四川盆地典型城市PM_(2.5)污染过程组分特征和来源解析

Composition characteristics and source apportionment of PM_(2.5) pollution process in typical cities in the Sichuan Basin

为探究四川盆地典型城市PM_(2.5)污染特征和来源,利用成都市、绵阳市、自贡市超站数据分析2020年冬季典型污染过程PM_(2.5)组分特征,并采用CMB模型模拟获得研究期间PM_(2.5)来源及演变特征.结果表明,不同城市PM_(2.5)组分变化特征不尽相同,成都市污染过程整体呈现NO_(3)^(-)主导特征,但重度污染由OC主导.绵阳市污染期间呈现OC主导特征,是污染加重时增长最快的组分.EC是自贡市轻度污染增长最快的组分,NO_(3)^(-)、SO_(4)^(2-)、NH_(4)^(+)是中度污染增长较快的组分,OC、EC是重度污染增长较快的组分.3个城市均是二次硝酸盐对PM_(2.5)贡献率最高.比较而言,成都市机动车、扬尘源贡献率均最高;绵阳市二次有机碳贡献率最高,是成都市的2倍;自贡市燃煤源和二次硫酸盐贡献率分别比成都市和绵阳市高出4%~6%和7%~9%.成都市由优良天气到中度污染,二次硝酸盐贡献率随着污染程度的加重而增加,轻度污染较优良天气上升6%,中度污染较轻度污染天气上升3%.中度到重度污染,二次有机碳、机动车贡献率分别上升2%和1%.绵阳市由轻度到重度污染,二次有机碳对PM_(2.5)的贡献率上升3%,机动车贡献率上升2%,是其污染加重的主要原因.自贡市由轻度到重度污染,各污染源贡献率变化幅度较小.

To explore the characteristics and sources of ambient PM_(2.5)in typical cities in the Sichuan Basin,the characteristics of PM_(2.5)components during the winter of 2020 were analyzed by using the superstation data of Chengdu,Mianyang and Zigong,and their source and evolution were revealed by using the CMB model.Results showed that the characteristics of PM_(2.5)components varied with cities.Except for heavy pollution,which was dominated by OC,most pollution events in Chengdu were NO_(3)^(-)dominant.In Mianyang,OC was the dominant component during the pollution period,which was the fastest⁃growing component when pollutions aggravate.In Zigong,however,EC had the fastest growth rate during the light pollutions,while NO_(3)^(-),SO_(4)^(2-),and NH_(4)^(+)grew fastest during moderate pollutions,OC and EC grew fastest during heavy pollutions.Secondary nitrate was the largest contributor to PM_(2.5)in the three cities.In comparison,the contribution of motor vehicles and dust in Chengdu was the highest.The contribution of secondary organic carbon in Mianyang was the highest,which was twice that of Chengdu.The contributions of coal combustion and secondary sulfate in Zigong were 4%~6%and 7%~9%higher than those in Chengdu and Mianyang,respectively.The contribution of secondary nitrate in Chengdu increased with the aggravation of pollutions,which respectively increased by 6%and 9%in light pollutions and moderate pollutions compared with normal periods.From moderate to severe pollution,the contribution of secondary organic carbon and motor vehicles increased by 2%and 1%respectively.In Mianyang,the contribution of secondary organic carbon to PM_(2.5)increased by 3%from light pollution to heavy pollution,and the contribution of motor vehicles increased by 2%,which was the main reason for the pollution aggravation.In Zigong,the contribution of pollution sources changed slightly from light pollution to heavy pollution.