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Insights into coarse particle optics based on field evidence of particle morphology, chemical composition and internal structure

Goel, Vikas, Mishra, Sumit K., Ahlwat, Ajit, Kumar, Prashant, Senguttuvan, T.D, Shrama, Chhemendra and Reid, Jeffrey S. (2020) Insights into coarse particle optics based on field evidence of particle morphology, chemical composition and internal structure Atmospheric Environment.

Goel Mishra.. Kumar (2020)_Delhi SEM AEPaper.pdf - Accepted version Manuscript

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Aerosol particles scatter and absorb solar radiation and affect the Earth's radiation budget. The aerosol particles are usually non-spherical in shape and inhomogeneous in chemical composition. For simplicity, these particles are approximated as homogeneous spheres/spheroids in radiative models and in retrieval algorithms of the ground and spaceborne observations. The lack of information on particle morphology (especially shape), chemical composition (that govern their spectral refractive indices) and most importantly internal structure (three dimensional spatial distribution of chemical species) lead to uncertainty in the numerical estimation of their optical and radiative properties. Here, we present a comprehensive assessment of the particles' volumetric composition. The particles were collected from Jaisalmer (arid environment) and Delhi (urban environment) of India and subjected to Focused Ion-Beam (FIB) coupled with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscope (EDS). Based on analysis of #2 particles from Jaisalmer, particles were observed to be composed of Fe, Ca, C, Al, Cu and Mg rich shell with Si and O rich core as opposed to those of Delhi particles (no #3) which were observed to be with Cu and S rich core and Hg, Ag, C, S and N rich shell. Based on the homogeneous sphere/spheroid assumption, conventional SEM-EDS and FIB-SEM-EDS results, different particle model shapes [single species homogeneous sphere (SP1) and spheroid (SPH1); multiple species homogeneously mixed sphere (SP2) and spheroid (SPH2); and core-shell (CS)] were considered for simulating their respective optical properties; SSA (Single Scattering Albedo) and g (Asymmetry parameter). The effect of internal structure on SSA was found to be prominent in particles having low value of the imaginary part of refractive index (k). While the same was observed to be low (nearly negligible) for the particle with the high value of k. The particles rich in copper are found to have high light absorbing property which causes positive radiative forcing.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Civil and Environmental Engineering
Authors :
Goel, Vikas
Mishra, Sumit K.
Ahlwat, Ajit
Senguttuvan, T.D
Shrama, Chhemendra
Reid, Jeffrey S.
Date : 9 February 2020
Funders : CSIR Network
DOI : 10.1016/j.atmosenv.2020.117338
Grant Title : CSIR Network Project
Copyright Disclaimer : © 2020 Published by Elsevier Ltd.
Uncontrolled Keywords : Aerosols particles FIB-SEM-EDS 3D characterisation Core-shell Single scattering albedo
Depositing User : James Marshall
Date Deposited : 08 Apr 2020 08:37
Last Modified : 10 Feb 2021 02:08

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