I am thinking on the Moon if it would have an oxygen atmosphere. What would be the characteristic time of its escape?
Although the Moon has a much lower escape velocity as the Earth, it is still around 5 Mach, which results that an air atmosphere there could be relative stable.
Somewhere I've read the characteristic time of its escape would be in the order of some ten millions of years. Unfortunately, I can't find my source.
Furthermore, I think a simple boltzman-statistic based model is not enough, because - similarly to the Earth - the processes of the rare gas in the upper atmosphere would be significant.