Wet and speciated Hg dry deposition to a tropical mountain-top site in central Taiwan

Guey-Rong Sheu1, Da-Wei Lin2, Neng-Huei Lin3 and Leiming Zhang4

Taiwan is located downwind of the East Asian continent, which is the largest anthropogenic mercury (Hg) source region globally. Speciated atmospheric Hg has been measured since mid-April 2006 and weekly rainwater samples have been collected for total Hg analyses since early 2009 at the Lulin Atmospheric Background Station (LABS; 120.87ºE, 23.47ºN, 2862 m a.s.l.) in central Taiwan. Here we report and characterize the wet and dry deposition of Hg on LABS in 2010. The annual rainfall at LABS was 3173.2 mm in 2010. A total of 36 weekly rainwater samples were collected for Hg analysis with an annual volume-weighted mean Hg concentration of 8.8 ng L-1. The annual wet deposition flux was 33.7 µg m-2. Seasonal VWM concentrations and wet deposition flux were both higher in summer than in the other seasons. The high summertime wet deposition flux was primarily a result of elevated amount of rainfall (1632 mm) and to a lesser extent, higher rainwater Hg concentration (12.7 ng L-1). As there is no anthropogenic Hg emission source near 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. Speciated Hg dry depositions were estimated based on a model calculation. For the year of 2010, dry deposition fluxes of GEM, RGM, and PHg were estimated to be 58.8, 10.6, and 0.1 μg m-2, respectively, with a total dry flux of 69.5 μg m-2. Wet deposition dominated in summer/fall, but dry deposition dominated in spring/winter. Nonetheless, overall wet deposition was more important than the dry deposition of RGM plus PHg at this tropical mountain-top site because of abundant rainfall. Concentration-weighted trajectory (CWT) approach was applied to identify potential source regions of each atmospheric Hg species. Southwest and Southeast China and northern Indochina Peninsula were the common major source regions of GEM, RGM and PHg. An additional source region for GEM was identified extending from northeast China along the coastal region of east China. Moreover, air from the South China Sea and the Pacific Ocean could also be enriched with RGM, suggesting sources other than anthropogenic emissions, such as Hg0 oxidation.

 

1National Central University, grsheu@atm.ncu.edu.tw
2National Central University, linda79515@gmail.com
3National Central University, nhlin@cc.ncu.edu.tw
4Environment Canada, Leiming.Zhang@ec.gc.ca