St. Louis Air Quality in Summer
Across 2019–2025, St. Louis's summer (June–August) air quality had a median AQI of 62 (Moderate) over 644 monitored days in the St. Louis, MO-IL area. 10.3% of summer days (66 of 644) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 52.8% of days. The cleanest summer on record here was 2025 (median AQI 58, 4 days above 100) and the worst was 2023 (median 74, 16 days above 100, peak AQI 185).
- Good: 12.4%
- Moderate: 77.3%
- Unhealthy for Sensitive Groups: 8.7%
- Unhealthy or worse: 1.6%
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 is the air in St. Louis in summer?
Moderate on a typical day: median AQI 62 across 2019–2025, with 10.3% of summer days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓12.4% of summer days were Good (AQI 0–50), 77.3% Moderate (51–100).
- ✓66 days of 644 reached AQI 101+; the summer peak was 187.
- ✓Cleanest month: August; worst month: June.
Frequently asked questions
What is the air quality like in St. Louis in summer?▾
Across 2019–2025, the median daily AQI in St. Louis in summer was 62 (Moderate). 12.4% of days were Good, 77.3% Moderate, and 10.3% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in St. Louis?▾
A typical summer day in St. Louis is Moderate (median AQI 62): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 10 of summer days (10.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes St. Louis's summer air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 52.8% of summer days in St. Louis. The highest summer AQI recorded in 2019–2025 was 187 (Unhealthy), in 2023.
St. Louis summer air quality, year by year
St. Louis summer air quality by year (St. Louis, MO-IL, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 92 | 59 | 7 | 156 | O3 |
| 2020 | 92 | 61 | 9 | 156 | O3 |
| 2021 | 92 | 65 | 12 | 187 | PM2.5 |
| 2022 | 92 | 62 | 12 | 147 | PM2.5 |
| 2023worst | 92 | 74 | 16 | 185 | O3 |
| 2024 | 92 | 61 | 6 | 165 | PM2.5 |
| 2025cleanest | 92 | 58 | 4 | 142 | PM2.5 |
What summer air means in St. Louis
A typical summer day in St. Louis is Moderate (median AQI 62): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 10 of summer days (10.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Summer's median AQI of 62 is above St. Louis's whole-year median of 58, making it one of the area's dirtier periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so St. Louis runs above the national Summer norm; 10.3% of its Summer days topped AQI 100 versus 3.6% nationally (above average).
Within the season, August is the cleanest month (median AQI 58, 4.1% of days above 100) and June the worst (median 71, 17.6% above 100).
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 season 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.