As an important component of carbonaceous matters, dissolved organic carbon (DOC) can absorb and scatter the solar radiation at ultraviolet and blue wavelengths. The wet deposition process has great impact on the concentration and light absorption ability of precipitation DOC, affecting the climatic effect caused by DOC in the atmosphere. In this study, light absorption and fluorescence characteristics of precipitation DOC was investigated in the central Tibetan Plateau (TP). The results showed that the mean DOC concentration and mass absorption cross- measured at 365 nm (MAC365) in Tanggula (TGL) station were 0.59 +/- 0.42 mg/L and 0.37 +/- 0.19 m2/g, respectively, while both values showed much higher volatilities than those of aerosols. DOC concentrations had significant negative correlation with the precipitation amount, while MAC365 values increase with the precipitation amount in TGL station. Therefore, DOC with high light-absorbing ability was preferred to be retained in the atmosphere during wet deposition. In this study, precipitation DOC contained three fluorescent components (one humic-like component and two tyrosine-like components) mainly from local biomass burning sources. DOC concentration showed a negative relationship with MAC365 value in TGL station. The wet deposition of DOC with low light-absorbing ability can reduce the strong negative radiative forcing caused by secondary organic aerosol due to high proportion of DOC in secondary organic carbon. Similar phenomenon was also found in Nam Co, Lulang and Everest stations of previous study, which may have a potential impact on radiative forcing in the atmosphere of TP.

Carbonaceous matter (CM) (such as water-insoluble organic carbon (WIOC), black carbon (BC), and water-soluble organic carbon (WSOC)) has a significant impact on the carbon cycle and radiative forcing (RF) of glacier. Precipitation samples and glacier's snow/ice samples (snowpit, surface snow, and granular ice) (Xiao dongkemadi Glacier) were collected at the Dongkemadi River Basin (DRB) in the central Tibetan Plateau (TP) between May and October 2016 to investigate the characteristics and roles of CM in the TP River Basin. WIOC, BC, and WSOC concentrations in precipitation were relatively higher than that in snowpit, but lower than that in surface snow/ice, with the wet deposition fluxes of 0.10 +/- 0.002, 0.04 +/- 0.001, and 0.12 +/- 0.002 g C m(-2) yr(-1) at DRB, respectively. The positive matrix factorization model identified four major sources (biomass burning source, secondary precursors, secondary aerosol, and dust source) of CM in precipitation at DRB. Two source areas (South Asia and the interior of TP) contributing to the pollution at DRB were identified using a potential source contribution function model, a concentration-weighted trajectory method, and the back-trajectory model. Moreover, the light-absorption by WSOC in the ultraviolet region was 23.0%, 12.1%, and 3.4% relative to the estimated total light-absorption in precipitation, snowpit, and surface snow/ice, respectively. Optical indices analysis revealed that WSOC in snowpit samples presented higher molecular weight, while presented higher aromatic and higher molecule sizes in surface snow/ice and precipitation samples, respectively. RF by WSOC relative to that of BC was estimated to be 17.6 +/- 17.6% for precipitation, 10.9 +/- 5.8% for snowpit, and 10.7 +/- 11.6% for surface snow/ice, respectively, during the melt season in the central TP River Basin. These results help us understand how CM affects glaciers, and they can be utilized to create policies and recommendations that efficiently reduce emissions.

South Asian pollutants can be transported and deposited via wet/dry deposition to the remote areas of the Himalayas and could pose a serious threat to the mountain ecosystems. Therefore, in order to understand the concentrations, fluxes, seasonal variation and origin of the mercury (Hg), major ions and trace elements, precipitation samples were collected during 2012-2013 from a data gap region, Jomsom, the high elevation semiarid mountain valley in the central Himalayas. The volume-weighted mean (VWM) concentrations of ions followed the order of Ca2+ > Mg2+ > Na+ > NH4+ > SO42- > Cl- > NO3- > K+. The concentration of Cd was lowest (0.07 mu g L-1) whereas that of Fe was the highest (1073.59 mu g L-1) in the precipitation samples. Wet deposition level of all the measured inorganic species was comparable to urban Lhasa but higher than those in remote alpine sites of the Tibetan Plateau (TP). This study shows that Hg and other inorganic constituents were higher in the non-monsoon season compared to monsoon due to enhanced washout of aerosols. Enrichment factor (EF), sea salt fraction, crustal and anthropogenic fractions, principal component analysis (PCA) and correlation coefficient analysis suggested that crustal dust and anthropogenic activities as the major sources of measured chemical species whereas the influence of sea-salt was minimal. In addition, local anthropogenic emissions were low suggesting that the majority of the pollutants could have been transported from the South Asian region to the high elevation mountains. Meanwhile, low precipitation and dry environment could have enhanced the concentrations of inorganic species in the arid region than other sites over the central Himalayas. This work adds new dataset of inorganic pollutants in wet precipitation and provides baseline information for an arid region environmental protection. However, there is a need for further long-term monitoring to understand the precipitation chemistry of the arid regions.

Situated in the south edge of the Tibetan Plateau, the Himalayas is expected to receive direct anthropogenic Hg perturbations from South Asia, yet the measurements of atmospheric Hg deposition in the Himalayan region remain scarce. Here we report wet Hg deposition measured in the Yarlung Tsangpo Grand Canyon of the Eastern Himalayas, which is the deepest and longest canyon on earth. The precipitation Hg concentration (56.3 ng L-1) and wet Hg deposition flux (84.7 mu g m(-2) yr(-1)) from the Motuo station were observed among the highest ever reported for the Tibetan Plateau. Together with analysis of principal component suggesting Hg was mainly clustered with anthropogenic ions and backward trajectories indicating 88.8% of air masses came from South Asia, our results show that transboudary pollution influences from South Asia could be largely responsible for the unexpectedly high levels of wet Hg deposition. Moreover, the wet Hg flux measurements (84.7 mu g m(-2) yr(-1)) are found an order of magnitude (similar to 13 times) higher than the GEOS-Chem estimates (6.8 mu g m(-2) yr(-1)), most likely due to the underestimation of transboundary Hg pollution influence by this model. Our study has important implications for better understanding Hg dynamics and verifying atmospheric Hg models in the Tibetan Plateau and Himalayas region.

The quantitative and qualitative characterization of ions and inorganic nitrogen in precipitation assists in understanding the accompanying sources and chemistry of regional precipitation. A total of 212 event-based precipitation samples were collected from four sites in Bangladesh in 2017 to investigate the physicochemical characteristics, sources, and deposition of atmospheric ionic constituents and inorganic nitrogen. During the entire monitoring period, 5.7% of the total samples were acidic (i.e., pH Cox's Bazar > Dinajpur > Sylhet, whereas the anthropogenic species exhibited the order of Dinajpur > Satkhira > Sylhet > Cox's Bazar, underlining the local and regional impacts of these species in Bangladesh. Based on the source apportionment, the sources were categorized as marine (Na+ and Cl-), terrigenous (Ca2+, Mg2+, and HCO3-), fossil fuel combustion (NO3- and SO42-), agriculture (NH4+), and biomass burning (K+). The Cl- in Sylhet and Satkhira suggests additional sources associated with anthropogenic activities. The back-trajectory analyses and the National Centers for Environmental Prediction's final (NCEP FNL) datasets illustrate the presence of significantly diverse air masses with contributions from various sources in the monsoon and non-monsoon climates. Both the amount of precipitation and the ionic quantity governs the fluxes in Bangladesh. The Na+ % and SAR lie under the safe category suggesting a good precipitation water quality for agriculture and soil in Bangladesh, while the deposition of inorganic nitrogen has resulted in a value above the threshold line (10 kg ha(-1) y(-1)). Thus, this study conveys a comprehensive picture of the ionic composition, providing a baseline dataset to assess the atmospheric environment in this lowland region.

The major ions in precipitation can reflect the conditions of the atmosphere, while stable isotopic characteristics provide information on the moisture source. In order to understand the local hydro-chemical features and regional geochemical cycle, it is essential to assess the chemical composition of precipitation and the associated sources. Therefore, a total of 57 precipitation samples (2016 to 2017) for major ions and 178 samples (2013 to 2017) for stable isotopes were collected from the Wengguo station and analyzed to explore the major ionic deposition and stable isotopic characteristics in the northern slopes of the Himalayas. The average pH and electrical conductivity were 6.82 +/- 0.45 and 15.36 +/- 11.67 mu S cm(-1), respectively. Ca2+ followed by K+ and Mg2+ played a crucial role in neutralizing the precipitation acidity. The major ionic sources in the region were terrigenous (Ca2+, HCO3-, and Mg2+) and sea salt (Na+, Cl-, and Mg2+), as well as anthropogenic emissions (SO42- and NO3-) and biomass burning (K+). The total deposition flux of the major ions was higher in 2016 than in 2017 and was influenced by the higher precipitation. The average values of delta O-18 and delta D in precipitation were - 15.22 +/- 5.17 parts per thousand and - 116.01 +/- 41.31 parts per thousand, respectively. The precipitation stable isotopes were not significantly correlated to the local air temperature but the precipitation amount. Moreover, the variation in stable isotopes, local meteoric water line, and d-excess indicated the existence of continental and monsoon moisture transport systems. The transport of chemicals over the high elevation region from polluted cities in South Asia via moisture originating in the Bay of Bengal and the Arabian Sea was determined based on the source identification, clusters of air mass backward trajectory analysis, and the National Center for Environmental Prediction Final dataset. Thus, the ionic concentrations and stable isotopic characteristics of the precipitation from this study provided a valuable dataset to assess the atmospheric environment in the northern slopes of the Himalayas at Southern Tibetan Plateau.

As an important component of carbonaceous matters, dissolved organic carbon (DOC) can absorb and scatter the solar radiation at ultraviolet and blue wavelengths. The wet deposition process has great impact on the concentration and light absorption ability of precipitation DOC, affecting the climatic effect caused by DOC in the atmosphere. In this study, light absorption and fluorescence characteristics of precipitation DOC was investigated in the central Tibetan Plateau (TP). The results showed that the mean DOC concentration and mass absorption cross- measured at 365 nm (MAC365) in Tanggula (TGL) station were 0.59 +/- 0.42 mg/L and 0.37 +/- 0.19 m2/g, respectively, while both values showed much higher volatilities than those of aerosols. DOC concentrations had significant negative correlation with the precipitation amount, while MAC365 values increase with the precipitation amount in TGL station. Therefore, DOC with high light-absorbing ability was preferred to be retained in the atmosphere during wet deposition. In this study, precipitation DOC contained three fluorescent components (one humic-like component and two tyrosine-like components) mainly from local biomass burning sources. DOC concentration showed a negative relationship with MAC365 value in TGL station. The wet deposition of DOC with low light-absorbing ability can reduce the strong negative radiative forcing caused by secondary organic aerosol due to high proportion of DOC in secondary organic carbon. Similar phenomenon was also found in Nam Co, Lulang and Everest stations of previous study, which may have a potential impact on radiative forcing in the atmosphere of TP.

Information about the long-term trends of wet mercury (Hg) deposition is important for assessing the impact of atmospheric pollution on environmental health. As the most populated and capital city of Tibet, Lhasa is isolated far away from the heavily-polluted urban clusters in China. In this study, a 10-year observation was conducted in Lhasa to establish the long-term trend of wet Hg deposition and investigate the possible causes of this variation trend. Our study showed no significant increase in wet Hg deposition while Lhasa has achieved rapid population and economic growth during the study period. The contrasting changes in long-term wet Hg deposition and so-cioeconomic development (e.g., GDP growth) could be greatly attributed to the efforts in preventing and control-ling air pollution at regional and local levels. This trend in Lhasa differs greatly from those observed by a rapid increase of Hg trend in the remote areas of the Tibetan Plateau. Our findings indicate that the remote cryospheric areas over the Tibetan Plateau are prone to be affected by transboundary Hg pollution, and more attention should be paid to its environmental and health effects for future study. (c) 2021 Elsevier B.V. All rights reserved.

The Himalayan-Tibetan Plateau is a typical remote region with sparse air pollution. However, air pollution in cites of the inner Himalayan-Tibetan Plateau is relatively serious due to emissions from local residents. Carbonaceous aerosols are not only an important component of air pollutants that affect the health of local residents but also an important trigger of climate change. In this study, the annual wet and dry deposition rates of carbonaceous particles were investigated in Lhasad-a typical city in the Himalayan-Tibetan Plateau, by collecting precipitation and dry deposition samples and analyzing with a thermal-optical measurement protocol. The results showed that the in-situ annual wet deposition rates of water-insoluble organic carbon (WIOC) and black carbon (BC) were 169.6 and 19.4 mg m(-2) yr(-1), respectively, with the highest and lowest values occurring in the monsoon and non-monsoon periods, respectively. Both precipitation amounts and concentrations of WIOC and BC contributed to wet deposition rates. The dry deposition rates of WIOC and BC in Lhasa had an opposite seasonal variation to that of wet deposition, with annual average deposition rates of 2563.9 and 165.7 mg m(-2) yr(-1), respectively, which were much higher than those of the nearby glacier region and remote area. These values were also much higher than the results from modeling and empirical calculations, indicating that Lhasa is a high pollution point that cannot capture by models. The results in this study have significant implications for the transport of local emissions in Lhasa to the nearby remote and glacier regions. (C) 2020 Elsevier Ltd. All rights reserved.