Insights into the characteristics of aerosols using an integrated single particle-bulk chemical approach

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 PM2.5 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 PM2.5 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%)

Automated summary

The integrated use of single particle and bulk chemical analysis proved to be more effective in determining the sources and formation mechanisms of pollution. Different pollution episodes were identified in Chengdu's PM2.5 pollution, including combustion sources and vehicular emissions. Local emissions were found to be the dominant source of various species, with regional transport usually originating from the southwest or northeast of Chengdu.