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

Abstract. Owing to the complex composition of organic aerosols (OAs), it is challenging to elucidate their sources and dynamics, particularly in urban environments in China, where natural and anthropogenic influences converge. We attempted to clarify the relative contributions of primary emissions and secondary formations to urban OAs and confirm the sources and influencing factors of OA pollution. To achieve this, we conducted a comprehensive analysis of major polar organic compounds in fine particulate matter (PM_2.5) samples collected over a year in Nanchang, Central China. The results indicated that the concentrations of fatty acids, fatty alcohols, and saccharides were relatively high, whereas lignin and resin products, sterols, glycerol, hydroxy acids, and aromatic acids were present at low concentrations. An analysis of molecular characteristics and concentration ratios revealed that they originate from anthropogenic and natural sources. Using the tracer-based method, we observed that the primary organic carbon (POC) and primary organic aerosols (POA) contributed 53 % of OC and 21 % of PM_2.5 mass, respectively, compared with a mere 8 % and 4 % from secondary organic carbon (SOC) and secondary organic aerosols (SOA). Anthropogenic sources were the most dominant determinant, contributing approximately 89 % of POC and POA and 60 % of SOC and SOA. Seasonal variations indicated that biogenic emissions exerted a stronger influence during spring and summer, whereas anthropogenic emissions were more pronounced in autumn and winter. Short-term winter pollution episodes were characterized by rapid secondary transformation, promoted by elevated primary emissions and favorable oxidation conditions, including increased light intensity and nitrogen oxides.