More than 20.9 million people, approximately 6.4% of the nation, live in one of the 17 counties where year-round particle pollution levels are worse than the national air quality limit, and that receive a failing grade in “State of the Air” 2021. The number of people living in counties with unhealthy levels of year-round particle pollution is slightly smaller than in last year’s report, but higher than in reports published in 2017, 2018 and 2019.
Of the 25 cities most polluted year-round by particle pollution in the U.S., 13 suffered worse year-round levels during 2017, 2018 and 2019 than in last year’s report, and two reported their worst ever. In contrast, 10 of the 25 most polluted cities had lower year-round levels, of which three achieved their lowest levels ever. Across all 25 cities, the year-round levels of particle pollution worsened only very slightly.
There was a good deal of shuffling positions on the list of 25 most polluted cities this year. Three cities improved enough to leave the list: Birmingham, Alabama; Atlanta, Georgia and Brownsville, Texas. Three cities saw their air quality deteriorate enough in 2017, 2018 and 2019 to be added to the list (See Figure 3).