Cancer risk of air pollution: epidemiological evidence.

Epidemiological studies on the effect of urban air pollution on lung cancer were surveyed. Overall, the studies from many countries point to a smoking-adjusted risk in urban areas over countryside areas that is higher by a factor of up to 1.5. The extent to which urban air pollution contributes to this excess remains unknown. Studies on diesel-exposed occupational groups show that urban air pollution may have a causative role in lung cancer. Model calculations on unit risk factors of known human carcinogens were carried out to rank carcinogens according to their current ambient air concentrations.