Contributions of primary anthropogenic sources and rapid secondary transformations to organic aerosol pollution in Nanchang, Central China

Abstract. Due to the complex composition of organic aerosols (OAs), identifying their sources and understanding their dynamics remain challenging, particularly in urban environments of China where natural and anthropogenic influences to OAs intersect. This study aimed to clarify the relative contributions of primary emissions and secondary formation to urban OAs and confirm the sources and influencing factors of OA pollution. We analyzed major polar organic compounds in fine particulate matter (PM2.5) collected over one year in Nanchang, Central China. Specific biomarkers and diagnostic ratios were applied to characterize OA sources and distribution patterns, while chemical mass balance (CMB) models and tracer-based approaches were used to estimate source contributions. Statistical analyses were conducted to investigate OA characteristics and drivers during winter pollution episodes. Notably, fatty acids, fatty alcohols, and saccharides predominated over lignin, resin products, sterols, glycerol, hydroxy acids, and aromatic acids, with molecular profiles indicating both anthropogenic and biogenic origins. Source apportionment results showed that primary organic carbon (POC) and primary OAs (POAs) contributed 58 % of total organic carbon and 23 % of PM2.5 mass, respectively, compared with 8 % and 4 % from secondary organic carbon (SOC) and secondary OAs (SOAs). Anthropogenic sources dominated, accounting for approximately 90 % of POC and POAs as well as 60 % of SOC and SOAs. Seasonal patterns revealed stronger biogenic influences in spring–summer, whereas anthropogenic emissions dominated in autumn–winter. Short-term winter episodes were characterized by rapid secondary formation, facilitated by elevated primary emissions and favorable oxidation conditions, including enhanced light intensity and nitrogen oxides.