Bad Air Days in Mesa County, Colorado: 2 a Year
2 bad air days a year
Fewer bad air days than most monitored US counties. Ranked 496 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (19% particle days).
When the bad days come in Mesa
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in August and June and July and May. Averaged over 2016 to 2025.
What to buy, and what not to
- 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
In 2000 to 2009 this county averaged 2 bad days a year; in 2016 to 2025, 2. Not much has changed. The worst recent year was 2024, with 7 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2018-06-11 | 150 | Ozone |
| 2021-08-07 | 139 | PM2.5 |
| 2024-07-22 | 136 | Ozone |
| 2024-07-23 | 126 | Ozone |
| 2018-06-12 | 112 | Ozone |
The air on a normal day
Across 3,652 monitored days from 2016 to 2025, the air in Mesa County rated Good on 65% of them, less often than the 72% typical of monitored counties, and Moderate on 34%. The median day sat at AQI 46; one day in ten went above 67.
The pollutant setting the AQI on an ordinary day here:
- ozone77%2,821 days
- fine particles (PM2.5)22%821 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 238 | 127 | 0 | 0 | 46 | 97 |
| 2024 | 366 | 215 | 144 | 7 | 0 | 48 | 136 |
| 2023 | 365 | 246 | 119 | 0 | 0 | 46 | 90 |
| 2022 | 365 | 282 | 82 | 1 | 0 | 44 | 108 |
| 2021 | 365 | 247 | 116 | 2 | 0 | 46 | 139 |
| 2020 | 366 | 262 | 101 | 3 | 0 | 44 | 108 |
| 2019 | 364 | 238 | 125 | 1 | 0 | 47 | 101 |
| 2018 | 365 | 193 | 167 | 5 | 0 | 49 | 150 |
| 2017 | 365 | 213 | 151 | 1 | 0 | 48 | 101 |
| 2016 | 366 | 245 | 120 | 1 | 0 | 47 | 102 |
| 2015 | 365 | 225 | 137 | 3 | 0 | 48 | 105 |
| 2014 | 365 | 216 | 148 | 1 | 0 | 48 | 101 |
| 2013 | 365 | 225 | 136 | 4 | 0 | 47 | 117 |
| 2012 | 366 | 190 | 165 | 11 | 0 | 50 | 122 |
| 2011 | 365 | 191 | 164 | 10 | 0 | 50 | 119 |
| 2010 | 365 | 217 | 142 | 6 | 0 | 48 | 120 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Jefferson County28/yr
- Teller Countythin data
- Douglas County20/yr
- Larimer County18/yr
- Boulder County13/yr
- Weld County12/yr
- Arapahoe County12/yr
- Denver County12/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.