Tropical cyclone amplifies anthropogenic influences on aerosol-cloud interactions over the South China Sea

Abstract. Tropical cyclones can influence marine aerosol-cloud interactions by transporting continental anthropogenic pollutants over the ocean. However, this process and its impact remain poorly understood due to lack of direct measurements. Using shipborne measurements over the South China Sea (SCS) from 22 June to 5 July 2022, we investigated how a typical TC Chaba altered aerosol physicochemical properties and cloud microphysical responses. As TC Chaba developed, its circulation altered regional transport pathways, shifting air masses from local marine origin to long-range transport from the Indochina Peninsula and causing pronounced increases in non-refractory submicron particulate matter (NR-PM₁) concentrations. Organic aerosol (OA) increased from 14.6 % to 44.9 % of NR-PM₁ after the influence of TC Chaba, mainly due to enhanced oxygenated OA (OOA) from long-range transport together with enhanced local heterogeneous oxidation, as indicated by the higher OA oxidation state and increasing OOA concentrations with Ox and relative humidity. These changes led to a ~60 % decrease in aerosol hygroscopicity (κ), while an ~27 % increase in κ_OA, which outweighed the modest particle size increase and resulted in a lower bulk activation ratio. Furthermore, CCN concentrations increased by up to sixfold because of enhanced aerosol concentrations. Combined observations and cloud parcel simulations indicate that the aerosol perturbations decreased cloud droplet effective radius by 11–37 % and increased the autoconversion radius by 6–26 %, enhancing cloud reflectivity and suppressing warm-rain formation. Satellite observations further confirmed smaller cloud droplets. These results demonstrate a strong TC influence on marine cloud microphysics and radiative effects.