(Forthcoming Article) - Many environmental hazards have long-run health effects, but quasi-experimental studies typically measure outcomes and treatment over short time periods. We develop a new framework for quantifying the effect of air pollution exposure on life expectancy. Using daily changes in wind direction as an instrument for air pollution, we first charac- terize the dynamic mortality effects of short-run exposure. We then incorporate these estimates into a demographic model to quantify the lifelong effects of a permanent re- duction in air pollution exposure. Ninety percent of the survival benefits accrue after the first fifty years of life.