Morphology of Atmospheric Particles over Semi-Arid Region (Jaipur, Rajasthan) of India: Implications for Optical Properties

Sumit Kumar Mishra,Pawan Kumar Yadav,Rashmi Rashmi,Sukhvir Singh,Nidhi Dixit Mishra,Rajesh Agnihotri,Puppala Siva Praveen,Chhemendra Sharma,Bhuwan Chandra Arya,Jai Shankar Tawale,M.V.S.N Prasad

doi:10.4209/aaqr.2014.10.0244

Abstract

The regional dust morphology and spectral refractive indices (RIs; governed by hematite, Fe2O3 content at short wavelengths) are key elements for ascertaining direct radiative forcing of mineral dust aerosols. To provide morphological features of background mineral dust from a semi-arid zone in the vicinity of the Thar Desert, we carried out an expedition to the Jaipur city during late winter of 2012. Morphological analysis reveals the predominance of “Layered”, “Angular” and “Flattened” particles, while the frequency distribution of a total of 235 dust particles shows the aspect ratio, AR and circularity parameter, CIR (measures of particle’s non-sphericity) typically ~1.4 and ~0.8, respectively. Sensitivity analysis at 550 nm wavelength reveals the equivalent sphere model may underestimate Single Scattering Albedo, SSA for the dust with low (~1.1%) hematite by ~3.5%. Both underestimation (by ~5.6%) and overestimation (up to 9.1%) are probable in case of dust with high hematite content (~5.68%). In addition, the effect of AR on the dust scattering is significant in case of dust with high hematite content. More such regionally representative dust morphological data are required for better estimation of regional radiative forcing of mineral dust aerosols.

Highlights

The direct radiative forcing (DRF) imposed by aerosol remains still uncertain to large extent (Boucher et al, 2013)
The effect of aspect ratio (AR) on the dust scattering is significant in case of dust with high hematite content
A field observation has been conducted over a semi-arid zone in the vicinity of the Thar Desert during late winter of 2012 to carry out morphological analysis of regional aerosols

Summary

Introduction

The direct radiative forcing (DRF) imposed by aerosol remains still uncertain to large extent (Boucher et al, 2013). Based on the measurement and modeling studies (accounting for particle morphology), the optical properties of real dust particles have been found to be quite different compared to that of volume-equivalent spheres (Volten et al, 2005; Mishra and Tripathi, 2008). Morphological Parameters (AR, CIR) of Sampled Dust Fig. 3(c1) and 3(c2) show the frequency distribution of AR and CIR for the total dust particles sampled from the sites considered in this study

Results

Conclusion