[ycui1986]

i think it had something to do with CO2 can be made into supercritical state relatively easily, not for nitrogen or other common gases.

[raverbashing]

This pretty much

You can liquefy CO2 at a higher temperature than N2

[nine_k]

You can do it easily with something like propane, or other larger molecules. But CO2 is non-flammable, largely non-toxic, and easily available.