Are anti-pollution masks effective?
I get this question once in a while (working in Danish Cyclist Federation). It seems to be based on the idea that commuting by bike will expose you to more pollution than commuting by car. I have seen no research that proves this. However, I have seen research indicating that the opposite might be true. Some was in danish, but here's some in english and french (links to pdf's at the end of this article): http://www.pollution-china.com/Blog/More-exposed-to-pollution-in-a-car.html

You should also consider the possible danger of wearing a mask while being physically active. There has been little research in this field that I'm aware of but there could be a risk of creating negative pressure by obstructing the airway which has been known in some cases to produce pulmonary edema. We (again Danish Cyclist Federation) sent some masks to some danish specialists who concluded that the risk was very small, but since pulmonary edema is a very serious thing, I still want to lead your attention to this. Maybe you can find some research (I would be interested to hear about it).

Also keep in mind that if the research on "in-car pollution" vs "on-bike pollution" cited above is true it is much more important for car drivers to consider wearing a mask than it is for bicycle commuters.

On top of this comes all the additional beneficial factors that bike commuting produces.

Happy cycling.