Influence of tropical cyclones on organic aerosols in a coastal city of South China

With the increasing frequency of tropical cyclones (TCs) due to global climate change, their impact on air pollution, particularly particulate matter and Ozone (O3), in China has become more evident. However, the effects of TCs on organic aerosol (OA) formation remain less understood. This study examined the influence of TCs on the abundance, chemical composition, and origins of atmospheric OA, using PM2.5 samples collected from a coastal city in southern China before and after two TCs in October 2021. The average OA concentration before the TCs (5.64 ± 3.00 μg⋅m- 3) was higher than after TCs (4.45 ± 1.38 μg⋅m- 3). Pre-TC OA levels were primarily linked to stagnant weather conditions, whereas post-TC levels were influenced by regional transport of anthropogenic OA and aqueous-phase secondary formation processes. Fluorescence spectra analysis revealed that OA was predominantly composed of protein-like substances (57 ± 10%), with changes in composition driven by oxidized humic-like substances, especially the low-oxygenated component. Using a dispersionnormalized method, we found that primary anthropogenic emissions and O3-driven oxidation consistently made significant contributions to OA throughout the study period. However, during the stagnant phase of the
pre-TC period, OA concentrations normalized by dispersion were low, likely due to reduced primary emissions and lower isoprene SOA production yields. Furthermore, OA levels decreased during the pre-TC period, which
was associated with increases in temperature and changes in NOx/O3 ratios, thereby affecting gas-phase photochemical reactions. Our study reveals for the first time the impact of TCs on OA formation, offering new insights into the occurrence of summer particulate matter pollution and the feedback mechanism between aerosols and meteorological conditions.