环境地球化学国家重点实验室知识库

Precipitation samples collected at a remote high elevation site (i.e., Nam Co Station, 4730 m a.s.l.) in the southern Tibetan Plateau were analyzed for total mercury (Hg_T) between July 2009 and 2011, particulate-bound mercury (Hg_P) between July 2010 and 2011 and methylmercury (MeHg) from July through August of 2009. The volume-weighted mean (VWM) concentrations and wet deposition fluxes of Hg_Tand MeHg in precipitation were 4.8 ng L⁻¹ and 1.75 μg m⁻² yr⁻¹, 0.031 ng L⁻¹ and 0.01 μg m⁻² yr⁻¹, respectively. VWM Hg_T concentration was approximately two times higher during the non-monsoon season than during the monsoon season, while 83% of the Hg_T wet deposition fluxes occurred during the monsoon season. The Hg_T and MeHg concentrations are comparable to the reported data for some of the most remote alpine and polar regions worldwide (e.g., Churchill), but the wet deposition fluxes of Hg_T and MeHg were among the lowest in the world. Analysis of Hg speciation has presented that Hg_P and MeHg concentrations are high, making up 71.2% and 1.82% of the Hg_T on average (VWM), respectively. The high Hg_P%, as well as a significantly positive between Hg_T and Hg_P (R² = 0.91; n = 44; p < 0.001), confirmed that atmospheric deposition of Hg in the Tibetan Plateau was occurring in the form of Hg_P. A decreasing trend in Hg_T concentrations with increasing amount of precipitation (R² = 0.08; N = 101; p < 0.005) was found at Nam Co Station, indicative that scavenging of Hg_P from the atmosphere was an important mechanism contributing Hg to precipitation. The precipitation amount, rather than Hg_T concentration, was found to be the governing factor affecting Hg_T wet deposition flux. Moreover, a comparison between measured wet deposition flux of Hg at Nam Co Station and the estimates from environmental records indicated that both snowpits and lake sediments appear to be reliable archives for estimating historical Hg accumulation rates over the Tibetan Plateau.