Simultaneous retrievals of column ozone and aerosol optical properties from direct and diffuse solar irradiance measurements

A retrieval technique has been developed to simultaneously determine column ozone amounts and aerosol optical properties using surface observations of solar ultraviolet direct normal and diffuse horizontal irradiance from a multifilter rotating shadowband radiometer. The retrieval consists of a Bayesian scheme involving a tropospheric ultraviolet radiative transfer model. The technique was tested using cloud-free observations collected during a Mexico City Metropolitan Area air pollution field campaign from April to May 2003. Retrieval results compared favorably to those of independent techniques, including ozone amounts from a direct-Sun method, Langley-derived aerosol optical depths, and aerosol single-scattering albedos from a direct-to-diffuse irradiance ratio technique. Further comparisons were performed between the measurements and model simulations when using the retrieval results as inputs, both from the proposed technique and the combined independent methods. Simulations using the results of the new method were found to agree with the observations within the assumed limits of measurement and model uncertainty. It is anticipated that the technique will be applied across a 33-site network of radiometers maintained by the U. S. Department of Agriculture UV-B Monitoring and Research Program for development of aerosol climatologies and for providing ground validation for satellite measurements.