上甸子本底站湿沉降化学成分变化与来源解析

ariations and source identification of chemical compositions in wet deposition at Shangdianzi background station

利用上甸子本底站自1999-2004年的降水资料,对8种离子（K^＋、Na^＋、Ca^2＋、Mg^2＋、NH4^＋、SO4^2-、NO3^-、Cl^-）浓度做了统计分析,并通过PMF（positive matrix factorization）方法对该地区的湿沉降来源做了解析.结果表明,①pH分布在4.41~6.55之间,电导率分布在40.97~69.64μS.cm^-1之间.②上甸子本底站的电导率结果明显高于清洁地区降水背景点（瓦里关全球大气本底监测站）、低于北京城区的观测结果,表明降水化学成分受大气污染显著,但污染水平要低于人类活动集中的地区.③SO4^2-、NO3^-、NH4^＋、Ca^2＋是上甸子站降水样品中最主要的水溶性离子;从季节变化来看,SO4^2-离子春季最高、夏季最低,NO3^-离子冬春两季浓度水平相当,夏季略偏低,H＋离子浓度春季最低,夏秋两季相当,冬季最高.④源解析结果表明,土壤尘是上甸子本底站降水化学成分最主要的来源;与施肥有关的农田排放是本底站降水成分的另一个重要的源;此外,来自污染地区的交通运输排放和燃煤排放的输送作用同样影响着该地区降水化学成分.

The paper analyzes the chemical characteristics of precipitation at Shangdianzi regional atmospheric background station, basing on the observational data from the period of 1999 -2004. Positive matrix factorization （ PMF, a new variant of factor analysis） was applied to the data set of concentrations of ions （K^＋、Na^＋、Ca^2＋、Mg^2＋、NH4^＋、SO4^2-、NO3^-、Cl^- ） in wet deposition. The results show that the annual mean pH value for the period was in the range of 4.41 - 6.55, and the annual mean conductivity varied from 40.97μS.cm^-1 to 69.64μS.cm^-1. The average conductivity at Shangdianzi is much higher than that at Waliguan Global Baseline Station but lower than that observed in the urban area of Beijing, suggesting that the chemical composition of precipitation at Shangdianzi is influenced by regional anthropogenic activities. SO4^2- , NO3^-, NH4^＋ , and Ca^2＋ were the major ions of precipitation at Shangdianzi. The seasonal variations of ion concentrations show that SO4^2- reached its maximum concentration in spring and minimum in summer; NO3^- had equally high values in summer and fall; H^＋ peaked in winter and had a minimum in spring. Four main sources of chemical compositions of wet precipitation at Shangdianzi station were identified using the PMF method. Soil dust was the most important source of the ions. The next most important source was farm emissions related to fertilization. Finally, transportation of pollutants from traffic and coal combustion emissions in polluted areas also contributed to the composition of precipitation at Shangdianzi station.