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.

As an important component of carbonaceous aerosols (CA), organic carbon (OC) exerts a strong, yet insufficiently constrained perturbation of the climate. In this study, we reported sources of OC based on its natural abundance radiocarbon (14C) fingerprinting in aerosols and water-insoluble organic carbon (WIOC) in snowpits across the Tibetan Plateau (TP) - one of the remote regions in the world and a freshwater reservoir for billions of people. Overall, the proportions from C-14-based non-fossil fuel contribution (f(non-fossil)) for OC in aerosols was 74 +/- 10%, while for WIOC in snowpits was 81 +/- 10%, both of which were significantly higher than that of elemental carbon (EC). These indicated sources of OC (WIOC) and EC were different at remote TP. Spatially, high f(non-fossil) of WIOC of snowpit samples appeared at the inner part of the TP, indicating the important contribution of local non-fossil sources. Therefore, local non-fossil sources rather than long-range transportation OC dominants its total amount of the TP. In addition, the contribution of local non-fossil sourced WIOC increased during the monsoon period because heavy precipitation removed a high ratio of long-range transportation WIOC. The results of this study showed that not only OC and EC but also their different fuel sources should be treated separately in models to investigate their sources and atmospheric transportation.

Carbonaceous particles play an important role in climate change, and an increase in their emission and deposition causes glacier melting in the Himalayas and the Tibetan Plateau (HTP). This implies that studying their basic characteristics is crucial for a better understanding of the climate forcing observed in this area. Thus, we investigated characteristics of carbonaceous particles at a typical remote site of southeastern HTP. Organic carbon and elemental carbon concentrations at this study site were 1.86 +/- 0.84 and 0.18 +/- 0.09 mu g m(-3), respectively, which are much lower than those reported for other frequently monitored stations in the same region. Thus, these values reflect the background characteristics of the study site. Additionally, the absorption coefficient per mass (alpha/rho) of water-soluble organic carbon (WSOC) at 365 nm was 0.60 +/- 0.19 m(2) g(-1), with the highest and lowest values corresponding to the winter and monsoon seasons, respectively. Multi-dimensional fluorescence analysis showed that the WSOC consisted of approximately 37% and 63% protein and humic-like components, respectively, and the latter was identified as the component that primarily determined the light absorption ability of the WSOC, which also showed a significant relationship with some major ions, including SO42-, K+, and Ca2+, indicating that combustion activities as well as mineral dust were two important contributors to WSOC at the study site. (C) 2020 Elsevier Ltd. All rights reserved.

At present, the glaciers in the Himalayas and the Tibetan Plateau (HTP) are retreating partly due to albedo reduction caused by deposited light-absorbing impurities such as mineral dust (MD) and black carbon (BC). Because BC also exists widely in MD from surface soil, it is necessary to further evaluate the contribution of BC from MD to the total BC at glacier region. This will help to improve the study of BC sources by considering the relative contributions from MD and direct combustion sources. Therefore, in this study, concentrations of total organic carbon (TOC) and fine particles of BC from 43 surface soil samples of the HTP were investigated. The contribution of BC from MD to total BC deposited at the glacier region was evaluated. The results showed strong correlations between TOC and BC of studied samples (R-2 = 0.70, p < 0.01), suggesting that they have similar sources and activity characteristics. The average BC concentration of studied samples was 2.02 +/- 1.55 mg g(-1), much lower than those of particles deposited at the glacier region and other regions with high soil TOC concentration. The contributions of BC from MD to total surface BC at two glaciers of the inner HTP (Zhadang and Xiaodongkemadi) were 17.66 +/- 10.84% and 20.70 +/- 16.35%, respectively. Therefore, the contribution of MD to glacier melting of the HTP is higher than that of previously assumed after BC coming along with MD is considered. Because MD concentration is higher at north and west part of the HTP, the contributions of MD at these glacier regions should be larger than previously assumed.

At present, the glaciers in the Himalayas and the Tibetan Plateau (HTP) are retreating partly due to albedo reduction caused by deposited light-absorbing impurities such as mineral dust (MD) and black carbon (BC). Because BC also exists widely in MD from surface soil, it is necessary to further evaluate the contribution of BC from MD to the total BC at glacier region. This will help to improve the study of BC sources by considering the relative contributions from MD and direct combustion sources. Therefore, in this study, concentrations of total organic carbon (TOC) and fine particles of BC from 43 surface soil samples of the HTP were investigated. The contribution of BC from MD to total BC deposited at the glacier region was evaluated. The results showed strong correlations between TOC and BC of studied samples (R-2 = 0.70, p < 0.01), suggesting that they have similar sources and activity characteristics. The average BC concentration of studied samples was 2.02 +/- 1.55 mg g(-1), much lower than those of particles deposited at the glacier region and other regions with high soil TOC concentration. The contributions of BC from MD to total surface BC at two glaciers of the inner HTP (Zhadang and Xiaodongkemadi) were 17.66 +/- 10.84% and 20.70 +/- 16.35%, respectively. Therefore, the contribution of MD to glacier melting of the HTP is higher than that of previously assumed after BC coming along with MD is considered. Because MD concentration is higher at north and west part of the HTP, the contributions of MD at these glacier regions should be larger than previously assumed.