This year marks the 70th Anniversary of the Great Smog of London, a deadly and consequential air pollution event in which a thick smog overtook the city for five days in December 1952. The smog, which was caused by a combination of emissions from burning coal and natural weather patterns that trapped the pollution in place, ended up killing thousands of Londoners.  

What exactly is the Great Smog of London and how did it happen? The event took place from December 5 to 9 in 1952 when an anticyclone settled over the city which caused an inversion that trapped the cold air below a layer of warm air higher up. As a result, the pollution from the city, namely emissions from domestic fireplaces and factory chimneys, was trapped near ground level. It was reported that the smog made visibility so poor in certain areas of the city that pedestrians could not see their own feet

The devastating long-term impacts of the Great Smog weren't fully understood until years after the incident. Today, the pollution is estimated to have led to roughly 12,000 deaths, in addition to hospitalizations related to pneumonia and bronchitis. Here in the United States, a similar major air pollution event happened in late October in 1948 in Donora, Pennsylvania, where trapped air pollutants made thousands sick and killed 20 people shortly thereafter (and likely more in the long term). Cities across the U.S. experienced similar ghastly smog events, some captured in this The New York Times slideshow

These deadly smog events helped lead to laws being passed to improve air quality. The Great Smog was followed by the passage of the Clean Air Acts of 1956 and 1968 in England. Similarly, the devastation that occurred in Donora and across the U.S. helped lead to the creation of the U.S. Clean Air Act in 1970 and its strengthening in 1990. (Learn more in our blog post celebrating the 50th anniversary of this law.) 

While these laws and others have helped clean up air pollution in many areas, smog remains a problem around the world. For instance, over the summer, air pollution spiked across Europe due to record-breaking temperatures and wildfires, with ozone exposure exceeding the World Health Organization’s limit in areas like Southeast England and northern France. And in India, where air pollution is a frequent issue, a thick smog covered New Delhi for multiple days last month. As a result of the intense air pollution, schools, factories and construction sites were shut down across the capital

Fortunately today, U.S. cities don't look like these images from the past thanks to the strong Clean Air Act, one of America's best protections for public health. And the specific weather conditions that resulted in the dramatic air pollution events in London and Donora are rare – but winter air inversions still occur today. For example, Salt Lake City frequently experiences inversion episodes that result in elevated levels of harmful particle pollution.  

Despite the progress we have made to reduce pollution in the air we breathe, too many U.S. communities continue to face unhealthy air. To fully protect the lung health of all Americans, the Americans Lung Association is working to make sure the National Ambient Air Quality Standards (NAAQS) for ozone and particle pollution are strengthened and follow the most up-to-date science. Join us today by adding your name to this petition that urges EPA to set strong new limits on particle pollution. 

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