First Measurement of Atmospheric Mercury Species in Qomolangma Nature Preserve, Tibetan Plateau, and Evidence of Transboundary Pollutant Invasion

Located in the world’s ‘Third Pole’ and a remote region connecting the Indian Ocean plate and the Eurasian plate, Qomolangma National Nature Preserve (QNNP) is an ideal region to study the long-range transport of atmospheric pollutants. In this study, gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) were continuously measured during the Indian monsoon transition period in QNNP. A slight increase in GEM concentration was observed from the period preceding the Indian Summer Monsoon (1.31±0.42 ng m−3) to the Indian Summer Monsoon period (1.44±0.36 ng m−3), while significant decreases were observed in GOM and PBM concentrations, decreasing from 35.2±18.7 to 19.1±11.0 pg m−3 and from 30.5±12.6 to 24.7±19.9 pg m−3, respectively. A unique daily pattern of GEM concentration in QNNP was observed, with a peak value before sunrise and a low value at noon. Unexpectedly, GOM concentrations (with a mean value of 21.3±13.5 pg m−3) in this region were considerably higher than the values in other clean or even polluted regions. A cluster analysis indicated that the air masses transported to QNNP changed significantly at different stages of the monsoon, and the major potential Hg sources shifted from north India and west Nepal to east Nepal and Bangladesh. With large coverage of glacier in QNNP, local glacier winds could enforce the transboundary transport of pollutants and transport the polluted air masses to the Tibetan Plateau. It should be noted that the atmospheric Hg concentrations in QNNP are higher than the reported values in some background regions, which addresses the need for a more specific identification of Hg sources in QNNP and the importance of international cooperation for global Hg controls.