This study investigated the behavior and sources of atmospheric methylmercury (MeHg) in wet deposition in a suburban area of South Korea. Weekly rainwater samples were collected from April 2016 to December 2023 in Gwangju, and the volume-weighted mean (VWM) concentration of MeHg was determined to be 0.036 ng L-1. The annual wet deposition flux of MeHg was found to be 0.041 ng m-2, indicating a significant pathway for the transport of atmospheric pollutants into local ecosystems. Seasonal variations were observed, with the highest VWM concentrations of MeHg found in winter and the highest wet deposition fluxes in summer. The study identified a positive correlation between PM2.5 and MeHg concentrations. The sources of MeHg were investigated using cluster analysis of backward trajectory and concentration weighted trajectory analysis. Air masses inflow from the northwest were identified as a significant source of MeHg in spring rainwater, while photodemethylation of dimethylmercury and domestic fuel combustion emissions were found to contribute to MeHg in summer and winter, respectively. Additionally, the study found that high MeHg concentrations in spring rainwater were likely due to the migration of atmospheric PMeHg over long distances. To confirm in-situ methylation of mercury, the methylation incubations with  bulk rainwater samples were performed in each season. In contrast to seasonal MeHg concentrations, methylation rates were higher in summer. When potential role of dissolved organic matter (DOM) as a methyl donor was tracked, DOM of marine origin contributed to the methylation of mercury. Meanwhile, in winter, DOM of terrestrial origin was found to contribute to the methylation process.This study provides insights into the behavior and sources of atmospheric MeHg in a suburban area of South Korea. The study emphasizes the potential risks of atmospheric pollutants to local ecosystems and human health, highlighting the importance of monitoring atmospheric mercury pollution.

deposition,mercury,rainwater,atmosphere