Bicycling in the City is Good for You, Despite Air Pollution
Conrad deFiebre dissects the argument, explaining that yes, studies show a small increase in mortality for bicyclists in polluted areas:
"But this downside is outweighed nearly 100 to 1 by the health and fitness advantages of cycling. The British Medical Journal study found that one more bicyclist might die over seven or eight years from air pollution compared with drivers, while more than 12 lives would be saved each year by the health benefits of cycling."
DeFiebre also takes on Wendell Cox, who argues that the increase in pollution is an argument against densification.