St. Louis Air Quality in Spring
Across 2019–2025, St. Louis's spring (March–May) air quality had a median AQI of 56 (Moderate) over 644 monitored days in the St. Louis, MO-IL area. 2.2% of spring days (14 of 644) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 62.9% of days. The cleanest spring on record here was 2022 (median AQI 54, 0 days above 100) and the worst was 2023 (median 62, 7 days above 100, peak AQI 147).
- Good: 28.7%
- Moderate: 69.1%
- Unhealthy for Sensitive Groups: 1.9%
- Unhealthy or worse: 0.3%
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 spring?
Moderate on a typical day: median AQI 56 across 2019–2025, with 2.2% of spring days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓28.7% of spring days were Good (AQI 0–50), 69.1% Moderate (51–100).
- ✓14 days of 644 reached AQI 101+; the spring peak was 738.
- ✓Cleanest month: April; worst month: May.
Frequently asked questions
What is the air quality like in St. Louis in spring?▾
Across 2019–2025, the median daily AQI in St. Louis in spring was 56 (Moderate). 28.7% of days were Good, 69.1% Moderate, and 2.2% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is spring a good time for outdoor exercise in St. Louis?▾
A typical spring day in St. Louis is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 45 of spring days (2.2%) 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 spring air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 62.9% of spring days in St. Louis. The highest spring AQI recorded in 2019–2025 was 738 (Hazardous), in 2023.
St. Louis spring air quality, year by year
St. Louis spring 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 | 0 | 100 | PM2.5 |
| 2020 | 92 | 55 | 1 | 105 | PM2.5 |
| 2021 | 92 | 58 | 2 | 126 | PM2.5 |
| 2022cleanest | 92 | 54 | 0 | 100 | PM2.5 |
| 2023worst | 92 | 62 | 7 | 147 | PM2.5 |
| 2024 | 92 | 55 | 2 | 142 | PM2.5 |
| 2025 | 92 | 54 | 2 | 738 | PM2.5 |
What spring air means in St. Louis
A typical spring day in St. Louis is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 45 of spring days (2.2%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Spring's median AQI of 56 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 Spring AQI across every EPA metro area (307,196 metro-days, 2019–2025) is 43, so St. Louis runs above the national Spring norm; 2.2% of its Spring days topped AQI 100 versus 0.8% nationally (above average).
Within the season, April is the cleanest month (median AQI 55, 1.0% of days above 100) and May the worst (median 57, 3.2% 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.