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[33.20] Ice Nucleation in the Martian Atmosphere

A. Maattanen, H. Vehkamaaki, A. Lauri (Department of Physical Sciences, University of Helsinki), S. Merikallio (Space Research, Finnish Meteorological Institute), J. Kauhanen, H. Savijaarvi, M. Kulmala (Department of Physical Sciences, University of Helsinki)

We have studied homogeneous and heterogeneous nucleation of CO₂ (Wood, Ph.D. thesis, 1999), and H₂O nucleation following the same schemes. We compared our results to the measurements of Glandorf et al. (2002, Icarus 160). The H₂O nucleation results were compared to those of Inada (Ph.D. thesis, 2002). Simulations were conducted with a realistic atmospheric composition with dust profile calculated as in Conrath (1975, Icarus 24) for a low dust loading of the atmosphere (\tau=0.1). In our basic cases the dust particle radius r_{\rm CN} was 1.0\mum.

For both substances homogeneous nucleation is very unlikely to happen in Mars. Anyhow, the onset saturation ratio (the saturation ratio for nucleation rate of 1s^-1) of heterogeneous nucleation for CO₂ on dust particles of 1.0\mum radius is 1.32. This is in fair agreement with measured values (Glandorf et al., 2002, Icarus 160). For constant concentration of CO₂ it gives a treshold temperature of 145K. For water with average concentration of 300 ppm the onset saturation ratio would be 1.18 and the corresponding temperature 200K.

We modelled nucleation as a function of height at different locations, e.g. Mars Pathfinder landing site, and compared results with observations. We used atmospheric profiles acquired from modelling and observations. The results agree well with other modelling results (Savij"arvi, 1999, QJRMS 125; Inada, Ph.D. thesis 2002, Colaprete et al., 1999, JGR 104) and observations by Mars Pathfinder (Schofield, 1997, Science) and Viking Orbiter 1 (Briggs et al., 1977, JGR 82).

We have started studies on binary nucleation of CO₂ and H₂O. Heterogeneous nucleation has been added to the original homogeneous model (Noppel et al., 2002, J. Chem. Phys., 116).

This work was supported by the Academy of Finland and the V"ais"al"a Foundation of the Finnish Academy of Science and Letters.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.