in Shanghai was caused by long-range land-based sources of air pollution material transfer. The correlation coefficients of SO42-with 7Be and 210Pb were significantly greater than that of NO3-, indicating the long-range land-based transfer had greater influence of SO42-, compared with the influence of NO3-. The ratio of 7Be/210Pb had stronger correlation with the F-, but with other ions poor correlation, indicating that high-level the vertical transport of atmospheric and surface emissions of substances from natural sources upward contributed little to the ion source in precipitation of Shanghai, while the long-range land-based sources of atmospheric pollutant transport and the local anthropogenic emissions had more contribution.
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