Impact of anthropogenic emissions on biogenic secondary organic aerosol: Observation in the Pearl River Delta, South China

Secondary organic aerosol (SOA) formation from biogenic precursors is affected by anthropogenic emissions, which are not well understood in polluted areas. In this study, we accomplished a year-round campaign at nine sites in polluted areas located in the Pearl River Delta (PRD) region during 2015. We measured typical biogenic SOA (BSOA) tracers from isoprene, monoterpenes, and beta-caryophyllene, as well as major gaseous and particulate pollutants and investigated the impact of anthropogenic pollutants on BSOA formation. The concentrations of BSOA tracers were in the range of 45.4 to 109 ng m(-3) with the majority composed of products from monoterpenes (SOA(M), 47.2 +/- 9.29 ng m(-3)), isoprene (SOA(I), 23.1 +/- 10.8 ng m(-3)), and beta-caryophyllene (SOA(C), 3.85 +/- 1.75 ng m(-3)). We found that atmospheric oxidants, O-x (O-3 plus NO2), and sulfate correlated well with later-generation SOA(M) tracers, but this was not the case for first-generation SOA(M) products. This suggested that high O-x and sulfate levels could promote the formation of later-generation SOA(M) products, which probably led to the relatively aged SOA(M) that we observed in the PRD. For the SOA(I) tracers, both 2-methylglyceric acid (NO/NO2-channel product) and the ratio of 2-methylglyceric acid to 2-methyltetrols (HO2-channel products) exhibit NOx dependence, indicating the significant impact of NOx on SOA(I) formation pathways. The SOA(C) tracer was elevated in winter at all sites and was positively correlated with levoglucosan, O-x, and sulfate. Thus, the unexpected increase in SOA(C) in wintertime might be highly associated with the enhancement of biomass burning, O-3 chemistry, and the sulfate component in the PRD. The BSOAs that were estimated using the SOA tracer approach showed the highest concentration in fall and the lowest concentration in spring with an annual average concentration of 1.68 +/- 0.40 mu g m(-3). SOA(M) dominated the BSOA mass all year round. We also found that BSOA correlated well with sulfate and O-x. This implied a significant effect from anthropogenic pollutants on BSOA formation and highlighted that we could reduce BSOA by controlling the anthropogenic emissions of sulfate and O-x precursors in polluted regions.