SmogRank / World / Canada / Ontario / January 2023

Most polluted cities in Ontario, Canada, January 2023

17 cities in Ontario, Canada ranked by their average PM2.5 over the 31 days. Worst: London at 10.6 µg/m³, #425 of 1,225 cities in the world. Cleanest: North Bay at 2.9. A city needs measurements on 70% of the days to be ranked.

OpenAQ's archive, where our readings come from, has almost none for 7 of these 31 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.

← London 0% 0.75%0
Every city in Ontario, Canada ranked for January 2023, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

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 2023 · All cities in Canada, January 2023 · Ontario now

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SmogRank, most polluted cities in Ontario, Canada, PM2.5, January 2023, smogrank.com/ca/region/ontario/history/2023-01 (accessed 6 Oct 2026).

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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.