Chemical composition, sources and evolution of PM2.5 during wintertime in the city cluster of southern Sichuan, China

The city cluster of southern Sichuan is not only the key haze area in the Sichuan Basin, China, but also seriously affects the air quality of surrounding areas. In order to obtain comprehensive information on the characteristics of air pollution in this area, this study conducted synchronous sampling and analysis of fine particulate matter (PM2.5) in four cities (Zigong, Luzhou, Neijiang and Yibin) in this area during the wintertime of 2018-2019. The results showed that the average concentration of PM2.5 in these four cities was 111-124 mu g m(-3), with more than 90% of days being polluted days. The contributions from carbonaceous components, water-soluble inorganic ions (WSIIs) and trace elements to PM2.5 were 17.3-18.9%, 34.3-38.2% and 2.2-3.0%, respectively. The contributions of secondary inorganic ions (SO42- NO(3)(-)and NH4+) to WSIIs were 91.1-93.0%. The changes in the chemical components during the process of pollution aggravation were significantly different from those in most cities in China, with the contribution from organic carbon increasing, while the contribution from WSIIs decreased. PM2.5 mainly came from dust, combustion, vehicular emissions, industrial processes and secondary inorganic sources. Compared with most megacities or provincial capitals in China, the contributions from dust (18.1-23.6%), combustion (17.9-21.1%) and industrial processes (9.2-12.0%) were at a higher level, and these sources can be regarded as the primary targets for pollution reduction in the future. The formulation of air pollution reduction policies needs to consider local conditions, such as sources, energy structure, management level.