SmogRank / World / Canada / Ontario / January 2025
Most polluted cities in Ontario, Canada, January 2025
27 cities in Ontario, Canada ranked by their average PM2.5 over the 31 days. Worst: Windsor at 8.5 µg/m³, #1,271 of 2,426 cities in the world. Cleanest: Sault Ste. Marie at 3.6. A city needs measurements on 70% of the days to be ranked.
About 0 people in these 3 cities breathed unhealthy air on an average day of January 2025.
Ranked by people: each city's population times its share of unhealthy days, those with a daily mean over 35.4 µg/m³ (US AQI 101+). That is how many people living there breathed unhealthy air on an average day. Only cities measured at 2 or more places at least 3 km apart are ranked: one monitor shouldn't speak for a whole city. Population is the city itself, not its wider metro area.
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
All cities in the world, January 2025 · All cities in Canada, January 2025 · Ontario now
Use this board
SmogRank, most polluted cities in Ontario, Canada, PM2.5, January 2025, smogrank.com/ca/region/ontario/history/2025-01 (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.