Factors affecting atmospheric turbidity are discussed. The solar radiometer measurements carried out from Pune using narrow band interference filters are analysed to determine aerosol extinction coefficient, atmospheric turbidity coefficients and their monthly variations. Values of Angstrom turbidity coefficients α and β are computed and the results are discussed. Coefficient α which is correlated with aerosol size spectrum shows seasonal variation. For the visible region the mean value of α is about -0.49, showing the dominance of large-sized aerosols. Angstrom turbidity coefficient β and Schuepp's turbidity coefficient B have a similar trend of variation with high values in summer and low values in winter. Angstrom turbidity coefficient β and Linke's turbidity factor T follow a linear relation. Their mean values for Pune lie in the ranges 0.16-0.42 and 3.4-4.6 respectively. Compared to the earlier reported study by Mani et al. [Tellus (Sweden), 21 (1969) 829], summer turbidity at Pune has increased by 2.5-3 times. There is a rise in turbidity level at Pune even from 1986 to 1996, which is the period covered by the present study. The results show that atmospheric haze is a major contributor to the high turbidity value in February, while wind-blown dust and influx of aerosols through pre-monsoon circulation is a major source of high turbidity value during April-May.
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