I live in a bad air-quality area (central CA), the local 'air pollution control district' issues 'air alerts' on high pollution days (mainly during summer months/days). They say to not use your vehicle, but also not to do any outside strenuous exercise ... so where does that leave the bicycle commuter? I think that leaves him sucking bad quality air. Like was mentioned above, I'm probably better off for commuting by bicycle for the health benefits, regardless of the black-lung that I'm nurturing.