• Energy Research

Glaciers, particularly alpine glaciers, have been receding globally at an accelerated rate in recent decades. The glacial melt-induced release of pollutants (e.g., mercury) and its potential impact on the atmosphere and glacier-fed ecosystems has drawn increasing concerns. During 15th-20th August, 2011, an intensive sampling campaign was conducted in Qugaqie Basin (QB), a typical high mountain glacierized catchment in the inland Tibetan Plateau, to investigate the export and transport of mercury from glacier to runoff. The total mercury (THg) level in Zhadang (ZD) glacier ranged from <1 to 20.8 ng L-1, and was slightly higher than levels measured in glacier melt water and the glacier-fed river. Particulate Hg (PHg) was the predominant form of Hg in all sampled environmental matrices. Mercury concentration in Qugaqie River (QR) was characterized by a clear diurnal variation which is linked to glacier melt. The estimated annual Hg exports by ZD glacier, the upper river basin and the entire QB were 8.76, 7.3 and 157.85 g, respectively, with respective yields of 4.61, 0.99 and 2.74 μg m-2 yr-1. Unique landforms and significant gradients from the glacier terminus to QB estuary might promote weathering and erosion, thereby controlling the transport of total suspended particulates (TSP) and PHg. In comparison with other glacier-fed rivers, QB has a small Hg export yet remarkably high Hg yield, underlining the significant impact of melting alpine glaciers on regional Hg biogeochemical cycles. Such impacts are expected to be enhanced in high altitude regions under the changing climate.

Glaciers, particularly alpine glaciers, have been receding globally at an accelerated rate in recent decades. The glacial melt-induced release of pollutants (e.g., mercury) and its potential impact on the atmosphere and glacier-fed ecosystems has drawn increasing concerns. During 15th-20th August, 2011, an intensive sampling campaign was conducted in Qugaqie Basin (QB), a typical high mountain glacierized catchment in the inland Tibetan Plateau, to investigate the export and transport of mercury from glacier to runoff. The total mercury (THg) level in Zhadang (ZD) glacier ranged from <1 to 20.8 ng L-1, and was slightly higher than levels measured in glacier melt water and the glacier-fed river. Particulate Hg (PHg) was the predominant form of Hg in all sampled environmental matrices. Mercury concentration in Qugaqie River (QR) was characterized by a clear diurnal variation which is linked to glacier melt. The estimated annual Hg exports by ZD glacier, the upper river basin and the entire QB were 8.76, 7.3 and 157.85 g, respectively, with respective yields of 4.61, 0.99 and 2.74 μg m-2 yr-1. Unique landforms and significant gradients from the glacier terminus to QB estuary might promote weathering and erosion, thereby controlling the transport of total suspended particulates (TSP) and PHg. In comparison with other glacier-fed rivers, QB has a small Hg export yet remarkably high Hg yield, underlining the significant impact of melting alpine glaciers on regional Hg biogeochemical cycles. Such impacts are expected to be enhanced in high altitude regions under the changing climate.

To understand distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in the Himalayas, 77 soil samples were collected from the northern side of the Himalayas, China (NSHC), and the southern side of the Himalayas, Nepal (SSHN), based on altitude, land use and possible trans-boundary transport of PAHs driven by wind from Nepal to the Tibetan Plateau, China. Soils from the SSHN had mean PAH concentration greater than those from the NSHC. Greater concentrations of PAHs in soils were mainly distributed near main roads and agricultural and urban areas. PAHs with 2-3 rings were the most abundant PAHs in the soils from the Himalayas. Concentrations of volatile PAHs were significantly and positively correlated with altitude. Simulations of trajectories of air masses indicated that distributions of soil PAH concentrations were associated with the cyclic patterns of the monsoon. PAH emissions from traffic and combustion of biomass or coal greatly contributed to concentrations of PAHs in soils from the Himalayas.

To understand distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in the Himalayas, 77 soil samples were collected from the northern side of the Himalayas, China (NSHC), and the southern side of the Himalayas, Nepal (SSHN), based on altitude, land use and possible trans-boundary transport of PAHs driven by wind from Nepal to the Tibetan Plateau, China. Soils from the SSHN had mean PAH concentration greater than those from the NSHC. Greater concentrations of PAHs in soils were mainly distributed near main roads and agricultural and urban areas. PAHs with 2-3 rings were the most abundant PAHs in the soils from the Himalayas. Concentrations of volatile PAHs were significantly and positively correlated with altitude. Simulations of trajectories of air masses indicated that distributions of soil PAH concentrations were associated with the cyclic patterns of the monsoon. PAH emissions from traffic and combustion of biomass or coal greatly contributed to concentrations of PAHs in soils from the Himalayas.

This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS-BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 ± 27.1, 9.9 ± 5.8, and 17.4 ± 12.5 μg m-3, respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 ± 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECS) below 15 μg cm-2 but ceased as ECS increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross-section of EC (MACEC) (7.0 ± 4.2 m2 g-1) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MACEC during the monsoon season, whereas increased biomass burning was a major factor leading to lower MACEC in other seasons. The average MACWS-BrC at 365 nm was 1.4 ± 0.3 m2 g-1 with minimal seasonal variations. In contrast to MACEC, biomass burning was the main reason for a higher MACWS-BrC in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300-700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region.

This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS-BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 ± 27.1, 9.9 ± 5.8, and 17.4 ± 12.5 μg m-3, respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 ± 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECS) below 15 μg cm-2 but ceased as ECS increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross-section of EC (MACEC) (7.0 ± 4.2 m2 g-1) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MACEC during the monsoon season, whereas increased biomass burning was a major factor leading to lower MACEC in other seasons. The average MACWS-BrC at 365 nm was 1.4 ± 0.3 m2 g-1 with minimal seasonal variations. In contrast to MACEC, biomass burning was the main reason for a higher MACWS-BrC in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300-700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region.

Organic aerosols have profound and far-reaching influences on the Earth's climate, ecosystems, environmental quality, and public health. Elucidating the precise composition and sources of these aerosols over the Tibetan Plateau, a region highly sensitive to climate change and vulnerable to ecosystems, is critically important. Sixteen organic molecular tracers in aerosols were quantified using solvent extraction-BSTFA derivatization, and GC/MS analysis at six sites over the Tibetan Plateau during 2014 and 2016. Average total tracer concentration was 32.5 ± 20.1 ng m-3. The highest levels of biomass burning tracers (anhydrosugars and aromatic acids) were found at southeastern Tibetan Plateau site Yulong (20.8 ± 21.3 ng m-3) followed by the western site Ngari (13.3 ± 10.6 ng m-3). Biomass burning tracers decreased from southern sites like Everest (9.50 ± 10.5 ng m-3) to northern aeras such as Laohugou (2.59 ± 2.19 ng m-3). Biomass burning tracers peaked in non-monsoon seasons while primary saccharides and sugar alcohols predominated during monsoon months. Using tracer-based methods, biomass burning contributed 0.4%-8.4% of organic carbon over the plateau, with higher non-monsoon contributions (3.6% ± 3.7%). Backward air mass trajectories and fire spots indicated South Asian biomass burning impacts on organic aerosols at western, southern, and southeastern Tibetan Plateau sites, particularly in non-monsoon periods. Fungal spores and plant debris comprised 0.6%-6.3% and 0.3%-1.2% of organic carbon respectively, with higher monsoon contributions (4.2% ± 4.7%) of fungal spores. Secondary organic carbon was estimated to contribute substantially (45.5%-73.5%) over the plateau but requires further investigation. These results provide insights into pollution mitigation and the assessments of climate and ecology changes for the Tibetan Plateau.

Organic aerosols have profound and far-reaching influences on the Earth's climate, ecosystems, environmental quality, and public health. Elucidating the precise composition and sources of these aerosols over the Tibetan Plateau, a region highly sensitive to climate change and vulnerable to ecosystems, is critically important. Sixteen organic molecular tracers in aerosols were quantified using solvent extraction-BSTFA derivatization, and GC/MS analysis at six sites over the Tibetan Plateau during 2014 and 2016. Average total tracer concentration was 32.5 ± 20.1 ng m-3. The highest levels of biomass burning tracers (anhydrosugars and aromatic acids) were found at southeastern Tibetan Plateau site Yulong (20.8 ± 21.3 ng m-3) followed by the western site Ngari (13.3 ± 10.6 ng m-3). Biomass burning tracers decreased from southern sites like Everest (9.50 ± 10.5 ng m-3) to northern aeras such as Laohugou (2.59 ± 2.19 ng m-3). Biomass burning tracers peaked in non-monsoon seasons while primary saccharides and sugar alcohols predominated during monsoon months. Using tracer-based methods, biomass burning contributed 0.4%-8.4% of organic carbon over the plateau, with higher non-monsoon contributions (3.6% ± 3.7%). Backward air mass trajectories and fire spots indicated South Asian biomass burning impacts on organic aerosols at western, southern, and southeastern Tibetan Plateau sites, particularly in non-monsoon periods. Fungal spores and plant debris comprised 0.6%-6.3% and 0.3%-1.2% of organic carbon respectively, with higher monsoon contributions (4.2% ± 4.7%) of fungal spores. Secondary organic carbon was estimated to contribute substantially (45.5%-73.5%) over the plateau but requires further investigation. These results provide insights into pollution mitigation and the assessments of climate and ecology changes for the Tibetan Plateau.