Temperature Inversions and Deadly Smog

Common to all three tragedies were two key elements. First, large factories in each area had been spewing enormous amounts of pollutants into the air, the most deadly being sulfur dioxide. And second, Mother Nature came calling in the form of something called a temperature inversion.

Death in Donora

On Tuesday October 26, the air over Donora became foggy from cool air being trapped beneath warmer air above in what meteorologists term a temperature inversion. Normally inversions last less than a day, but this one lasted a devastating five days. Within two days the fog had turned into a stinging, yellowish-gray shroud so thick that many people couldn't drive, couldn't even walk without stumbling. "It was so bad," said one resident, "that I'd accidentally step off the curb and turn my ankle because I couldn't see my feet."