Not that it really matters, but CO2 poisoning isn't possible - you breathe it out with every breath. You may have meant CO (carbon monoxide). Also, getting outdoors prevents you from having to deal with people who correct you :)
Conventions can be a mixed bag. For as much as I've been wanting to return to the con scene (specifically giving furry cons a second chance), I would never choose it over the opportunity to visit a national park like this one.
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(Grand Canyon)