Sulfur hexafluoride in the marine atmosphere and surface seawater of the Western Pacific and Eastern Indian Ocean.

Sulfur hexafluoride (SF) is a powerful greenhouse gas with a high global warming potential. While SF emissions from urban areas have been extensively studied, our knowledge about SF concentrations in the oceanic atmosphere and its air-sea exchange remains limited. Herein, the concentrations of SF in the atmosphere and surface seawater of the WPO (Western Pacific Ocean) and EIO (Eastern Indian Ocean) were comprehensively characterized from 2019 to 2022 in the first long-term study. The mean mixing ratios of SF over the WPO and EIO during 2019-2020 (2021-2022) were 10.9 (11.2) and 10.9 (11.1) ppt, respectively. The atmospheric SF concentration over the WPO and EIO increased at rates of 0.40 ± 0.06 and 0.58 ± 0.28 ppt yr, respectively, surpassing previously reported annual growth rates. The faster growth was primarily attributed to the influence of polluted air masses originating from eastern Asian countries, particularly Japan, Northeast China, and India. This might explain why the radiative forcing caused by SF in the study region was higher than the global average. The concentrations of SF in the surface seawater of the WPO and EIO ranged from 0.33 to 2.54 fmol kg, and the distribution was affected by atmospheric concentrations and ocean currents. Estimated air-sea fluxes revealed that the ocean acted as a significant sink of atmospheric SF, and the preliminary estimation suggested oceanic uptake accounts for about 7% of annual global SF emissions. Based on these findings, we tentatively suggest that the strength of the ocean as a sink of SF may warrant reassessment. The global oceanic uptake of SF has the potential to reduce its global abundance and environmental impacts.