SmogRank / Canada / Ontario / St. Catharines
St. Catharines, month by month
St. Catharines has a measured daily mean on 1,287 days since 1 January 2023. Its worst month was June 2023, at 82 US AQI (25.8 µg/m³), 162nd of 1,603 cities on that month's world ranking. Its cleanest was May 2025, at 24 US AQI (4.3 µg/m³). 2025 averaged 40 US AQI (7.2 µg/m³), against 35 US AQI (6.3 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
Months without a mean, and why
2 months
| Month | Why |
|---|---|
| Mar 2023 | 11 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive. |
| Feb 2023 | 3 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
St. Catharines's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| June 2023 | 8225.8 µg/m³ | 162ndof 1,603 | Eastern United States and Canada, June and July 2023 United States and Canada, June 2023and 1 more |
| July 2026 | 6818.0 µg/m³ | 391stof 2,784 | Northern United States and Canada, July 2026 |
| August 2025 | 5913.5 µg/m³ | 493rdof 2,901 | South-eastern Canada and United States, August 2025 North-eastern United States and Canada, 29 July to 9 August 2025 |
| June 2025 | 5611.6 µg/m³ | 875thof 2,508 | Northern United States and Canada, May and June 2025 |
| July 2025 | 5511.5 µg/m³ | 942ndof 2,889 | North-eastern United States and Canada, 29 July to 9 August 2025 Northern United States and Canada, July 2025 |
| July 2023 | 5511.0 µg/m³ | 538thof 1,432 | United States and Canada, July 2023 Eastern United States and Canada, June and July 2023 |
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. Catharines's worst days
| Day | US AQI | Episode |
|---|---|---|
| 17 Jul 2026 | 187107.0 µg/m³ | Northern United States and Canada, July 2026 |
| 28 Jun 2023 | 186106.0 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 16 Jul 2026 | 186106.0 µg/m³ | Northern United States and Canada, July 2026 |
| 30 Jun 2023 | 16474.4 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 29 Jun 2023 | 15256.6 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 18 Jul 2026 | 14352.6 µg/m³ | Northern United States and Canada, July 2026 |
| 7 Jun 2023 | 13950.9 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 14 Jul 2025 | 13449.1 µg/m³ | Northern United States and Canada, July 2025 |
| 6 Jun 2023 | 13247.9 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 15 Jul 2026 | 12846.6 µg/m³ | Northern United States and Canada, July 2026 |
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. Catharines, Canada, 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/ca/st-catharines/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. Catharines now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 22:07 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).