Airy alternatives to a pressurized environment.

[warcrimes]

I think hyperoxegenating plants is an awesome

dunno if they already do, but plants ought to scrub CO2 and release O2. Could be a modifiable property, so the botanists can splice and breed super-scrubbing trees that convert CO2 to oxygen on an industrial scale. 

Set up a complex with the engine, take burn exhaust, cool it though a radiator, pump it into the grow-room, siphon off the excess oxygen, burn it again.