Compiled aerosol optical depth and extinction-to-backscatter climatology for Tucson, AZ

The AERONET network has had a wide-ranging impact on the study of atmospheric aerosols, both temporally and geographically. This paper examines the results of measurements from the Aeronet network from a radiometer deployed in Tucson, Arizona during 1999 and 2000. Monthly averages of aerosol optical depth and Ångstrom parameter values are presented. These show that a maximum in aerosol loading occurs in summer months with an average value for optical thickness of 0.11 at 670 nm compared to 0.03 during winter months. The Ångstrom coefficient shows a similar trend with largest values, corresponding to smaller-sized aerosols dominating during the summer months. These results show significant differences from results obtained from similar measurements during the period of 1975-77. In addition to optical depth, aerosol extinction-to-backscatter ratio, or lidar aerosol ratio, is calculated and examined using size distribution data available from Aeronet and Mie scatter computations. This ratio varies from an average value of near 25 in March, April, and May to values near 100 for October, November, and December. Comparison of a subset of these data to those from an independent solar radiometer supports these conclusions.