Wet Deposition Monitoring Network of Mercury in Taiwan

Guey-Rong Sheu* and Neng-Huei Lin
Department of Atmospheric Sciences
National Central University
300 Chung-Da Rd.
Chung-Li, Taiwan

Taiwan is located in the downwind region of the East Asian continent, which is the largest anthropogenic mercury (Hg) source region globally. Modeling simulations suggested that Taiwan could receive high Hg input via wet deposition. Therefore, a national Hg wet deposition monitoring network, consisting of 12 sampling sites, was established along with the existing acid deposition monitoring network to collect rainwater for total Hg analysis since 2009. The objective of this network is to build a national database of total Hg concentration in precipitation and the associated wet depositional fluxes. The data will later be used to develop information on spatial and seasonal trends in Hg wet deposition and to evaluate the contribution of regional/long-range transport. Weekly rainwater samples were collected using automated wet-only precipitation collection systems. Acid-cleaned glass funnels were used for rainwater collections and samples were collected into acid-cleaned 1L Teflon bottles. Samples were retrieved and sampling trains were changed every Tuesday morning. Total Hg was quantified by dual amalgamation CVAFS after BrCl oxidation, NH2OH•HCl neutralization, and SnCl2 reduction. Total Hg concentrations of all the rainwater samples ranged from 2.1 to 82.2 ng L-1 in 2009. The volume-weighted mean (VWM) total Hg concentrations of all the sampling sites ranged between 7.6 and 17.2 ng L-1, comparable to the 2008 values (2.1-18.7 ng L-1) reported by NADP/MDN. Eight of the 12 sampling sites had VWM Hg concentrations higher than 10 ng L-1. In general, rainwater Hg concentrations were lower in northern Taiwan sites, likely due to the dilution effect caused by higher rainfall amount. Annual wet depositional Hg fluxes ranged between 12.3 and 37.0 g m-2 in 2009, somewhat higher than the 2008 MDN values (1.9-25.0 g m-2). Higher wet depositional Hg fluxes were observed in northern Taiwan sites. The geographical distribution of wet depositional Hg flux mimicked the distribution of accumulative rainfall amount, indicating precipitation depth is the primary factor in determining the magnitude of the wet depositional Hg flux.

*Corresponding author: Phone: +886-3-4227151 ext. 65514, Email: