邯郸市大气污染过程PM_(2.5)中水溶性离子特征与来源解析

Characteristics and source analysis of water-soluble ions in PM_(2.5) during air pollution in Handan City

为研究邯郸市污染过程大气PM_(2.5)中水溶性离子浓度特征与来源,于2021年10—12月采集了大气PM_(2.5)样品,并结合温度、相对湿度等气象因素以及气态污染物(SO_(2)、NO_(2))浓度对水溶性离子进行分析.结果表明,采样期间PM_(2.5)浓度范围为(41.34—216.96)μg·m^(−3),浓度均值(111.12±38.6)μg·m^(−3);TWSII(总水溶性离子)质量浓度为(56.08±24.26)μg·m^(−3),其中主要离子物种SNA(SO_(4)^(2−)、NO_(3)^(−)、NH_(4)^(+))在TWSII中占比89.48%;PM_(2.5)昼、夜浓度均值接近,其中NO_(3)^(−)、NH_(4)^(+)、SO_(4)^(2−)、Ca^(2+)、Na^(+)和Mg^(2+)的浓度白天高于夜晚,Cl^(−)、K^(+)和F^(-)等离子则是夜晚浓度较高;AE/CE(阴阳离子电荷当量比)昼、夜比值分别为1.12、1.16,说明大气气溶胶呈酸性;依据相关性分析判断各个离子间的结合方式,NH_(4)^(+)与NO_(3)^(-)、SO_(4)^(2-)之间具有显著相关性,结合经验公式计算结果确定铵盐主要存在状态为(NH_(4))_(2)SO_(5)和NH4NO_(3);采样期间SOR、NOR值分别为0.38、0.33(白天为0.38、0.38,夜间为0.37、0.28),说明存在明显的SO_(2)和NO_(2)二次转化过程,且NO_(3)^(−)/SO_(4)^(2−)比值为1.88,说明移动源(机动车尾气排放)对于PM_(2.5)的贡献大于固定源(燃煤);主成分分析结果表明,PM_(2.5)水溶性离子主要来源有二次转化、生物质燃烧、固定源(燃煤)和扬尘源;后向轨迹模型中聚类分析得出,外部污染传输持续存在,整个采样过程中主要污染气团来源均为来自于偏西方向的短距离传输.

In order to study the characteristics and sources of water-soluble ions in atmospheric PM_(2.5) during the pollution process in Handan city,samples of atmospheric PM_(2.5) were collected from October to December 2021.The water-soluble ions were analyzed in combination with meteorological factors such as temperature,relative humidity and the concentrations of gaseous pollutants(SO_(2),NO_(2)).The concentration range of PM_(2.5) during the sampling period is(41.34—216.96)μg·m^(-3),with the mean concentration of(111.12±38.6)μg·m^(-3).The mass concentration of TWSII(total water-soluble ions)was(56.08±24.26)μg·m^(-3),with the main ion species SNA(SO_(4)^(2−),NO_(3)^(−),NH_(4)^(+))accounting for 89.48%.The day and night concentrations of PM_(2.5) are simar.NO_(3)^(−),NH_(4)^(+),SO_(4)^(2−),Ca^(2+),Na^(+)and Mg^(2+)concentrations are higher during the day than at night,while Cl^(-),K^(+)and F-concentrations are higher at night.The day and night ratio of AE/CE(anion cation charge equivalent ratio)is 1.12 and 1.16,respectively,indicating that atmospheric aerosols are acidic.According to correlation analysis,there is a significant correlation between NH_(4)^(+)and NO_(3)^(−),also with SO_(4)^(2−).Based on empirical formula calculations,the main existing states of ammonium salts are(NH_(4))_(2)SO_(5) and NH_(4)NO_(3).During the sampling period,the SOR and NOR values were 0.38 and 0.33,respectively(0.38 and 0.38 during the day,and 0.37 and 0.28 at night),indicating a significant secondary conversion process of SO_(2) and NO_(2).The NO_(3)^(−)/SO_(4)^(2−)ratio was 1.88,indicating that the contribution of mobile sources(motor vehicle exhaust emissions)to PM_(2.5) was greater than that of fixed sources(coal combustion).The principal component analysis results indicate that the main sources of water-soluble ions in PM_(2.5) are secondary conversion,biomass combustion,fixed sources(coal combustion),and dust sources.The clustering analysis in the backward trajectory model shows that external pollution transmission persists,and the main source of pollution air mass is short distance transmission from the westward direction.