In the years 2022, 2023 and 2024, there were 61.5 million people living in counties across the U.S. that earned an “F” grade for unhealthy spikes in particle pollution. This represents a change of 15.6 million fewer people than in last year’s report, ending a seven-year stretch of continuous increases. Nevertheless, this is significantly higher than the historic low total of 35.1 million seen in the 2018 report. Moreover, there were 59 metro areas across the country whose worst county earned a failing grade.
62 million people live in counties with F grades for daily particle pollution
Compared with last year’s “State of the Air” report, the occurrence of days with elevated fine particle pollution generally improved in much of the United States, especially in several states in the West. Even so, notable increases were observed in a band of states ranging from Arizona to South Carolina, with the worst changes seen in Texas. Six states (Arkansas, Florida, Hawaii, Louisiana, Mississippi and South Carolina) and Puerto Rico showed no improvement in any county for this pollutant measure. Texas worsened in 18 counties, but it did improve in two and remained unchanged in six. In this year’s report, only three cities on the Worst 25 list posted their highest weighted average number of days for fine particle pollution ever reported, compared to last year’s report where four cities did so. In “State of the Air” 2026, 120 counties in 23 states get failing grades for short-term particle pollution. Though smaller than last year’s total of 154 counties in 27 states, this year’s tally is the second largest over the most recent 17 “State of the Air” reports.
Compared to last year’s report, this year five states (Colorado, Connecticut, New Hampshire, South Dakota and Vermont) and the District of Columbia saw the number of unhealthy days for fine particle pollution improve in every one of their counties graded for this pollutant. Thirteen other states had no counties with worse performances, though they did have counties that were unchanged as well as improved. By far, the largest improvement among statewide averages occurred in Nevada, with the average number of days with unhealthy particle pollution decreasing by nearly 11, although Clark County still showed an increase.
Smoke from wildfires continues to be reflected in the severity of the grades for particle pollution. While this year’s report shows an improvement over the prior report’s highest-ever number of Unhealthy (red) and Very Unhealthy (purple) days of particle pollution, the effects of smoke remain a key factor in pollution exposures. Specifically, last year’s report had 1,280 red days and 231 purple days, and this year’s report had 960 red days and 182 purple days which is an improvement even though still among historically higher values. These are the levels of the pollutant that carry strong health warnings on the Air Quality Index. On red Unhealthy days, not only are members of sensitive groups likelier to “experience more serious health effects,” but also “some members of the general public may experience health effects.” On purple Very Unhealthy days, “the risk of health effects is increased for everyone.”
Remarkably, despite the general improvement in the number of people living with failing grades compared to last year’s report, the total population that experienced at least one day when particle pollution reached the red, purple or maroon (Hazardous) air quality index categories did increase from 133.4 million to 145.0 million.
There were also 26 maroon Hazardous days, the highest category (when everyone is more likely to be affected) for which a health warning of emergency conditions is issued. Although this number is smaller than in each of the past four “State of the Air” reports, it is a sharp change from the zero to eight maroon days in each report from 2004 to 2019.
This year’s report finds that the health of 55.1 million people across 126 counties in 26 states was put at risk on severely polluted Very Unhealthy (purple) and Hazardous (maroon) days for fine particle pollution. Though one million fewer people than in last year’s report, it still drastically exceeds the findings in “State of the Air” 2024 by nearly 23 million people, with more than twice as many counties and states affected.
Flipping the ratio seen for ozone, of the worst 25 metropolitan areas for the daily measure of fine particle pollution, 18 improved but only 7 worsened compared with last year’s report. Rankings for short-term particle pollution showed more variability than did those for ozone except for seven of the worst eight cities, which remained within two places of their position in last year’s report. Eight metro areas saw their ranks for particle pollution change by more than ten places, and six of them worsened enough to be added to the Worst 25 list—most notably, Brownsville-Harlingen-Raymondville, Texas, falling from 82nd (and a “D” grade) to 4th worst, and McAllen-Edinburg, Texas jumping from 125th (and a “C” grade) to 10th worst, both with local counties posting “F” grades for their highest-ever weighted averages. The other four were Bend, Oregon (also posting its worst weighted average); El Centro, California; Phoenix-Mesa, Arizona; and Boise City-Mountain Home-Ontario, Idaho-Oregon.
This leapfrogging meant that six metro areas improved enough to leave the Worst 25 list. All of them cut their worst counties’ weighted averages by at least half: Fargo-Wahpeton, North Dakota-Minnesota; Missoula, Montana; Redding-Red Bluff, California; Reno-Carson City-Gardnerville Ranchos, Nevada-California; Sacramento-Roseville, California; and Spokane-Spokane Valley-Coeur d'Alene, Washington-Idaho.
In other good news, comparing cities that ranked the worst 25 in this year’s report with those in last year’s, the average number of days per year that the people in these cities experienced high levels of fine particle pollution decreased by more than three days (still a seriously poor weighted average of 12.9 days). Five of the worst 25 metro areas posted their best-ever weighted averages: Both Fresno-Hanford-Corcoran, California and San Jose-San Francisco-Oakland, California recorded their lowest weighted averages for the second consecutive year. Bakersfield-Delano, California, Logan, Utah-Idaho and Salt Lake City-Provo-Orem, Utah-Idaho also posted their lowest levels. Among those on the Worst 25 list, four metro areas posted the largest improvements in their worst counties’ weighted averages of days with spikes in particle pollution in this year’s report: Bakersfield-Delano, California, with 18.1 fewer bad air days; Visalia, California, with 17.5 fewer; Fresno-Hanford-Corcoran, California, down by 12.3; and Yakima, Washington whose change from 13.8 to 5.8 improved its ranking from 8th worst in last year’s report to 24th.
The geographical distribution of cities on the Worst 25 list for short-term fine particle pollution, though still predominant in western states, is less focused on California. California retains its position of being the state with the most metro areas on the list with 6 of the 25 most-polluted cities. In the West, Oregon claims 3; followed by North Dakota, Texas, Utah and Washington, with 2 each. Lastly Alaska, Arizona, Idaho and Montana each have one. They are joined this year by four cities with their worst counties in three more easterly states—Indiana and Michigan each with one, and Pennsylvania with two.
Page last updated: March 11, 2026