西沙永兴岛大气降水化学特征及来源分析

于2013年对南海西沙永兴岛雨水进行采集，分析了其主要阴阳离子，利用PMF模型对不同离子组成的来源进行解析并运用TrajStat软件模拟后向气团轨迹污染物来源区域的分析.结果表明，永兴岛降水离子浓度顺序为：Cl^-、SO₄^2-、NO₃^-和Na⁺、Ca²⁺、Mg²⁺、NH₄⁺、K⁺.Na⁺和Cl^-是降水中主要的阴阳离子，表现出海洋性降水的特征.SO₄^2-、Mg²⁺、K⁺主要来源于海水，但SO₄^2-也受化石燃料燃烧等影响，而K⁺可能受生物质燃烧的影响.Ca²⁺主要来源于土壤，少数来源于其他影响.NO₃^-主要来源于化石燃料燃烧释放，而NH₄⁺有多种来源，包括内陆人为活动的排放和海洋本身有机物降解过程释放的影响.根据Redfield比，可以初步计算出降水中NO₃^-和NH₄⁺对南海新生产力的贡献约为4.8%~13.5%.后向气团轨迹表明，永兴岛降水的离子来源区域相对复杂，包括我国东北地区、南方区域，以及马来西亚等国家、地区的影响，或者来源于南海局地的影响.

Chemical characteristics and source apportionment of atmospheric precipitation in Yongxing Island

Concentrations of major ions concentration were analyzed in rainwater collected at Yongxing Island of Xisha, South China Sea during 2013. The positive matrix factorization (PMF) and backward trajectories of air mass were used to identify the sources of major ions. The results showed that the orders of volume-weighted average concentrations of anions and cations were: Cl^-, SO₄^2-, NO₃^- and Na⁺, Ca²⁺, Mg²⁺, NH₄⁺, K⁺, respectively. The Na⁺ and Cl^- were the major anion and cation, respectively, indicating that they were derived from sea water. The SO₄^2-, Mg²⁺, and K⁺ were also mainly from sea water; while part of SO₄^2- might come from the combustion of fossil fuel and K⁺ from biomass burning. The Ca²⁺ was mainly from soil, while NO₃^- mainly from combustion of fossil fuel. Furthermore, this study found that NH₄⁺ had more complex sources, such as the emissions of human activities, organic matter degradation in marine environment, and etc. According to the Redfield ratio of carbon to nitrogen, the contribution of NO₃^- and NH₄⁺ in rainwater to new production in South China Sea was about 4.8% to 13.5%. Back trajectories indicated that the sources of ions in rainwater at Yongxing Island derived from many regions, such as the northeast China and south China, and Malaysia, or South China Sea itself.