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

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. Ångström Exponent (AE) and Extinction Ångström Exponent (EAE) vs. Absorption Ångström 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.