Atmospheric Turbidity conditions were monitored during 2009-2010 in Zanjan rural site (36.7 N, 48.5 E, 1805m) in Iran. About 10000 observations of atmospheric optical properties were taken with CIMEL sun photometer. These measurements were used to recover aerosol optical depth in different wave lengths (i.e. 440,675, 870 and 1020nm). Linke turbidity factor and Angstrom turbidity indices have been calculated and analysed on daily, monthly, seasonal and annual basis. The annual average of AOD in four wave lengths is between 1.6 -1.9 for this region.

Results show that Angstrom turbidity indices, á and â, vary throughout on individual day because of changes in the atmospheric meteorological parameters. â is highest during summer and lowest during winter. An anti-correlation between a and b in warm season, specially, is observed throughout the day during all seasons indicating continuous redistribution of fine and coarse particles under the influence of meteorological parameters. The annual behavior of the Angstrom turbidity coefficient and Linke turbidity factor recorded maximum values of 0.7 and 12.0 over Zanjan in late 2009/early 2010 respectively. The daily, monthly and yearly comparison of a and b along with the atmospheric visibility is also analyzed and presented in the paper.