The pork industry was looking for a humane way to slaughter pigs, so they tried having the pigs breathe pure nitrogen which did the trick. This has been suggested as a humane way to do capital punishment, and there is a political movement of people who support suicide for terminally ill patients who were encouraging people to breathe pure helium, which is easy to obtain, as a painless way to die.
There is gas exchange between the oceans and the air. CO2 in the oceans forms carbonic acid, which is used by calcifying marine organisms to combine with calcium to make calcium carbonate to create shells. This process is sequestering atmospheric CO2 over the long term, turning CO2 into limestone deposits, which is why atmospheric CO2 has been on a serious decline over the last 40 million years.