Measurement report: Molecular Insights into Organic Aerosol Sources and Formation at a Regional Background Site in South China

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Abstract. Organic aerosols (OA) in fine particulate matter (PM) significantly impact air quality, climate, and human health. Understanding their chemical composition and quantifying their sources are crucial for assessing their formation and human-related effects. In this study, we examined OA at a background site in South China, analyzing from bulk to molecular levels, utilizing a high‐resolution time‐of‐flight aerosol mass spectrometer (AMS), a thermal-desorption aerosol gas-chromatograph-mass spectrometer (TAG-MS), and an electrospray ionization high‐resolution orbitrap mass spectrometer (HR‐MS). Our findings indicate that low-oxidized and more-oxidized oxygenated OA (LO-OOA1 and MO-OOA) comprised over 70 % of the OA mass. Biomass burning and gas-phase secondary OA (gas-pSOA) were the primary sources of LO-OOA1, while the high-oxidization degree of MO-OOA was mainly due to isoprene-derived SOA. HR-MS analysis revealed that oxidation processes significantly increased the accumulation of CHO compounds, and human-biological interactions enhanced the diversity of CHON compounds. Using a constrained non-negative matrix factorization method on offline HR-MS data, we identified differences in molecular associations between OA origins. Overall, our results underscore the prominent impact of anthropogenic emissions and their photo-oxidation on ambient OA, emphasizing the need for local emission reduction and regional cooperation to control OA in areas with low PM pollution but high O3 levels.

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