Pittsburgh's air pollution estimated to claim 3,000+ lives per year, and EPA rollbacks aren't helping

In October 1948, a thick haze rolled into Donora, Pennsylvania, a steel town in the Monongahela Valley, south of Pittsburgh. For five days, toxic fumes from a zinc smelter—a plant that turns zinc ore into pure zinc metal—poured out of the factory's stacks, became trapped in the valley and thus blanketed Donora. The air was filled with sulfur oxides, heavy metal dust and airborne particulates.