SmogRank / World / Canada / Ontario / 2023
Most polluted cities in Ontario, Canada, 2023
17 cities in Ontario, Canada ranked by their average PM2.5 over the 365 days; 17 above the WHO annual guideline (5.0 µg/m³). Worst: Windsor at 12.3 µg/m³, #184 of 1,302 cities in the world. Cleanest: Sault Ste. Marie at 7.7. A city needs measurements on 70% of the days to be ranked.
OpenAQ's archive, where our readings come from, has almost none for 56 of these 365 days. Cities in the United States and Europe have them from the EPA's and the European Environment Agency's own records of the same monitors; elsewhere a city's average is over its other days. Why.
Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.
- 1North Bay 4%
- 2Windsor 3%
- 3Greater Sudbury 3%
- 4Barrie 3%
- 5Ottawa 3%
- 6Belleville 3%
- 7Peterborough 3%
- 8St. Catharines 2%
- 9Kitchener 2%
- 10Cornwall 2%
- 11Sarnia 2%
- 12St. Thomas 2%
- 13Brantford 2%
- 14Kingston 2%
- 15Sault Ste. Marie 2%
- 16London 2%
- 17Hamilton 1%
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
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SmogRank, most polluted cities in Ontario, Canada, PM2.5, 2023, smogrank.com/ca/region/ontario/history/2023 (accessed 6 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.