My local guy says "wait here" and he walks out back, then you hear a loud hiss for awhile.....and it does take awhile. Nothing you could evacuate in to the atmosphere will hold a candle (no pun intended, please don't do that) to all of the crap big corporations and our yokel brethren have been spewing in to the atmosphere for hundreds of years.
I'd say your contribution will be a trillionth at most. Plus, it's kinda cool. I did it with a Westy tank not too long ago.