Three-dimensional on-line chemical modeling in a Mars general circulation model

In this paper we present the design and some results of an on-line chemical model of the atmosphere of Mars using a three-dimensional dynamical–chemical model. A chemistry module has been added to the 3D Mars Global Multiscale Model (GM3), a general circulation model based on the Canadian weather forecast model. As water is a major fuel for chemistry on Mars, we have taken care to simulate the atmospheric water vapor content, taking into account evaporation from and condensation to the polar caps and in the atmosphere we allow for freezing and formation of a bulk cloud and sedimentation. The chemical module includes the main neutral carbon–oxygen–hydrogen–nitrogen species and associated relevant reactions. The outputs of the model are analyzed in the light of our current understanding of the chemistry on Mars. The results are in general accordance with 1D models and with two other 3D models with more limited chemistry. The model does not require elevated diffusion coefficients to fit observational data in the thermosphere as was suggested in some 1D studies. The large scale transport and the downward thermospheric transport in the winter pole appear to have a significant role in the concentrations of some trace species.