Characteristics and pollution formation mechanism of atmospheric fine particles in the megacity of Chengdu, China

To investigate the characteristics and pollution formation mechanism of fine particles in the atmosphere of Chengdu, one of the cities most affected by haze in China, ambient single aerosol particles were measured by single particle aerosol mass spectrometry from April to May 2021. All particles collected during the study period could be divided into seven categories: Dust, vehicle emission (VE), biomass burning (BB), coal combustion (CC), organic carbon (OC), K-nitrate (KNO3) and K-sulfate (KSO4) particles. BB and VE particles contributed 29.2% and 25.0% to the total particles, respectively, and these two types of particles can be used as the focus of pollution reduction in the future. The mixed state analysis showed that all types of particles highly mixed with their tracer ions, and the non secondary inorganic particles (i.e., Dust, VE, BB, CC and OC particles) showed stronger mixing with nitrate than sulfate. The increase of PM2.5 concentration can be divided into three stages, and the increase of PM2.5 concentration in these three stages was dominated by Dust and OC particles, BB and KNO3 particles, and the remaining three types of particles, respectively. The air masses mainly originated from the area northeast of Chengdu, while the southwest trajectory corresponded to the highest PM2.5 and PM10 concentrations. Meanwhile, the potential source areas of the different types of particles were different and the area southwest of Chengdu was the most important potential source of PM2.5 and of most particle types. [Display omitted] •Mass spectrum and chemical composition of single particles were measured by SPAMS.•Non secondary inorganic particles showed stronger mixing with nitrate than sulfate.•The increase of PM2.5 in three stages was caused by different types of particles.•The potential source area was mainly distributed in areas southwest of Chengdu.