武汉市夏冬季典型大气污染过程的成因与来源分析

为了解武汉市夏冬季大气污染特征、成因及来源，基于武汉市20个监测点的观测数据，针对2017年7月21-31日及2018年1月13-25日两段典型大气污染过程分别展开研究.结果表明:武汉市大气污染呈现明显的季节性变化特征，夏季空气质量最优，春秋次之，冬季相对较差，夏冬季分别呈现明显的O₃和PM_2.5污染特征.夏季大气污染过程中平均ρ（O₃-8 h）为151.6 μg/m3，高温、低湿的气象条件有利于前体物VOCs和NO_x向O₃的转化，O₃的生成主要受VOCs控制，其中芳香烃和烯烃对O₃生成潜势的贡献较大，相对贡献率分别为43.7%和35.6%.冬季污染过程中平均ρ（PM_2.5）为129.1 μg/m3，静稳、高湿的气象条件会促进PM_2.5的吸湿增长及二次生成，二次离子和有机碳的贡献显著，约占ρ（PM_2.5）总量的72.4%.随着污染程度的加重，二次离子的转化程度及VOCs对SOA的生成潜势都逐渐增大，重度污染天气下前体物的二次转化程度约为非污染期的2.1~11.4倍.源解析结果显示，武汉市夏季大气污染过程受溶剂涂料使用、机动车尾气排放和工业排放VOCs的影响较大；冬季则受二次气溶胶源、燃煤工业源及机动车源的影响更大，三者平均贡献率分别为40.5%、30.0%和25.2%.区域传输对武汉市污染天气的发生也有一定影响，夏冬季的污染气团分别来自湖北省东南和西北方向.研究显示，受到不同的气象条件影响，武汉市夏季及冬季分别表现出O₃和PM_2.5污染特征，两段污染过程的发生均与污染前体物较高的二次转化程度和不利的污染扩散条件相关，污染来源呈现一定差异，但均受到区域传输作用的影响. 

Analysis of Causes and Sources of Typical Air Pollution Events in Summer and Winter in Wuhan City

Based on the observation data of 20 ambient air quality monitoring points in Wuhan City, the characteristics, causes and sources of summer and winter pollution in Wuhan City were analyzed for the two typical atmospheric pollution processes from July 21st to 31st, 2017 and January 13th to 25th, 2018. The results show that the seasonal air pollution characteristics in Wuhan City were obvious. The air quality was good in summer, followed by spring and autumn, but relatively poor in winter. Significant characteristics of O₃ and PM_2.5 pollution were shown in summer and winter, respectively. The average concentration of O₃-8 h during the summer pollution process was 151.6 μg/m3. The meteorological environment with high temperature and low humidity were conducive to the conversion of precursor VOCs and NO_x to O₃. The generation of ozone was mainly controlled by VOCs, among which the aromatic hydrocarbons and olefins contribute more to the ozone generation potential, with the relative contributions of 43.7% and 35.6%, respectively. The average concentration of PM_2.5 during the winter pollution process was 129.1 μg/m3. The meteorological conditions of static and high humidity promoted the hygroscopic growth and secondary formation of particulate matter. The contribution of the secondary ions and organic carbon was significant, accounting for 72.4% of the total PM_2.5. As the pollution level increases, the conversion degree of the secondary ions and the formation potential of VOCs to SOA gradually increase. The degree of secondary conversion of precursor under severely polluted weather was about 2.7 to 11.4 times that of the non-polluted. The source analysis results show that the summer pollution process was strongly affected by VOCs generated by solvent coating, vehicle exhaust emission and industrial emission. While in winter, the secondary aerosol, coal-fired industrial and motor vehicle sources affected more, with the average contribution of 40.5%, 30.0% and 25.2%, respectively. Regional transmission also had a definite impact on the occurrence of polluted weather in Wuhan City. Pollution air masses in summer and winter came from the southeast and northwest of Hubei Province, respectively. The studies show that the pollution was affected by different meteorological conditions, Wuhan City showed significant characteristics of O₃ and PM_2.5 pollution in summer and winter, respectively. The occurrence of the two pollution processes were all related to the higher secondary conversion degree of the contaminated precursors and the unfavorable pollution diffusion conditions. There are some differences in the sources of pollution, but both are affected by the regional transmission.