Controversial opinion that shouldn't be if people would bother to read the rules: air elementals do not, by their description or the rules as clarified in Spelljammer, inherently refresh the air of a spelljammer. Summoning one does. If one did, then fire elementals and other magical fire also consumes air.
By extension, an Eberron elemental airship, which in 3e uses air or fire elementals, has no effect as written. When I tried pointing this as I explained why I was going treat the elementals as crew members for purposes of air consumption I got weird ass rules-lawyering.