"The NBER Bulletin on Aging and Health provides summaries of publications like this. You can sign up to receive the NBER Bulletin on Aging and Health by email. Airports are some of the largest sources of air pollution in the United States. We demonstrate that daily airport runway congestion contributes significantly to local pollution levels and contemporaneous health of residents living nearby and downwind from airports. Our research design exploits the fact that network delays originating from large airports on the East Coast increase runway congestion in California, which in turn increases daily pollution levels around California airports. Using the component of California air pollution driven by airport congestion, we find that carbon monoxide (CO) leads to significant increases in hospitalization rates for asthma, respiratory, and heart related emergency room admissions that are an order of magnitude larger than conventional estimates: A one standard deviation increase in daily pollution levels leads to an additional $1 million in hospitalization costs for respiratory and heart related admissions for the 6 million individuals living within 10km (6.2 miles) of the 12 largest airports in California. While infants and the elderly are more sensitive to air pollution, we also find significant relationships for the adult population. The health impacts are driven by CO, not NO2 or O3, and occur at levels far below existing EPA mandates. Our results suggest there may be sizable morbidity benefits from lowering the existing CO standard"--National Bureau of Economic Research web site.