Is pollution a problem in urban cycling? 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.
Rank, Folke and Jespersen (2001), "Differences in cyclists and car drivers exposure to air pollution from traffic in the city of Copenhagen", The Science of The Total Environment, 279:131-136


  teams of two cyclists and two car drivers in two cars were equipped with personal air samplers while driving for 4 hours on 2 different days in the morning traffic of Copenhagen. The air sample charcoal tubes were analysed for their benzene, toluene, ethylbenzene and xylene (BTEX) content and the air filters for particles (total dust). The concentrations of particles and BTEX in the cabin of the cars were 2–4 times greater than in the cyclists’ breathing zone, the greatest difference being for BTEX. Therefore, even after taking the increased respiration rate of cyclists into consideration, car drivers seem to be more exposed to airborne pollution than cyclists.