Bad Air Days in Grand County, Utah: under 1 a Year
under 1 bad air day a year
Fewer bad air days than most monitored US counties. Ranked 741 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
Which months to watch
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in July. Averaged over 2016 to 2025.
Is a purifier worth it here?
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
The worst days on file
The worst recent year was 2024, with 2 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2024-07-22 | 105 | Ozone |
| 2024-07-23 | 105 | Ozone |
| 2024-05-20 | 97 | Ozone |
| 2024-10-07 | 96 | PM2.5 |
| 2025-07-25 | 96 | PM2.5 |
Most days, not the worst ones
Across 990 monitored days from 2023 to 2025, the air in Grand County rated Good on 60% of them, less often than the 72% typical of monitored counties, and Moderate on 40%. The median day sat at AQI 48; one day in ten went above 63.
The pollutant setting the AQI on an ordinary day here:
- ozone59%586 days
- fine particles (PM2.5)41%402 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 364 | 219 | 145 | 0 | 0 | 47 | 96 |
| 2024 | 365 | 229 | 134 | 2 | 0 | 48 | 105 |
| 2023 | 261 | 144 | 117 | 0 | 0 | 49 | 80 |
*2025 may be a partial year in EPA's file.
Elsewhere in Utah
- Salt Lake County30/yr
- Davis County15/yr
- Uintah County13/yr
- Weber County11/yr
- Utah County10/yr
- Duchesne County10/yr
- Cache County8/yr
- Tooele County8/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.