EFFECTS OF MULTIPLE SCATTERING AND SURFACE ALBEDO ON THE PHOTOCHEMISTRY OF THE TROPOSPHERE

A one-dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families has been developed and used to investigate the vertical profiles and the natural (including atmospheric chemical reactions) and anthropogenic sources and sinks of these species. The species continuity equations are solved numerically applying prescribed boundary conditions. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. Heterogeneous losses (e.g. rainout, gas-to-particle chemistry, and dry deposition), are parameterized to make calculated profiles consistent with measurements. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Comparisons of vertical profiles of tropospheric species are made between the Leighton approximation, widely used in most tropospheric models, and the detailed radiative transfer matrix inversion model used in this study. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption and surface albedo on the transfer of incoming solar radiation. The results indicate that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with the more detailed radiative transfer matrix inversion technique used in this study. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included. Furthermore, most species increase in concentration as a function of increasing surface albedo. A few species, notably ozone, exhibit decreased levels of concentration when the realistic radiative transfer model is used. The effect of the detailed treatment of incoming solar radiation on the photochemistry of the troposphere is discussed.