Investigating the characteristics and source analyses of PM seasonal variations in Chengdu, Southwest China.

In 2015, comprehensive observations were carried out in Chengdu, Sichuan Province, China, to elucidate the seasonal variation characteristics of the concentrations, chemical compositions, and the sources of PM pollution. The meteorological parameters, gaseous pollutants and chemical compositions of PM were measured. The annual average concentration of PM in Chengdu was 67.44 ± 48.78 μg/m. The highest seasonal PM mass concentration occurred in winter with an average of 103.04 ± 66.76 μg/m, followed by spring, autumn, and summer, and the wind speed had an important impact on the diffusion of PM. The seasonal variation characteristics of chemical components in PM were analysed. The contribution and chemical conversion ability of secondary aerosols increased with increasing of PM concentration. Source appointment of positive matrix factorization (PMF) shows that the main sources of PM were secondary aerosols, coal combustion, biomass burning, vehicle emissions, dust and industrial sources, which have more obvious seasonal differences than other sources, and secondary aerosols and coal combustion were the major sources. Conditional probability function (CPF) analysis showed that the local sources of high PM concentrations were mainly from the eastern and southeastern areas of Chengdu. Potential source contribution function (PSCF), concentration weighted trajectory (CWT) and backward trajectory cluster analyses indicated that the southern, southeast and eastern parts of the Sichuan Basin were the most likely potential sources of PM, and the unique geographical and topographical factors in Chengdu play important roles in the transport and diffusion of pollutants in this region.