Epidemiologic studies over the last 40 years suggest rather consistently that general ambient air pollution, chiefly due to the incomplete combustion of fossil fuels, may be responsible for increased rates of lung cancer. This evidence derives from studies of lung cancer trends, studies of occupational groups, comparisons of urban and rural populations, and case-control and cohort studies using diverse exposure metrics. Recent prospective cohort studies observed 30 to 50% increases in lung cancer rates associated with exposure to respirable particles. While these data reflect the effects of exposures in past decades, and despite some progress in reducing air pollution, large numbers of people in the United States continue to be exposed to pollutant mixtures containing known or suspected carcinogens. It is not known how many people in the United States are exposed to levels of fine respirable particles that have been associated with lung cancer in recent epidemiologic studies, These observations suggest that the most widely cited estimates of the proportional contribution of air pollution to lung cancer occurrence in the United States based largely on the results of animal studies, may be too low. It is important that better epidemiologic research be conducted to allow improved estimates of lung cancer risk from air pollution among the general population. The development and application of new epidemiologic methods, particularly the improved characterization of population-wide exposure to mixtures of air pollutants and the improved design of ecologic studies, could improve our ability to measure accurately the magnitude of excess cancer associated with air pollution.
