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 is not well understood in polluted areas. In the study, we accomplished a year-round campaign at nine sites in the polluted areas located in Pearl River Delta (PRD) region during 2015. We measured typical biogenic SOA (BSOA) tracers from isoprene, monoterpenes, and β-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 (SOAM, 47.2 ± 9.29 ng m−3), followed by isoprene (SOAI, 23.1 ± 10.8 ng m−3), and β-caryophyllene (SOAC, 3.85 ± 1.75 ng m−3). We found that atmospheric oxidants, Ox (O3 plus NO2), and sulfate correlated well with high-generation SOAM tracers, but not so for first-generation SOAM products. This suggested that high Ox and sulfate could promote the formation of high-generation SOAM products, which probably led to relatively aged SOAM we observed in the PRD. For the SOAI tracers, not only 2-methylglyceric acid (NO/NO2-channel product), but also the ratio of 2-methylglyceric acid to 2-methyltetrols (HO2-channel products) exhibit NOx dependence, indicating the significant impact of NOx on SOAI formation pathways. The SOAC tracer elevated in winter at all sites and positively correlated with levoglucosan, Ox, and sulfate. Thus, the unexpected increase of SOAC in wintertime might be highly associated with the enhancement of biomass burning, atmospheric oxidation capacity and sulfate components in the PRD. The BSOAs that were estimated by 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 μg m−3. SOAM dominated the BSOA mass all year round. We also found that BSOA correlated well with sulfate and Ox. This implicated the significant effects of anthropogenic pollutants on BSOA formation and highlighted that we could reduce the BSOA through controlling on the anthropogenic emissions of sulfate and Ox precursors in polluted regions.