西安市PM_(2.5)中水溶性离子特征及重污染过程分析

Analysis of Water-soluble Ions Characteristics and Heavy Pollution Process in PM_(2.5) in Xi'an City

为了解西安市大气污染特征及成因,更好的为后续大气污染防治提出可行建议。利用2020年采暖季西安市污染监测数据与气象要素观测数据,采用在线观测方法,对西安市不同污染水平下PM_(2.5)中水溶性离子组分特征及重污染事件进行分析,结果表明:2020年西安市采暖季空气质量首要污染因子为PM_(2.5),且其浓度提升与SO_(2)、NO_(2)大量排放及二次转化率升高有关;不同污染水平下,污染因子及离子组分浓度与污染水平呈正相关,并且二次离子组分及K^(+)、Cl^(-)明显升高;污染天气下,PM_(2.5)与PM_(10)的相关性较弱,SO_(2)转化为SO_(4)^(2-)的速率稍高于NO_(2)转化为NO_(3)^(-)的速率,且不利的气象条件更加有利于NO_(2)转化为NO_(3)^(-);新冠疫情期间,各污染物浓度有明显降低趋势;根据N/S可知,西安市采暖季污染源以氮排放源为主,污染天气下,氮排放源升高趋势明显,重污染事件分析表明西安市重污染应对过程与采暖季机动车尾气排放、燃煤排放及不利气象导致的二次污染有较大关系。根据西安市采暖季空气质量污染现状,结合气象要素分析,为西安市采暖季大气污染防治提供实质性建议与参考。

n order to understand the characteristics and causes of air pollution in Xi'an,and put forward feasible suggestions for subsequent prevention and control of air pollution,based on the pollution monitoring data and meteorological observation data of Xi'an in the heating season of 2020,the characteristics of water-soluble ion components in PM_(2.5) and heavy pollution events under different levels were analyzed by online observation method.The results showed that the primary pollution factor of air quality in Xi'an in the heating season of 2020 was PM_(2.5),the increase of its concentration is related to the large emission of SO_(2) and NO_(2) and the increase of secondary conversion rate.Under different pollution levels,the concentrations of pollution factors and ion components were positively correlated with the pollution levels,and the secondary ion components,K^(+)and Cl^(-)increased significantly.In polluted weather,the correlation between PM_(2.5) and PM_(10) is weak.the conversion rate of SO_(2) to SO_(4)^(2-)is slightly higher than that of NO_(2) to NO_(3)^(-),adverse meteorological conditions are more conducive to conversion of the latter.During the period of COVID-19,the concentrations of various pollutants showed a significant decreasing trend.According to N/S,the source of pollution in the heating season is mainly Nitrogen emission sources with an obvious increasing trend.The analysis of heavy pollution events showed that the process of dealing with heavy pollution has a great relationship with vehicle exhaust emissions,coal burning emissions and secondary pollution caused by adverse weather.According to the current situation of air quality pollution in Xi'an,combined with the analysis of meteorological elements,this paper provides substantive suggestions and references for the prevention and control of air pollution in Xi'an in the heating season.