Abstract
Abstract. China is regarded as the largest contributor of mercury (Hg) to the global atmospheric Hg budget. However, concentration levels and depositions of atmospheric Hg in China are poorly known. Continuous measurements of atmospheric gaseous elemental mercury (GEM) were carried out from May 2008 to May 2009 at the summit of Mt. Leigong in south China. Simultaneously, deposition fluxes of THg and MeHg in precipitation, throughfall and litterfall were also studied. Atmospheric GEM concentrations averaged 2.80±1.51 ng m−3, which was highly elevated compared to global background values but much lower than semi-rural and industrial/urban areas in China. Sources identification indicates that both regional industrial emissions and long range transport of Hg from central, south and southwest China were corresponded to the elevated GEM level. Seasonal and diurnal variations of GEM were observed, which reflected variations in source intensity, deposition processes and meteorological factors. Precipitation and throughfall deposition fluxes of THg and MeHg in Mt. Leigong were comparable or lower compared to those reported in Europe and North America, whereas litterfall deposition fluxes of THg and MeHg were higher compared to Europe and North America. This highlights the importance of vegetation to Hg atmospheric cycling. In th remote forest ecosystem of China, deposition of GEM via uptake of foliage followed by litterfall was very important for the depletion of atmospheric Hg. Elevated GEM level in ambient air may accelerate the foliar uptake of Hg through air which may partly explain the elevated litterfall deposition fluxes of Hg observed in Mt. Leigong.
Highlights
Mercury (Hg), especially its organic forms (e.g. methylmercury (MeHg) and dimethylmercury (DMeHg)), is a highly toxic pollutant that poses a serious threat to human health and wildlife (National Research Council, 2000)
Episodes with 4extremely high gaseous elemental mercury (GEM) concentrations were abundant (0.4% of values were greater than 10 ng m−3), and 62% of these events was observed in the daytime
These episodes were probably attributed to encounters of air masses from industrial and urbanized areas which probably related to heavily atmospheric Hg pollutions (Kim and Kim, 2001; Liu et al, 2002; Feng et al, 2004)
Summary
Mercury (Hg), especially its organic forms (e.g. methylmercury (MeHg) and dimethylmercury (DMeHg)), is a highly toxic pollutant that poses a serious threat to human health and wildlife (National Research Council, 2000). Atmospheric Hg consists of three chemical and physical forms, including gaseous elemental Hg (GEM or Hg0), divalent reactive gaseous Hg (RGM), and particulate Hg (PHg). GEM, the predominant form of atmospheric Hg (generally constitutes more than 90% the total Hg in atmosphere), is very stable in atmosphere with a residence time between 6 month and 2 years (Schroeder and Munthe, 1998). This enables Hg to undergo a long range transport and makes it well-mixed in a global scale. Long range transport of Hg in the atmosphere has been identified as the predominant source of Hg in pristine ecosystem in remote areas
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