1. Introduction: CO in Martian atmosphere

Observed concentration is much smaller than that calculated by using 1D model.
McElroy & Donahue (1972)
(observed) << (modeled)
It is caused by difference of reaction rate.
	(fast!)
	(slow)

The observed value is explained by catalytic reaction of HOx.
	(fast!)

Parameterized vertical diffusionof H2O is assumed.

It is larger than that used in 1D photochemical  
        model of terrestrial atmosphere.