崇明东滩湿地降水化学特征及来源解析

2009年5月~2010年4月收集了崇明东滩湿地降水,测定了样品的pH值、电导率和主要水溶性离子的浓度,并利用富集因子法和后向轨迹分析对降水中无机离子成分进行源解析.结果表明,崇明东滩整体空气质量良好,大气污染物浓度较低.降水的pH值和电导率的加权均值分别为5.24,17.49μS/cm,为轻度污染的弱酸性水平;SO42?和NO3?是主要的致酸离子,加权浓度分别为52.27,21.39μeq/L;NH4+和Ca2+是主要的碱性离子,加权浓度分别为33.36,27.13μeq/L;离子来源分析表明,Na+和Cl?主要来自于海洋,NH4+的中和作用大于Ca2+和Mg2+,大气颗粒物主要以(NH4)2SO4、NH4HSO4、NH4NO3的形式存在;后向轨迹分析表明降水主要受海洋风向影响,西北、西南方向和长江三角洲地区的人为污染物的中长尺度传输是造成崇明东滩酸雨的重要原因.

Chemical characteristics and source apportioment of precipitation at Dongtan Wetland, Chongming

The rainfalls had been collected from May 2009 to April 2010 at Chongming Dongtan National Wetland. The pH value, electrical conductivity and major water-soluble ions of rain samples were measured. Enrichment factors and backward trajectory analysis were used to identify the potential sources of inorganic ions. The results showed that the air quality of Chongming Dongtan was good with much lower concentrations of air pollutants. The volume-weighted pH value and electrical conductivity were 5.24 and 17.49μS/cm respectively, which indicated low pollution and acidity level. SO42? and NO3? were the major acidic anions, with the volume-weighted mean concentrations values of 52.27 and 21.39μeq/L respectively. NH4+ and Ca2+ were the major alkaline cations with volume-weighted mean concentrations were 33.36 and 27.13μeq/L, respectively. Source attributions of inorganic ions in rainwater indicated that Na+ and Cl? mainly derived from the seawater spray. NH4+ showed the dominant neutralization effect over Ca2+ and Mg2+, which suggested the main forms of the atmospheric particles were (NH4)2SO4, NH4HSO4 and NH4NO3. Back trajectory analysis implied that the precipitation was mostly affected by air mass from sea, in which the air mass from Northwest, Southwest China and Yangtze River Delta might bring large amounts of anthropogenic pollutions through long and moderate range transport, which resulted the acid rain events at Chongming Dongtan.