Air-Sea Gas Exchange and Its Potential Influence on the Regional Fate of Polycyclic Aromatic Hydrocarbons in the East China Marginal Sea

To investigate the air-sea gas exchange and its potential influence on the regional fate of polycyclic aromatic hydrocarbons (PAHs) in the East China Marginal Seas (ECMS), which consist of the East China Sea (ECS) and Yellow Sea (YS), we collected air and surface seawater samples of this area in the summer 2018 and winter 2019, respectively. Generally, PAHs underwent a strong volatilization process in the ECMS in both summer and winter. Good correlations between wind speed and the magnitude of air-sea gas exchange were found for low molecular weight PAHs, suggesting the rate of their air-sea gas exchange was influenced by the static stability of overlying atmosphere. However, such an influence for high molecular weight PAHs was constrained by their low Henry's law constant. Dissolved concentration of PAHs in surface seawater was another key factor regulating their air-sea gas exchange, which not only influenced the rate of air-sea gas exchange but also was involved in the exchange direction. Higher air-sea gas exchange fluxes of PAHs in winter were attributed to their increasing dissolved concentrations in seawater during this season. A mass conservation analysis revealed a huge volatilization loss of PAHs from seawater to atmosphere, suggesting air-sea gas exchange might be a key process to modulate the distribution and occurrence of PAHs in the ECS and YS. Such a loss of PAHs in seawater might be compensated by the sediment resuspension, which implied that the sedimentary deposit could serve as a secondary source of PAHs in seawater and overlying atmosphere. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous semi-volatile organic compounds that pose a substantial threat to human health and ecological safety due to their carcinogenicity, teratogenicity, and bioaccumulation. Air-sea gas exchange is a critical mass transfer process influencing the occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in marginal seas. We found that the air-sea gas exchange of PAHs was mainly controlled by their dissolved concentrations in seawater and the wind speed in the East China Marginal Seas (ECMS). Seasonal variation of air-sea gas exchange of PAHs was observed, especially in the Yellow Sea (YS). Influenced by a greater PAH input from Northern China and the ECMS cross-shelf circulation system, the volatilization fluxes of PAHs in the YS were higher in winter, despite of lower temperature. Besides, resuspension of PAHs from sediments contributed to the dissolved PAHs in seawater, which compensated the massive loss of PAHs from seawater triggered by air-sea gas exchange. Our study highlights the significant influence of air-sea gas exchange and the role of sediment resuspension on the regional fate of PAHs in this area. Air-sea gas exchange of PAHs is mainly controlled by dissolved concentrations in seawater and wind speedAir-sea gas exchange triggers a massive loss of PAHs from seawater in the East China Marginal SeasDissolved PAHs from sediment resuspension are a potential source of PAH volatilization at air-sea interface