DPS 35th Meeting, 1-6 September 2003
Session 3. Mars Atmosphere I
Oral, Chairs: T. A. Livengood and A. Colaprete, Tuesday, September 2, 2003, 10:30am-12:00noon, DeAnza I-II

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[3.03] Three-dimensional chemical modeling of the martian atmospheric composition

S. Lebonnois (LMD/IPSL, Paris, France), F. Lefevre (SA/IPSL, Paris, France), F. Montmessin (NRC, NASA Ames Research Center, USA), F. Forget (LMD/IPSL, Paris, France)

Hydrogen peroxide (H2O2) and ozone (O3) are important products of the chemistry in the martian atmosphere. Ozone has already been observed, and will be mapped in more details with SPICAM onboard the european mission Mars-Express. Hydrogen peroxide might be responsible for the lack of organic material at the surface. Although predicted by 1D photochemical models, this coumpound has never been detected so far and only upper limits of the martian H2O2 abundance could be given in recent observational studies.

We will present here three-dimensional simulations of Mars' atmospheric composition using our new photochemical model coupled to the LMD general circulation model of the Martian atmosphere. The chemical module includes 11 species (H, H2, O, O(1D), O2, O3, OH, HO2, H2O, H2O2, and CO), and takes into account 9 photodissociations and 29 chemical reactions. Considering the main UV absorbers (CO2, O2, H2O, and O3), transmission is calculated for every wavelengths with a resolution varying from 0.1 nm to 5 nm. The vertical profiles of the photodissociation coefficients are then tabulated for all altitudes, and as a function of solar zenith angles, overhead CO2 and O3 column densities, and temperature. The chemical evolution of the tracers is calculated on-line using the temperature calculated by the GCM, takes into account the diurnal cycle, and is interactively coupled to the water cycle.

The global seasonal cycles of H2O2 and O3 will be described. Emphasis will be given to the interactions with the water cycle. Since the LMD-GCM now includes a water cloud scheme, the hypothesis (formulated by Krasnopolsky, sixth Mars Conference, 2003) that heterogenous reactions of HOx species on water ice particles strongly affect H2O2 and O3 budget in Mars' atmosphere will be tested. The results of our simulations will be compared to the constraints derived from observational data.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.