Chemical components and distributions of aerosols in the third pole

Abstract

The crustal and anthropogenic emission sources play an important role in moderating not only aerosol composition but also have a profound impact on rainwater composition and neutralization processes over the Third Pole (TP). This chapter reports on key findings on spatiotemporal variations in chemical composition of aerosols and rainwater based on ground measurement and satellite retrievals, cryoconites of glaciers and ice-cores over the TP. Carbonaceous species [elemental carbon (EC), organic carbon (OC), and water-soluble organic carbon (WSOC)] are ubiquitously present in the entire TP with pronounced spatial and temporal variability in their concentrations. The western and southern parts of the TP are influenced by the transport of aerosols from the source regions in the Indo-Gangetic plain, Nepal, and neighboring areas. The elevated OC/EC ratios, together with K+ and levoglucosan markers, reflect biomass burning emissions as a major source of primary carbonaceous aerosols. In addition, a significant positive gradient observed in WSOC/OC ratios from the Gangetic plains toward high-altitude sites indicates a contribution from secondary organic aerosols (SOAs). In contrast, the eastern and southeastern TP is mostly influenced by emissions from both China and Southeast Asia. The ground-based measurements, as well as satellite retrievals, unveil a clear seasonal pattern over TP with relatively lower concentrations of chemical species and aerosol optical depth (AOD) during monsoon. In contrast, higher AOD values, along with lower fine-mode aerosol fraction, during spring and summer seasons, are attributed to an increase in the contribution of mineral aerosols from desert regions in the Middle East, and Taklamakan and Gobi, as well as the Thar, deserts. Studies on rainwater composition indicate its alkaline nature and the presence of high concentrations of neutralizing species further ascertaining that crustal aerosols have a profound impact on rainwater composition and neutralization processes over the region. © 2020 Elsevier Inc. All rights reserved.