St. Louis Air Quality in August
Across 2019–2025, St. Louis's August air quality had a median AQI of 58 (Moderate) over 217 monitored days in the St. Louis, MO-IL area. 4.1% of August days (9 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 64.1% of days. The cleanest August on record here was 2023 (median AQI 56, 0 days above 100) and the worst was 2019 (median 56, 3 days above 100, peak AQI 156).
- Good: 16.1%
- Moderate: 79.7%
- Unhealthy for Sensitive Groups: 3.2%
- Unhealthy or worse: 0.9%
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 August?
Moderate on a typical day: median AQI 58 across 2019–2025, with 4.1% of August days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓16.1% of August days were Good (AQI 0–50), 79.7% Moderate (51–100).
- ✓9 days of 217 reached AQI 101+; the August peak was 156.
- ✓Best August: 2023; worst August: 2019.
Frequently asked questions
What is the air quality like in St. Louis in August?▾
Across 2019–2025, the median daily AQI in St. Louis in August was 58 (Moderate). 16.1% of days were Good, 79.7% Moderate, and 4.1% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is August a good time for outdoor exercise in St. Louis?▾
A typical August day in St. Louis is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 24 of August days (4.1%) 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 August air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 64.1% of August days in St. Louis. The highest August AQI recorded in 2019–2025 was 156 (Unhealthy), in 2019.
St. Louis August air quality, year by year
St. Louis August air quality by year (St. Louis, MO-IL, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 31 | 56 | 3 | 156 | O3 |
| 2020 | 31 | 58 | 1 | 105 | PM2.5 |
| 2021 | 31 | 64 | 2 | 122 | PM2.5 |
| 2022 | 31 | 57 | 0 | 80 | PM2.5 |
| 2023cleanest | 31 | 56 | 0 | 93 | PM2.5 |
| 2024 | 31 | 58 | 2 | 151 | PM2.5 |
| 2025 | 31 | 56 | 1 | 142 | O3 |
What August air means in St. Louis
A typical August day in St. Louis is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 24 of August days (4.1%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
August's median AQI of 58 is in line with St. Louis's whole-year median of 58, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median August AQI across every EPA metro area (104,152 metro-days, 2019–2025) is 45, so St. Louis runs above the national August norm; 4.1% of its August days topped AQI 100 versus 3.5% nationally (about the same).
August is part of St. Louis's summer season (June, July, August); the summer page pools all three months.
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 month 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.