Characteristics of secondary organic aerosols tracers in PM2.5 in three central cities of the Yangtze river delta, China

Secondary organic aerosols (SOA) are important atmospheric pollutants that affect air quality, radiation, and human health. In this study, 14 typical SOA tracers were measured in PM2.5 collected from three central cities of the Yangtze River Delta (YRD) region in the winter of 2014 and the summer of 2015. Among the determined SOA tracers, alpha/beta-pinene SOA tracers contributed 55.9%, followed by isoprene SOA tracers (33.7%), anthropogenic benzene SOA tracer (6.4%) and beta-caryophyllene SOA tracer (4.0%). There was no significant difference in the concentration of individual SOA tracers among the three cities (p > 0.05), indicating a high degree of regional consistency. The concentrations of isoprene, alpha/beta-pinene, and toluene SOA tracers were significantly higher in summer than in winter. A correlation of SOA tracers with temperature implies that the isoprene and alpha/beta-pinene SOA tracers in summer were greatly boosted by plant emissions and the high DHOPA in summer could be attributed to evaporation of paint and solvent. In contrast, the elevated beta-caryophyllene SOA tracer in winter was likely associated with active biomass burning. Furthermore, we observed a close correlation of summer isoprene and alpha/beta-pinene SOA tracers with sulfate only in Shanghai, which verifies that biogenic SOA formation was facilitated by high concentration of sulfate. The ratios of MGA/MTLs and P/M were applied to reveal the impact of NOx on SOA formation and the aging degree of SOA, respectively. The MGA/MTLs ratios were comparable for the three cities, but much higher than the background value of this region as expected. The P/M ratios suggest that the aging degree of SOA in the YRD region was generally low, but the winter SOA were fresher than the summer SOA. Our research helps to understand pollution characteristics of SOA tracers in the urban agglomeration.

Automated summary

This study investigates the pollution characteristics of secondary organic aerosols (SOA) in the urban agglomeration of the Yangtze River Delta region. The results show a high degree of regional consistency in the concentration of SOA tracers among the three central cities. The concentrations of isoprene and alpha/beta-pinene SOA tracers were significantly higher in summer, attributed to plant emissions, while the higher concentration of beta-caryophyllene SOA tracer in winter can be linked to biomass burning. The study also reveals the correlation between SOA tracers and sulfate, indicating that biogenic SOA formation is facilitated by high concentrations of sulfate.