This year saw mixed results in terms of annual particle levels among the 26 most polluted cities in the United States: 13 of these cities saw increased particle levels; 11 cities improved; one was not included in last year's report, and one maintained the same levels as last year's report. Nine cities among the most polluted achieved their lowest ever annual particle levels. (The list of most polluted cities for annual particle pollution contains 26 cities instead of 25 due to a tie for 25th place.)
More people live in areas with unhealthy year-round particle pollution than in last year's report. More than 21.2 million people live in 19 counties where the annual average concentration of particle pollution was too high. This is higher than the 20.5 million Americans living in 18 counties in the 2019 report.
Bakersfield, CA returned to the rank of most polluted city for year-round particle pollution in 2016-2018. As with the short-term particle category, Bakersfield and Fresno also swapped rankings for annual particle pollution levels. Bakersfield returns to #1 most polluted in the nation while Fresno ranks #2, having tied its lowest annual average.
Thirteen of the 26 cities most polluted year-round by particle pollution saw increases over levels in the 2019 report: Bakersfield, CA; Visalia, CA; San Jose-San Francisco-Oakland, CA; Phoenix, AZ; El Centro, CA; Detroit-Warren-Ann Arbor, MI; McAllen-Edinburgh, TX; Philadelphia-Reading- Camden, PA-NJ-DE-MD; Sacramento-Roseville, CA; Shreveport-Bossier City-Minden, LA; Medford-Grants Pass, OR; Chico, CA and St. Louis-St. Charles-Farmington, MO-IL.
Eleven of the 26 most polluted cities had lower year-round particle levels, of which 9 matched (Pittsburgh and Fresno) or newly achieved (Atlanta, Birmingham, Chicago, Cincinnati, Cleveland, Houston, and Indianapolis) their lowest respective averages ever.
Of the remaining two cities among the most polluted in the nation by annual particles, Los Angeles, CA had the same level as last year, while Brownsville, TX did not have annual particle pollution data available last year for comparison.
Nine cities among the most polluted for annual particle pollution fail to meet the current national air quality standards. However, evidence shows that no threshold exists for harmful effects from particle pollution—that is, that even levels lower than the official standard are not safe to breathe.
More cities among the most polluted by annual particle levels saw increases than improved in the 2020 report.
Overall, cities in the western United States dominate the list, with 15 cities among the 26 most polluted by annual particles. California continues to claim more places on the list than any other state, with six of the 10 most polluted, including each of the worst five – and six of the nine cities that fail to achieve the national standard. Fairbanks, Phoenix, Pittsburgh and Detroit are also among the ten most polluted, with only Detroit achieving the national standard. Beyond cities in western states, the remainder of the most particle-polluted cities all meet the standard and are distributed throughout the Midwest, Southeast and Mid-Atlantic regions.
Cities with high power plant emissions as well as local, industrial sources continue to show up on the list, including Pittsburgh; Detroit; Cleveland; Philadelphia; Cincinnati; Birmingham; Indianapolis; Shreveport, LA; and Atlanta.
Fortunately, year-round particle pollution continues to decline across most of the nation, unlike the days with high ozone and high short-term particle pollution.
Because of their high numbers and long duration, western wildfires contributed to some of the elevated annual averages in western cities. That is especially true in California and Pacific Northwest communities that experienced major wildfire smoke impacts in 2018.