Characteristics of submicron aerosols (PM1) in a Yangtze River Delta megacity: Composition, sources, and light absorption

We conducted a field campaign to investigate the chemical composition, sources, and light absorption of submicron aerosols (PM1) from in early 2022 in Nanjing, China. The average concentration of PM1 was 31 µg m-³, organics (33%) constituted the largest fraction, followed by nitrate (30%), sulfate (18%), ammonium (15%), chloride (3%), and rBC (2%). Four organic aerosol (OA) subcomponents were identified, including two primary OA (POA) and two secondary OA (SOA). The less-oxidized SOA (LO-OOA) contributes the most to the total OA mass (59%). LO-OOA is tightly correlated with the tracer ion C2H4O2+ from levoglucosan, and another aged biomass-burning derived species, K3SO4+, suggesting it was likely influenced by aged biomass-burning OA. Our study also revealed that fireworks during the Spring Festival have a detrimental impact on air quality, contributing to secondary formation and accumulation under static winter meteorological conditions, prolonging the pollution duration. Also, LO-OOA was found to have the strongest light-absorbing ability. Our results highlighted that the light absorption of LO-OOA was mainly attributed to the CxHyN+ family, increased with the double bond equivalent (DBE) value. The more-oxidized SOA (MO-OOA) exhibited a negligible light absorption and was strongly correlated with daytime photochemical processes, implying a light-bleaching effect. This study enhances our understanding of the regional contribution of biomass combustion and fireworks to PM1 pollution in Nanjing, a typical megacity in the YRD during winter, aiding in the development of strategies for long-term air quality improvement in the region.