Aerosol single scattering albedo and phase function were retrieved from Cimel Sun photometer observations of sky radiance during the May 2003 Atmospheric Radiation Measurement (ARM) Aerosol Intensive Observation Period. Single scattering albedo and backscattered fraction were compared to data obtained from the ARM program In situ Aerosol Profile (IAP) flights and a similar airborne experiment conducted by the University of Washington. The retrieved single scattering albedo was within about 0.05 of the in situ measurements for many of the considered cases, though much larger deviations were also seen. The retrieved aerosol properties were also used to compute the ratio of diffuse and direct irradiance at the surface, which was compared to the same ratio measured by a Multi Filter Rotating Shadowband Radiometer. The radiation model included correction factors to account for the effect of the instrument cosine response on both the direct and diffuse irradiance components. These comparisons showed very good agreement for most of the cases considered.