SmogRank / World / Canada / Ontario / October 2023
Most polluted cities in Ontario, Canada, October 2023
29 cities in Ontario, Canada ranked by their average PM2.5 over the 31 days. Worst: Windsor at 7.8 µg/m³, #808 of 1,965 cities in the world. Cleanest: Thunder Bay at 4.0. A city needs measurements on 70% of the days to be ranked.
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.
- 1Windsor 0%
- 2London 0%
- 3Sarnia 0%
- 4Brantford 0%
- 4Toronto 0%
- 6Oakville 0%
- 7Kitchener 0%
- 8Milton 0%
- 9Barrie 0%
- 9Guelph 0%
- 9Mississauga 0%
- 9Waterdown 0%
- 13Chatham 0%
- 13Hamilton 0%
- 15Newmarket 0%
- 15Ottawa 0%
- 15St. Thomas 0%
- 18Brampton 0%
- 19Cornwall 0%
- 20Peterborough 0%
- 21Brooklin 0%
- 22St. Catharines 0%
- 23Kingston 0%
- 24Parry Sound 0%
- 25North Bay 0%
- 26Belleville 0%
- 27Greater Sudbury 0%
- 28Sault Ste. Marie 0%
- 29Thunder Bay 0%
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, October 2023, smogrank.com/ca/region/ontario/history/2023-10 (accessed 7 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.