SmogRank / Episodes / Canada
South-eastern Canada and United States, August 2025
For 2 days, from 14 to 15 August 2025, 18 cities in Canada and the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Windsor, Ontario, Canada: 31.0 µg/m³ on 14 August, about 3.1× its usual 10.0.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 18 in 2 countries
Days 2 14 to 15 August 2025
Worst day 14 August 14 cities counted
Furthest above usual 3.9× Toronto
Day by day
Play 14 August 14 cities at twice their usual or more
Bay City Southfield Redford Ann Arbor Ypsilanti Dearborn Taylor Eastpointe Lincoln Park Lansing Toledo Chatham Wyoming Kalamazoo Jenison Lima Fort Wayne St. Thomas Holland Cleveland Heights Medina Shaker Heights Elkhart Painesville Akron South Bend Canton Warren Brantford Michigan City Youngstown Hermitage Erie Waterdown Portage Alliston Gary East Chicago Hammond Calumet City Chicago Barrie Dolton South Milwaukee Zion Milwaukee Northbrook Elmwood Park Oak Lawn Bridgeview Des Plaines Franklin Park Brookfield Waukesha Cary Naperville Joliet Elgin Buffalo Aurora Oconomowoc Appleton Peterborough Rockford Cleveland Detroit Grand Rapids Port Huron Windsor Newmarket London Sarnia Kitchener Hamilton Oakville Milton Guelph St. Catharines Brampton Green Bay Mississauga Toronto 11 Aug 12 13 14 15 16 17 18 Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.
How it spread
Windsor Windsor, 11 August: 14.7 µg/m³, 1.5× usual Windsor, 12 August: 15.5 µg/m³, 1.6× usual Windsor, 13 August: 13.5 µg/m³, 1.4× usual Windsor, 14 August: 31.0 µg/m³, 3.1× usual Windsor, 15 August: 28.2 µg/m³, 2.8× usual Windsor, 16 August: 23.7 µg/m³, 2.4× usual Windsor, 17 August: 10.3 µg/m³, 1.0× usual Windsor, 18 August: 3.5 µg/m³, 0.4× usual Toronto Toronto, 11 August: 18.5 µg/m³, 2.3× usual Toronto, 12 August: 14.3 µg/m³, 1.8× usual Toronto, 13 August: 11.2 µg/m³, 1.4× usual Toronto, 14 August: 30.8 µg/m³, 3.9× usual Toronto, 15 August: 18.2 µg/m³, 2.3× usual Toronto, 16 August: 17.2 µg/m³, 2.2× usual Toronto, 17 August: 7.0 µg/m³, 0.9× usual Toronto, 18 August: 2.9 µg/m³, 0.4× usual Milton Milton, 11 August: 17.3 µg/m³, 2.0× usual Milton, 12 August: 12.3 µg/m³, 1.4× usual Milton, 13 August: 11.1 µg/m³, 1.3× usual Milton, 14 August: 29.7 µg/m³, 3.4× usual Milton, 15 August: 20.4 µg/m³, 2.3× usual Milton, 16 August: 16.6 µg/m³, 1.9× usual Milton, 17 August: 6.5 µg/m³, 0.7× usual Milton, 18 August: 2.8 µg/m³, 0.3× usual Brampton Brampton, 11 August: 16.0 µg/m³, 2.0× usual Brampton, 12 August: 11.2 µg/m³, 1.4× usual Brampton, 13 August: 9.4 µg/m³, 1.2× usual Brampton, 14 August: 28.6 µg/m³, 3.6× usual Brampton, 15 August: 19.0 µg/m³, 2.4× usual Brampton, 16 August: 15.1 µg/m³, 1.9× usual Brampton, 17 August: 5.6 µg/m³, 0.7× usual Brampton, 18 August: 2.8 µg/m³, 0.4× usual Green Bay Green Bay, 11 August: 12.3 µg/m³, 1.6× usual Green Bay, 12 August: 11.5 µg/m³, 1.5× usual Green Bay, 13 August: 17.3 µg/m³, 2.2× usual Green Bay, 14 August: 28.4 µg/m³, 3.6× usual Green Bay, 15 August: 18.3 µg/m³, 2.3× usual Green Bay, 16 August: 7.9 µg/m³, 1.0× usual Green Bay, 17 August: 3.2 µg/m³, 0.4× usual Green Bay, 18 August: 2.6 µg/m³, 0.3× usual Oakville Oakville, 11 August: 15.5 µg/m³, 1.9× usual Oakville, 12 August: 11.5 µg/m³, 1.4× usual Oakville, 13 August: 10.8 µg/m³, 1.3× usual Oakville, 14 August: 28.1 µg/m³, 3.4× usual Oakville, 15 August: 18.2 µg/m³, 2.2× usual Oakville, 16 August: 14.7 µg/m³, 1.8× usual Oakville, 17 August: 6.3 µg/m³, 0.8× usual Oakville, 18 August: 2.7 µg/m³, 0.3× usual Hamilton Hamilton, 11 August: 13.7 µg/m³, 1.7× usual Hamilton, 12 August: 9.3 µg/m³, 1.1× usual Hamilton, 13 August: 9.3 µg/m³, 1.1× usual Hamilton, 14 August: 26.7 µg/m³, 3.3× usual Hamilton, 15 August: 21.9 µg/m³, 2.7× usual Hamilton, 16 August: 14.5 µg/m³, 1.8× usual Hamilton, 17 August: 7.2 µg/m³, 0.9× usual Hamilton, 18 August: 2.8 µg/m³, 0.3× usual London London, 11 August: 14.7 µg/m³, 1.8× usual London, 12 August: 10.2 µg/m³, 1.3× usual London, 13 August: 7.0 µg/m³, 0.9× usual London, 14 August: 25.5 µg/m³, 3.2× usual London, 15 August: 25.0 µg/m³, 3.1× usual London, 16 August: 17.8 µg/m³, 2.2× usual London, 17 August: 6.3 µg/m³, 0.8× usual London, 18 August: 2.8 µg/m³, 0.4× usual Guelph Guelph, 11 August: 14.7 µg/m³, 2.0× usual Guelph, 12 August: 11.2 µg/m³, 1.5× usual Guelph, 13 August: 9.4 µg/m³, 1.3× usual Guelph, 14 August: 25.4 µg/m³, 3.4× usual Guelph, 15 August: 20.0 µg/m³, 2.7× usual Guelph, 16 August: 14.9 µg/m³, 2.0× usual Guelph, 17 August: 5.4 µg/m³, 0.7× usual Guelph, 18 August: 2.4 µg/m³, 0.3× usual Mississauga Mississauga, 11 August: 14.0 µg/m³, 2.1× usual Mississauga, 12 August: 10.2 µg/m³, 1.5× usual Mississauga, 13 August: 9.3 µg/m³, 1.4× usual Mississauga, 14 August: 25.3 µg/m³, 3.7× usual Mississauga, 15 August: 15.8 µg/m³, 2.3× usual Mississauga, 16 August: 13.3 µg/m³, 2.0× usual Mississauga, 17 August: 5.6 µg/m³, 0.8× usual Mississauga, 18 August: 2.5 µg/m³, 0.4× usual Kitchener Kitchener, 11 August: 14.6 µg/m³, 1.9× usual Kitchener, 12 August: 10.4 µg/m³, 1.4× usual Kitchener, 13 August: 10.2 µg/m³, 1.3× usual Kitchener, 14 August: 25.3 µg/m³, 3.3× usual Kitchener, 15 August: 22.5 µg/m³, 3.0× usual Kitchener, 16 August: 15.6 µg/m³, 2.1× usual Kitchener, 17 August: 6.0 µg/m³, 0.8× usual Kitchener, 18 August: 2.6 µg/m³, 0.3× usual Newmarket Newmarket, 11 August: 18.2 µg/m³, 2.3× usual Newmarket, 12 August: 12.0 µg/m³, 1.5× usual Newmarket, 13 August: 9.8 µg/m³, 1.2× usual Newmarket, 14 August: 25.3 µg/m³, 3.2× usual Newmarket, 15 August: 14.7 µg/m³, 1.8× usual Newmarket, 16 August: 16.1 µg/m³, 2.0× usual Newmarket, 17 August: 6.1 µg/m³, 0.8× usual Newmarket, 18 August: 2.8 µg/m³, 0.4× usual Grand Rapids Grand Rapids, 11 August: 8.2 µg/m³, 0.9× usual Grand Rapids, 12 August: 5.7 µg/m³, 0.6× usual Grand Rapids, 13 August: 11.8 µg/m³, 1.2× usual Grand Rapids, 14 August: 25.2 µg/m³, 2.7× usual Grand Rapids, 15 August: 19.6 µg/m³, 2.1× usual Grand Rapids, 16 August: 14.5 µg/m³, 1.5× usual Grand Rapids, 17 August: 6.3 µg/m³, 0.7× usual Grand Rapids, 18 August: 3.3 µg/m³, 0.3× usual St. Catharines St. Catharines, 11 August: 12.6 µg/m³, 1.8× usual St. Catharines, 12 August: 10.8 µg/m³, 1.5× usual St. Catharines, 13 August: 6.8 µg/m³, 1.0× usual St. Catharines, 14 August: 25.0 µg/m³, 3.6× usual St. Catharines, 15 August: 20.5 µg/m³, 2.9× usual St. Catharines, 16 August: 13.8 µg/m³, 2.0× usual St. Catharines, 17 August: 8.0 µg/m³, 1.1× usual St. Catharines, 18 August: 2.7 µg/m³, 0.4× usual Sarnia Sarnia, 11 August: 13.3 µg/m³, 1.6× usual Sarnia, 12 August: 7.7 µg/m³, 0.9× usual Sarnia, 13 August: 6.5 µg/m³, 0.8× usual Sarnia, 14 August: 24.5 µg/m³, 3.0× usual Sarnia, 15 August: 27.0 µg/m³, 3.3× usual Sarnia, 16 August: 18.7 µg/m³, 2.3× usual Sarnia, 17 August: 5.5 µg/m³, 0.7× usual Sarnia, 18 August: 2.3 µg/m³, 0.3× usual Detroit Detroit, 11 August: 14.8 µg/m³, 1.6× usual Detroit, 12 August: 12.6 µg/m³, 1.3× usual Detroit, 13 August: 9.1 µg/m³, 1.0× usual Detroit, 14 August: 24.2 µg/m³, 2.5× usual Detroit, 15 August: 25.6 µg/m³, 2.7× usual Detroit, 16 August: 17.8 µg/m³, 1.9× usual Detroit, 17 August: 7.0 µg/m³, 0.7× usual Detroit, 18 August: 3.4 µg/m³, 0.4× usual Cleveland Cleveland, 11 August: 17.8 µg/m³, 1.8× usual Cleveland, 12 August: 15.8 µg/m³, 1.6× usual Cleveland, 13 August: 6.4 µg/m³, 0.6× usual Cleveland, 14 August: 16.6 µg/m³, 1.7× usual Cleveland, 15 August: 25.6 µg/m³, 2.6× usual Cleveland, 16 August: 21.1 µg/m³, 2.1× usual Cleveland, 17 August: 10.1 µg/m³, 1.0× usual Cleveland, 18 August: 3.8 µg/m³, 0.4× usual Port Huron Port Huron, 11 August: 12.2 µg/m³, 1.5× usual Port Huron, 12 August: 8.2 µg/m³, 1.0× usual Port Huron, 13 August: 6.7 µg/m³, 0.8× usual Port Huron, 14 August: 23.3 µg/m³, 2.9× usual Port Huron, 15 August: 25.3 µg/m³, 3.1× usual Port Huron, 16 August: 18.4 µg/m³, 2.3× usual Port Huron, 17 August: 5.5 µg/m³, 0.7× usual Port Huron, 18 August: 2.8 µg/m³, 0.3× usual 11 Aug 12 13 14 15 16 17 18 Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Toronto Ontario, Canada 1 14 August 8.0 3.9× Mississauga Ontario, Canada 1 14 August 6.8 3.7× Brampton Ontario, Canada 1 14 August 7.9 3.6× Green Bay Wisconsin, United States 1 14 August 7.9 3.6× St. Catharines Ontario, Canada 1 14 August 7.0 3.6× Guelph Ontario, Canada 1 14 August 7.4 3.4× Oakville Ontario, Canada 1 14 August 8.3 3.4× Milton Ontario, Canada 1 14 August 8.8 3.4× Kitchener Ontario, Canada 1 14 August 7.6 3.3× Hamilton Ontario, Canada 1 14 August 8.1 3.3× Sarnia Ontario, Canada 1 15 August 8.2 3.3× London Ontario, Canada 2 14 August 8.0 3.2× Newmarket Ontario, Canada 1 14 August 8.0 3.2× Port Huron Michigan, United States 1 15 August 8.1 3.1× Windsor Ontario, Canada 2 14 August 10.0 3.1× Detroit Michigan, United States 1 15 August 9.5 2.7× Grand Rapids Michigan, United States 1 14 August 9.5 2.7× Cleveland Ohio, United States 1 15 August 9.9 2.6×
Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.
Against other episodes in Canada and the United States
Number 45 of 106 episodes in Canada and the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 279 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 260 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 241 North-eastern United States and Canada, June 2025 196 North-eastern United States and Canada, June 2023 161 North-eastern United States and Canada, July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States, June 2025 104 North-western United States and Canada, August 2026 99 North-eastern United States and Canada, February 2026 96 South-eastern Canada and United States, August 2025 18 Bars: cities reached; colour: the level of the episode's highest daily reading. All 106 .
Use this page SmogRank, South-eastern Canada and United States, August 2025: 18 cities with PM2.5 at twice their usual or more, 14 to 15 August 2025, smogrank.com/episodes/2025-08-south-eastern-canada-and-united-states (accessed 2 October 2026).
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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms .
An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes . Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.
