I biked in an N95 in Vancouver during forest fire season in 2018. Not fun, but doable and it definitely helped -- without the mask I felt absolutely awful.
That's for a different situation, though. The smoke particulates are very small and are omnipresent, so a mask definitely helps. Coronavirus, by contrast, is only airborne for a short while, so unless you're close to someone who's infected you're not going to be breathing it in anyway. That's why they're saying the masks have limited effectiveness outside.
Oh, when the GP said it's unrealistic to bike in a mask, I thought they meant it would be too difficult. Maybe they just meant unnecessary, in which case I agree.
Yeah, I'm thinking that's what they must mean. An N95 mask doesn't cut down your breathing that much, and you can simply down-moderate your effort a little bit so that you never hit a pant. It's no gas mask.
