I'd be more understanding of people who use CO2 if it weren't for the fact that everyone I've seen use one seems to think it's fine to just chuck the empty in the ditch when done. I've picked up a few CO2 carts from the side of the road and taken them home to recycle. I wouldn't use them personally even though I would take them home and put them in recycling, just because it is more material to have to process needlessly; I can't even understand the mindset of thinking the world is a trash can.
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Work: the 8 hours that separates bike rides.