There is strong evidence that short-run fluctuations in air pollution negatively impact infant health and contemporaneous adult health, but there is less evidence on the causal link between long-term exposure to air pollution and increased adult mortality. This project estimates the impact of long-term exposure to air pollution on mortality by leveraging quasi-random variation in pollution levels generated by wind patterns near major highways. Combine geocoded data on the residence of every decedent in Los Angeles over three years, high-frequency wind data, and Census Short Form data. Using these data, estimate the effect of downwind exposure to highway-generated pollutants on the age-specific mortality rate by using bearing to the nearest major highway as an instrument for pollution exposure. Find that doubling the percentage of time spent downwind of a highway increases mortality among individuals 75 and older by 3.6 to 6.8 percent. These estimates are robust and economically significant.