During the 1940s and 1950s some parts of the United States experienced pollution episodes like those now occurring across parts of China. And even on good days the air wasn’t as clean as it generally is now.

One of the worst of these episodes, and one that helped focus attention on U.S. air pollution, was the choking, deadly smog that covered Donora, Pa., in the Monongahela River Valley, 20 miles southeast of Pittsburgh from Oct. 27 to 31, 1948.

In the 1940s residents of Donora considered the smoke coming from the town’s U.S. Steel Corp. Donora Zinc Works and the American Steel & Wire factory as a price they paid for the jobs held by roughly half of the town’s 14,000 residents. (Note: The U.S. Census Bureau says the current population of Donora is 4,745.)

By Friday evening Oct. 28, 1948, though, thick gray fog covered Donora and the town’s eight physicians were rushing to the homes of people who were having trouble breathing. The town’s firefighters and police were taking oxygen tanks to residents who needed them, and firefighters from surrounding communities were helping keep Donora supplied with oxygen.

On Oct. 31 an area of low pressure moved in with rain, breaking the temperature inversion that had trapped the smog near the ground and allowing the air to begin clearing. The pollution killed 20 people and left roughly 7,000 ill in hospitals or at home.

Before 1948 some U.S. cities had adopted ordinances restricting air pollution, but it wasn’t seen as a national problem. But the Donora disaster and serious air quality problems in other places, including Los Angeles, helped make air pollution national news and encouraged efforts to control it. These efforts led to the Federal Air Pollution Control Act of 1955. This was the first national law designed to improve air quality.

The Donora disaster “was the first time that people really understood that a lot of air pollution in a short period of time could kill people,” said Dr. Devra Davis, director of the Center for Environmental Oncology at the University of Pittsburgh and author of “When Smoke Ran Like Water,” which is about environmental hazards. She is also a Donora native who was 2 at the time of the “Big Smog.” She didn’t remember what happened in 1948.

In her book Davis describes learning about it after her family had moved to Pittsburgh before she entered high school. She read about the disaster in a book and and asked her mother whether there was another “Donora.”

It wasn’t surprising that she didn’t associate the pollution disaster she read about with the Donora where she lived through elementary school. Residents rarely talked about it until they marked the 50th anniversary in 1998 with an historical marker in town.

On the 60th anniversary the town opened the Donora Smog Museum with the slogan “Clean Air Started Here.” While the slogan might exaggerate a little, what happened in Donora did help the country focus on air pollution.

An English physician, Henry Antoine Des Voeux coined the term “smog” in 1905 to better describe the famous “London fog,” which was a rally mixture of fog, coal smoke and other pollutants.

That’s a good-enough description of the kind of pollution that affected Donora and of what’s happening in China now.

Most of the time now in the U.S. “smog” refers to photochemical smog created by atmospheric chemical reactions involving nitrogen oxides, hydrocarbons and sunlight. While it is not as evil looking nor quite as dangerous as the Donora smog, it’s still a health hazard.

This year Donora is making the 65th anniversary on Oct. 30-Nov. 3 with a conference on connections between what happened in 1947 and today’s concerns as well as other events.