SmogRank / World / Canada / Ontario / August 2024

Most polluted cities in Ontario, Canada, August 2024

29 cities in Ontario, Canada ranked by their average PM2.5 over the 31 days. Worst: Nepean at 16.3 µg/m³, #125 of 1,962 cities in the world. Cleanest: Chatham at 7.3. 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.

← Nepean 3% 3%0

Every city in Ontario, Canada ranked for August 2024, 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.

1Nepeanlow-cost sensors
3%
2Windsor
0%
3Barrie
0%
3Brantford
0%
3Milton
0%
6Newmarket
0%
6Toronto
0%
8Oakville
0%
9Ottawa
0%
10Guelph
0%
10Kitchener
0%
12Brampton
0%
12London
0%
12Thunder Bay
0%
15Greater Sudbury
0%
15Hamilton
0%
17Brooklin
0%
17Sarnia
0%
17Waterdown
0%
20Parry Sound
0%
20Peterborough
0%
22Sault Ste. Marie
0%
23St. Thomas
0%
24Mississauga
0%
24St. Catharines
0%
26Belleville
0%
26Kingston
0%
28North Bay
0%
29Chatham
0%

Low-cost sensors: consumer units, counted only in cities with no government-grade monitor; they read close to reference monitors on the whole, but 15 to 25% high in humid air. How we use them.

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, August 2024 · All cities in Canada, August 2024 · Ontario now

Use this board

SmogRank, most polluted cities in Ontario, Canada, PM2.5, August 2024, smogrank.com/ca/region/ontario/history/2024-08 (accessed 6 Oct 2026).

Download top 10 (PNG)

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.