Characterization of Organosulfates (OSs) in typical urban areas in Eastern China: Source, Process, and Volatility

Abstract

Organosulfates (OSs) are an important component of secondary organic aerosols (SOA), accounting for ~30% of total organic aerosol. In this study, OSs in eastern China were investigated to understand their diurnal evolution, source, and volatility using high-resolution mass spectrometry. In polluted days, we identified a total of 5,147 organic molecules, including 1,206 OS molecules. The average molecular weight (m.w.) and carbon chain length of OSs in this study exceeded the commonly recognized range (500 Da). OSs were mostly composed of newly formed low oxidation state compounds as well as aged aliphatic and aromatic ones. The number and abundance of aromatic and aliphatic OSs with low saturation, volatility, O/Cw as well as H/Cw increased greatly with rising PM2.5 concentrations. The daytime photo-oxidation resulted in a large number of high m.w. (HMW, > 500 Da) OSs. OSs with m.w. <500 Da, and many oxygen atoms were newly generated during the nighttime, mainly dominated by liquid-phase oxidation processes. The result of OSs with higher m.w. and lower volatility was due to increased dimerization and oligomerization. During pollution formatting, OSs with small DBE values (between 0 and 6) appeared; meanwhile, the number of highly unsaturated OSs with DBE > 7 (mainly aromatic OSs) increased by about 34%. This study is useful for clarifying the secondary formation and properties of HMW OSs in a polluted environment in China.