Discrimination of Aerosol Types and Validation of MODIS Aerosol and Water Vapour Products Using a Sun Photometer over Central India

Abstract

Aerosol optical properties were studied using handheld Microtops II sun photometer over Nagpur (79.028°E, 21.125°N) located in central India, suggests highest Aerosol Optical Depth (AOD) (0.64 ± 0.08) during Pre-Monsoon Season (PMS) and lowest AOD (0.38 ± 0.06) during Summer Monsoon Season (SMS). Using the scatter plot of AOD500 versus Angstrom exponent (α), dominating type of aerosol, during the most of the seasons is found to be urban/industrial and biomass burning (UB). Moderate Resolution Imaging Spectroradiometer (MODIS) active fire data suggests a large amount of biomass burning in different parts of India during PMS compared to other seasons. Aerosol transport analysis suggests during PMS, the air masses were originated from the biomass burning regions, desert regions and also from marine regions. Seasonal variation of AOD550 over India using MODIS data indicates significant AOD (> 0.7) over northwest during SMS, Indo - Gangetic region during Post Monsoon Season (PoMS) and north east region during winter. Southern part of India shows relatively less AOD (< 0.45) compared to north India during all the seasons. MODIS derived AOD and water vapor (NIR), compared against the ground-based observations from sun photometer, indicates an underestimation of 35% lower AOD compared to sun photometer and overestimation of 20% higher water vapor with correlation coefficients of 0.75 and 0.89 respectively. In view of the sizeable contribution of biomass burning aerosols, we suggest the use of a more absorbing type of aerosol model for central India, for an accurate retrieval of AOD from MODIS.