=?iso-8859-1?Q?CO2=97Heavier?= than air?

Is CO2 heavier than air? The reason I ask is I have some Marsilea
Quadrifolia that was languishing in my plant tank. I took it out and am
growing it emersed. It's happy now but I was thinking that it would be easy
to grow it in a CO2-rich environment  especially if CO2 is heavier than
air. Do you see any problems with doing this?
Justin P. Healy
jphealy at sysconn_com