Methylmercury concentrations and potential sources in atmospheric fine particles in Beijing, China

The characteristics and sources of methylmercury (MeHg) in atmospheric fine particles remain poorly elucidated. We obtained the concentrations of MeHg bound to atmospheric fine particles in four seasons, from September 2015 to July 2016, at an urban site in Beijing, China. Concentrations ranged from <0.01 to 1.33 pg m^-3, averaging at 0.21 ± 0.17 pg m^-3. The highest concentration of MeHg in atmospheric fine particles occurred in summer. Relatively high mass composition of MeHg in atmospheric fine particles occurred when the concentrations of PM_2.5 were low. Intense sunlight and atmospheric oxidants promoted the formation of MeHg that was then enriched on atmospheric fine particles. Moreover, precipitation scavenged 29.4-77.0% of the MeHg bound to atmospheric fine particles. The possible sources of MeHg in atmospheric fine particles were identified using Positive Matrix Factorization (PMF) model. Dimethylmercury (DMeHg) decomposition and MeHg surface volatilization, combustion and marine sources, dust, and heterogeneous reactions contributed 47.8%, 18.7%, 16.4%, and 13.2% of the MeHg in atmospheric fine particle, respectively. This study supplements knowledge on the concentrations, atmospheric processes, and sources of MeHg in atmospheric fine particles.