The Donora Smog Disaster and the Clean Air Act of 1970

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Many credit the literary works of Henry David Thoreau or Teddy Roosevelt’s patronage of national parks as the roots of the green movement in the US. However, after two world wars with the Great Depression thrown between them, environmentalism and sustainability were far from people’s minds. The tragedy and loss of life of the Donora Smog tragedy and the shock of awareness it created greatly contributed to the legislative drive that created the Clean Air Act.

In 1948, the people of Donora, Pennsylvania experienced the worst pollution disaster in the history of the United States.


Located less than 30 miles from Pittsburgh, Donora was a small, industrial town with a population of 14,000 people. Since Donora was home to unregulated steel mills and zinc works, the area had always been consistently smoggy, usually in the mornings. However, in late October of 1948, weather conditions trapped pollution in the town for several days through a meteorological condition known as thermal inversion. The smog was a thick yellow mixture of toxic pollutants including nitrogen dioxide, fluorine and sulfuric acid. At its worst, the smog made it impossible for Donora residents to see objects just a few feet away from them. After five days of this, 20 town residents had died and half of the population was sick or hospitalized.

The incident brought air pollution regulation into the consciousness of state legislators, and in 1949, Pennsylvania established the Division of Air Pollution Control. Six years later, the Pittsburgh area had reduced visible emissions by 97 percent. Similar industrial centers, including St. Louis and Cincinnati, followed suit. The federal government conducted inquiries into Donora as well, and in 1955 established the Air Pollution Control Act to research the issue of pollution control. This lead to the Clean Air Act of 1963, which regulated air pollution nationwide. In 1970, when the Clean Air Act was significantly expanded to include both mobile and industrial producers of pollutants, the Donora tragedy was a major issue in congressional debates regarding the health impacts of smog. The environmental protection agency was formed that same year.

The legislative results of the Donora Smog tragedy are reminder of a time when environmental issues were debated not because they were a polarizing symbol of political ideology, but because they have a direct effect on the health and safety of the people.