St. Louis Air Quality in April
Across 2019–2025, St. Louis's April air quality had a median AQI of 55 (Moderate) over 210 monitored days in the St. Louis, MO-IL area. 1.0% of April days (2 of 210) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 60.0% of days. The cleanest April on record here was 2022 (median AQI 53, 0 days above 100) and the worst was 2023 (median 59, 1 day above 100, peak AQI 103).
- Good: 33.3%
- Moderate: 65.7%
- Unhealthy for Sensitive Groups: 1.0%
- Unhealthy or worse: 0.0%
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 April?
Moderate on a typical day: median AQI 55 across 2019–2025, with 1.0% of April days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓33.3% of April days were Good (AQI 0–50), 65.7% Moderate (51–100).
- ✓2 days of 210 reached AQI 101+; the April peak was 133.
- ✓Best April: 2022; worst April: 2023.
Frequently asked questions
What is the air quality like in St. Louis in April?▾
Across 2019–2025, the median daily AQI in St. Louis in April was 55 (Moderate). 33.3% of days were Good, 65.7% Moderate, and 1.0% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is April a good time for outdoor exercise in St. Louis?▾
A typical April day in St. Louis is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 100 of April days (1.0%) 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 April air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 60.0% of April days in St. Louis. The highest April AQI recorded in 2019–2025 was 133 (Unhealthy for Sensitive Groups), in 2023.
St. Louis April air quality, year by year
St. Louis April 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 | 30 | 59 | 0 | 84 | O3 |
| 2020 | 30 | 54 | 0 | 84 | PM2.5 |
| 2021 | 30 | 55 | 0 | 93 | PM2.5 |
| 2022cleanest | 30 | 53 | 0 | 89 | PM2.5 |
| 2023worst | 30 | 59 | 1 | 103 | O3 |
| 2024 | 30 | 54 | 1 | 133 | O3 |
| 2025 | 30 | 56 | 0 | 84 | PM2.5 |
What April air means in St. Louis
A typical April day in St. Louis is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 100 of April days (1.0%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
April's median AQI of 55 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 April AQI across every EPA metro area (100,677 metro-days, 2019–2025) is 44, so St. Louis runs above the national April norm; 1.0% of its April days topped AQI 100 versus 0.7% nationally (about the same).
April is part of St. Louis's spring season (March, April, May); the spring 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.