Donora Smog Museum features a collection of archival materials documenting the Donora Smog of 1948, an air inversion of smog containing fluorine that killed 20 people in Donora, Pennsylvania, United States, a mill town 20 miles south of Pittsburgh on the Monongahela River. Donora was home to U.S. Steel's Donora Zinc Works and its American Steel & Wire plant. The event is sometimes credited for initiating the clean-air movement in the United States, whose crowning achievement was the Clean Air Act.