Indian monsoon circulation is the primary driver of the long-range transboundary mercury (Hg) pollution from South Asia to the Himalayas and Tibet Plateau region, yet the northward extent of this transport remains unknown. In this study, a strong delta Hg-202 signature overlapping was found between Lake Gokyo and Indian anthropogenic sources, which is an indicative of the Hg source regions from South Asia. Most of the sediment samples were characterized with relatively large positive Delta Hg-199 values (mean = 0.07 parts per thousand-0.44 parts per thousand) and small positive Delta Hg-200 values (mean = 0.03 parts per thousand-0.08 parts per thousand). Notably, the Delta Hg-199 values in the lake sediments progressively increased from southwest to northeast. Moreover, the Delta Hg-199 values peaked at Lake Tanglha (mean = 0.44 parts per thousand +/- 0.04 parts per thousand) before decreased at Lake Qinghai that is under the influence of the westerlies. Our results suggest that transboundary atmospheric transport could transport Hg from South Asia northwards to at least the Tanglha Mountains in the northern Himalaya-Tibet.

The concentration and isotopic composition of mercury (Hg) were studied in frozen soils along a southwest-northeast transect over the Himalaya-Tibet. Soil total Hg (Hg-T) concentrations were significantly higher in the southern slopes (72 +/- 54 ng g(-1), 2SD, n = 21) than those in the northern slopes (43 +/- 26 ng g(-1), 2SD, n = 10) of Himalaya-Tibet. No significant relationship was observed between Hg T concentrations and soil organic carbon (SOC), indicating that the Hg-T variation was not governed by SOC. Soil from the southern slopes showed significantly negative mean delta Hg-202 (-0.53 +/- 0.50 parts per thousand, 2SD, n = 21) relative to those from the northern slopes (-0.12 +/- 0.40 parts per thousand, 2SD, n = 10). The delta Hg-202 values of the southern slopes are more similar to South Asian anthropogenic Hg emissions. A significant correlation between 1/Hg-T and delta Hg-202 was observed in all the soil samples, further suggesting a mixing of Hg from South Asian anthropogenic emissions and natural geochemical background. Large ranges of Delta Hg-199 (-0.45 and 0.24 parts per thousand) were observed in frozen soils. Most of soil samples displayed negative Delta Hg-199 values, implying they mainly received Hg from gaseous Hg(0) deposition. A few samples had slightly positive odd-MIF, indicating precipitation-sourced Hg was more prevalent than gaseous Hg(0) in certain areas. The spatial distribution patterns of Hg-T concentrations and Hg isotopes indicated that Himalaya-Tibet, even its northern part, may have been influenced by transboundary atmospheric Hg pollution from South Asia. (C) 2019 Elsevier Ltd. All rights reserved.

Air pollution is a global issue that often transcends national borders, leading to disputes over environmental concerns and climate-mitigation responsibilities. Between March and July 2020, we collected aerosol samples in Jimunai, a town in western China neighboring Kazakhstan, to assess transboundary air pollution in the region. Our analysis focused on major water-soluble inorganic ions (WSIs), with Ca2+ and SO42- accounting for almost 60% of the total ion loading. The ratio of cations to anions was greater than one (1.33 & PLUSMN; 0.27), indicating alkaline aerosols during the sampling period. Our results suggest that the pollutants measured were primarily sourced from Kazakhstan, as demonstrated by local meteorological data, air-mass trajectory analysis, and pollutant emission inventories in Kazakhstan. Correlation and primary component analysis indicated that NH4+ played an important role in neutralizing NO3- and SO42-, while Cl- was significantly depleted by the probable reaction HNO3 & UARR; + NaCl = HCl & UARR; + NaNO3. These findings highlight the need for continued monitoring and regulation of air pollution sources in the region to address transboundary air pollution.

The Tibetan Plateau holds the largest mass of snow and ice outside of the polar regions. The deposition of light-absorbing particles (LAPs) including mineral dust, black carbon and organic carbon and the resulting positive radiative forcing on snow (RFSLAPs) substantially contributes to glacier retreat. Yet how anthropogenic pollutant emissions affect Himalayan RFSLAPs through transboundary transport is currently not well known. The COVID-19 lockdown, resulting in a dramatic decline in human activities, offers a unique test to understand the transboundary mechanisms of RFSLAPs. This study employs multiple satellite data from the moderate resolution imaging spectroradiometer and ozone monitoring instrument, as well as a coupled atmosphere-chemistry-snow model, to reveal the high spatial heterogeneities in anthropogenic emissions-induced RFSLAPs across the Himalaya during the Indian lockdown in 2020. Our results show that the reduced anthropogenic pollutant emissions during the Indian lockdown were responsible for 71.6% of the reduction in RFSLAPs on the Himalaya in April 2020 compared to the same period in 2019. The contributions of the Indian lockdown-induced human emission reduction to the RFSLAPs decrease in the western, central, and eastern Himalayas were 46.8%, 81.1%, and 110.5%, respectively. The reduced RFSLAPs might have led to 27 Mt reduction in ice and snow melt over the Himalaya in April 2020. Our findings allude to the potential for mitigating rapid glacial threats by reducing anthropogenic pollutant emissions from economic activities.

Since the beginning of the 21st century, our knowledge of the sources and fate of Hg over the Tibetan Plateau (TP), the Roof of the World, has been greatly enhanced with growing literature. Here, we reviewed the available literature to obtain a comprehensive understanding of Hg biogeochemistry over the TP. The biogeochemical Hg cycling is characterized by the following features: (1) There are existing but limited local emission sources of anthropogenic Hg in the TP. The Indian Summer Monsoon is an important transporter of atmospheric Hg pollution into the inland TP; (2) Cold trapping effect plays an important role in the atmospheric Hg deposition over the TP. Glacier, vegetation, and soil act as important sinks of atmospheric Hg pollution; (3) Enhanced anthropogenic activities around the TP, climate warming and glacier melting have the potential impacts to affect the behavior and distribution of Hg; (4) Significant bioaccumulation of MeHg (>100 ng/g) has been found in the Tibetan aquatic food chains. Considering that transboundary transport is responsible for the widespread Hg pollution in the TP, international/regional collaborations regarding Hg emission regulations are needed to reduce the migration of Hg and to mitigate adverse Hg pollution impacts on the TP.