2018—2020年包头市大气PM_(2.5)中4种水溶性离子特征分析及源解析

Characteristic analysis and source apportionment of four water-soluble ions in PM_(2.5) in baotou atmosphere from 2018 to 2020

目的探讨包头市城区大气PM_(2.5)中4种水溶性离子(Cl^(-)、NO_(3)^(-)、SO_(4)^(2-)、NH_(4)^(+))的质量浓度水平、变化规律、存在形式及污染来源。方法于2018—2020年采集包头市大气PM_(2.5)样品249份,以离子色谱法分析Cl^(-)、NO_(3)^(-)、SO_(4)^(2-)和NH_(4)^(+)的质量浓度,分析其季节变化规律及与温度、相对湿度之间的相关性,拟合曲线分析其存在形式,以PMF模型解析其污染来源。结果2018—2020年包头市大气PM_(2.5)中4种水溶性无机离子NO_(3)^(-)、SO_(4)^(2-)、NH_(4)^(+)、Cl^(-)平均质量浓度总体呈下降趋势,其季节变化规律明显,SO_(4)^(2-)和NO_(3)^(-)质量浓度高于NH_(4)^(+)和Cl^(-)。SO_(4)^(2-)和NO_(3)^(-)的质量浓度与温度呈负相关,与相对湿度呈正相关,差异有统计学意义(P<0.01或P<0.05)。PMF模型解析结果显示,机动车排放源和燃煤源对大气PM_(2.5)中水溶性离子的贡献率较大,分别占39.46%和37.96%。结论包头市大气PM_(2.5)中水溶性离子各组分质量浓度总体呈下降趋势,SO_(4)^(2-)、NO_(3)^(-)是水溶性离子中贡献最大的两种离子,以燃煤等固定源对大气污染的影响为主。

Objective To study the concentration level,variation regularity,existing form and pollution source of four watersoluble ions(Cl^(-),NO_(3)^(-),SO_(4)^(2-)and NH_(4)^(+))in PM_(2.5)of Baotou urban area.Methods 249 samples of PM_(2.5)were collected from 2018 to 2020.The concentrations of Cl^(-),NO_(3)^(-),SO_(4)^(2-)and NH_(4)^(+)were analyzed by ion chromatography,the pollution sources were analyzed by fitting curve and PMF model.Results The annual average concentrations of four water soluble inorganic ions(NO_(3)^(-),SO_(4)^(2-),NH_(4)^(+)and Cl^(-))in PM_(2.5)from 2018 to 2020 in Baotou were variate regularity.The mass concentrations of SO_(4)^(2-)and NO_(3)^(-)were higher than those of NH_(4)^(+)and Cl^(-)in seasonal comparison.Temperature and relative humidity are the key meteorological factors affecting the formation of SO_(4)^(2-)-and NO_(3)^(-).The correlation analysis shows that the concentration of SO_(4)^(2-)and NO_(3)^(-)is negatively correlated with temperature and positively correlated with relative humidity.The Analytical results of PMF model show that the contribution rates of motor vehicle emission sources and coal-fired sources to water-soluble Ions in PM_(2.5)are 39.46%and 37.96%,respectively.Conclusion In Baotou,the total components of water-soluble ions show a decreasing trend.SO_(4)^(2-)and NO_(3)^(-)are the two most important water-soluble ions in PM_(2.5).Among them,coal burning and other fixed sources have a prominent impact on air pollution.