天津市典型区域PM2.5中水溶性离子污染特征

为了解天津市不同区域PM_2.5中水溶性离子污染特征，于2015年7月、10月及2016年1月、4月，在天津市南开区（简称“市区”）及武清区采集PM_2.5样品，结合气象因素、气态污染物研究，分析了样品中水溶性离子污染特征及来源.结果表明:①天津市市区及武清区PM_2.5中水溶性离子组分主要为二次离子（SO₄2-、NO₃-、NH₄+）；不同区域PM_2.5中二次离子各季节占比略有不同，市区为夏季（54.0%）>秋季（42.5%）>春季（41.3%）>冬季（40.7%），武清区为夏季（53.0%）>春季（44.6%）>秋季（43.4%）>冬季（33.2%）.②冬季市区、武清区PM_2.5中水溶性离子组成差异较大，其他季节水溶性离子组成相似；夏季市区及武清区颗粒物呈酸性，其他季节均呈碱性，冬季武清区颗粒物碱性强于市区.③不同季节市区及武清区PM_2.5中SO₄2-均以（NH₄）₂SO₄形式存在，NO₃-冬季以NH₄NO₃形式存在，其他季节NO₃-主要以NH₄NO₃和HNO₃形式共存；市区Cl-主要以NH₄Cl、KCl和NaCl形式存在，武清区Cl-主要以NH₄Cl、KCl形式存在.④对市区及武清区来说，均相反应和非均相反应是SO₄2-重要生成途径，均相反应是生成NO₃-的主要途径.研究显示，代表一次排放的机动车源、燃煤源和二次无机粒子混合源对天津市PM_2.5中水溶性离子贡献率最高，工业源和扬尘源对市区的影响较大，农业源对武清区的影响较大. 

Characterization of Water-Soluble Ions in Typical Regional PM2.5 in Tianjin City

PM_2.5 samples were collected in the Tianjin City urban area and the Wuqing District in July and October of 2015 and January and April of 2016. The water soluble inorganic ions (WSⅡ) in the samples were analyzed. By combining the meteorological factors and gaseous pollutants, the characteristics and main sources of WSⅡ were researched. The results showed that: (1) The SNA (SO₄2-, NO₃- and NH₄+) were the dominant ions in the total WSⅡ. The proportion of SNA in total WSⅡ showed different seasonal variations in different regions: summer (54.0%) > autumn (42.5%) > spring (41.3%) > winter (40.7%) in the urban area, and summer (53.0%) > spring (44.6%) > autumn (43.4%) > winter (33.2%) in the Wuqing District. (2) For two sampling sites, the WSⅡ compositions were obviously different in winter, and were similar in the other seasons. The PM_2.5 samples were acidic in summer and were alkaline in the other seasons in two areas. The PM_2.5 samples were more alkaline in the Wuqing District than in the urban area. (3) SO₄2- existed in the form of (NH₄)₂SO₄ in four seasons, NO₃- existed in the form of NH₄NO₃ in winter, and in the other seasons NO₃- existed in the form of NH₄NO₃ and HNO₃. Cl- existed in the form of NH₄Cl, KCl and NaCl in the urban area, while in the Wuqing District, Cl- existed in the form of NH₄Cl and KCl. For the two sampling areas. (4) SO₄2- were formed mainly through homogeneous and heterogeneous reactions and NO₃- were formed through homogeneous reactions. The research identified that the major sources of WSⅡ were vehicles, coal combustion and secondary inorganic particles, in addition, industrial source and dust source were also contributors in urban area, and agricultural source was a contributor in Wuqing District.