Single particle analysis and bulk chemical analysis are two complementary approaches used to study aerosols from different perspectives. Most previously published studies have been based on only one of these two approaches, which has limited our understanding of particle pollution. We therefore integrated the single particle (single particle aerosol mass spectrometer) and bulk chemical (filter sampling) approaches to sample and analyze PM_2.5 pollution in Chengdu, a megacity in Southwest China, during the autumn season. Our results showed that there was a strong correlation between the results obtained by the two approaches. Seven major particle types (vehicular emissions, biomass burning, coal combustion, K with sulfate, K with nitrate, K with secondary inorganic species and dust particles) were resolved, corresponding to the different chemical components measured by filter sampling. Two different pollution episodes were identified. Pollution episode 1 was caused by combustion sources (coal and biomass), whereas pollution episode 2 was caused by a combination of local vehicular emissions and regional transport from regions to the east and south of Chengdu. Integrated single particle and bulk chemical analysis can determine the sources and formation mechanisms of pollution more efficiently than either one of these methods used alone. Bivariate polar plots showed that in addition to SO₂, local emissions were the dominant source of all species. Regional transport was usually from areas located to the southwest or northeast of Chengdu. Six sources of PM_2.5 were apportioned based on positive matrix factorization: Combustion (16.1%), vehicular emissions (26.5%), soil dust (4.5%), industrial processes (12.2%), secondary nitrate (18.6%) and secondary sulfate (22.1%).

PM2.5; Pollution episodes; Formation mechanisms; Source apportionment; SPAMS