Probably not. I remember there was a study done sometime during the mid-70s bike boom that was reported on in the LAW (now LAB) magazine. The study looked at bike and car commuters using the same urban road (Ibelieve it was in the Wash. DC area) and tested their blood for CO and other pollutants. The conclusion was that the bike commuters were getting substantially less pollution than the car drivers in the lane next to them. AIRC there were a few hypotheses to account for the findings: car air intakes are lower to the ground than cyclists; cyclists can take an active role in avoiding pockets of high pollution (i.e. if you smell the exhaust from a poorly maintained truck you can slow down and minimize your time in the vicinity - a car driver is likely to stay behind that truck much longer); cyclists are running their metabolism at a faster rate and that may help the body eliminate polluting chemicals. Don't remember is they were able to determine which factors were most important.