Aerosol transport over the Gangetic basin during ISRO-GBP land campaign-II

Abstract. MODIS (Moderate Resolution Imaging Spectroradiometer) Level-3 aerosol optical depth (AOD) data and NCEP (National Centre for Environmental Prediction) reanalysis winds were incorporated into an aerosol flux continuity equation, for a quantitative assessment of the sources of aerosol generation over the Ganga basin in the winter month of December 2004. Preliminary analysis on the aerosol distribution and wind fields showed wind convergence to be an important factor which, supported by the regional topography, confines aerosols in a long band over the Indo Gangetic plain (IGP) stretching from the west of the Thar desert into the Head-Bay-of-Bengal. The prevailing winds of the season carry the aerosols from Head-Bay-of-Bengal along the east coast as far as the southern tip of the peninsular India. A detailed examination of MODIS data revealed significant day-to-day variations in aerosol loading in localised pockets over the central and eastern parts of the Indo Gangetic plain during the second half of December, with AOD values even exceeding unity. Aerosols over the Ganga basin were dominated by fine particles (geometric mean radius ~0.05–0.1μm) while those over the central and western India were dominated by large particles (geometric mean radius ~0.3–0.7μ). Before introducing it into the flux equation, the MODIS derived AOD was validated through a comparison with the ground-based measurements collected at Kharagpur and Kanpur; two stations located over the Ganga basin. The strength of the aerosol generation computed using the flux equation indicated the existence of aerosol sources whose locations almost coincided with the concentration of thermal power plants. The quantitative agreement between the source strength and the power plant concentration, with a correlation coefficient 0.85, pointed to thermal power plants as substantial contributors to the high aerosol loading over the Ganga Basin in winter. The layout of aerosol sources also nearly matched the spatial distribution of the Respirable Suspended Particulate Matter (RSPM), derived from the Central Pollution Control Board (CPCB) data, lending additional support to our inference.