Abstract
Secondary organic aerosols (SOAs) are important components of fine particulates in the atmosphere. However, the sources of SOA precursor and atmospheric processes affecting SOAs are poorly understood. This limits our abilities to improve air quality and model aerosol-mediated climate forcing. Here, we use novel compound-specific dual-carbon isotope fingerprints (Δ14C and δ13C) for dominant SOA tracer molecules (oxalic acid and related polar compounds) to investigate the fates of SOAs in the atmosphere at five emission hotspots in China. Coal combustion and vehicle exhausts accounted for ~55 % of the sources of carbon in oxalic acid in Beijing and Shanghai, but biomass-burning and biogenic emissions accounted for ~70 % of the sources of carbon in oxalic acid in Chengdu, Guangzhou, and Wuhan. The dual-carbon isotope signatures of SOA molecules and bulk organic carbon pools (e.g., water-soluble organic carbon) were compared to investigate the fates of SOAs in the atmosphere. Photochemical aging of organic aerosols was dominant in summer, but fresh SOA formation from precursor volatile organic compounds was dominant in winter. The results indicated that SOA carbon sources and chemical processes producing SOAs vary spatially and seasonally and these variations need including in Chinese climate projection models and air quality management practices.
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