Study of winter aerosol optical depths over a tropical urban station

At Pune (18°32'N, 73°51'E, 559 m AMSL), a tropical urban station in India, aerosol characteristics during the winter season exhibit unique features such as low-level inversions and dust haze formation during morning hours. Moreover, this station experiences abundance of sub-micron sized aerosols due to passage of continental air mass during winter. With a view to examine these winter aerosol properties, in detail, the PC-based high spectral resolution radiometer has been operated in the 0.4-0.7 μm wavelength region at the Indian Institute of Tropical Meteorology, Pune, India. The details of the spectroradiometer together with the data acquisition and analysis procedures have been briefly described. In this paper, the results obtained from the observations carried out on 75 cloud-free days during the successive winters of 1993-94, 1994-95 and 1995-96 have been presented and discussed in the light of local meteorological and environmental conditions. Of the three winters considered for the study, aerosol optical depths during the 1995-96 winter indicate greater values and forenoon aerosol size spectra exhibit bimodal distribution suggesting the dominant combined influence of transport of continental aerosols and trapping of surface-generated aerosols due to close-to-ground inversion during the season over the experimental station