With the tone of you reply, I regret to inform you that in my car I'm on the interstate in stop and go traffic where thousands of cars go through and someone's tail pipe is right in front of me. Where on the bike I'm on far less travelled back roads with much less vehicle traffic and thus far better air. I am working harder, but there's much less tailpipe in the air to begin with. And that's not even counting the miles of off-street bike trails I'm fortunate enough to enjoy that don't even parallel a street, or the how the exercise you would get would likely to offset any additional pollution. Or that I seem to remember some article about how the air in the cabin of a car being much more polluting that simply being outside on the road, though I can't seem to find it again so I'm not sure it counts...

There are disadvantages to bike commuting, like the weather or taking additional time or not being able to hop in your car and go to lunch with someone else....I just don't think air pollution is one of them unless you're under some really unusual circumstances (like the only way you could bike is a path running alongside a busy freeway), and even then it's up in the air.