2020年1月哈尔滨PM_(2.5)重污染形成机制

Formation Mechanism of Heavy PM_(2.5) Pollution in Harbin in January 2020

分析2020年1月哈尔滨重污染事件期间PM_(2.5)的化学组成和影响因素,采用后向轨迹聚类和权重潜在源贡献因子法定量评估区域传输对PM_(2.5)的贡献,讨论该重污染事件的形成机制。结果表明:PM_(2.5)重污染事件主要来源于一次排放,其中生物质燃烧的贡献显著,而极低气温(-18.0℃)和高相对湿度(80.0%)条件可显著促进二次气溶胶的生成。基于气团后向轨迹以及权重潜在源贡献因子研究发现,绥化、大庆、长春和松原等周边城市的区域传输对哈尔滨空气质量的影响也不可忽视。

In the context of China’s commitment to improve air quality enhancement,cities within severe cold climate zones,exemplified by Harbin continue to confront the exigent issue of fine particulate matter(PM_(2.5))pollution,notably during winter.Despite nationwide initiatives aimed at mitigating air pollution,Harbin’s unique geographical and climatic conditions,combined with its predominant economic activities,have led to consistently high levels of PM_(2.5) during winter.An episode of severe PM_(2.5) pollution is observed in January 2020,with the monthly average mass concentration of PM_(2.5) peaking at 155.0μg·m^(-3),significantly surpassing national standards.To explore the mechanism of this severe PM_(2.5) pollution episode,an integrated analysis of chemical compositions and influencing factors is conducted during this period.In the meantime,methods of backward trajectory clustering and the weighted potential source contribution function(WPSCF)are employed to investigate source areas and transport pathways of air pollutants.Results indicate that the severe PM_(2.5) pollution in Harbin mainly originates from primary emissions,with biomass burning contributing significantly.During the observation period,the concentration of levoglucosan in PM_(2.5),a common tracer of biomass burning,reaches as high as 1.1μg·m^(-3),which is 3.7 to 5.5 times higher than that in other regions experiencing severe biomass burning pollution during winter.Furthermore,research findings indicate that meteorological conditions play a significant role in exacerbating PM_(2.5) pollution in Harbin.High relative humidity(averaging at 80.0%)combined with extremely low temperatures(averaging at -18.0℃)provided favorable conditions for secondary aerosol formation.Under such low-temperature and high-humidity conditions,the average sulfur oxidation rate reaches as high as 25.6%,and the nitrogen oxidation rate reaches 10.8%.It significantly increases the contribution of secondary aerosols to PM_(2.5) in Harbin.Additionally,this study also reveals the impact of regional transportation on the air quality of Harbin.It indicates that the air quality of Harbin is influenced not only by local emissions but also by the transportation of pollutants from neighboring cities such as Suihua,Daqing,Changchun,and Songyuan.The inter-city transfer of pollution highlights the close connection of air pollution issues within the region.Through the comprehensive analysis of causes of a severe PM_(2.5) pollution event in Harbin during winter from multiple perspectives,a scientific basis is provided for understanding causes for air pollution in similar cold climate.