The Na'vi and our oxygen

[Human No More]

They would be able to... carbon dioxide has no useful biological function except for presence is part of what speeds up breathing and circulation. Hydrogen sulphide has no useful biological properties, and is in fact poisonous. Humans can survive a low concentration, but a higher concentration kills them (although the levels of CO2 would first). The other main difference is more Xenon and less Argon, both of which are inert.
The Na'vi's respiration is oxygen based, just like humans. Red blood implies haemoglobin, so it's the same but with a higher tolerance for CO2 and H2S.

Woodsprite, the vehicles and buildings on Pandora are pressurised ABOVE the air pressure on Pandora (which is close to Earth's) so that in the case of any minor damage, air leaks OUT rather than in, stopping the atmosphere from incapacitating and killing the occupants.