Like many cities in the eastern United States, Washington, D.C., has seen major improvements in air quality in recent decades. Levels of fine particle pollution (PM2.5) have declined by roughly 50 percent in the city since 2000 due to passage of a series of clean air laws. Cleaner air has yielded significant health benefits. The number of DC residents killed by diseases related to exposure to PM2.5 (chronic obstructive pulmonary disease, ischemic heart disease, lung cancer, and stroke) declined by 50 percent during that period, according to a new NASA-funded analysis of city-wide air quality and health data. However, the resulting health benefits have not accrued evenly.