Global Analysis of the Effects of Dust on the Photodissociation Rates

Aerosols scatter and absorb UV radiation and consequently either enhance or reduce the actinic fluxes and photolysis rates. Mineral dust particles are known to absorb UV radiation, but the impact on the photolysis rates is complicated by the optical properties dependency on the particle size, composition and wavelength. The high spatial and temporal variabilities of the dust size distribution add difficulties to the global analysis. The Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model has been used to simulate several years of the global distribution of mineral dust in the troposphere. The optical parameters (extinction efficiency, single scattering albedo and asymmetry parameter) of the seven particle sizes (from 0.1 to 5 microns), transported by the model, have been inserted in the Tropospheric Ultraviolet-Visible (TUV) radiation model version 4. The photodissociation rates of J(N02) and J(03 to O(1D)) have been calculated with TUV-4 with and without dust particles on the global scale. The effects of dust on J(N02) and J(03) will be analyzed with an emphasis on the difference between major dust sources in Africa and Asia.