St. Louis Air Quality in 2025
In 2025, St. Louis's air quality (St. Louis, MO-IL area) had a median daily AQI of 56 (Moderate) across 365 monitored days. 15 days (4.1%) reached Unhealthy for Sensitive Groups or worse, 114 were Good, and the year's peak AQI was 738 (Hazardous). Fine particulate matter (PM2.5) set the daily AQI on 224 of those days. The cleanest month of 2025 was January (median AQI 48, 0 days above 100) and the worst was September (median 73, 7 days above 100, peak 164).
- Good: 31.2%
- Moderate: 64.7%
- Unhealthy for Sensitive Groups: 3.0%
- Unhealthy or worse: 1.1%
Extra Protection for St. Louis Homes
Air quality in St. Louis is moderate (AQI 60), with fine particles (PM2.5) the main concern. A True-HEPA purifier gives sensitive groups — kids, seniors and anyone with asthma or allergies — cleaner air indoors on days like today.
Recommended: Coway AP-1512HH Mighty — True HEPA + carbon · CADR ~246 CFM · rooms up to 361 sq ft
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How was St. Louis's air quality in 2025?
Moderate on a typical day: median AQI 56, with 15 days above AQI 100 out of 365 monitored — the 3rd cleanest of 7 years on record for the area.
- ✓Peak AQI in 2025: 738 (Hazardous).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 224 days.
- ✓Cleanest month: January; worst: September.
Frequently asked questions
What was the average AQI in St. Louis in 2025?▾
EPA's Air Quality System puts St. Louis's (St. Louis, MO-IL) median daily AQI for 2025 at 56, which is Moderate. 15 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 738.
Which month had the worst air quality in St. Louis in 2025?▾
The cleanest month of 2025 was January (median AQI 48, 0 days above 100) and the worst was September (median 73, 7 days above 100, peak 164).
Was 2025 a good or bad year for St. Louis's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 3rd cleanest by days above AQI 100. 2025's median of 56 is in line with the area's typical annual median of 58.
St. Louis month by month in 2025
St. Louis air quality month by month, 2025 (St. Louis, MO-IL, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| Januarycleanest | 31 | 48 | 0 | 70 | PM2.5 |
| February | 28 | 52 | 0 | 71 | PM2.5 |
| March | 31 | 54 | 2 | 738 | O3 |
| April | 30 | 56 | 0 | 84 | PM2.5 |
| May | 31 | 52 | 0 | 87 | O3 |
| June | 30 | 63 | 2 | 119 | PM2.5 |
| July | 31 | 57 | 1 | 101 | PM2.5 |
| August | 31 | 56 | 1 | 142 | O3 |
| Septemberworst | 30 | 73 | 7 | 164 | O3 |
| October | 31 | 57 | 1 | 108 | PM2.5 |
| November | 30 | 59 | 1 | 109 | PM2.5 |
| December | 31 | 62 | 0 | 81 | PM2.5 |
How 2025 compares
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 3rd cleanest by days above AQI 100.
2025's median of 56 is in line with the area's typical annual median of 58.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in St. Louis
The latest EPA AirNow observation puts St. Louis's AQI at 60 (PM2.5). The figures above are multi-year annual statistics, not today's reading.
View current St. Louis air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (St. Louis, MO-IL), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.