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When the smoke clears: The legacy of killer smogs

On the right, smog in Beijing in August 2005. On the left, taken from the same location, following several days of rain. (Image: Bobak Ha'Eri, shared under a Creative Commons License)

Recently Beijing suffered a smog event that elicited measures previously unseen in China's capital. For the first time, restrictions were placed on vehicle use, industrial activity, and construction. Schools were ordered to avoid outdoor activities, and people were cautioned to stay indoors.

The air quality index number was literally off the charts. At the U.S. Embassy in Beijing, an air monitor showed an air quality index of 755 micrograms per cubic meter, well into the hazardous zone of 301 — 500, which is at the top of the chart.

While Beijing deals with its latest smog event, other dangerous smog events in history led to the passage of clean air legislation.   

On December 3—5, 1930, 60 people died and several thousand became seriously ill when industrial coal emissions were trapped in a fog in the Meuse Valley area of Belgium. It was one of the first industrial air pollution disasters to be well-documented. Most of those who died were elderly people who already suffered from respiratory problems, but young, otherwise healthy people became gravely ill as well.

The most significant air pollution disaster in the United States occurred in late October of 1948 in Donora, Pennsylvania, a mill town 25 miles southeast of Pittsburgh. The circumstances were similar to the Belgium event. A deadly soup of industrial emissions consisting of carbon monoxide, sulfur dioxide, and fluorine (a byproduct of the zinc smelting plant) were combined with fog and trapped in the valley under a high pressure system over a period of five days.  

During the 1948 event, 20 people died, 600 were hospitalized, and almost 6,000 people, 42% of the population, were sickened. Their symptoms included shortness of breath, irritation in the eyes, nose and throat, severe headaches, nausea, and vomiting. In addition, 800 animals died. This was a key event that triggered the clean air movement in the U.S. and led to the passage of the first federal air pollution legislation, the Air Pollution Control Act of 1955.

While London is known for its fog, in December of 1952 it became known for the "Great Smog," one of the deadliest air pollution events in history. Cold weather, high pressure and a lack of wind formed the basis of the event in which pollutants caused from burning coal combined with fog to sit over the city for four days.

But this "pea soup" fog was different from others Londoners had experienced. This one was particularly deadly, though no one realized just how deadly until there was a shortage of coffins and flowers for funerals. In the following weeks, the Great Smog was blamed for up to 12,000 deaths and for causing 100,000 to fall ill. This event led to the passage by the British Parliament of the Clean Air Act of 1956, which limited the burning of coal.

The smoggiest area in the U.S. is Los Angeles. The first recognized smog event occurred in 1943, during World War II, when some residents thought they were under a chemical warfare attack by the Japanese. In time, they came to understand that the enemy was in fact their own vehicles. 

While London's smog events depended on coal smoke combining with fog, the smog common to Los Angeles is a photochemical smog. This type is dependent on sunlight creating a chemical reaction with partially unburned exhaust from vehicles and hydrocarbons from oil refineries, which creates an ozone haze. This discovery was made in 1952 by Dr. Arie Haagen-Smit, a chemist at the California Institute of Technology.

The City of Los Angeles began an air pollution control program in 1945, and in 1947, the California Air Pollution Control Act was passed. In 1959, California was the first state to set air quality standards and restrict vehicle emissions.

With industry comes responsibility. Dangerous smog events, though tragic, have taught us that to preserve the air we breathe, we must conitnually look for ways to minimize the release of hazardous chemicals by changing the way we live and do business.