The Effects of Long-Term Exposure to Pollution on Health

We provide the first causal evidence on how long-term exposure to fine particulate matter (PM2.5) at contemporary ambient levels contributes to the development of chronic disease in a young, initially healthy population. Our analysis links detailed personnel records for roughly 150,000 U.S. Army soldiers to high-resolution annual measures of PM2.5. Because soldiers enter service exceptionally healthy and receive uniform access to care, new diagnoses reflect pollution’s physiological impact rather than preexisting conditions or differential health care access. They are also required to relocate based on the needs of the Army, which provides us with quasi-random variation in initial duty-station assignments that we use as an instrument for average annual pollution exposure over a soldier’s career. We find that sustained PM2.5 exposure substantially increases circulatory disease, particularly hypertension, with mixed evidence on respiratory conditions that are sensitive to specification. Exposure over shorter durations, by contrast, has little detectable effect, a pattern consistent with the cumulative nature of pollution’s health burden. These findings demonstrate that even moderate long-term exposure to air pollution can erode health capital in ways that are invisible to studies focused on short-run variations or mortality alone, and they highlight the importance of regulatory standards that account for chronic exposure risks.