Deposition of Atmospheric Mercury to the Lulin Atmospheric Background Station (LABS) in Taiwan in 2009-2016

Guey-Rong Sheu1, Nguyen Ly Sy Phu2, Da-Wei Lin3, Leiming Zhang4 and Neng-Huei Lin5

Although East Asia is the major anthropogenic mercury (Hg) emission source region, studies concerning atmospheric Hg deposition in its downwind region are still limited. Taiwan is considered downwind of the East Asian continent in fall, winter and spring because of regional monsoon activity. Monitoring of various atmospheric Hg species, including gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM) and particle-bound Hg (PBM), began since April 2006, whereas collection of weekly rainwater samples for total Hg analyses began since early 2009, at the Lulin Atmospheric Background Station (LABS; 120.87ºE, 23.47ºN, 2862 m a.s.l.), a tropical mountain-top site in central Taiwan. Here we reported the wet and dry deposition of atmospheric Hg to the LABS between 2009 and 2016. Dry deposition of speciated Hg was estimated using bidirectional air-surface resistance model. Amounts of annual rainfall ranged from 2160 to 4991 mm and the volume-weighted mean concentrations of rainwater Hg ranged from 5.04 to 13.08 ng L-1. Annual wet Hg deposition fluxes ranged between 10.89 and 46.05 µg m-2, with a grand average of 27.3 µg m-2 yr-1. Wet Hg deposition fluxes were higher in summer as a result of higher rainfall and rainwater Hg concentrations. Weekly wet deposition fluxes and rain depths were highly correlated (R2 = 0.654, p < 0.01). As there is no anthropogenic Hg emission source around the LABS, the high summertime rainwater Hg concentration hints the importance of Hg0 oxidation and/or scavenging of upper-altitude Hg(II) by deep convection. Annual dry deposition fluxes ranged from 51.79 to 70.15 µg m-2, with a grand average of 60.8 µg m-2 yr-1. On average, the annual dry deposition flux was 2.2 times that of wet flux. Nighttime GOM dry deposition flux (8.09±1.96 µg m-2 yr-1) was higher than that of daytime (5.21±1.58 µg m-2 yr-1) because of higher GOM concentration and wind speed at night. Due to the high percentage of forest canopy coverage around the LABS, average annual GEM dry deposition flux (47.2 µg m-2) was significantly higher than GOM (13.31 µg m-2) and PBM (0.21 µg m-2). Results of this research indicate that wet and dry Hg deposition fluxes to the tropical mountain site are significantly higher than values reported from sites in temperate region.

 

1National Central University, grsheu@atm.ncu.edu.tw
2National Central University
3National Central University
4Environment and Climate Change Canada
5National Central University