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The Tibetan Plateau is generally considered to be a significantly clean area owing to its high altitude; however, the transport of atmospheric pollutants from the Indian subcontinent to the Tibetan Plateau has influenced the Tibetan environments. Nyingchi is located at the end of an important water vapor channel. In this study, continuous monitoring of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) was conducted in Nyingchi from 30 March to 3 September 2019, to study the influence of the Indian summer monsoon (ISM) on the origin, transport, and behavior of Hg. The GEM and PBM during the preceding Indian summer monsoon (PISM) period (1.20±0.35 ng m -3 and 11.4±4.8 pg m -3 for GEM and PBM, respectively) were significantly higher than those during the ISM period (0.95±0.21 ng m -3 , and 8.8±6.0 pg m -3); the GOM during the PISM period (13.5±7.3 pg m -3) was almost at the same level as that during the ISM period (12.7±14.3 pg m -3). The average GEM concentration in the Nyingchi region, obtained using passive sampler, was 1.12±0.28 ng m -3 (from 4 April 2019 to 31 March 2020). The GEM concentration showed that the sampling area was very clean compared to other high-altitude sites. The GEM has several patterns of diurnal variation during different periods. Stable high GEM concentrations occur at night and low concentrations occur in the afternoon during PISM, which may be related to the nocturnal boundary layer structure. High values occurring in the late afternoon during the ISM may be related to long-range transport. Low concentrations of GEM observed during the morning in the ISM may originate from vegetation effects. The results of the trajectory model demonstrate that the sources of pollutants at Nyingchi are different with different circulation patterns. During westerly circulation in the PISM period, pollutants mainly originate from central India, northeastern India, and central Tibet. During the ISM period, the pollutants mainly originate from the southern part of the SET site. The strong precipitation and vegetation effects on Hg species during the ISM resulted in low Hg concentrations transmitted to Nyingchi during this period. Further, principal component analysis showed that long-distance transport, local emissions, meteorological factors, and snowmelt factors are the main factors affecting the local Hg concentration in Nyingchi. Long-distance transport factor dominates during PISM and ISM3, while local emissions is the major contributor between PISM and ISM3. Our results reveal the Hg species distribution and possible sources of the most important water vapor channel in the Tibetan Plateau and could serve as a basis for further transboundary transport flux calculations. [ABSTRACT FROM AUTHOR]

Characterizing the vertical distribution of aerosol optical properties is crucial to reduce the uncertainty in quantifying the radiative forcing and climate effects of aerosols. The analysis of four-year (2007–2010) Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar measurements revealed the existence of tropospheric aerosol layers associated with the Asian summer monsoon. The measurements of five typical aerosol optical and microphysical parameters were used to explore the properties, spatial/vertical distributions, annual evolution of tropopause aerosols over the South Asia region. Results extracted from various latitude-height and longitude-height cross sections of aerosol extinction coefficient at 532 and 1064 nm, backscatter coefficient at 532 nm, and depolarization ratio at 532 nm demonstrated that a large amount of aerosols vertically extended up to the tropopause (12 km) during the monsoon season over the north Arabian Sea, India, north Bay of Bengal, and equatorial Indian Ocean, finally reaching the southeast of the Tibetan Plateau. Convective transport associated with Asian summer monsoon is an important factor controlling the vertical distribution of tropopause aerosols. The evolution of aerosol scattering ratio at 532 nm indicated that from equatorial Indian Ocean to South Asia, there exists an upward tilting and ascending structure of the aerosols layer during the monsoon season, which typically indicates enhanced aerosols over the Asian monsoon region. Information on aerosol size distribution and detailed composition are needed for better understanding the nature and origin of this aerosol layer. Enhancement of the tropopause aerosols should be considered in the future studies in evaluating the regional or global climate systems. Further satellite observations of aerosols and in-situ observations are also urgently needed to diagnose this aerosol layer, which likely originate from anthropogenic emissions. Image 1 • Aerosol optical and microphysical parameters have been used to specify the vertical distribution. • CALIPSO lidar measurements have revealed the existence of tropospheric aerosol layers. • There exists a tilting and ascending structure of aerosols layer during the monsoon season. [ABSTRACT FROM AUTHOR]

To explore the spatio-temporal dynamics and mechanisms underlying vegetation cover in Haryana State, India, and implications thereof, we obtained MODIS EVI imagery together with CHIRPS rainfall and MODIS LST at annual, seasonal and monthly scales for the period spanning 2000 to 2022. Additionally, MODIS Potential Evapotranspiration (PET), Ground Water Storage (GWS), Soil Moisture (SM) and nighttime light datasets were compiled to explore their spatial relationships with vegetation and other selected environmental parameters. Non-parametric statistics were applied to estimate the magnitude of trends, along with correlation and residual trend analysis to quantify the relative influence of Climate Change (CC) and Human Activities (HA) on vegetation dynamics using Google Earth Engine algorithms. The study reveals regional contrasts in trends that are evidently related to elevation. An annual increasing trend in rainfall (21.3 mm/decade, p < 0.05), together with augmented vegetation cover and slightly cooler (−0.07 °C/decade) LST is revealed in the high-elevation areas. Meanwhile, LST in the plain regions exhibit a warming trend (0.02 °C/decade) and decreased in vegetation and rainfall, accompanied by substantial reductions in GWS and SM related to increased PET. Linear regression demonstrates a strongly significant relationship between rainfall and EVI (R2 = 0.92), although a negative relationship is apparent between LST and vegetation (R2 = −0.83). Additionally, increased LST in the low-elevation parts of the study area impacted PET (R2 = 0.87), which triggered EVI loss (R2 = 0.93). Moreover, increased HA resulted in losses of 25.5 mm GSW and 1.5 mm SM annually. The relative contributions of CC and HA are shown to vary with elevation. At higher elevations, CC and HA contribute respectively 85% and 15% to the increase in EVI. However, at lower elevations, reduced EVI is largely (79%) due to human activities. This needs to be considered in managing the future of vulnerable socio-ecological systems in the state of Haryana. [Display omitted] • Vegetation change during 2000–2022 is strongly elevation-dependent. • Rainfall increased in higher elevation regions but decreased in the lower altitude plains. • LST increased in the plains but declined in the mountains. • Spatio-temporal variations in driving factors are reflected in vegetation change (EVI). • The relative importance of climate and human activities varies markedly with altitude. [ABSTRACT FROM AUTHOR]

The Yarlung Tsangbo (YT) is a large river running across southern Tibet and has significant effects on its lower reaches, the Ganges-Brahmaputra Basin. In order to investigate the geochemical features of the YT, 18 surface sediment samples were collected; ten trace element concentrations were measured for bulk sediments and two fine grain size fractions. Meanwhile, basic physicochemical parameters and element concentrations of river water were also analyzed. Results indicated that the river water was alkaline (pH 8.42) and that dissolved oxygen was mainly controlled by river water temperature. Some elements (e.g., Zn and Ni) showed close negative relationship to mean grain size of the sediments. Concentrations of most heavy metals, except As of the YT bulk sediments, were similar to those of Upper Crustal Concentration and its lower reaches, indicating almost no anthropogenic impact. Arsenic of the YT sediments was derived fundamentally from the parent rocks of the YT Basin and was far higher than that of its lower reaches. This indicates that relatively small amounts of As from the study area were transported down to the Brahmaputra River under present, relatively dry climatic conditions. However, more YT sediments might have been transported to its low reaches during the Holocene due to the wet climate, giving high As concentration in Holocene sediments of the Ganges-Brahmaputra Basin. Thus, As transported by the YT may produce important influence on the Ganges-Brahmaputra Basin and contribute to its high As concentration in groundwater. [ABSTRACT FROM AUTHOR]

Abstract: Rare earth element (REE) concentrations in ice samples from the upper 8.4m of a Mt. Everest ice core retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518ma.s.l.) on the northeast ridge of Mt. Everest in September 2002 are presented. REEs display large seasonal variations, with high concentrations in the non-monsoon season and low concentrations in the summer monsoon season. This seasonality is useful for ice core dating. When normalized to a shale standard, the Mt. Everest REEs exhibit a consistent shale-like pattern with a slight enrichment of middle REEs during both seasons. However, individual monsoon REE patterns display differences, possibly resulting from diversified sources. Non-monsoon REE patterns are stable and are associated with the westerlies. Investigation of potential sources for the Everest REEs suggests an absence of anthropogenic contributions and minimal input from local provenances. REEs in Mt. Everest samples are most likely representative of a stable well-mixed REE background of the upper troposphere consisting of a mixture of aerosols transported by the atmospheric circulation from the west windward arid regions such as the Thar Desert, West Asia, the Sahara Desert and other uncertain provenances. [Copyright &y& Elsevier]

Indo–Gangetic Plain (IGP) is one of the most polluted regions in the world. Despite numbers of studies conducted at urban site, few data are available at rural area. In this study, characteristics of 15 particle-bound priority polycyclic aromatic hydrocarbons (PAHs) of total suspended particles (TSPs) collected at a typical rural area (Lumbini) of IGP from April 2013 to March 2014 were reported. The results showed that annual average TSP and PAH concentrations were 209 ± 123 μg/m 3 and 94.8 ± 54.6 ng/m 3 , respectively, which were similar to those of large cities such as Agra and Delhi in the upwind adjacent regions. Clear seasonal variation of TSP and PAH concentrations was observed, with the highest average concentration occurring in winter followed by the pre-monsoon, post-monsoon, and monsoon seasons, reflecting combined influence of source strength and monsoon circulation on PAH concentrations of Lumbini. Positive matrix factorization analysis showed that biomass combustion (50.6%) and vehicular emissions (30.4%) were first two sources of PAHs, followed by coal combustion (11.6%) and air-soil exchange (7.4%), in line with that of diagnostic molecular ratios results. Because of extensive agro-residue burning, intensive forest fires, and conducive weather conditions, contribution of biomass burning during non-monsoon season (55.7%) was higher than that of monsoon season (42.1%). The total BaP equivalent concentration (BaP eq ) of particulate PAHs ranged between 2.51 and 47.3 ng/m 3 , was 2–40 times higher than the WHO guideline (1 ng/m 3 ), implying local residents were at risk for adverse health effects. [ABSTRACT FROM AUTHOR]

Assessing the relative importance of climate change and human activities is important in developing sustainable management policies for regional land use. In this study, multiple remote sensing datasets, i.e. CHIRPS (Climate Hazard Group InfraRed Precipitation with Station Data) precipitation, MODIS Land Surface Temperature (LST), Enhanced Vegetation Index (EVI), Potential Evapotranspiration (PET), Soil Moisture (SM), WorldPop, and nighttime light have been analyzed to investigate the effect that climate change (CC) and regional human activities (HA) have on vegetation dynamics in eastern India for the period 2000 to 2022. The relative influence of climate and anthropogenic factors is evaluated on the basis of non-parametric statistics i.e., Mann-Kendall and Sen's slope estimator. Significant spatial and elevation-dependent variations in precipitation and LST are evident. Areas at higher elevations exhibit increased mean annual temperatures (0.22 °C/year, p < 0.05) and reduced winter precipitation over the last two decades, while the northern and southwest parts of West Bengal witnessed increased mean annual precipitation (17.3 mm/year, p < 0.05) and a slight cooling trend. Temperature and precipitation trends are shown to collectively impact EVI distribution. While there is a negative spatial correlation between LST and EVI, the relationship between precipitation and EVI is positive and stronger (R 2  = 0.83, p < 0.05). Associated hydroclimatic parameters are potent drivers of EVI, whereby PET in the southwestern regions leads to markedly lower SM. The relative importance of CC and HA on EVI also varies spatially. Near the major conurbation of Kolkata, and confirmed by nighttime light and population density data, changes in vegetation cover are very clearly dominated by HA (87%). In contrast, CC emerges as the dominant driver of EVI (70-85%) in the higher elevation northern regions of the state but also in the southeast. Our findings inform policy regarding the future sustainability of vulnerable socio-hydroclimatic systems across the entire state., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Atmospheric aerosols play a crucial role in climate change, especially in the Himalayas and Tibetan Plateau. Here, we present the seasonal and diurnal characteristics of aerosol vertical profiles measured using a Mie lidar, along with surface black carbon (BC) measurements, at Mt. Qomolangma (QOMS), in the central Himalayas, in 2018-2019. Lidar-retrieved profiles of aerosols showed a distinct seasonal pattern of aerosol loading (aerosol extinction coefficient, AEC), with a maximum in the pre-monsoon (19.8 ± 22.7 Mm -1 of AEC) and minimum in the summer monsoon (7.0 ± 11.2 Mm -1 of AEC) seasons. The diurnal variation characteristics of AEC and BC were quite different in the non-monsoon seasons with enriched aerosols being maintained from 00:00 to 10:00 in the pre-monsoon season. The major aerosol types at QOMS were identified as background, pollution, and dust aerosols, especially during the pre-monsoon season. The occurrence of pollution events influenced the vertical distribution, seasonal/diurnal patterns, and types of aerosols. Source contribution of BC based on the weather research and forecasting chemical model showed that approximately 64.2% ± 17.0% of BC at the QOMS originated from India and Nepal in South Asia during the non-monsoon seasons, whereas approximately 47.7% was from local emission sources in monsoon season. In particular, the high abundance of BC at the QOMS in the pre-monsoon season was attributed to biomass burning, whereas anthropogenic emissions were the likely sources during the other seasons. The maximum aerosol concentration appeared in the near-surface layer (approximately 4.3 km ASL), and high concentrations of transported aerosols were mainly found at 4.98, 4.58, 4.74, and 4.88 km ASL in the pre-monsoon, monsoon, post-monsoon, and winter seasons, respectively. The investigation of the vertical profiles of aerosols at the QOMS can help verify the representation of aerosols in the air quality model and satellite products and regulate the anthropogenic disturbance over the Tibetan Plateau., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This study discusses year-long (October 2016-September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28°12'49.21″N, 85°36'33.77″E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 μg m -3 ) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96-542 ng g -1 and 152-827 ng g -1 , respectively. The source apportionment study using the absorption Ångström exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated ∼14% contribution of BC from open-burning and ∼77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model - Snow, Ice, and Aerosol Radiation - was in the range of 0.8-3.8% during the pre-monsoon season. The glacier mass balance analysis suggested that BC contributed to approximately 39% of the total mass loss in the pre-monsoon season., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study used a regional climate-chemistry transport model, WRF-Chem v3.9.1, to evaluate the impact of South Asian biomass burning on black carbon (BC) over the Tibetan Plateau (TP) and its climatic effects for an entire year. The simulation, which was validated by comparing surface meteorological parameters and BC concentration against in-situ observations over South Asia and the TP, provided a perspective on the seasonal variations and regional spatial patterns of BC concentration. Using a sensitivity simulation where BC emissions from biomass burning were removed from South Asia, this study found South Asian biomass burning emissions contributed up to 90% of BC mass over the TP during the pre-monsoon season, specifically emissions from western India for the simulated year. The emissions led to reduced surface radiative forcing, causing the temperature to decrease accordingly. However, column cloud water was increased. This study suggested that the biomass burning emissions from South Asia have significant impact on atmospheric BC over the TP, especially during the pre-monsoon season. Therefore, reducing biomass burning emissions from South Asia is potentially important for alleviating the effects of BC on climatic and environmental conditions over the TP and surrounding regions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Nitrogenous aerosols are ubiquitous in the environment and thus play a vital role in the nutrient balance as well as the Earth's climate system. However, their abundance, sources, and deposition are poorly understood, particularly in the fragile and ecosensitive Himalayan and Tibetan Plateau (HTP) region. Here, we report concentrations of nitrogen species and isotopic composition (δ 15 N) in aerosol samples collected from a forest site in the HTP (i.e., Southeast Tibet). Our results revealed that both organic and inorganic nitrogen contribute almost equally with high abundance of ammonium nitrogen (NH 4 + N exhibit a significant seasonality with ∼2 times higher in winter than in summer with no significant diurnal variations for any species. Moreover, winter aerosols mainly originated from biomass burning emissions from North India and East Pakistan and reached the HTP through a long-range atmospheric transport. The TN dry deposition and total deposition fluxes were 2.04 kg ha 15 N exhibit a significant seasonality with ∼2 times higher in winter than in summer with no significant diurnal variations for any species. Moreover, winter aerosols mainly originated from biomass burning emissions from North India and East Pakistan and reached the HTP through a long-range atmospheric transport. The TN dry deposition and total deposition fluxes were 2.04 kg ha -1 yr -1 and 6.12 kg ha -1 yr -1 respectively. Our results demonstrate that the air contamination from South Asia reach the HTP and is most likely impacting the high altitude ecosystems in an accepted scenario of increasing emissions over South Asia.

Snowpack and glacial melt samples were collected to understand the hydrochemical, isotopic characteristics and the source of Hg contamination in high altitude glacierized Himalayan catchment. Both the snow and glacial melt were acidic in nature with calcium and magnesium as the dominant cations and bicarbonate and chloride as the dominant anions. The major ion concentrations for cations were found to be Ca 2+  > Mg 2+  > Na +  > K + and HCO 3 -  > Cl -  > SO 4 2-  > NO 3 - for anions. The atmospheric processes like the precipitation source and aerosol scavenging control the snow chemistry and the weathering of the rocks modify the hydrochemistry of glacial melt. The samples of both the snow and glacial melt were classified as Ca-Mg-HCO 3 - type. The concentration of Hg in snow (154.95 ng L -1 ) and glacial melt (112.04 ng L -1 ) was highest (still lower compared to the maximum permissible limit (1000 ng L -1 ) by WHO in drinking water) during summer season (August-September) and lowest (snow 2.2 and 40.01 ng L -1 for glacial melt) during winter (November). The results reveal that mercury concentration in snowpacks is attributed to the combined mixing of long-range transport of pollutants via westerlies throughout the year and the industrial effluents coming from highly industrial belts of Panjab, Haryana, Rajasthan, Indo-Gangetic plains, and neighboring areas via southwest monsoons during August-September. However, in glacial melt, the Hg concentration was typically controlled by rate of melting, leaching, and percolation. Higher degree and rate of glacial melting decreases the Hg concentration in glacial melt. Stable isotopic analysis and backward air mass trajectory modeling also corroborate the source of precipitation from southwest monsoons during August-September, with its air mass trajectories passing through the highly industrialized belts of Indo-Gangetic plain and adjoining areas.

Humic-like substances (HULIS) are major components of light-absorbing brown carbon that play an important role in Earth's radiative balance. However, their concentration, optical properties, and sources are least understood over Tibetan Plateau (TP). In this study, the analysis of total suspended particulate (TSP) samples from central of TP (i.e., Nam Co) reveal that atmospheric HULIS are more abundant in summer than that in winter without obvious diurnal variations. The light absorption ability of HULIS in winter is 2-3 times higher than that in summer. In winter, HULIS are mainly derived from biomass burning emissions in South Asia by long-range transport. In contrast, the oxidation of anthropogenic and biogenic precursors from northeast part of India and southeast of TP are major sources of HULIS in summer.

Atmospheric aerosols were collected during the scientific expedition to Mt. Qomolangma (Everest) in May-June, 2005. The elemental concentrations of the aerosols were determined by inductively coupled plasma mass spectrometry. This yielded data for the concentration of 14 elements: Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, and Pb. The mean elemental concentrations were generally comparable with those from central Asia and the Arctic, while much higher than those from Antarctic. Size, morphology, and chemical composition of 900 individual aerosol particles were determined by scanning electron microscopy and energy-dispersive X-ray microanalysis. Based on morphology and elemental composition, the particles were clustered into eight groups: soot (8%), tar ball (3%), alumosilicates/silica (55%), calcium sulfate (16%), Ca/Mg carbonate (2%), Fe/Ti-rich particles (3%), Pb-rich particles (1%), and biological particles (12%). The sampling site, located at 6,520 m in the Himalayas, is particularly remote and located at high altitude. Nonetheless, high aerosol enrichment factors for copper, chromium, lead, nickel, vanadium, and zinc all suggest the influence of long-range transported pollution, while enrichment in calcium and the presence of alumino-silicates in individual particle analyses indicates a distinct mineral dust influence. The backward air mass trajectories showed that the northwestern part of India may contribute to the atmospheric aerosol in the central high Himalayas.

The Tibetan Plateau (including the Himalayas) is one of the most remote and cold regions in the world. It has very limited to nonexistent industry but is adjacent to the two most populous and rapidly industrializing countries (China and India) and thus provides a unique location for studying the atmospheric transport of mercury. Here we report the first study on the atmospheric transport of mercury to the Tibetan Plateau. The total mercury profiles in four snowpits from glaciers above 5700 m asl along a southwest-northeast transect across the central Tibetan Plateau were obtained in 2005-2006. In general, the total mercury concentrations in the snow samples ranged from < 1 to 9 ng L(-1), increasing northeastward from the southernmost site at Mount Everest. Higher total mercury concentrations were found in the snow deposited in the nonmonsoon season, as indicated by seasonal variation of delta18O values and major ions in the snowpack. The annual atmospheric depositional flux of total Hg was estimated to range from 0.74 to 2.97 microg m(-2) yr(-1) in the region, the majority of which occurred via particulate matter deposition.