Retrieval of aerosol optical depths, Angström exponent, and single scattering albedo in the UV at Atlanta, Georgia, USA

Investigation of the effects of aerosols on the surface UV irradiance were conducted as part of the Atlanta Supersite experiment in August, 1999. The aerosol optical depth at UV wavelengths, and the single scattering albedo, which provides information about the absorption properties of the aerosols, are both important factors in determining surface UV irradiance. Measurements of direct and global (direct + diffuse) UV radiation and total column ozone were taken using a Brewer spectroradiometer under cloud-free conditions. Aerosol optical depths (t) in the UV are retrieved at 320, 340, and 360 nm. The spectral dependence of the aerosol optical depth is calculated via the Angström exponent (a). The retrieved values of t and a are used in the Tropospheric Ultraviolet and Visible (TUV) radiation model to calculate the surface UV radiation. Estimates of aerosol single scattering albedo (ωo) are made from matching the measured irradiance values to the model computed irradiances by varying ωo. The effects of the variation in ωo on the erythemal UV radiation and UV Index are presented. The values of t and a are compared with the ones obtained at Griffin, GA using a UV-MFRSR from the US Department of Agriculture. The retrieved values of t, a, and ωo are explained in context of ancillary measurements and the meteorological conditions.