Thin moon-atmosphefor protection? (was Qualifying and quantifying impactors)

--- In spacesettlers, Combs, Mike wrote:
> the once-every-3-years-or-so impact would not represent
> an emergency situation. It would only represent a minor
> repair job which probably shouldn't get procrastinated
> too many days (weeks?).

It occurs to me that the creation and maintenance of a thin (Martian-
thin, or thinner?) atmosphere might economically offset the ongoing
meteorite-repair costs, without impeding launches and mass-driving too
much. Thinking about this further, it seems to me that ordinary human
activity, by itself, on the moon would create at least a tiny bit of
an atmosphere. Maybe there would be a way to model the damage-cost
reduction to air-density and air-maintenance-cost.