Exchange fluxes of Hg between surfaces and atmosphere in the eastern flank of Mount Gongga, Sichuan province, southwestern China

Abstract

In situ total gaseous mercury (TGM) concentrations and mercury exchange fluxes from 17 sampling sites of three representative landscapes (agriculture, grassland, and forest) were intensively measured in the eastern flank of Mount Gongga area, Sichuan province, southwestern China, from October 2005 to September 2006. Average TGM concentrations in ambient air ranged from 1.60 to 5.10 ng m−3 in warm season, while the values were highly elevated in cold season with the highest mean TGM concentration of 7.65 ng m−3. Hg fluxes from agriculture and grassland sampling sites showed clearly seasonal distribution pattern with net depositions observed in cold season and net emissions observed in warm season. Mean Hg fluxes at agriculture and grassland field fell in the range from −4.1 to 132.0 ng m−2 h−1 and from −18.7 to 13.4 ng m−2 h−1, respectively, while mean Hg fluxes from forest sites varied from 0.5 to 9.3 ng m−2 h−1. Notable diurnal pattern of Hg fluxes were observed from all sampling sites, with the maximum Hg fluxes observed at midday and the minimum values observed during the nighttime. TGM concentrations in cold season significantly negatively correlated with Hg flux, suggesting that highly elevated TGM concentration could inhibit Hg emission even cause significant deposition. Vegetation acted as a great sink of air Hg in cold season, while in warm season, it could significantly inhibit Hg emission from surfaces.