Aerosol variability and glacial chemistry over the western Himalayas

Abstract

Environmental context While it is known that aerosol deposition causes exacerbated melt of the glaciers, information about aerosol variability and deposition in the glaciated environments in the western Himalayas is still lacking. We analysed the aerosol variability, modelled the potential aerosol sources and assessed physicochemical characteristics of glacier ice in the region. This information could be foundational for initiating studies on aerosol impacts on the glacier melt besides climate change. Rationale There is increasing scientific evidence of aerosol deposition triggering glacier melting but very little understanding about the spatiotemporal variability of aerosols over the Indian Himalayas. The current study is a maiden effort to ascertain the aerosol variability in glacial environments of the Indian Himalayas. Aerosol sources were modelled and physicochemical characteristics of glacial ice were evaluated to draw firsthand insights into the light-absorbing impurities over three glaciers. Methodology Aerosol variability over four decades was analysed using MERRA-2 data (Modern-Era Retrospective analysis for Research and Applications) over five different topographically distinct mountain ranges of the western Himalayas. Information about nine physicochemical variables was analysed over the ablation zone of glaciers in the region. HYSPLIT model was used to track the air mass sources at a weekly time-step from December 2020 to November 2021 over the selected glaciers. Results and discussion MERRA-2 data analyses indicate increasing trends in surface dust, columnar dust and black carbon. The highest columnar dust concentration was found in Pir Panjal Mountain Range (PP: 125 648 µg m−2) followed by the Greater Himalayan Mountain Range of Kashmir (GH: 64 384 µg m−2), Karakoram (KA: 47 574 µg m−2), Ladakh (LA: 45 861 µg m−2) and Zanskar (ZA: 38 416 µg m−2), however, the black carbon indicated a PP > GH > LA > KA > ZA trend. HYSPLIT trajectories indicate that the contribution of global sources is highest (65%) followed by local (21%) and regional (14%) sources. Ice chemistry analysis revealed a higher concentration of total solid particles (830 mg L−1) and sulfates (14.33 mg L−1) indicative of the contribution from anthropogenic footprint and lithology. Conclusion The research underpins the need for establishing long-term aerosol observatories and a detailed hydrochemical assessment for precisely ascertaining the black carbon and allied constituents to unravel their contribution to glacier melt in the north-western Himalayas.