成都市PM2.5中无机组分与硝酸盐氮氧同位素变化特征

Characteristics of Inorganic Components and Nitrate Nitrogen-oxygen Isotopes of PM2.5 in the Chengdu City

2013年1月12日~2013年1月23日和2014年8月10日~2014年8月21日在成都市城东成都理工大学校园内按昼夜采集PM2.5样品,分析了PM2.5样品的质量浓度、9种水溶性无机离子含量和硝酸盐的δ15N和δ18O。结果表明,采样期间成都市PM2.5冬、夏季的质量浓度分别为161~677μg/m3(360±118μg/m3)和87~137μg/m3(92±18μg/m3),冬季超标2~9倍,属于重度污染,夏季超标1~2倍,属于轻度污染;SO42-、NO3-和NH4+(SNA)的质量浓度占总水溶性无机离子和PM2.5质量浓度的比值冬夏季分别为72%±14.3%和65%±9.2%,21.1%±2.5%和30.3%±6.9%,是主要的无机离子组分。结合离子相关性分析,SNA的存在形式在白天以(NH4)2SO4或NH4HSO4为主,部分以NH4NO3的形式存在,而在夜间则以NH4NO3为主,部分以(NH4)2SO4或NH4HSO4形式存在。成都市PM2.5中硝酸盐的δ15N和δ18O呈冬季高、夏季低的特征。冬季,硝酸盐来源于燃煤和机动车尾气;夏季,硝酸盐来源于机动车尾气、燃煤和农业土壤释放,根据其[NO3-]/[SO42-]值说明成都市冬夏季均以固定污染源(燃煤)为主,移动污染源(机动车尾气)为辅。成都市冬季大气颗粒物中硝酸盐主要由NOx经O3氧化形成,夏季主要经·OH氧化形成硝酸盐或N2O5水解生成硝酸盐。

PM2.5 samples were collected in the campus of Chengdu University of Technology in Chengdu day and night from 12 to 23 January 2013 and from 10 to 21 August 2014,mass concentrations of nine water soluble inorganic ion species and values ofδ15N andδ18O in nitrate were analyzed.The results showed that mass concentrations of PM2.5 in summer and winter were 161~677μg/m3(360±118μg/m3)and 87~137μg/m3(92±18μg/m3),respectively,implying the severe PM2.5 pollution in winter,2 to 9 times exceeding the PM2.5 standard,and the light PM2.5 pollution in summer,1 to 2 times exceed the PM2.5 standard.SO42-,NO3-and NH4+(SNA)were the major water-soluble inorganic ionic components,they accounted for 72±14.3%and 65±9.2%of the total mass of water-soluble inorganic ions and 21.1±2.5%and 30.3±6.9%of the total mass of PM2.5 in winter and summer,respectively.According to the ionic correlation analysis,the main form of SNA in PM2.5 might be(NH4)2SO4 and/or NH4HSO4 in daytime and NH4NO3 in nighttime.The values ofδ15N andδ18O of nitrate in PM2.5 of Chengdu were higher in winter than in summer,indicating that sources of nitrate were coal combustion and vehicle exhaust in winter and were vehicle exhaust,coal combustion and agricultural soil release in summer.The mass ratio of[NO3-]/[SO42-]implied that the stationary sources,e.g.the coal combustion emission,were more important than the mobile sources,e.g.the vehicle emission.Nitrate in PM2.5 was mainly formed from the O3 oxidation of NOxduring winter and from the·OH oxidation of NOx and/or the hydrolysis of N2O5 in summer.