This difficult spell creates not merely air, but a magically self-renewing atmosphere that survives for one standard (28-day) month per level of the caster. It lasts until exhausted or until countered by the reverse; dispel magic has no effect.
The create atmosphere spell can be cast on an object of any size, and remains with it regardless of the object's gravity or state (for example, if a ship is destroyed, the spell remains centered on the largest chunk, or a random fragment, as the DM desires). This created atmosphere replenishes the atmosphere of another ship it encounters if their combined atmospheres are within the spell's volume limit, at the rate of 1 ship-ton per turn (that is, the atmosphere of a 24-ton ship can be renewed completely in 1 day). This spell cannot be cast on a creature of any sort.
This spell requires a small, stoppered flask and a drop of water. One hit point is permanently drained from the caster each and every time this spell is cast (a limited wish or wish can restore a hit point lost in this manner).
The reverse, destroy atmosphere, does not destroy an existing atmosphere, but alters it from fresh to foul (or from foul to deadly). This alteration can quench flames or lessen fiery damage in some cases. Note that the reverse differs from the wizard's version.
Notes: Common for priests from a spelljamming culture; otherwise, very rare.