This paper expoloits a unique merger of air quality and county manufacturing data to quantify manufacturing's pollution externality by industry. By linking pollution to local production, I estimate cross-sectional pollution production regressions. Rust Belt cities that were endowed with the largest concentrations of the dirtiest industries experience reduced pollution externalities. I estimate that Gary, Indiana adn Pittsburgh, Pennsylvania experienced substantial pollution declines as local primary metals activity declined in the 1970s and 1980s.