In Situ Observations of Light‐Absorbing Carbonaceous Aerosols at Himalaya: Analysis of the South Asian Sources and Trans‐Himalayan Valleys Transport Pathways

Abstract

The mountain-valleys along the south margin of the Himalaya-Tibetan Plateau (HTP), referred to as trans-Himalayan valleys, are transport pathways of atmospheric pollutants from the South Asia lifting to the HTP based on atmospheric models and satellite detections. However, few field studies can be conducted to confirm the aerosol transport along these valleys due to the harsh environment and limited power supply. Individual particle collection instruments offer the unique advantage of collecting samples and tracing particle sources in remote areas due to their portability and efficiency. In this study, transmission electron microscopy was used to study individual particles collected in two trans-Himalayan valleys. We found that 49-70% of thousands of particles were light-absorbing carbonaceous aerosols including soot-bearing and tarball-bearing particles in December of 2017. The dominant sizes of soot-bearing and tarball-bearing particles were 151-370 and 198-255 nm, respectively. The WRF-Chem model and wind field analyses show that the intense regional air pollution with high mass concentrations of light-absorbing carbonaceous aerosol occurred in the South Asia and southwest wind normally prevailed along the trans-Himalayan valleys in the afternoon of each day during wintertime. Backward trajectory and CALIPSO data further confirm that these light-absorbing carbonaceous aerosols from the South Asia were transported to the southern HTP. These carbonaceous aerosols exhibited significantly internally mixing with secondary sulfates. Here individual particle analysis coupled with the WRF-Chem model, the meteorological observation data, and satellite data confirm the trans-Himalayan valleys as the direct channels for abundant carbonaceous aerosols lifting from the South Asia to the HTP.

Tracing Atmospheric Anthropogenic Black Carbon and Its Potential Radiative Response Over Pan‐Third Pole Region: A Synoptic‐Scale Analysis Using WRF‐Chem

“…Considering the topographic effect on BC transport, we took transect in such a manner where the two most polluted IGP and EC regions fall in-between. In this study, columnar profile exhibits BC injected to the higher elevation where the presence of BC was found to be up to an elevation of about 6-km over SA and EA, which is similar to previous finding (Yuan, Wan, et al, 2020;Zhang et al, 2015Zhang et al, , 2017Zhang, Zhao, et al, 2020;Zhao et al, 2017). However, the overall picture illustrated in Figure 11 confirms the topographic barrier effect on BC distribution where the higher BC concentration (1.4-2 µgm −3 ) is confined in the valley-type topography within a 2-km altitudinal distance from the surface.…”

“…As explained by Yuan, Chen, et al (2020), high BC over the east slope of TP resulted from the weakness of westerly winds over the northern TP, eastward movement of EA major trough, and dominant westerly wind over southern TP. Such a circulation pattern along with trans-Himalaya transport through mountain-valley conduits systems (Khumbu valley, Dudh Koshi basin, Kali Gandaki, Langtang valley, Chumbi valley, and Yarlung Tsangpo Grand Canyon), through which BC could have made way up to the TP (Dhungel et al, 2018;Yuan, Wan, et al, 2020;Zhang, Zhao, et al, 2020).…”

Carbonaceous Aerosols over Lachung in the Eastern Himalayas: Primary Sources and Secondary Formation of Organic Aerosols in a Remote High-Altitude Environment

“…Similar to Lachung, Wan et al reported significant contribution by biomass burning sources to OC at Kathmandu valley in the Nepal Himalayas, averaging 24.9% annually and up to 36.3% in the post-monsoon season. Biomass burning emissions have also been identified as one of the most important sources of atmospheric particles, accounting for a significant portion of the total organic aerosol mass in other studies. − Apart from biomass burning influence, Sarkar et al reported a significant influence of carbonaceous pollutants from vehicular emissions and fossil fuel burning over the eastern Himalayan site Darjeeling. Since the Himalayan region is very close to densely populated and industrialized areas, open combustion of garbage and crop residues, the use of brick kilns and household cooking/heating with firewood, as well as the burning of animal dung and coal briquettes, could play a significant role in modulating carbonaceous species, while the traffic-related sources cannot be ignored.…”

“…The Himalayan and Tibetan Plateau (HTP), containing the largest ice mass outside the polar region, has been the most sensitive region of the globe to the influence of carbonaceous aerosols. Being in the proximity of South Asia, aerosols from the pollution hotspots are lifted up and influenced further by long-range transport as well as valley winds. − The transported carbonaceous aerosols, when deposited onto the snow surfaces, influence snow albedo changes and leads to rapid loss of snow/ice − during their postdepositional period. − As the Himalayan glaciers and snowpack feed Asia’s major rivers, the changes in the hydrological system might disturb billions of people relying on freshwater from these glacial sources. Apart from the impact on snow, carbonaceous aerosols also influence the atmospheric stability over the Himalayas and affect the Asian monsoon circulation .…”

Evidence for Large Amounts of Brown Carbonaceous Tarballs in the Himalayan Atmosphere

“…16 To date, few studies have provided sufficient direct evidence of primary BrC in the Himalayan atmosphere. 17,18 The main challenge is to reliably identify the primary BrC subcategory of carbonaceous aerosol by using online/filter-based bulk measurements, including aerosol mass spectrometry 19,20 and single particle soot photometry, 21 especially in the clean Himalayan atmosphere with low concentrations of carbonaceous aerosol (mostly <5 μg/m 3 ). 15 If primary BrC particles occur in the Himalayan atmosphere, as is probable, they must influence atmospheric optical properties and contribute to the glacier retreating problem alongside BC and secondary BrC.…”