Infrared Radiative Transfer in Polluted Atmospheres

Abstract

A four-stream, multi-layered radiative transfer model has been developed to treat the problem of the transfer of infrared radiation in an atmosphere containing both scatterers and absorbers. Each atmospheric layer is isothermal and contains a uniform concentration of scatterers and absorbers. To facilitate the computations, the infrared spectrum was divided into four bands. In each band empirical transmission functions were fitted by a series of exponential functions. Test calculations of the infrared cooling rate were made using the empirical transmission functions and the fitted transmission functions. The resulting cooling rate profiles exhibit good agreement with each other. A model of a typical urban aerosol was developed using recent experimental results on the spectral dependence of the complex refractive index and the size distributions of aerosols. Atmospheric cooling rates as a function of height were computed on a band by band basis, with and without aerosols, in order to compare the effect of aerosols to the effect of H2O and CO2 in cooling the boundary layer. The presence of large, but realistic, concentrations of aerosol can substantially increase the infrared cooling of the aerosol-containing layer.