The American Lung Association has named Fremont County and Casper as having the cleanest air in the United States. At the same time, some Wyoming cities and counties received failing grades for certain types of air pollution.
Air quality monitors in South Pass, Lander and Riverton recorded the lowest levels in the U.S. for year-round particle pollution, according to the American Lung Association’s 2025 “State of the Air” report.
Fremont County, “Is in fact the cleanest county in the United States when it comes to year-round particles,” Will Barrett told Cowboy State Daily.
Barrett is the American Lung Association’s senior director for nationwide clean air advocacy.
“The report does help local communities with putting their local air quality in the context of the progress that’s been made and the fragility of that progress,” said Barrett, who raised concerns about federal funding cuts to air monitoring programs and noted the good news-bad news results for Wyoming in the 2025 report.
While Fremont County registered low 24-hour particle air pollution, Teton County received a failing grade in that category.
Maybe it was the Boulder Lake Fire or the Saddle Butte Fire in 2019 that kicked off a spike in poor air quality around Jackson. Barrett couldn’t pinpoint the exact cause of increased particle pollution in Teton County, but the data shows smoke billowing in starting the summer of 2019.
That’s when Jackson’s State or Local Air Monitoring Station (SLAMS) — which is shown online near the intersection of Gregory Lane and High School Road — started registering more days with high levels of particle pollution in the air.
This spike in particle pollution continued through 2022 and dropped off in 2023
“There were a lot of wildfire activities and some of that was in California and Oregon and Washington that would've blown across,” said Barrett.
Cleanest City Air
“In a notable achievement, Casper tied with Honolulu, Hawaii, for the No. 1 ranking on the list of cleanest cities for year-round particle pollution,” said Barrett. “We did see both Casper and Cheyenne ranking among the cleanest cities in the country for particle pollution.”
In Wyoming’s two largest cities, the wind could help blow out pollution that might linger in less windy cities, especially those in north-south valleys where air sits trapped.
“The air gets stagnant, so no wind and pollution can just build up for days and days at a time,” said Barrett, noting how wind and rain help.
“The particles are being dispersed through the air on windy days or rainy days,” said Barrett, noting, “Obviously the best way to reduce particles is to prevent them from happening in the beginning.”
Monitoring System
The Air Quality Division of the Wyoming Department of Environmental Quality (WDEQ) uses the EPA’s methodology for health-based standards, the agency says.
“The American Lung Association’s methodology for calculating ‘grades’ differs from EPA’s health-based standards methodology,” Kimberley Mazza, DEQ’s public information supervisor, told Cowboy State Daily.
Mazza confirmed Wyoming’s air can be significantly impacted by prolonged wildfire smoke from within and outside the state, and that influences how places are graded.
While wildfire smoke cannot be controlled by Wyoming’s air pollution regulations, Mazza said Wyoming can and does control emissions from industrial sources.
The Air Quality Division oversees the network of SLAMS in Wyoming and the air quality data gather feeds into a nationwide network of data-collecting sites, and this is what the American Lung Association uses to create its annual “State of the Air” report.
"After the collected ambient air monitoring data undergoes a thorough validation process, it is then submitted to the Environmental Protection Agency's Air Quality System (AQS), which serves as a central repository for air quality data," said Mazza. "The AQS integrates ambient air pollution data from thousands of monitors managed by the EPA, as well as state, local, and tribal air pollution control agencies."
“That’s the data set that we pull from for the report, in this case the 2021 through 2023 data," added Barrett.
With the release of its 2025 report, the American Lung Association is speaking out against rolling back the EPA’s work on air quality, including its regulation of the energy industry.
“There are a lot of specific policies that would help to continue cleanup in the oil and gas sector for the country,” said Barrett. “Those are all now at risk of going away. Those health protections and that's really the key message from our report this year is we need to save the mission of the U.S. EPA to be a public health protective agency.”
“We will see more asthma attacks, more exposure to cancer-causing pollutants, more premature death as the air becomes more polluted.”
More Mixed Results
The 2025 report’s findings about Sublette County demonstrate the mix of good and bad pollution levels found across Wyoming.
Like Teton County, Sublette County received an "F" grade. But not for particle pollution.
Instead, Sublette County was found to have high levels of ozone pollution.
In fact, the Upper Green River Basin — including Sublette County — remains classified as a nonattainment area under EPA standards.
Emissions from natural gas operations contribute to ground-level ozone, particularly during winter temperature inversions.
The EPA and the American Lung Association report that ground-level ozone causes respiratory inflammation, aggravating lung diseases like asthma, and increasing risks of cardiovascular issues and premature death due to prolonged exposure to airborne pollutants reacting with sunlight.
It’s not all bad news for Sublette County. It ranks in the Top 10 “Cleanest Counties for Year-Round Particle Pollution,” according to the 2025 report.
The report goes on to deliver good and bad news about the western states with some of the worst pollution in the country.
Los Angeles, Salt Lake City and Denver continue to be home to the dirtiest air.
But the 2025 report offers this hopeful tidbit: “It is worthwhile pointing out that a handful of western states experienced something of a respite in this year’s report. More counties improved than worsened in California, Idaho, Nevada, New Mexico and Wyoming, even though ozone levels in many of their counties continued to be unhealthy on many days.”
David Madison can be reached at david@cowboystatedaily.com.
