It's about the balance of positive and negative effects. There's always some kind of pollution and there's always some kind of benefit from exercise. The benefi

It's about the balance of positive and negative effects. There's always some kind of pollution and there's always some kind of benefit from exercise. The benefit from commuting on a bicycle is considerable. Question is how does the effect of pollution compare. If air quality is better indoors and you can do it indoors, great, but for many people commuting is one of the few opportunities to be physically active.