This study evaluates the impact of fine particulate matter (PM2.5) air pollution on life expectancy in 217 counties across 51 U.S. metropolitan areas during the 1980s and 1990s. Using regression models, the researchers found that a 10 μg/m³ reduction in PM2.5 concentration was associated with an estimated increase in life expectancy of 0.77 years. The effect was consistent across various sensitivity analyses, including controlling for socio-economic, demographic, and proxy smoking variables, and restricting observations to larger counties. The study concludes that reductions in ambient fine particulate matter air pollution contributed significantly to improvements in life expectancy in the United States.This study evaluates the impact of fine particulate matter (PM2.5) air pollution on life expectancy in 217 counties across 51 U.S. metropolitan areas during the 1980s and 1990s. Using regression models, the researchers found that a 10 μg/m³ reduction in PM2.5 concentration was associated with an estimated increase in life expectancy of 0.77 years. The effect was consistent across various sensitivity analyses, including controlling for socio-economic, demographic, and proxy smoking variables, and restricting observations to larger counties. The study concludes that reductions in ambient fine particulate matter air pollution contributed significantly to improvements in life expectancy in the United States.