Utah County's winter inversions are real, but in the data they're more haze than hazard. In EPA's daily air quality index for 2021 through 2025, Utah County spent 45% of January days in the "moderate" range, yet none of those Januarys reached "unhealthy for sensitive groups." The county's worst air came in summer: 31 of its 33 days rated unhealthy for sensitive groups or worse fell between June and September, mostly from ozone.
Figures are our tally of the U.S. Environmental Protection Agency's AirData daily AQI files for Utah County, downloaded Nov. 9, 2026. Each day's value is the worst reading among the county's monitors. Background on inversions and burn rules is from the Utah Department of Environmental Quality and news reports.
What an inversion is
Normally air gets colder as you go up. In an inversion, warmer air sits on top of colder air in the valley and acts like a lid. Utah's Division of Air Quality says snow cover, long nights and calm wind set it up, and the mountains around the valley make it stronger. Pollution from tailpipes, wood smoke and industry builds up underneath, mostly as PM2.5, fine particles smaller than 2.5 microns. The state says most of that PM2.5 forms in the air from other pollutants rather than coming straight out of a tailpipe.
Utah County, month by month (2021-2025)
| Month | Days | Good | Moderate | Unhealthy for sensitive groups or worse | Average AQI |
|---|---|---|---|---|---|
| January | 155 | 85 | 70 | 0 | 49 |
| February | 141 | 114 | 27 | 0 | 42 |
| March | 155 | 149 | 6 | 0 | 43 |
| April | 150 | 103 | 47 | 0 | 50 |
| May | 155 | 69 | 86 | 0 | 56 |
| June | 150 | 21 | 125 | 4 | 65 |
| July | 155 | 11 | 130 | 14 | 73 |
| August | 155 | 42 | 102 | 11 | 66 |
| September | 150 | 89 | 59 | 2 | 53 |
| October | 155 | 126 | 29 | 0 | 42 |
| November | 150 | 111 | 38 | 1 | 42 |
| December | 155 | 95 | 59 | 1 | 47 |
Read it this way: January is the inversion month, with nearly half its days in the moderate range, but July is the county's worst month by every measure, with the highest average AQI and the most unhealthy days. March and October are the cleanest.
The worst days
| Date | AQI | Main pollutant |
|---|---|---|
| Aug. 2, 2024 | 151 | Ozone |
| Aug. 6, 2021 | 144 | PM2.5 |
| June 17, 2021 | 140 | Ozone |
| July 24, 2021 | 136 | Ozone |
| Aug. 7, 2021 | 136 | Ozone |
| Aug. 18, 2021 | 129 | PM2.5 |
| July 31, 2024 | 126 | Ozone |
Of the 33 days rated unhealthy for sensitive groups or worse, 25 were driven by summer ozone and 5 by summer PM2.5. Only 2 were winter PM2.5 days, the classic inversion. 2021 was the worst year, with 17 such days; 2023 and 2025 had one each.
Year by year
| Year | Unhealthy for sensitive groups or worse | Good days |
|---|---|---|
| 2021 | 17 | 192 |
| 2022 | 5 | 206 |
| 2023 | 1 | 201 |
| 2024 | 9 | 210 |
| 2025 | 1 | 206 |
| 2026 (Jan.-May) | 0 | 95 of 152 |
The 2025-26 winter was unusually warm and nearly snowless in Utah; see how much snow Provo gets. With little snow cover to set up inversions, Utah County had no unhealthy days from January through May 2026 in the data so far.
Compared with Salt Lake County
Over the same five years, Salt Lake County had 151 days rated unhealthy for sensitive groups or worse, against 33 in Utah County. Salt Lake County has more people and more monitors.
What to do on a bad-air day
- Check the forecast. The Utah Department of Environmental Quality's UtahAir app and air.utah.gov give each county's daily action alert and health forecast.
- Don't burn on mandatory days. When a mandatory action alert is in effect, wood and coal stoves and fireplaces must not be used; KUTV has reported penalties of up to $299 a day.
- Plan outdoor exercise around it. DEQ says to use its forecast to plan physical activity; on orange days, people sensitive to pollution should take it easier outdoors.
- Masks help with particles. DEQ says properly worn N95 and KN95 masks filter PM2.5.
- Head for the canyon. For a winter outing out of the valley, see Provo Canyon in winter.
Related guides
- Provo weather by month
- How much snow Provo gets
- Kids' crafts for snow, red-air and heat days
- Indoor tracks for winter running
- Utah County Health Department guide
Frequently Asked Questions
When is inversion season in Utah County?
How bad is the inversion in Utah County?
When is air quality worst in Utah County?
Is Utah County's air better than Salt Lake County's?
How do I check air quality in Provo?
Can I use my fireplace during an inversion?
Sources
The facts in this guide were checked against these sources. Hours, fees and rules change, so confirm anything time-sensitive with the source before you go. How we make Provo.com.
- Frequently Asked Questions About Utah's Inversion Season, Utah Department of Environmental Quality. Checked November 9, 2026.
- Seasonal wood burning restrictions begin Nov. 1, KUTV. Checked November 9, 2026.
- Pre-Generated Data Files: Daily AQI by County, 2021-2026, U.S. Environmental Protection Agency AirData. Checked November 9, 2026.
