Coupling photochemistry with haze formation in Titan's atmosphere, Part I: Model description

We introduce a new 1D coupled Radiative/Convective-Photochemical-Microphysical model for a planetary atmosphere and apply it to Titan. The model incorporates detailed radiation transfer calculations for the description of the shortwave and longwave fluxes which provide the vertical structure of the radiation field and temperature profile. These are used for the generation of the photochemistry inside the atmosphere from the photolysis of Titan's main constituents, nitrogen (N2) and methane (CH4). The resulting hydrocarbons and nitriles are used for the production of the haze precursors, whose evolution is described by the microphysical part of the model. The calculated aerosol and gas opacities are iteratively included in the radiation transfer calculations in order to investigate their effect on the resulting temperature profile and geometric albedo. The main purpose of this model is to help in the understanding of the missing link between the gas production and particle transformation in Titan's atmosphere. In this part, the basic physical mechanisms included in the model are described. The final results regarding the eddy mixing profile, the chemical composition and the role of the different haze precursors suggested in the literature are presented in Part II along with the sensitivity of the results to the molecular nitrogen photoinization scheme and the impact of galactic cosmic rays in the atmospheric chemistry.