| 其他摘要 | The rainwater in the studied areas was typically acidic with a volume-weighted mean pH of 4.54, ranged from 3.64 to 6.76. SO4 and NO3 were the main anions, while NH4,Ca and Mg were the main cations. Even though SO4 was the dominant anion in precipitation, the SO4 contribution to precipitation acidity was reduced obviously and its sulfur-pollution character was weaken, while that of NO3 was markedly enhanced. SO4, NH4, Ca, H, NO3 had relative high deposition flux among all the ions, the deposition loading of the other ions were low in the precipitation. Seasonal variations of wet depositions are extremely apparent for all the components. SO4 and NO3, Ca and Mg as well as Na and Cl showed obvious correlations in this study. Other relatively good correlations were observed between the acidic and alkaline ions such as Ca and SO4, Mg and SO4, Mg and NO3. However, H showed no significant correlations with other ionic species. The results suggested that SO4, NH4, NO3, F were mostly attributed to the anthropogenic activities, Ca, Mg and K came mainly from the terrestrial source as well as Na and Cl from the marine source.
The values of δ34S of precipitation vary in the range from +0.53‰ to +14.23‰, with a meanδ34S values of +5.04‰. Sulfur isotopic composition of precipitation is basically identical in the spatial distribution. The values of δ34S of atmospheric sulfur dioxide vary in the range from +0.95‰ to +7.50‰, with annual meanδ34S values of +4.73‰. The values of δ34S of sulfate aerosols vary in the range from +6.39‰ to +9.83‰, with annual meanδ34S values of +8.09‰. The results showed striking seasonality between summer and winterδ34S values of precipitation and atmospheric sulfur dioxide in the central region of Zhejiang province with the summer samples being generally depleted in 34S compared with winter. The seasonal pattern ofδ34S values of precipitation and atmospheric sulfur dioxide may be explained by the temperature dependence of the isotope equilibrium fractionation associated with SO2 oxidation reaction during sulfate formation in the atmosphere. A greater relative contribution of biogenic sulfur during the summer also may have contributed to the lowerδ34S value in the summer. Anthropogenic sulfur is major sulfur pollution source of precipitation in the studied areas. The relative contributions of anthropogenic sulfur of different seasons in precipitation range from 53% to 91%, with an annual mean of 73%. The relative contributions of biogenic sulfur of different seasons in precipitation range from 8% to 44%, with an annual mean of 26%. Long distance transport sulfur is another important sulfur source in precipitation and its relative contributions vary in the range from 27% to 44%. The results suggested that heterogeneous oxidation of sulfur dioxide was dominant in the atmosphere of the studied areas. On the other hand, the obtained data also showed that homogeneous oxidation also played an important role in the mechanisms of oxidation reaction. Furthermore, the results also suggested that relative humidity in the atmosphere has an important influence on the oxidation mechanisms of sulfur dioxide in the studied areas. |
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