Wyoming Air Quality
EPA monitor data through 2025 · Updated August 13, 2026 · Methods
In 2025, Wyoming recorded 30 days above an Air Quality Index of 100, the level at which EPA begins warning sensitive groups, out of 365 days with monitoring data. Most of those bad days were driven by fine particles. Under the AQI rules that applied before 2013, the same air would have scored 28 days. Since 2000, unhealthy days are 115% higher on a consistent definition.
How to read a statewide figure. The Air Quality Index describes one place at one time. A statewide number is the worst monitor anywhere in the state on each day, so it answers “was the air unhealthy somewhere in Wyoming?” — not “what did a typical resident breathe?” In a large state with many monitors it will read high even if most of the state was clean. EPA publishes the AQI for metropolitan areas rather than states for exactly this reason. For what people actually breathed, use the metro pages below.
Unhealthy days by year, scored two ways
EPA changed what an AQI of 100 means in 2013 and again in 2015, so a count published before those changes is not comparable to one published after. Each panel below applies a single fixed rulebook to every year, so each is internally consistent. Why this matters.
Scored by today's rules
Scored by the pre-2013 rules
What 2025 looked like
| Air quality category | Days | Share of monitored days |
|---|---|---|
| Good | 98 | 27% |
| Moderate | 237 | 65% |
| Unhealthy for sensitive groups | 17 | 5% |
| Unhealthy or worse | 13 | 4% |
Median AQI 61 · 90th-percentile AQI 96 · worst day 723. Scored under current rules.
What drove the unhealthy days
Of the 30 days above 100 in 2025, 2 were driven by ozone and 4 by fine particles, with 24 from another pollutant. The two behave differently. Ozone peaks on hot sunny afternoons; fine particles now spike mainly with wildfire smoke. In the western United States, ozone is a different problem: the floor is rising, with even the cleanest summer days at high elevation now near 40 ppb, and bad years track wildfire seasons. Domestic emission cuts have less room to work against that.
The unhealthy days in 2025
Every day the index passed 100, what it reached, and which pollutant drove it. 2 of these 30 would not have counted as unhealthy under the pre-2013 rules.
| Date | Peak AQI | Driven by | Pre-2013 score |
|---|---|---|---|
| Jan 16 | 181 | Coarse particles | 181 |
| Jan 17 | 283 | Coarse particles | 283 |
| Jan 21 | 104 | Coarse particles | 104 |
| Feb 1 | 175 | Coarse particles | 175 |
| Feb 23 | 283 | Coarse particles | 283 |
| Feb 25 | 144 | Coarse particles | 144 |
| Mar 16 | 171 | Coarse particles | 171 |
| Apr 9 | 109 | Coarse particles | 109 |
| Apr 13 | 101 | Ozone | 87 (not unhealthy) |
| May 10 | 108 | Ozone | 93 (not unhealthy) |
| May 13 | 115 | Coarse particles | 115 |
| Jun 10 | 103 | Coarse particles | 103 |
| Jun 11 | 113 | Coarse particles | 113 |
| Jun 20 | 406 | Coarse particles | 415 |
| Jul 9 | 116 | Coarse particles | 116 |
| Jul 17 | 103 | Coarse particles | 103 |
| Aug 14 | 103 | Coarse particles | 103 |
| Aug 23 | 164 | Fine particles | 156 |
| Aug 24 | 121 | Fine particles | 118 |
| Aug 26 | 157 | Fine particles | 149 |
| Sep 4 | 154 | Fine particles | 139 |
| Nov 2 | 139 | Coarse particles | 139 |
| Nov 4 | 109 | Coarse particles | 109 |
| Nov 6 | 127 | Coarse particles | 127 |
| Nov 24 | 104 | Coarse particles | 104 |
| Dec 2 | 119 | Coarse particles | 119 |
| Dec 9 | 723 | Coarse particles | 701 |
| Dec 12 | 151 | Coarse particles | 151 |
| Dec 17 | 723 | Coarse particles | 701 |
| Dec 19 | 444 | Coarse particles | 450 |
Metro areas in Wyoming
Ranked by unhealthy days in their latest year. These are the geographies EPA actually reports the AQI for.
| Metro area | Unhealthy days | Pre-2013 rules | Main driver |
|---|---|---|---|
| Laramie, WY | 11 | 11 | ozone and fine particles equally |
| Rock Springs, WY | 8 | 8 | ozone and fine particles equally |
| Gillette, WY | 2 | 2 | ozone and fine particles equally |
| Cheyenne, WY | 1 | 0 | ozone |
| Casper, WY | 0 | 0 | ozone and fine particles equally |
| Evanston, WY | 0 | 0 | ozone and fine particles equally |
| Jackson, WY-ID | 0 | 0 | ozone and fine particles equally |
| Riverton, WY | 0 | 0 | ozone and fine particles equally |
| Sheridan, WY | 0 | 0 | ozone and fine particles equally |
The full series
| Year | Unhealthy days, current rules | Pre-2013 rules | Days monitored |
|---|---|---|---|
| 2000 | 26 | 13 | 366 |
| 2001 | 23 | 14 | 365 |
| 2002 | 39 | 23 | 365 |
| 2003 | 43 | 26 | 365 |
| 2004 | 21 | 12 | 366 |
| 2005 | 32 | 23 | 365 |
| 2006 | 25 | 13 | 365 |
| 2007 | 28 | 19 | 365 |
| 2008 | 26 | 24 | 366 |
| 2009 | 16 | 9 | 365 |
| 2010 | 9 | 3 | 365 |
| 2011 | 28 | 20 | 365 |
| 2012 | 53 | 32 | 366 |
| 2013 | 11 | 6 | 365 |
| 2014 | 10 | 9 | 365 |
| 2015 | 14 | 6 | 365 |
| 2016 | 4 | 2 | 366 |
| 2017 | 23 | 16 | 365 |
| 2018 | 20 | 12 | 365 |
| 2019 | 16 | 10 | 365 |
| 2020 | 37 | 35 | 366 |
| 2021 | 49 | 30 | 365 |
| 2022 | 30 | 30 | 365 |
| 2023 | 29 | 21 | 365 |
| 2024 | 46 | 36 | 366 |
| 2025 | 30 | 28 | 365 |
Sources
- EPA AirData daily monitor files, recomputed under both breakpoint tables. Methods and validation.
- Download the full dataset for every state and metro.