Insights into PM pollution of four small and medium-sized cities in Chinese representative regions: Chemical compositions, sources and health risks.

Fine particles (PM) pollution is still a severe issue in some cities in China, where the chemical characteristics of PM remain unclear due to limited studies there. Herein, we focused on PM pollution in small and medium-sized cities in key urban agglomerations and conducted a comprehensive study on the PM chemical characteristics, sources, and health risks. In the autumn and winter of 2019-2020, PM samples were collected simultaneously in four small and medium-sized cities in four key regions: Dingzhou (Beijing-Tianjin-Hebei region), Weinan (Fenwei Plain region), Fukang (Northern Slope of the Tianshan Mountain region), and Bozhou (Yangtze River Delta region). The results showed that secondary inorganic ions (43.1 %-67.0 %) and organic matter (OM, 8.6 %-36.4 %) were the main components of PM in all the cities. Specifically, Fukang with the most severe PM pollution had the highest proportion of SO (31.2 %), while the dominant components in other cities were NO and OM. The Multilinear Engine 2 (ME2) analysis identified five sources of PM in these cities. Coal combustion contributed most to PM in Fukang, but secondary sources in other cities. Combined with chemical characteristics and ME2 analysis, it was preliminarily determined that the primary emission of coal combustion had an important contribution to high SO in Fukang. Potential source contribution function (PSCF) analysis results showed that regional transport played an important role in PM in Dingzhou, Weinan and Bozhou, while PM in Fukang was mainly affected by short-range transport from surrounding areas. Finally, the health risk assessment indicated Mn was the dominant contributor to the total non-carcinogenic risks and Cr had higher carcinogenic risks in all cities. The findings provide a scientific basis for formulating more effective abatement strategies for PM pollution.