Study of aerosol optical depth, ozone, and precipitable water vapour content over Sinhagad, a high-altitude station in the Western Ghats

This article reports the results of a study related to variations in columnar aerosol optical depth (AOD), total column ozone (TCO), and precipitable water content (PWC) over a high-altitude station, Sinhagad (18° 21′ N, 73° 45′ E, 1450 m above mean sea level (AMSL)), employing a microprocessor-based total ozone portable spectrometer, MICROTOPS-II, comprising both a sun photometer and ozonometer, during November 2009–April 2010. The aerosol optical depth at 500 nm (AOD500 nm) portrayed seasonal variation with higher values (0.39) in summer and lower values (0.15) in winter. The TCO and PWC also exhibited lower values in winter and started increasing by the pre-monsoon season. The Ångström wavelength exponent, α, was found to be high (1.79) during February, indicating the relative dominance of accumulation-mode particles. During the summer season, the lower value (0.94) of the Ångström wavelength exponent indicates the relative dominance of coarse-mode particles. The ground-based observations from MICROTOPS-II revealed good correlation with satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI). The observed short-wave solar flux at the bottom of the atmosphere decreased due to aerosol extinction and was found to be 19 and 78 W m–2 for the winter and pre-monsoon seasons, respectively. This implies that greater concentrations of accumulation-mode particles – which are due to local anthropogenic sources – affected the down-welling radiation than those from natural sources – which are due to long-range transport processes – over the experimental location