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Airborne in situ measurements of aerosol size distributions and black carbon across the Indo-Gangetic Plain during SWAAMI-RAWEX

Gogoi, MM and Jayachandran, VN and Vaishya, A and Babu, SNS and Satheesh, SK and Moorthy, KK (2020) Airborne in situ measurements of aerosol size distributions and black carbon across the Indo-Gangetic Plain during SWAAMI-RAWEX. In: Atmospheric Chemistry and Physics, 20 (14). pp. 8593-8610.

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Official URL: https://dx.doi.org/10.5194/acp-20-8593-2020


During the combined South-West Asian Aerosol-Monsoon Interactions and Regional Aerosol Warming Experiment (SWAAMI-RAWEX), collocated airborne measurements of aerosol number-size distributions in the size (diameter) regime 0.5 to 20 μ m and black carbon (BC) mass concentrations were made across the Indo-Gangetic Plain (IGP), for the first time, from three distinct locations, just prior to the onset of the Indian summer monsoon. These measurements provided an east-west transect of region-specific properties of aerosols as the environment transformed from mostly arid conditions of the western IGP (represented by Jodhpur, JDR) having dominance of natural aerosols to the central IGP (represented by Varanasi, VNS) having very high anthropogenic emissions, to the eastern IGP (represented by the coastal station Bhubaneswar, BBR) characterized by a mixture of the IGP outflow and marine aerosols. Despite these, the aerosol size distribution revealed an increase in coarse mode concentration and coarse mode mass fraction (fractional contribution to the total aerosol mass) with the increase in altitude across the entire IGP, especially above the well-mixed region. Consequently, both the mode radii and geometric mean radii of the size distributions showed an increase with altitude. However, near the surface and within the atmospheric boundary layer (ABL), the features were specific to the different subregions, with the highest coarse mode mass fraction (FMC � 72 ) in the western IGP and highest accumulation fraction in the central IGP with the eastern IGP in between. The elevated coarse mode fraction is attributed to mineral dust load arising from local production as well as due to advection from the west. This was further corroborated by data from the Cloud-Aerosol Transport System (CATS) on board the International Space Station (ISS), which also revealed that the vertical extent of dust aerosols reached as high as 5 km during this period. Mass concentrations of BC were moderate (� 1 μ g m-3) with very little altitude variation up to 3.5 km, except over VNS where very high concentrations were seen near the surface and within the ABL. The BC-induced atmospheric heating rate was highest near the surface at VNS (� 0:81 K d-1), while showing an increasing pattern with altitude at BBR (� 0:35 K d-1 at the ceiling altitude). © 2020 Author(s).

Item Type: Journal Article
Publication: Atmospheric Chemistry and Physics
Publisher: Copernicus GmbH
Additional Information: The copyright of this article belongs to Copernicus GmbH
Department/Centre: Division of Mechanical Sciences > Divecha Centre for Climate Change
Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited: 17 Aug 2020 10:52
Last Modified: 17 Aug 2020 10:52
URI: http://eprints.iisc.ac.in/id/eprint/66312

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