Bad Air Days in Gilpin County, Colorado: 8 a Year
8 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 123 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 and August. Averaged over 2016 to 2025.
Is a purifier worth it here?
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
The record for Gilpin
The worst recent year was 2021, with 19 bad days on 363 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2021-09-07 | 151 | Ozone |
| 2021-07-12 | 150 | Ozone |
| 2024-07-31 | 150 | Ozone |
| 2024-07-23 | 147 | Ozone |
| 2021-07-19 | 143 | Ozone |
Most days, not the worst ones
Across 2,316 monitored days from 2019 to 2025, the air in Gilpin County rated Good on 73% of them, close to the 72% typical of monitored counties, and Moderate on 24%. The median day sat at AQI 46; one day in ten went above 70.
The pollutant setting the AQI on an ordinary day here:
- ozone100%2,316 days
Gilpin County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 360 | 273 | 86 | 1 | 0 | 46 | 101 |
| 2024 | 363 | 240 | 111 | 12 | 0 | 48 | 150 |
| 2023 | 365 | 258 | 103 | 4 | 0 | 47 | 129 |
| 2022 | 365 | 286 | 75 | 4 | 0 | 45 | 112 |
| 2021 | 363 | 250 | 94 | 19 | 1 | 46 | 151 |
| 2020 | 357 | 278 | 70 | 9 | 0 | 45 | 136 |
| 2019 | 143 | 117 | 25 | 1 | 0 | 45 | 115 |
*2025 may be a partial year in EPA's file.
Colorado compared
- 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.