EPA air quality + NOAA smoke
Colorado air quality by county
Bad-air days, typical county
8
per year, AQI over 100 (US: 2.4)
Smoke days, average county
16
per year, medium or heavy plume (US: 24)
Mold pros licensed?
No state license
found in our check
Wildfire smoke days by year
Days with a medium or heavy smoke plume overhead, averaged across Colorado's 64 counties. Smoke days come from NOAA satellite analysts, who draw where smoke plumes are overhead each day. A plume overhead does not always reach the ground, so these days measure exposure risk, not what you breathed. We count only medium and heavy plumes.
Every monitored Colorado county
Sorted by bad-air days. EPA monitors 21 of 64 counties; the rest have smoke data only.
| County | Good days | Bad days / yr | Main pollutant | Worst AQI | Smoke days / yr |
|---|---|---|---|---|---|
| Jefferson | 58.5% | 30.8 | ozone | 174 (2024) | 17 |
| Douglas | 60.2% | 21.4 | ozone | 177 (2021) | 17 |
| Larimer | 46.9% | 19.8 | ozone | 161 (2024) | 19 |
| Denver | 40.1% | 16.6 | ozone | 179 (2023) | 19 |
| Weld | 42.9% | 16.4 | ozone | 164 (2024) | 21 |
| Arapahoe | 60.5% | 15.2 | ozone | 161 (2021) | 19 |
| Adams | 49% | 13 | ozone | 174 (2023) | 20 |
| Boulder | 54.5% | 12.2 | ozone | 181 (2023) | 18 |
| Clear Creek | 61.5% | 9.4 | ozone | 154 (2021) | 15 |
| El Paso | 63.7% | 9.2 | ozone | 166 (2024) | 17 |
| Gilpin | 72% | 8 | ozone | 151 (2021) | 15 |
| Garfield | 57.7% | 4.4 | ozone | 158 (2021) | 16 |
| Rio Blanco | 66.3% | 4 | ozone | 166 (2023) | 17 |
| Pueblo | 77% | 3.2 | ozone | 143 (2024) | 17 |
| La Plata | 66.1% | 2.8 | ozone | 240 (2024) | 10 |
| Mesa | 67.3% | 2 | ozone | 139 (2021) | 15 |
| Archuleta | 86.7% | 1.4 | ozone | 227 (2022) | 9 |
| Prowers | 93% | 1.4 | coarse dust (PM10) | 652 (2025) | 20 |
| Gunnison | 71.4% | 0.8 | ozone | 115 (2025) | 11 |
| Montezuma | 77.1% | 0.8 | ozone | 115 (2021) | 10 |
| Routt | 98% | 0 | coarse dust (PM10) | 87 (2025) | 18 |
Most smoke days in Colorado: Phillips (28 days), Sedgwick (27 days), Logan (26 days), Yuma (25 days), Kit Carson (22 days).
EPA's Air Quality Index runs from 0 to 500. Up to 50 is good and 51-100 is moderate. Above 100 the air is unhealthy for sensitive groups (children, older adults, and people with asthma or heart or lung disease), and above 150 it is unhealthy for everyone. We count a county's bad days as days above 100, averaged over 2021-2025.
Mold and indoor air in Colorado
We found no Colorado state license for mold inspectors or remediators. Only a handful of states (Texas, Florida, New York, Louisiana and DC) license them. In Colorado, ask for a national certification and a written report, and avoid a company that profits from finding mold by also doing the cleanup.
No agency measures indoor air city by city, so nobody can tell you your home's numbers except a monitor in your home. What research does show: Americans spend about 90% of their time indoors (EPA's National Human Activity Pattern Survey, 2001), EPA studies in the 1980s often found indoor levels of some chemical vapors two to five times outdoor levels, and during wildfire smoke the particles get inside unless windows stay shut and a filter runs.
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Radon + air quality monitor
Radon zone 1: one device answers radon and air quality.
One battery device that tracks radon alongside particles, CO2, humidity and VOCs. Worth it in a radon zone 1 or 2 county where you want both answers.
Airthings View Plus (radon + PM2.5, CO2, VOC)
Price at Airthings, checked Oct 5, 2026Sold directly by Airthings
Airthings Wave Plus (radon + CO2, VOC)
Price at Airthings, checked Oct 5, 2026Sold directly by Airthings
HEPA air purifier
More unhealthy-air days than most US counties.
A true HEPA purifier sized to the room removes fine particles such as smoke, dust and pollen. Check the CADR rating and skip anything that makes ozone.
Levoit Core 300 (bedroom-size HEPA)
BudgetWinix 5520 (large-room HEPA)
Mid-rangeCO2 monitor
Stuffy bedroom or home office? CO2 tells you when to open a window.
CO2 is the best quick check on whether a room gets enough fresh air. Look for an NDIR sensor; cheap 'eCO2' sensors estimate it from VOCs instead of measuring it.
Aranet4 Home CO2 monitor (NDIR)
PremiumTemtop portable CO2 monitor
BudgetMold test kit
Musty smell or a past leak: a cheap first look before calling a pro.
A cheap first look. Settle-plate kits grow whatever spores are in the air, so they almost always show something; a visible patch or musty smell matters more than the plate.
Mold Armor DIY mold test kit
Budget12-test home mold test kit (air, HVAC, surfaces)
BudgetColorado cities: water, radon and air
Questions
How often is there wildfire smoke in Colorado?+
NOAA satellites placed a medium or heavy smoke plume over the average Colorado county on about 16 days a year from 2021-2025, below the typical US county. The worst year was 2021 (39 days on average). Smoke overhead does not always reach the ground.
Do mold inspectors need a license in Colorado?+
We found no Colorado state license for mold inspectors or remediators. Only a handful of states (Texas, Florida, New York, Louisiana and DC) license them. In Colorado, ask for a national certification and a written report, and avoid a company that profits from finding mold by also doing the cleanup.
Is indoor air worse than outdoor air?+
No agency measures indoor air city by city, so nobody can tell you your home's numbers except a monitor in your home. What research does show: Americans spend about 90% of their time indoors (EPA's National Human Activity Pattern Survey, 2001), EPA studies in the 1980s often found indoor levels of some chemical vapors two to five times outdoor levels, and during wildfire smoke the particles get inside unless windows stay shut and a filter runs.
Sources: EPA AirData annual AQI by county, 2021-2025; NOAA Hazard Mapping System smoke polygons, 2021-2025. Methodology.