Wet deposition fluxes of total mercury and methylmercury in core urban areas, Chongqing, China

Wet deposition fluxes of mercury (Hg) species were estimated during the period from June 2010 to July 2011 at 3 sites in core urban areas in Chongqing, China. Rain water was collected by automatic deposition sampler for total Hg (THg) and methylmercury (MeHg) analyses. Our results showed that annual wet deposition fluxes of THg and MeHg were 28.7 ± 5.1 and 0.28 ± 0.09 μg m−2 yr−1, respectively. We estimate that MeHg wet deposition contributes 9.2–19.6% of the total MeHg flux to a local reservoir. Cumulative THg fluxes collected from nine principal rainfall events (>1.5 μg m−2 yr−1) at three sampling sites accounted for 20% of annual overall THg wet deposition. Statistical analyses yielded significant relationship between rainfall amounts and Hg wet deposition fluxes (r2 = 0.76, p < 0.01 for THg; r2 = 0.65, p < 0.01 for MeHg), suggesting that rainfall is one of the most important factors controlling the Hg fluxes. Obvious seasonal variations of THg fluxes were observed, with the maximum value occurring in summer (accounting for 40% of total annual THg deposition) while minimum values occurred in winter in all the three sampling sites. 72-h backward trajectory analysis on nine large deposition events at the three sites, using HYSPLIT model indicated that most of air masses which contain a relatively high precipitation amount and pass through major Hg sources would have an elevated Hg load.