西安城市工业区和咸阳郊区大气降水S同位素地球化学

Sulfur isotope geochemistry of atmospheric precipitation in Xi'an and Xianyang,Shaanxi Province,China

对2007年度西安城市工业区(主要包括西安市区和咸阳市区)和咸阳郊区永寿县的大气降水SO24-含量及S同位素组成(δ34S值)进行了测定。结果显示,西安城市工业区和咸阳郊区大气降水的SO42-含量具有基本相同的年内变化规律,都表现为冬季高、夏季低的特征。而且除9月份外,其他各月份均是西安城市工业区高于咸阳郊区。西安和咸阳所有大气降水样品的δ34S值都为正值,西安大气降水δ34S值的变化范围为8.71‰～19.05‰,平均为13.41‰,咸阳永寿大气降水δ34S值的变化范围为4.67‰～20.59‰,平均为11.23‰。相比国内其他地区大气降水的S同位素组成,西安和咸阳两采样点的大气降水具有相对较高的δ34S值。在采样年度内,西安大气降水δ34S值的季节变化规律不明显,而咸阳永寿大气降水δ34S值则表现为冬季低、夏季高的季节波动规律。海相贡献比例计算结果显示,两地大气降水SO42-海相输入比例很小。再结合大气降水δ34S值特征,推断认为西安城市工业区大气降水SO42-主要来自工业生产燃煤释放的SO2的转化,属于燃煤型大气污染,而咸阳郊区永寿县大气SO2则主要来自西安城市工业区大气SO2的扩散。

The sulfate concentrations and sulfur isotopic compositions of precipitation samples collected from January 2007 to January 2008 in industrial regions of Xi＇an and Yongshou county, the rural area of Xianyang district, were determined to investigate the potential sources of SO4^2-. The results show that the variation patterns of SO4^2- concentrations are quite similar in Xi＇an and Xianyang sampling sites, with higher level in the winter and lower level in the summer. The SO4^2- concentrations of precipitations sampled in Xi＇an industrial regions are systematically higher than those of rural Xianyang samples collected at the same time, with the exception of September. The δ^34S values of SO4^2- range from 8. 71‰ to 19.05‰ with an average value of 13.41‰ in Xi＇an industrial regions and 4. 67‰ to 20. 59‰ with an average value of 11.23‰ in rural Xianyang. Furthermore, the δ^34S values of SO4^2- in winter are clearly lower than those of summer in the Xianyang precipitation samples. This kind of seasonal variations, however, is not observed in the Xi＇an rainwater. It is estimated that contributions of SO4^2- from sea salt is limited for both locations. We propose that SO4^2- in precipitation samples in the study regions came mainly from atmospheric SO2 released that the air pollution in during industrial coal combustion, based on S isotopic compositions of SO4^2-. This implies Xi＇an belongs to the type of coal consumption pollution. SO2 in Yongshou county, rural Xianyang comes mostly from the diffusion of SO2 originated from Xi＇an industrial regions.