Investigations of aerosol optical depth variations using spectroradiometer at an urban station, Pune, India

The high spectral resolution radiometer at the Indian Institute of Tropical Meteorology (IITM), Pune [18°, 32′N, 73° 51′ E, 559 m Above Mean Sea Level (AMSL)], India has been operated on 79 clear-sky days during April 1993–April 1995 in order to study the temporal-spectral variations in aerosol optical depth (AOD) at the station. From the records of solar irradiance at different zenith angles of the sun, AODs were estimated at a spectral interval of 5 nm in the wavelength region 400–700 nm. The temporal variations in AOD in different spectral regions showed a relationship with those observed in the concurrent surface-level meteorological parameters at the experimental site. The seasonal variations in AOD indicated maximum during summer months and minimum during winter months. In addition, the afternoon (AN) AODs are found to be higher as compared to the forenoon (FN) depths in summer months of the year, whereas the FN AODs dominate in winter months at almost all wavelengths over the observing station.