摘要
为探究昆明市大气中水溶性无机离子的化学组分、季节差异及主要来源,本研究于2019年12月至2020年11月在云南大学进行PM2.5样品采集,利用离子色谱仪分析样品中水溶性无机离子的质量浓度,并结合离子相关性分析、后向轨迹分析和主成分分析等方法,阐明了昆明市大气中PM2.5及其水溶性无机离子的季节污染特征及来源.结果表明,采样期间各季节总水溶性无机离子浓度均值排序为春季((5.6±2.2)μg·m-3)＞冬季((5.5±2.6)μg·m-3)＞秋季((4.3±2.8)μg·m-3)＞夏季((3.6±2.2)μg·m-3),水溶性无机离子年质量浓度的均值从大到小为SO42-＞Ca2+＞NO3-＞NH4+＞K+＞Cl-＞Na+＞Mg2+＞F-,其中SO42-、Ca2+、NO3-和NH4+是主要的水溶性无机离子.Ca2+主要源于土壤粉尘,其他三者由前体物(SO2、NOx和NH3)二次转化生成,主要受化石燃料燃烧排放影响.SOR和NOR全年均值分别为0.20和0.02,表明在相同的环境里,SO2二次转化为SO42-的过程更易发生,且在秋季转化速率最大(SOR=0.23).SO42-、NO3-和NH4+在秋季主要以NH4NO3和(NH4)2SO4的形式存在,其他三季则以NH4HSO4和NH4NO3的形式存在.昆明市大气PM2.5中水溶性无机离子在冬、秋和春季一致,主要来自二次源和生物质燃烧源,其次是工业源和土壤尘,而夏季则主要来自机动车尾气、生物质燃烧源和土壤尘.除本地排放的影响外,冬季和夏季受到来自缅甸、老挝和贵州污染气团的影响,春季污染气团来自缅甸、云南本地和贵州,而秋季则受到云南东部和南部地区的气团输送影响.
Abstract
In this study,PM2.5 samples were collected at Yunnan University,Kunming from December 2019 to November 2020 to explore the chemical composition,seasonal variation,and sources of water-soluble inorganic ions in Kunming.The analyzed mass concentration of water-soluble inorganic ions(WSⅡs)were combined with correlation,backward trajectory,and principal component analysis to clarify the seasonal characteristics and potential sources of PM2.5 and WSⅡs in Kunming.The results indicated that the mean concentrations of WSIIs peaked in spring((5.6±2.2)μg·m-3),followed by winter((5.5±2.6)μg·m-3),autumn((4.3±2.8)μg·m-3),and summer((3.6±2.2)μg·m-3).The average annual mass concentration of WSIIs was SO42-＞Ca2+＞NO3-＞NH4+＞K+＞Cl-＞Na+＞Mg2+＞F-,among which SO42-,Ca2+,NO3-,and NH4+dominant the fractions in WSIIs.Ca2+mainly came from soil dust,while the other three were generated by the secondary formation of its precursors(i.e.,SO2,NOx,and NH3),which are mainly emitted by anthropogenic emissions(i.e.,fossil fuel combustion).Here,the annual average values of SOR and NOR are 0.20 and 0.02,respectively,indicating that the secondary conversion from SO2 to SO42-is more likely to occur with the same weather conditions.The conversion rate was highest in autumn(SOR=0.23).SO42-,NO3-,and NH4 mainly exist in the form of NH4NO3 and(NH4)2SO4 in autumn,and the other seasons exist in the form of NH4HSO4 and NH4NO3.The WSIIs and PM2.5 in Kunming showed the similar sources,which were mainly from the secondary reaction and biomass combustion sources,followed by industrial and soil dust sources,in winter,autumn,and spring.In contrast,WSIIs and PM2.5 were mainly from motor vehicle exhaust,biomass burning sources,and soil dust in summer.Apart from the local emissions,the polluted air masses showed a seasonal variation:Myanmar,Laos,and Guizhou in winter and summer;Myanmar,Yunnan,and Guizhou in spring;eastern and southern parts of Yunnan in autumn.
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