华中背景地区大气颗粒物中水溶性离子特征与来源解析

Characteristics and source apportionment of water-soluble inorganic ions in PM_(2.5) in central China background region

为探究华中背景地区大气PM_(2.5)中水溶性无机离子(WSIIs)的特征、形成机制及来源,本研究在金沙国家大气本底站进行了为期一年的采样观测.结果表明:PM_(2.5)年均质量浓度为(31.40±2.05)µg/m^(3),季节变化明显,冬季最高,夏季最低.二次无机气溶胶(SNA,即SO_(4)^(2-)、NO_(3)^(-)和NH_(4)^(+))是WSIIs的重要组成部分,春季、夏季、秋季和冬季SNA在WSIIs所占比例分别为84.0%、77.6%、79.8%和84.5%.研究期间阴阳离子物质的量当量比值(AE/CE)的平均值为0.91,PM_(2.5)呈现弱碱性.(NH_(4))2SO_(4)、NH_(4)NO_(3)和NH_(4)Cl是夏季离子形态的主要形式,而(NH_(4))2SO_(4)是春、秋、冬季的主要离子形态.硫氧化率(SOR)和氮氧化率(NOR)分别为0.48和0.14,与PM_(2.5)呈显著正相关,表明SO_(4)2-和NO_(3)-主要来自二次生成,二次转化是PM_(2.5)浓度上升重要原因.WSIIs的潜在来源和传输路径具有明显的季节特征,近距离输送气流的SOR和NOR均较大,污染物从源区向背景地区迁移过程中二次转化明显,来自西北或者正北方的远距离气团携带的污染物浓度较大,受到明显的区域传输影响.

To investigate the characteristics,formation mechanisms,and sources of water-soluble inorganic ions(WSIIs)in PM_(2.5) in the central China background area,the study conducted a one-year sampling observation at the Jinsha atmospheric background station.The results showed that the average annual mass concentration of PM_(2.5) was(31.40±2.05)µg/m^(3),showing remarkable seasonal variations of the highest level in winter and lowest in summer.Secondary inorganic aerosol(SNA,i.e.,SO_(4)^(2-),NO_(3)^(-),and NH_(4)^(+))was an important component of PM_(2.5).The proportions of SNA in WSIIs in spring,summer,autumn,and winter were 84.0%,77.6%,79.8%,and 84.5%,respectively,indicating secondary formation was pronounced.The average molar equivalent ratio of anions and cations(AE/CE)during the study period was 0.91,and PM_(2.5) showed weak alkalinity.(NH_(4))2SO_(4),NH_(4)NO_(3),and NH_(4)Cl were the main forms of ion species in summer,while(NH_(4))2SO_(4) may be the main form in spring,autumn,and winter.The sulfur oxidation rate(SOR)and nitrogen oxidation rate(NOR)were 0.48 and 0.14,respectively,showing a significant positive correlation with PM_(2.5),indicating that secondary conversion was an important reason for the increase in PM_(2.5) concentration.The potential sources and transmission paths of WSIIs had obvious seasonal characteristics.The secondary transformation of pollutants during the migration process from the source area to the background area was obvious,and the concentration of pollutants carried by long-distance air masses from the northwest or due north was relatively high.