Analysis of Aerosol Optical Properties due to a Haze Episode in the Himalayan Foothills: Implications for Climate Forcing

Khan Alam,Armin Sorooshian,Humera Bibi,Rehana Khan,Thomas Blaschke,Samina Bibi

doi:10.4209/aaqr.2017.06.0222

Abstract

A super haze episode occurred over the Himalayan region in October 2010. This haze reduced the air quality in the region and spread across India and Pakistan. The purpose of this study is to investigate the optical and radiative properties of aerosols during this episode using data from the MODerate resolution Imaging Spectroradiometer (MODIS) and the AErosol RObotic NETwork (AERONET). Maximum Aerosol Optical Depth (AOD) values on 19 October exceeded two at various locations in Pakistan (Sialkot = 2.56, Faisalabad = 2.67) and India (Ambala = 2.03, Amritsar = 3.4, Ludhiana = 4.29). Maximum AOD values recorded on 20 October were slightly lower in parts of Pakistan (Lahore = 2.5) and India (Gurdaspur = 1.89, New Delhi = 1.90, Batala = 2.89, Bathinda = 1.89, Kanpur = 1.6). Data for aerosol properties such as Volume Size Distributions (VSD), Single Scattering Albedo (SSA), Refractive Index (RI), and ASYmmetry parameter (ASY) suggest that fine mode aerosols were predominant relative to coarse mode aerosols during the haze episode. The dominant aerosol types were classified by analyzing AOD vs. Angstrom Exponent (AE) and Extinction Angstrom Exponent (EAE) vs. Absorption Angstrom Exponent (AAE). The results revealed that during the haze episode, the prevailing aerosol types were biomass burning and urban/industrial aerosol. The Aerosol Radiative Forcing (ARF) values were computed during the hazy and non-hazy days using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model. The shortwave ARF values at the Top Of the Atmosphere (TOA), SuRFace (SRF), and within the atmosphere were found to be in the range of –17.6 to –81.6, –64 to –193, and +47 to +119 W m–2, respectively, over Lahore. Likewise, over Kanpur, the ARF values were found to be in the range of +15.32 to –91.6, –38 to –134 and +33 to +75.91 W m–2, respectively.

Highlights

South Asia has experienced rapid economic growth over the past few decades, characterized by expanding urbanization with increasing population, industrialization, and anthropogenic activity
We report aerosol properties measured from the AErosol RObotic NETwork (AERONET) and MODerate resolution Imaging Spectroradiometer (MODIS) over India and Pakistan during the heavy haze episode of October 2010
We examine daily mean spatio-temporal variations in Aerosol Optical Depth (AOD) over 12 sites in the studied region extending towards the Himalayan Mountains

Summary

Introduction

South Asia has experienced rapid economic growth over the past few decades, characterized by expanding urbanization with increasing population, industrialization, and anthropogenic activity. These changes have resulted in high aerosol loadings (Li et al, 2013a), reduction in visibility (Ramanathan et al, 2001), and alterations in aerosol radiative forcing (Kim and Ramanathan, 2008; Alam et al, 2014b) and air quality (Oanh and Leelasakultum, 2011; Li et al, 2017) in the Indo-Gangetic plain (Ram et al, 2012). Satellite imagery is used to monitor aerosol optical thickness, which is an effective way to assess air pollution levels. Ground-based remote sensing data from networks such as the AErosol RObotic NETwork (AERONET) are suitable for the assessment of aerosol optical/radiative properties and aerosol loading at a particular site (Sorooshian et al, 2011; Alam et al, 2014; Dumka et al, 2014; Boiyo et al, 2017)

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