Metro area air quality · 2025
St. Louis, MO-IL
Median AQI 52 (Moderate). 42.1% of monitored days rated Good across this metro's EPA monitoring network.
- 52
- Median AQI
- 42.1%
- Good-air days
- 3
- Unhealthy days
- 7%
- Cleaner than US metros
Aggregated from EPA Air Quality System (2025), 304 monitored days. EPA AQS →
The verdict
The St. Louis, MO-IL metro runs moderate on the EPA scale, among the more polluted US metros, a median AQI of 52 with 42.1% of 304 monitored days in the Good band.
- 52
- median AQI · Moderate
- 42.1%
- days rated Good
- 7%
- cleaner than US metros
- 738
- worst single reading
3 days reached Unhealthy or worse across the metro's monitors in 2025.
Insights: St. Louis, MO-IL metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 52 over 304 measured days in 2025, which corresponds to a Moderate band and a Poor metro-wide health grade. The monitored-day split lands at 128 Good days (42%), 168 Moderate (55%), and 5 Unhealthy-for-Sensitive-Groups (2%). The 90th-percentile AQI finished at 80 while the highest single-day reading hit 738 (Hazardous). Metro residents averaged roughly 12.6 clean-air days per 30-day window across the reporting year.
Across the 2020–2025 trend window, good days shifted by +48 and the median AQI moved -6 points, which classifies the multi-year trajectory as improving. The metro recorded 3 unhealthy-or-worse days combined, on those days the EPA recommends that sensitive groups limit prolonged outdoor exertion, and many schools and athletic programs adjust outdoor activity accordingly. Metros with comparable AQI profiles include Atlanta-Sandy Springs-Roswell, GA (45.3% good, AQI 52); El Dorado, AR (44.0% good, AQI 52); Greeley, CO (42.7% good, AQI 52).
Air Quality Summary
Median AQI
52
Moderate
Good Days
42.1%
128 of 304 days
Max AQI
738
Hazardous
Health Grade
Poor
90th pct: 80
AQI Day Breakdown (2025)
Distribution of 304 monitored days across EPA AQI categories.
Good
128
42%
Moderate
168
55%
USG
5
2%
Unhealthy
1
0%
Very Unhealthy
0
0%
Hazardous
2
1%
Health Impact Assessment
The St. Louis, MO-IL metro area's air quality is rated Poor based on 42.1% good air days. There were 3 unhealthy days in 2025 when outdoor activity should be limited.
Air quality posed significant health risk in 2025. Sensitive groups, including people with asthma, COPD, cardiovascular conditions, children, pregnant women, and adults over 65, should monitor AirNow.gov alerts and limit outdoor activity on Unhealthy (AQI 151+) and Very Unhealthy (201+) days. Peak readings reached AQI 738, beyond EPA's standard 0-500 scale, indicating an extreme event.
Sensitive group advisory
People with asthma, COPD, heart disease, children, pregnant women, and adults 65+ should follow EPA AQI alerts daily and limit outdoor exertion when AQI exceeds 100. Real-time conditions: airnow.gov.
Note: EPA's standard AQI scale caps at 500. The 738 peak reading represents an extreme event extrapolated beyond the index's design range. See EPA wildfire smoke guidance.
How does the St. Louis, MO-IL metro compare?
How St. Louis, MO-IL compares
5-Year Air Quality Trend
Air quality is improving in the St. Louis, MO-IL metro. Best year: 2025 (128 good days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 80 | 275 | 1 | 58 | 156 |
| 2021 | 45 | 305 | 2 | 59 | 187 |
| 2022 | 81 | 269 | 0 | 58 | 147 |
| 2023 | 51 | 290 | 3 | 60 | 185 |
| 2024 | 117 | 233 | 3 | 55 | 165 |
| 2025 | 128 | 168 | 1 | 52 | 738 |
Metros with Similar Air Quality
Metro areas across the US with a similar median AQI to St. Louis, MO-IL.
More Air Quality Data
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Cleanest Metro Areas
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Worst Air Quality
Counties and metros with the most unhealthy air days.
All Metro Areas
Annual AQI by CBSA for every monitored U.S. metro area.
Best and Worst City Air
What drives urban air quality and how metro areas compare.
Air Quality Guides
Frequently Asked Questions
What is the air quality in the St. Louis, MO-IL metro area? ▼
How many unhealthy air days does St. Louis, MO-IL have? ▼
Is air quality in St. Louis, MO-IL getting better or worse? ▼
What does AQI 52 mean for health? ▼
What is the 90th percentile AQI for St. Louis, MO-IL? ▼
How does St. Louis, MO-IL compare to other metro areas? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset, 2020–2025. See our methodology for how AQI, median, and coverage figures are computed.
Read our methodology , how this data is sourced, computed, and verified.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary files (metro-level) · 2020–2025
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.