Metro area air quality · 2025
St. Louis, MO-IL
Median AQI 56 (Moderate). 31.2% of monitored days rated Good across this metro's EPA monitoring network.
- 56
- Median AQI
- 31.2%
- Good-air days
- 4
- Unhealthy days
- 4%
- Cleaner than US metros
St. Louis, MO-IL posted a 2025 median AQI of 56 (Moderate) with 31.2% Good days
According to the U.S. EPA Air Quality System, the St. Louis, MO-IL CBSA recorded a median AQI of 56 across 365 monitored days in 2025, with 31.2% rated Good and 4 unhealthy or worse. This is an annual metro comparison, not a live advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US metros
- The St. Louis, MO-IL CBSA's 31.2% Good-day share places it cleaner than 4% of US metros in 2025.
- Closest median-AQI peer
- Chicago-Naperville-Elgin, IL-IN-WI (29.9% Good, median AQI 56) is the closest nationwide median-AQI peer to St. Louis, MO-IL.
- 2020–2025 Good-day shift
- St. Louis, MO-IL's Good-day share moved +9.9 points from 2020 to 2025 (median AQI -2).
- Median AQI
- Median AQI: 56
Aggregated from EPA Air Quality System (2025), 365 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 56 with 31.2% of 365 monitored days in the Good band.
- 56
- median AQI · Moderate
- 31.2%
- days rated Good
- 4%
- cleaner than US metros
- 738
- worst single reading
4 days reached Unhealthy or worse across the metro's monitors in 2025.
Annual release change
What changed in the 2025 EPA annual release
- St. Louis, MO-IL metro's peak single-day AQI rose from 165 to 738 between the 2024 and 2025 EPA annual releases, a change of +573 points.
- St. Louis, MO-IL metro's Unhealthy-category days fell from 3 to 2 between the 2024 and 2025 EPA annual releases, a change of -1 days.
Insights: St. Louis, MO-IL metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 56 over 365 measured days in 2025, which corresponds to a Moderate band and a Poor metro-wide health grade. The monitored-day split lands at 114 Good days (31%), 236 Moderate (65%), and 11 Unhealthy-for-Sensitive-Groups (3%). The 90th-percentile AQI finished at 84 while the highest single-day reading hit 738 (Hazardous). Metro residents averaged roughly 9.4 clean-air days per 30-day window across the reporting year.
Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +9.9 points and the median AQI moved -2 points, which classifies the multi-year trajectory as improving. The annual record contains 4 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Metros with comparable AQI profiles include Chicago-Naperville-Elgin, IL-IN-WI (29.9% good, AQI 56); Cincinnati, OH-KY-IN (26.0% good, AQI 56); Bishop, CA (37.3% good, AQI 55).
Air Quality Summary
Median AQI
56
Moderate
Good Days
31.2%
114 of 365 days
Max AQI
738
Hazardous
Health Grade
Poor
90th pct: 84
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
114
31%
Moderate
236
65%
USG
11
3%
Unhealthy
2
1%
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 31.2% good air days. There were 4 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. Highest Good-day share: 2024 (33.1%, 117 of 353 monitored 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 | 114 | 236 | 2 | 56 | 738 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near St. Louis, MO-IL (56).
Chicago-Naperville-Elgin, IL-IN-WI
Median AQI 56 · 29.9% Good-day share
Cincinnati, OH-KY-IN
Median AQI 56 · 26.0% Good-day share
Bishop, CA
Median AQI 55 · 37.3% Good-day share
Brownsville-Harlingen, TX
Median AQI 57 · 29.9% Good-day share
Hanford-Corcoran, CA
Median AQI 57 · 34.5% Good-day share
Little Rock-North Little Rock-Conway, AR
Median AQI 55 · 31.2% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to St. Louis, MO-IL's 4 (independent of median AQI).
Bakersfield, CA
4 unhealthy-or-worse days · median AQI 70
Bismarck, ND
4 unhealthy-or-worse days · median AQI 40
Dickinson, ND
4 unhealthy-or-worse days · median AQI 38
New York-Newark-Jersey City, NY-NJ-PA
4 unhealthy-or-worse days · median AQI 53
Wausau, WI
4 unhealthy-or-worse days · median AQI 36
Albuquerque, NM
3 unhealthy-or-worse days · median AQI 61
More Air Quality Data
Explore EPA air quality rankings and guides across U.S. metros and counties.
Cleanest Metro Areas
U.S. metros ranked by their share of Good air-quality days.
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 56 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
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Every figure on PlainAirData 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.