Secondary organic aerosols in PM2.5 on a coastal island in southeastern China: Impact of atmospheric process and biomass burning

Abstract

To better understand the formation and characteristics of secondary organic aerosols (SOA) in coastal areas, a four-season observation of PM2.5-bound SOA tracers was conducted on a coastal island in southeastern China. Typical organic tracers, including the tracer for biomass burning (levoglucosan) and tracers from isoprene (SOAI), α/β pinene (SOAM), β-caryophyllene (SOAC), and toluene (SOAA), were analyzed by GC-MS. The total concentrations of SOA tracers were found to be higher in the fall and summer compared to spring and winter. The highest concentration among the SOA tracers was observed for SOAI (12.96 ± 17.89 ng m−3), followed by SOAM (6.66 ± 6.03 ng m−3), SOAA (1.76 ± 1.73 ng m−3), and SOAC (1.52 ± 1.11 ng m−3). The study revealed that the production of SOAI was significantly influenced by the HO2 channel. Compared with the first generation products and the later generation products of α/β-pinene, we found the aerosols in the study area were relatively fresh. In summer, the majority of SOA tracers showed strong positive correlations with SO42−, H+, and Ox (O3+NO2), indicating the influence of acid sulfate and photochemical oxidation. However, based on the LEV/K+ ratio, it was concluded that crop residue burning has a substantial influence on SOA in winter and mostly comes from regional transportation. During biomass burning transport episodes, the concentration of β-caryophyllenic acid (CPA) increased along with LEV and K+. The average concentration of total secondary organic carbon (SOC) estimated from the SOA-tracer method was found to be 0.399 μg C m−3, with SOCA constituting the majority (0.220 ± 0.216 μg C m−3). Isoprene contributed the most to biogenic SOA (BSOA) in summer (42.1%), whereas sesquiterpene had the largest contribution (66.8%) in winter. This study provides valuable insights into the characteristics and formation mechanisms of SOA in coastal areas with low anthropogenic emissions.