C'mon, guys, think about it ... the making of the tire itself is probably more has more enviromental impact than all the CO2 you could possibly use in a lifetime no matter how it's made.
As far as nitrogen in bike or car tires ... unless you're driving a Formula One race car, you're getting hosed. Please don't believe me .. do a quick search for "nitrogen tire scam" and read one of the million articles on why this is a waste by worthy sources.