西安市降水化学组成及来源解析

Analysis on chemical composition of precipitation and its source apportionment in Xi′an City

为研究西安市大气降水污染特征以及来源,对2000—2017年西安市城市站和背景站大气降水组分、沉降以及来源进行对比分析.结果表明,2000—2017年西安市大气降水酸性较弱,城市站的大气降水电导率高于背景站,表明城区降水污染较严重.城市站主要无机酸离子为NO-3和SO42-,主要碱性离子为NH+4和Ca2+,而背景站的主要酸性和碱性离子分别为NO-3和Ca2+.由SO42-和NO-3的比值表明近年来西安市大气污染物排放类型由燃煤型向混合型转变的趋势.从湿沉降量上分析,背景站硫和氮的湿沉降量远小于城市站,表明西安市城市地区的大气硫和氮污染问题更严重.城市站和背景大气降水离子的来源除了扬尘、农业、化石燃料燃烧、机动车排放,城市站和背景站大气降水离子的来源还分别有海盐和生物质燃烧.

In order to study the characteristics and sources of the air pollution in Xi′an, the atmospheric precipitation components, deposition and source of urban site and background site in Xi′an in 2000—2017 were compared and analyzed. The results showed that from 2000 to 2017, the acidity of precipitation in Xi′an was weak, and the conductivity of precipitation in urban site was higher than that in background site, indicating that the precipitation pollution in urban area was serious. The main inorganic acid ions in the urban site were NO-3 and SO42-, and the main basic ions were NH+4 and Ca2+, while the main acid and basic ions in the background station were NO-3 and Ca2+, respectively. The ratio of SO42- to NO-3 indicated that the emission type of air pollutants in Xi′an had changed from coal-fired to mixed in recent years. From the analysis of wet deposition, the wet deposition of sulfur and nitrogen in the background site was far less than that in the urban site, which indicated that the air pollution of sulfur and nitrogen in Xi′an urban area was more serious. In addition to dust, agriculture, fossil fuel combustion and vehicle emission, the sources of atmospheric precipitation ions in urban and background site also included sea salt and biomass combustion, respectively.