DON'T DO IT!
Not that I, an individual with "moderately severe adult onset asthma - likely exacerbated by participating in endurance sports while out in less than healthly air conditions for several years prior to being diagnosed," really feels all that strongly about it or anything.
Don't be silly, GH. It's bad enough the crap we breathe in on a regular basis. The air right now is downright dangerous. Stay indoors, go to the gym or take it easy and drink a beer. But do not ride it the air outdoors, whatever you do.