SmogRank / Episodes / Canada
South-eastern Canada and United States, December 2024
For 4 days, from 26 to 29 December 2024, 23 cities in Canada and the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Nepean, Ontario, Canada: 48.2 µg/m³ on 28 December, about 9.3× its usual 5.2.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 23 in 2 countries
Days 4 26 to 29 December 2024
Worst day 27 December 13 cities counted
Furthest above usual 9.3× Nepean
Day by day
Play 27 December 13 cities at twice their usual or more
Utica Ottawa Kingston Syracuse Albany Belleville Pittsfield Rochester Scranton Newburgh Greenfield Keene North Chicopee Springfield New City Peterborough Waterbury Sherbrooke Hartford Randolph Paterson White Plains Fort Lee Bridgeport New Haven Bethlehem Jersey City Allentown Elizabeth New York City Bayonne Linden Worcester New Brunswick Derry Holbrook Ewing Reading Trenton Lowell Kenmore Milford Framingham New London Buffalo Bensalem Coventry Lexington Haverhill Pennsauken Philadelphia Pawtucket Providence Toms River St. Catharines Boston Chester Portsmouth Toronto Lynn Newmarket State College Sewell Quincy Wilmington Brockton Québec York Newark Fall River Bear Barrie Mississauga Elkton Oakville South Vineland Brampton Portland Lewiston Alliston Pleasantville Atlantic City North Bay Milton Hamilton Waterdown Edgewood Hunt Valley Altoona Augusta Guelph Hagerstown Brantford Erie Johnstown Kitchener Rouyn-Noranda Wilkinsburg West Mifflin Hermitage McKeesport Pittsburgh Youngstown Weirton Heights Weirton Steubenville Lancaster Brooklin Norristown Lebanon Harrisburg Carlisle Sorel-Tracy L'Ancienne-Lorette Granby Gatineau Rutland Danbury Saguenay Shawinigan Laconia Saint-Jean-sur-Richelieu Drummondville Montréal Dorval Brossard Rivière-des-Prairies–Pointe-aux-Trembles Trois-Rivières Nepean 23 Dec 24 25 26 27 28 29 30 31 1 Jan 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
Lancaster Lancaster, 23 December: 8.9 µg/m³, 1.1× usual Lancaster, 24 December: 14.6 µg/m³, 1.7× usual Lancaster, 25 December: 29.3 µg/m³, 3.5× usual Lancaster, 26 December: 12.6 µg/m³, 1.5× usual Lancaster, 27 December: 27.2 µg/m³, 3.2× usual Lancaster, 28 December: 11.6 µg/m³, 1.4× usual Lancaster, 29 December: 4.4 µg/m³, 0.5× usual Lancaster, 30 December: 3.0 µg/m³, 0.4× usual Lancaster, 31 December: 7.6 µg/m³, 0.9× usual Lancaster, 1 January: 4.6 µg/m³, 0.5× usual Brossard Brossard, 23 December: 5.6 µg/m³, 1.1× usual Brossard, 24 December: 14.5 µg/m³, 2.7× usual Brossard, 25 December: 28.8 µg/m³, 5.4× usual Brossard, 26 December: 37.2 µg/m³, 7.0× usual Brossard, 27 December: 39.6 µg/m³, 7.5× usual Brossard, 28 December: 25.7 µg/m³, 4.8× usual Brossard, 29 December: 23.1 µg/m³, 4.4× usual Brossard, 30 December: 1.6 µg/m³, 0.3× usual Brossard, 31 December: 2.7 µg/m³, 0.5× usual Brossard, 1 January: 3.5 µg/m³, 0.7× usual Drummondville Drummondville, 23 December: 5.2 µg/m³, 0.9× usual Drummondville, 24 December: 10.9 µg/m³, 1.8× usual Drummondville, 25 December: 27.3 µg/m³, 4.5× usual Drummondville, 26 December: 38.7 µg/m³, 6.3× usual Drummondville, 27 December: 22.7 µg/m³, 3.7× usual Drummondville, 28 December: 19.3 µg/m³, 3.2× usual Drummondville, 29 December: 15.7 µg/m³, 2.6× usual Drummondville, 30 December: 1.7 µg/m³, 0.3× usual Drummondville, 31 December: 3.3 µg/m³, 0.5× usual Drummondville, 1 January: 2.9 µg/m³, 0.5× usual Granby Granby, 23 December: 5.0 µg/m³, 0.9× usual Granby, 24 December: 15.6 µg/m³, 2.7× usual Granby, 25 December: 25.2 µg/m³, 4.3× usual Granby, 26 December: 24.5 µg/m³, 4.2× usual Granby, 27 December: 21.9 µg/m³, 3.8× usual Granby, 28 December: 27.4 µg/m³, 4.7× usual Granby, 29 December: 8.7 µg/m³, 1.5× usual Granby, 30 December: 1.5 µg/m³, 0.3× usual Granby, 31 December: 2.8 µg/m³, 0.5× usual Granby, 1 January: 4.1 µg/m³, 0.7× usual Rivière-des-Prairie… Rivière-des-Prairies–Pointe-aux-Trembles, 23 December: 5.5 µg/m³, 1.1× usual Rivière-des-Prairies–Pointe-aux-Trembles, 24 December: 8.0 µg/m³, 1.5× usual Rivière-des-Prairies–Pointe-aux-Trembles, 25 December: 16.1 µg/m³, 3.1× usual Rivière-des-Prairies–Pointe-aux-Trembles, 26 December: 40.4 µg/m³, 7.8× usual Rivière-des-Prairies–Pointe-aux-Trembles, 27 December: 36.6 µg/m³, 7.0× usual Rivière-des-Prairies–Pointe-aux-Trembles, 28 December: 24.9 µg/m³, 4.8× usual Rivière-des-Prairies–Pointe-aux-Trembles, 29 December: 29.8 µg/m³, 5.7× usual Rivière-des-Prairies–Pointe-aux-Trembles, 30 December: 3.8 µg/m³, 0.7× usual Rivière-des-Prairies–Pointe-aux-Trembles, 31 December: 2.7 µg/m³, 0.5× usual Rivière-des-Prairies–Pointe-aux-Trembles, 1 January: 3.4 µg/m³, 0.7× usual Sorel-Tracy Sorel-Tracy, 23 December: 5.9 µg/m³, 0.7× usual Sorel-Tracy, 24 December: 7.1 µg/m³, 0.8× usual Sorel-Tracy, 25 December: 21.7 µg/m³, 2.4× usual Sorel-Tracy, 26 December: 37.8 µg/m³, 4.2× usual Sorel-Tracy, 27 December: 35.0 µg/m³, 3.9× usual Sorel-Tracy, 28 December: 25.1 µg/m³, 2.8× usual Sorel-Tracy, 29 December: 26.3 µg/m³, 3.0× usual Sorel-Tracy, 30 December: 6.0 µg/m³, 0.7× usual Sorel-Tracy, 31 December: 2.9 µg/m³, 0.3× usual Sorel-Tracy, 1 January: 3.5 µg/m³, 0.4× usual Trois-Rivières Trois-Rivières, 23 December: 5.9 µg/m³, 1.1× usual Trois-Rivières, 24 December: 9.7 µg/m³, 1.7× usual Trois-Rivières, 25 December: 16.8 µg/m³, 3.0× usual Trois-Rivières, 26 December: 35.1 µg/m³, 6.3× usual Trois-Rivières, 27 December: 46.5 µg/m³, 8.3× usual Trois-Rivières, 28 December: 27.4 µg/m³, 4.9× usual Trois-Rivières, 29 December: 31.8 µg/m³, 5.7× usual Trois-Rivières, 30 December: 9.4 µg/m³, 1.7× usual Trois-Rivières, 31 December: 3.5 µg/m³, 0.6× usual Trois-Rivières, 1 January: 4.5 µg/m³, 0.8× usual Saint-Jean-sur-Rich… Saint-Jean-sur-Richelieu, 23 December: 3.6 µg/m³, 0.7× usual Saint-Jean-sur-Richelieu, 24 December: 7.3 µg/m³, 1.5× usual Saint-Jean-sur-Richelieu, 25 December: 23.1 µg/m³, 4.6× usual Saint-Jean-sur-Richelieu, 26 December: 31.5 µg/m³, 6.3× usual Saint-Jean-sur-Richelieu, 27 December: 24.9 µg/m³, 5.0× usual Saint-Jean-sur-Richelieu, 28 December: 23.2 µg/m³, 4.6× usual Saint-Jean-sur-Richelieu, 29 December: 6.5 µg/m³, 1.3× usual Saint-Jean-sur-Richelieu, 30 December: 1.0 µg/m³, 0.2× usual Saint-Jean-sur-Richelieu, 31 December: 1.5 µg/m³, 0.3× usual Saint-Jean-sur-Richelieu, 1 January: 3.3 µg/m³, 0.7× usual Montréal Montréal, 23 December: 5.3 µg/m³, 1.0× usual Montréal, 24 December: 9.0 µg/m³, 1.7× usual Montréal, 25 December: 16.9 µg/m³, 3.2× usual Montréal, 26 December: 28.9 µg/m³, 5.5× usual Montréal, 27 December: 38.2 µg/m³, 7.2× usual Montréal, 28 December: 24.8 µg/m³, 4.7× usual Montréal, 29 December: 30.8 µg/m³, 5.8× usual Montréal, 30 December: 3.1 µg/m³, 0.6× usual Montréal, 31 December: 2.8 µg/m³, 0.5× usual Montréal, 1 January: 3.9 µg/m³, 0.7× usual Saguenay Saguenay, 23 December: 6.0 µg/m³, 1.2× usual Saguenay, 24 December: 6.2 µg/m³, 1.2× usual Saguenay, 25 December: 18.1 µg/m³, 3.6× usual Saguenay, 26 December: 25.0 µg/m³, 5.0× usual Saguenay, 27 December: 17.7 µg/m³, 3.5× usual Saguenay, 28 December: 13.0 µg/m³, 2.6× usual Saguenay, 29 December: 10.7 µg/m³, 2.1× usual Saguenay, 30 December: 7.8 µg/m³, 1.6× usual Saguenay, 31 December: 2.3 µg/m³, 0.5× usual Saguenay, 1 January: 4.0 µg/m³, 0.8× usual Dorval Dorval, 23 December: 4.2 µg/m³, 0.8× usual Dorval, 24 December: 8.1 µg/m³, 1.6× usual Dorval, 25 December: 12.8 µg/m³, 2.6× usual Dorval, 26 December: 21.2 µg/m³, 4.2× usual Dorval, 27 December: 37.2 µg/m³, 7.4× usual Dorval, 28 December: 25.9 µg/m³, 5.2× usual Dorval, 29 December: 29.0 µg/m³, 5.8× usual Dorval, 30 December: 1.8 µg/m³, 0.4× usual Dorval, 31 December: 1.9 µg/m³, 0.4× usual Dorval, 1 January: 3.6 µg/m³, 0.7× usual Harrisburg Harrisburg, 23 December: 8.8 µg/m³, 1.1× usual Harrisburg, 24 December: 17.4 µg/m³, 2.1× usual Harrisburg, 25 December: 20.1 µg/m³, 2.4× usual Harrisburg, 26 December: 12.4 µg/m³, 1.5× usual Harrisburg, 27 December: 29.2 µg/m³, 3.5× usual Harrisburg, 28 December: 22.3 µg/m³, 2.7× usual Harrisburg, 29 December: 6.7 µg/m³, 0.8× usual Harrisburg, 30 December: 3.4 µg/m³, 0.4× usual Harrisburg, 31 December: 6.8 µg/m³, 0.8× usual Harrisburg, 1 January: 4.7 µg/m³, 0.6× usual Lebanon Lebanon, 23 December: 7.7 µg/m³, 0.9× usual Lebanon, 24 December: 15.0 µg/m³, 1.8× usual Lebanon, 25 December: 18.4 µg/m³, 2.2× usual Lebanon, 26 December: 11.6 µg/m³, 1.4× usual Lebanon, 27 December: 29.1 µg/m³, 3.5× usual Lebanon, 28 December: 20.4 µg/m³, 2.5× usual Lebanon, 29 December: 5.8 µg/m³, 0.7× usual Lebanon, 30 December: 2.5 µg/m³, 0.3× usual Lebanon, 31 December: 5.8 µg/m³, 0.7× usual Lebanon, 1 January: 4.5 µg/m³, 0.5× usual Carlisle Carlisle, 23 December: 9.8 µg/m³, 1.2× usual Carlisle, 24 December: 16.1 µg/m³, 2.0× usual Carlisle, 25 December: 19.7 µg/m³, 2.5× usual Carlisle, 26 December: 14.2 µg/m³, 1.8× usual Carlisle, 27 December: 28.8 µg/m³, 3.6× usual Carlisle, 28 December: 20.4 µg/m³, 2.6× usual Carlisle, 29 December: 6.2 µg/m³, 0.8× usual Carlisle, 30 December: 2.3 µg/m³, 0.3× usual Carlisle, 31 December: 6.4 µg/m³, 0.8× usual Carlisle, 1 January: 3.8 µg/m³, 0.5× usual L'Ancienne-Lorette L'Ancienne-Lorette, 23 December: 11.2 µg/m³, 1.7× usual L'Ancienne-Lorette, 24 December: 6.7 µg/m³, 1.0× usual L'Ancienne-Lorette, 25 December: 11.5 µg/m³, 1.8× usual L'Ancienne-Lorette, 26 December: 22.3 µg/m³, 3.4× usual L'Ancienne-Lorette, 27 December: 27.9 µg/m³, 4.3× usual L'Ancienne-Lorette, 28 December: 22.9 µg/m³, 3.5× usual L'Ancienne-Lorette, 29 December: 26.0 µg/m³, 4.0× usual L'Ancienne-Lorette, 30 December: 4.8 µg/m³, 0.7× usual L'Ancienne-Lorette, 31 December: 5.0 µg/m³, 0.8× usual L'Ancienne-Lorette, 1 January: 3.8 µg/m³, 0.6× usual Shawinigan Shawinigan, 23 December: 7.5 µg/m³, 1.4× usual Shawinigan, 24 December: 9.9 µg/m³, 1.9× usual Shawinigan, 25 December: 11.5 µg/m³, 2.2× usual Shawinigan, 26 December: 21.4 µg/m³, 4.1× usual Shawinigan, 27 December: 27.4 µg/m³, 5.3× usual Shawinigan, 28 December: 27.2 µg/m³, 5.2× usual Shawinigan, 29 December: 25.0 µg/m³, 4.8× usual Shawinigan, 30 December: 4.7 µg/m³, 0.9× usual Shawinigan, 31 December: 3.5 µg/m³, 0.7× usual Shawinigan, 1 January: 3.4 µg/m³, 0.7× usual Norristown Norristown, 23 December: 6.8 µg/m³, 0.9× usual Norristown, 24 December: 14.7 µg/m³, 2.0× usual Norristown, 25 December: 17.5 µg/m³, 2.4× usual Norristown, 26 December: 18.6 µg/m³, 2.6× usual Norristown, 27 December: 25.4 µg/m³, 3.5× usual Norristown, 28 December: 9.0 µg/m³, 1.3× usual Norristown, 29 December: 4.5 µg/m³, 0.6× usual Norristown, 30 December: 2.8 µg/m³, 0.4× usual Norristown, 31 December: 5.3 µg/m³, 0.7× usual Norristown, 1 January: 3.9 µg/m³, 0.5× usual Nepean Nepean, 23 December: 3.0 µg/m³, 0.6× usual Nepean, 24 December: 10.9 µg/m³, 2.1× usual Nepean, 25 December: 15.3 µg/m³, 2.9× usual Nepean, 26 December: 21.5 µg/m³, 4.1× usual Nepean, 27 December: 22.5 µg/m³, 4.3× usual Nepean, 28 December: 48.2 µg/m³, 9.3× usual Nepean, 29 December: 38.2 µg/m³, 7.3× usual Nepean, 30 December: 6.3 µg/m³, 1.2× usual Nepean, 31 December: 1.4 µg/m³, 0.3× usual Nepean, 1 January: 1.9 µg/m³, 0.4× usual Gatineau Gatineau, 23 December: 6.8 µg/m³, 1.0× usual Gatineau, 24 December: 9.3 µg/m³, 1.3× usual Gatineau, 25 December: 15.5 µg/m³, 2.2× usual Gatineau, 26 December: 17.7 µg/m³, 2.6× usual Gatineau, 27 December: 20.5 µg/m³, 3.0× usual Gatineau, 28 December: 32.3 µg/m³, 4.7× usual Gatineau, 29 December: 28.9 µg/m³, 4.2× usual Gatineau, 30 December: 5.8 µg/m³, 0.8× usual Gatineau, 31 December: 1.8 µg/m³, 0.3× usual Gatineau, 1 January: 1.5 µg/m³, 0.2× usual Danbury Danbury, 23 December: 6.8 µg/m³, 1.2× usual Danbury, 24 December: 10.6 µg/m³, 1.8× usual Danbury, 25 December: 9.5 µg/m³, 1.6× usual Danbury, 26 December: 14.9 µg/m³, 2.5× usual Danbury, 27 December: 24.3 µg/m³, 4.1× usual Danbury, 28 December: 29.5 µg/m³, 5.0× usual Danbury, 29 December: 14.7 µg/m³, 2.5× usual Danbury, 30 December: 2.7 µg/m³, 0.5× usual Danbury, 31 December: 4.9 µg/m³, 0.8× usual Danbury, 1 January: 3.7 µg/m³, 0.6× usual Rutland Rutland, 23 December: 12.1 µg/m³, 2.2× usual Rutland, 24 December: 10.6 µg/m³, 1.9× usual Rutland, 25 December: 11.9 µg/m³, 2.1× usual Rutland, 26 December: 17.5 µg/m³, 3.1× usual Rutland, 27 December: 17.1 µg/m³, 3.1× usual Rutland, 28 December: 27.9 µg/m³, 5.0× usual Rutland, 29 December: 15.7 µg/m³, 2.8× usual Rutland, 30 December: 0.9 µg/m³, 0.2× usual Rutland, 31 December: 4.7 µg/m³, 0.8× usual Rutland, 1 January: 2.2 µg/m³, 0.4× usual Brooklin Brooklin, 23 December: 5.6 µg/m³, 0.8× usual Brooklin, 24 December: 10.1 µg/m³, 1.4× usual Brooklin, 25 December: 4.8 µg/m³, 0.6× usual Brooklin, 26 December: 7.6 µg/m³, 1.0× usual Brooklin, 27 December: 7.7 µg/m³, 1.0× usual Brooklin, 28 December: 25.2 µg/m³, 3.4× usual Brooklin, 29 December: 13.7 µg/m³, 1.9× usual Brooklin, 30 December: 0.8 µg/m³, 0.1× usual Brooklin, 31 December: 2.5 µg/m³, 0.3× usual Brooklin, 1 January: no reading Laconia Laconia, 23 December: 13.6 µg/m³, 2.7× usual Laconia, 24 December: 10.9 µg/m³, 2.2× usual Laconia, 25 December: 13.9 µg/m³, 2.8× usual Laconia, 26 December: 16.9 µg/m³, 3.4× usual Laconia, 27 December: 22.2 µg/m³, 4.4× usual Laconia, 28 December: 23.8 µg/m³, 4.8× usual Laconia, 29 December: 29.4 µg/m³, 5.9× usual Laconia, 30 December: 13.4 µg/m³, 2.7× usual Laconia, 31 December: 11.5 µg/m³, 2.3× usual Laconia, 1 January: 5.6 µg/m³, 1.1× usual 23 Dec 24 25 26 27 28 29 30 31 1 Jan 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
Nepean Ontario, Canada 2 28 December 5.2 9.3× Trois-Rivières Quebec, Canada 4 27 December 5.6 8.3× Rivière-des-Prairies–Pointe-aux-Trembles Quebec, Canada 3 26 December 5.2 7.8× Brossard Quebec, Canada 3 27 December 5.3 7.5× Dorval Quebec, Canada 3 27 December 4.7 7.4× Montréal Quebec, Canada 3 27 December 5.3 7.2× Drummondville Quebec, Canada 1 26 December 6.1 6.3× Saint-Jean-sur-Richelieu Quebec, Canada 1 26 December 3.9 6.3× Laconia New Hampshire, United States 1 29 December 4.3 5.9× Shawinigan Quebec, Canada 3 27 December 5.2 5.3× Saguenay Quebec, Canada 1 26 December 4.2 5.0× Danbury Connecticut, United States 1 28 December 5.9 5.0× Rutland Vermont, United States 1 28 December 5.6 5.0× Granby Quebec, Canada 1 28 December 5.8 4.7× Gatineau Quebec, Canada 2 28 December 6.9 4.7× L'Ancienne-Lorette Quebec, Canada 2 27 December 6.5 4.3× Sorel-Tracy Quebec, Canada 4 26 December 8.9 4.2× Carlisle Pennsylvania, United States 1 27 December 8.0 3.6× Lebanon Pennsylvania, United States 1 27 December 8.2 3.5× Norristown Pennsylvania, United States 1 27 December 7.2 3.5× Harrisburg Pennsylvania, United States 1 27 December 8.3 3.5× Lancaster Pennsylvania, United States 1 25 December 8.4 3.5× Brooklin Ontario, Canada 1 28 December 7.4 3.4×
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 47 of 142 episodes in Canada and the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 280 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 261 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 240 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, December 2024 23 Bars: cities reached; colour: the level of the episode's highest daily reading. All 142 .
Use this page SmogRank, South-eastern Canada and United States, December 2024: 23 cities with PM2.5 at twice their usual or more, 26 to 29 December 2024, smogrank.com/episodes/2024-12-south-eastern-canada-and-united-states (accessed 3 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.
