Organosulfates (OSs) are important secondary organic aerosol (SOA) species in atmospheric fine particles (PM2.5) and can be considered as molecular indicators of SOA. To understand their seasonal and diurnal distribution characteristics and formation mechanism in northern China, PM2.5 samples collected in daytime and nighttime in winter and summer 2019 in Tianjin, China were studied for total OSs and three OS species (methyl sulfate (MS), glycolic acid sulfate (GAS), benzyl sulfate (BS)). The S contents of total OSs (SOSs) in winter and summer were 0.6 ± 1 μg m-3 and 0.4 ± 0.3 μg m-3, respectively, in PM2.5. BS found to be less abundant among the measured species, and accounted for only 0.8%-4.8% of methyl sulfate (MS), and 0.01%-0.3% of glycolic acid sulfate (GAS). Average content of GAS was higher in summer than in winter, while that of MS and BS were opposite. The fractions of MS, GAS, and BS in SOSs were higher in daytime than that in night during winter, despite their concentrations were higher in nighttime, indicating that the concentrations of unidentified OS species were much higher in nighttime than in daytime. Such diurnal variations implied that relative humidity (RH) played a major role in the formation processes of OSs, especially biogenic OSs and the acid catalyzed reaction of SO42- might be a main pathway of OSs formation during winter. High T, RH and O3 determined biological GAS in summer, while NO2 and SO2 determined anthropogenic OSs in winter. We also found that the fractions of SOSs in S contents of organic sulfur (SOS) and the S contents of MS + GAS+BS (SMS+GAS+BS) in SOSs were accounted for only less than 10% and 5%, respectively. Therefore, this study suggests the components of OS and OSs in PM2.5 have not been discovered fully yet and needs further research.
Keywords: Distribution characteristics; Influence factors; Organosulfates; Quantitative analysis; Transportation.
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