Source Apportionment of Organic Aerosol Using ¹⁴ C and Organic Molecular Tracers at a Regional Background Site of the Yangtze River Delta Region, China

Abstract To clarify the relative importance of anthropogenic and biogenic sources on organic aerosol (OA) in the background atmosphere, fossil and nonfossil contributions to both primary and secondary OA in fine aerosols (PM 2.5 ) were quantified at the regional receptor site in the Yangtze River Delta (YRD) region of China by measurements of dual‐carbon isotopes ( 14 C and 13 C) and organic tracers. Nonfossil sources dominated organic carbon (OC) with an average contribution of 58 ± 9%. Biogenic emissions dominated nonfossil OC during spring (68 ± 29%) and summer (86 ± 6%), while biomass burning emissions dominated in winter (87 ± 15%) and autumn (51 ± 8%). More than half of the biogenic‐derived OC in spring (58 ± 23%) and summer (64 ± 21%) originated from secondary formation, with monoterpene (35 ± 16%) and isoprene (49 ± 25%) as main secondary organic aerosol (SOA) precursors, respectively. The SOC contributed the most anthropogenic‐derived (i.e., fossil and biomass burning sources) OC with an average contribution of 71 ± 9%. In addition, anthropogenic OC was notably high during winter (93 ± 7%) and autumn (74 ± 5%), underscoring the significant impact of regional pollution transport on background aerosol. Correlations between anthropogenic pollutants and biogenic‐derived SOC indicated that mixed contributions from anthropogenic and biogenic emissions promoted SOA formation. This interaction may partially explain the relatively higher fractions of SOC in nonfossil (>60%) and fossil OC (>70%) at the background site of the YRD region compared to other global background sites.