Modelling the transport of trace gases in the Martian atmosphere

The European-Russian ExoMars Trace Gas Orbiter (TGO) is set to reach its scientific orbit at the end of 2017 after the aerobraking campaign. The data returned by the probe will help to understand the origin and evolution of trace gases, especially methane (CH4), in the Martian atmosphere. To analyze the data sent back by the probe we have developed a model of the photochemistry in the atmosphere of Mars. The model follows a few dozen molecules that are present or expected to exist in the atmosphere due to a few hundred considered chemical and photochemical reactions. The radiative transfer equation is solved by using two-stream approximation to calculate solar photon flux that determine the photochemistry at different altitudes above the surface. The model takes into account the role of dust, ice clouds as well as the densities and fluxes of considered gases at the surface as a result of their transport from subsurface/surface sources.