The effects of isotropic multiple scattering and surface albedo on the photochemistry of the troposphere

Abstract

A recent paper (Anderson and Meier, 1979) critically evaluated the treatment of the transfer of incoming solar radiation into and through the cloudless troposphere in most photochemical models of the troposphere. They concluded that the one- and two-stream approximations used in these models are poor representations of the radiation field. A one-dimensional global photochemical model of the troposphere has been coupled to a radiative transfer model that includes the effects of isotropic multiple scattering, pure absorption and ground albedo on the transfer of incoming solar radiation through the cloudless troposphere. The results obtained using the more realistic treatment of the radiation field are compared with results using the Leighton approximation, a one-stream approximation used in tropospheric photochemical models. Significant differences in the vertical profiles of several key tropospheric species were found. The tropospheric profiles of excited oxygen atom, O( 1D) and the hydroxyl radical, OH, were found to increase by about a factor of three when multiple scattering was included and a ground albedo of 0.25 was used. Even higher values of these species were found for higher ground albedos. The vertical distribution of ozone photolysis frequency calculated with the multiple scattering code are compared to some recent measurements.