Typhoons can largely alter hydrodynamic conditions and air-sea exchange processes in the upper ocean, thereby influencing the environmental behavior of organic pollutants, including polycyclic aromatic hydrocarbons (PAHs). Nonetheless, the comprehensive magnitude and mechanisms of these influences remain inadequately characterized. The passage of Typhoon Chaba through the South China Sea (SCS) in 2022 provided a unique opportunity to investigate PAH dynamics in response to typhoons. Field sampling was conducted one week pre-typhoon and one-week post-typhoon. In surface seawater, the total concentration of 15 US EPA priority PAHs (TPAHs) decreased markedly by 45%, from 220 ± 160 ng/L in the pre-typhoon region to 120 ± 42.5 ng/L in the post-typhoon region. Conversely, the water-particle partition coefficient (K d ) increased by 73%. Source apportionment revealed consistent PAHs origins between the two regions, primarily derived from fossil fuel combustion (51%), followed by petroleum leakage (38%), and biomass burning (11%). At a continuous 24-h monitoring site within the post-typhoon region, TPAH concentrations were higher in the surface layer than at the bottom of the upper mixed layer, while the K d values showed the inverse trend. The observed decline in PAH levels confirms that typhoons promote the removal of these pollutants from the mixed layer. A proposed mechanism involves typhoon-enhanced partitioning of dissolved PAHs (particularly 4-ring compounds) to particulate phase, subsequently removed by particle sinking. The total mass of PAHs removed by the typhoon was estimated to be 703 kg within the upper mixed layer across the 2.65 × 10 4 km 2 study area over 24 h. This study provides the first fine-scale elucidation of the cleansing effect of typhoons on organic pollutants, underscoring their critical role in regulating the fate of PAHs in upper ocean. • This study provides the first fine-scale field evidence of a significant cleansing effect on PAHs in the upper ocean following a typhoon. • Direct observations reveal typhoon-driven scavenging of PAHs, reducing total concentrations by 45% and enhancing particle-water partitioning by 73%. • The removal was particularly pronounced for 4-ring PAHs, which exhibited a strong tendency for adsorption onto particles and subsequent vertical export. • We quantify a rapid removal of 703 kg of PAHs, highlighting the pivotal role of typhoons in the marine biogeochemical cycling of persistent pollutants.
Li et al. (Thu,) studied this question.