Seasonal variations in chemical characterization of submicron aerosol particles in Shanghai, China: Insights from a high-resolution aerosol mass spectrometry

As a characteristic pollutant of urban compound pollution, submicron particulate matter (PM1) has significantly impacted on human health and climate change. In this study, four intensive campaigns using a high-resolution time-of-flight AMS (HR-ToF-AMS) and other online instruments from 2016 to 2017 were conducted to investigate the seasonal characteristics of submicron particles in Shanghai. The average mass concentrations of submicron particulate matter during spring, summer, autumn and winter observations in Shanghai are 23.9 ± 20.7 μg/m3, 28.5 ± 17.6 μg/m3, 22.0 ± 17.2 μg/m3 and 31.9 ± 22.7 μg/m3, respectively. The major chemical components in submicron particulate matter showed obvious seasonal and daily variations. The increase of submicron particulate matter is mainly due to the contribution of nitrate in spring, autumn and winter, while the photochemical reaction promotes the rapid growth of sulfate in summer. Detailed source apportionment of organic aerosol showed that the fraction of more oxidized oxygenated organic aerosol in organic aerosol in spring was much lower than primary organic aerosol. Oxygenated organic aerosol dominated organic aerosol in summer (69%). More oxidized oxygenated organic aerosol account for 28% in autumn, suggesting that organic aerosol was aging. The liquid phase oxidation and the strong photochemical reaction concentration have a significant contribution to the formation of more oxidized oxygenated organic aerosol and less oxidized oxygenated organic aerosol in the spring, summer and winter observations, respectively. However, the photochemical reaction process dominated the formation of more oxidized oxygenated organic aerosol in autumn.