I usually ride a bicycle in Barcelona. I'm concerned about pollution and I take an anti-pollution mask. Of course, some people scream because they confuse me with Hannibal Lecter but currently that's not a problem.
I've heard a lot of opinions about this: "don't care because pollution it's not harmful", "that masks make no sense" and so on...
What do you know about cycling and pollution? What about masks, are they effective at blocking pollution?
Note: I think objective/documented answers are the most useful. Please, try to avoid "I think that...", "my opinion is..." answers.