After decades of air quality improvement due to the Clean Air Act of 1970 and other regulations since, the Western U.S. is experiencing an increase in the number of days with extremely high levels of two key types of air pollutants due to climate change.
From 2000 to 2020, the growing number of wildfires — made more intense by climate change — and the increasingly common presence of stagnant, hot weather patterns combined to increase the number of days with hazardous levels of ground-level ozone and fine particulate matter. Those conditions are creating health risks for people throughout the region, according to a paper published in Science Advances.
Daniel Swain, a UCLA climate scientist and co-author of the paper, said the increased pollution affects densely populated regions across a broad swath of the West, including the Los Angeles basin, Salt Lake City, Denver and Oregon’s Willamette Valley. The study found that the number of days when both pollutant levels were extremely high increased in nearly every major city from the Pacific Coast to the eastern Rocky Mountains. (The scientists judged pollution levels to be “extremely high” on days when they were in the 90th percentile of their daily average for the study’s 20-year span.)
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