Radiative characterization of aerosols in the central Indo-Gangetic plain

Abstract

Gorakhpur (26.75°N, 83.38°E and 85 m amsl), is strategically located in the central Indo-Gangetic Plain (IGP), near the foot hills of Himalayas and hence is an ideal place for studying long-range transport as well as local sources of aerosols and its radiative implications. Here we present results from two years, October 2013 until September 2015, of measurements of spectral aerosol optical depth (AOD) utilizing ground based, Multi- Wavelength Radiometer (MWR), and satellite, MODIS Terra remote sensing platforms. Mean AOD at 500 nm (AOD500) is 0.63±0.35, associated with a moderate Angstrom exponent (α) of 1.03±0.22 is found for the study period using MWR measurements. Highest AOD500 is found during the pre-monsoon months of May and June while lowest AOD500 in the post-monsoon months of October and November. The MWR observations have been compared with MODIS Terra derived AOD and a good correlation of 0.74 is found. We used HYSPLIT Lagrangian trajectory model to investigate long-range transport of aerosols to the study region. Aerosol sources in winter season are from the North-West part of the study region while that during pre-monsoon season lies in the south-westerly arid regions. This finding is also reflected in the α values which are high during winter months suggesting significant urban and biomass-burning contribution. α values are low and the turbidity coefficient (β) is high during pre-monsoon months indicating long-range transport of coarse dust particles carried by south westerly winds from the westerly desert regions.