Variability of Aerosol Parameters Derived from Ground and Satellite Measurements over Varanasi Located in the Indo-Gangetic Basin

Atmospheric aerosol plays a very important role in the Earth's radiation budget and global climate studies. This study reports the variability of the physical and optical properties of columnar aerosol and water vapour over Varanasi (25.2 degrees N, 82.9 degrees E), located in the heart of the Indo-Gangetic Basin, for the first time. The study was carried out using a MICROTOPS-II sunphotometer to measure the Aerosol Optical Depth (AOD) and metrological parameters. It is observed that the AOD loading is enhanced during the pre-monsoon and winter seasons, while it is decreased during the monsoon season. The variability of the angstrom coefficient (alpha) and turbidity coefficient (beta) shows that in the pre-monsoon season coarse-mode aerosol particles are dominant, while fine-mode aerosol particles are dominant in the winter. We compared our MICROTOPS-II ground-based data with the level-3 data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra satellite. A good seasonal correlation (correlation coefficient, R-2 similar to 0.57) was observed between MICROTOPS-II and MODIS AOD data. The results of the variability of water vapor over Varanasi are also discussed. The correlation coefficient (R-2) between daily MICROTOPS-II and MODIS water vapor is found to be more than 0.85 for the year 2011.