Smoke: keep one room clean
Shut the windows and run an air purifier sized for the room.
Wildfire smoke guide →Air quality in Missouri, county by county
19 Missouri counties have enough EPA monitor data to count bad-air days. Weighted by population, they averaged about 5 days a year from 2021 to 2025 when the air was unhealthy for sensitive groups or worse.
CDC's model, which estimates every county from monitors and satellites, gives the average Missouri county, weighted by population, almost no smoky days (fine particles over 35.4 µg/m³, mostly wildfire smoke) and about 2 high-ozone days a year at its worst spot (2018 to 2022). See every county on the map.
Every Missouri county with monitors
Most bad-air days first. 11 have a full report. Compare with the worst and the cleanest counties in the US.
| County | Bad-air days a year | |
|---|---|---|
| St. Louis CityOzone and particles | 9.2 | |
| Clay CountyKansas CityOzone | 7.2 | |
| St. Charles CountyO'FallonOzoneparticles not measured | 6.2 | |
| St. Louis CountyFlorissantOzone | 6.0 | |
| Jefferson CountyArnoldOzone | 5.8 | |
| Lincoln CountyTroyOzoneparticles not measured | 4.2 | |
| Clinton CountyOzoneparticles not measured | 3.2 | |
| Perry CountyOzoneparticles not measured | 2.8 | |
| Ste. Genevieve CountyOzoneparticles not measured | 2.8 | |
| Jackson CountyKansas CitySmokeozone not measured | 2.2 | |
| Greene CountySpringfieldOzone and particles | 2.0 | |
| Buchanan CountySmokeozone not measured | 1.8 | |
| Cass CountyRaymoreOzone | 1.6 | |
| Andrew CountyOzoneparticles not measured | 1.4 | |
| Jasper CountyJoplinOzoneparticles not measured | 1.4 | |
| Boone CountyColumbiaOzoneparticles not measured | 1.0 | |
| Callaway CountyFultonOzoneparticles not measured | 1.0 | |
| Cedar CountyOzone | 1.0 | |
| Monroe CountyOzoneparticles not measured | 0.6 | |
| No Missouri county with a monitor matches “”. Counties without a monitor aren't listed; a neighbor's numbers are a fair guide, or find it on the map. | ||
Counties without a monitor aren't listed. Air doesn't stop at the county line, so a neighbor's numbers are a fair guide.
What helps on a bad-air day
Check AirNow for today's reading and tomorrow's forecast, then match the step to the pollutant.
Upgrade the furnace filter
MERV 13 catches far more smoke than thin fiberglass filters.
Furnace filters →Questions people ask about air quality in Missouri
Which county in Missouri has the worst air?
Among Missouri counties with EPA monitors, St. Louis City had the most bad-air days from 2021 to 2025: about 9 bad-air days a year with an AQI over 100. That's about 1 day in 40.
How often is the air bad in Missouri?
Weighted by population, Missouri counties with monitors averaged about 5 bad-air days a year from 2021 to 2025 with an AQI over 100, when children, older adults and people with asthma should cut back outdoors. That's about 1 day in 80.
Which county in Missouri has the cleanest air?
Of the 19 counties with enough monitor data, Monroe County had the fewest: 0.6 a year from 2021 to 2025. Counties without monitors aren't ranked.
Where can I check today's air quality in Missouri?
AirNow, run by the EPA and its partners, shows current readings and forecasts by ZIP code, and its fire and smoke map adds smoke plumes and low-cost sensors.
Sources: EPA AirData county AQI summaries, 2021 to 2025; CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone, 2018 to 2022. Updated November 8, 2026.