1948 Donora smog

The 1948 Donora smog was an air pollution disaster that occurred in Donora, Pennsylvania beginning on October 27, 1948 and lasting several days. It was caused by hydrogen fluoride and sulfur dioxide emissions from U.S. Steel's Donora Zinc Works and its American Steel & Wire plant during an atmospheric temperature inversion. It killed 20 people and caused respiratory problems for 6,000 of the 14,000 people living , a mill town on the Monongahela River 24 miles (39 km) southeast of Pittsburgh. The event is commemorated by the Donora Smog Museum.

Sixty years later, the incident was described by The New York Times as "one of the worst air pollution disasters in the nation's history." Even 10 years after the incident, mortality rates in Donora were significantly higher than those in other communities nearby.