SmogRank / United States / Missouri / St. Louis
St. Louis, month by month
St. Louis has a measured daily mean on 1,377 days since 1 January 2023. Its worst month was June 2023, at 72 US AQI (20.5 µg/m³), 259th of 1,603 cities on that month's world ranking. Its cleanest was April 2026, at 35 US AQI (6.3 µg/m³). 2025 averaged 48 US AQI (8.6 µg/m³), against 51 US AQI (9.1 µg/m³) in 2024.
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
St. Louis's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| June 2023 | 7220.5 µg/m³ | 259thof 1,603 | Eastern United States and Canada, June and July 2023 Eastern United States and Canada, May and June 2023 |
| May 2023 | 5813.0 µg/m³ | 212thof 1,600 | Eastern United States and Canada, May and June 2023 |
| July 2023 | 5511.5 µg/m³ | 467thof 1,432 | United States and Canada, July 2023 Eastern United States and Canada, June and July 2023 |
| July 2024 | 5511.3 µg/m³ | 520thof 2,566 | – |
| September 2023 | 5511.0 µg/m³ | 427thof 2,176 | – |
| July 2026 | 5511.0 µg/m³ | 1,114thof 2,784 | Northern United States and Canada, July 2026 |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
St. Louis's worst days
| Day | US AQI | Episode |
|---|---|---|
| 28 Jun 2023 | 16474.2 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 15 Mar 2025 | 15459.9 µg/m³ | Eastern United States, March 2025 |
| 1 Aug 2025 | 10637.7 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 20 Jul 2026 | 9633.4 µg/m³ | Northern United States and Canada, July 2026 |
| 6 Jun 2023 | 9432.1 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 7 Jun 2023 | 9231.3 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 27 Jun 2023 | 9231.0 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 16 Jul 2023 | 8828.9 µg/m³ | United States and Canada, July 2023 |
| 7 Jun 2025 | 8326.2 µg/m³ | Northern United States and Canada, May and June 2025 |
| 10 Jun 2023 | 8225.5 µg/m³ | Eastern United States and Canada, May and June 2023 |
Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, St. Louis, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/st-louis/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
St. Louis now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 20:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).