SmogRank / Episodes / United States
North-eastern United States and Canada, September and October 2023
For 2 days, from 30 September to 1 October 2023, 30 cities in the United States and Canada had PM2.5 at least twice their usual for the time of year. The worst reading was Worcester, Massachusetts, United States: 40.1 µg/m³ on 1 October, about 8.0× its usual 4.2.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 30 in 2 countries
Days 2 30 September to 1 October 2023
Worst day 30 September 17 cities counted
Furthest above usual 8.0× Worcester
Day by day
Play 30 September 17 cities at twice their usual or more
Lewiston Derry Burlington Augusta Saint-Jean-sur-Richelieu Trois-Rivières Montréal Québec Dorval Pittsfield Bangor Albany New Haven Danbury Bridgeport Newburgh Utica White Plains New City Ottawa Paterson Syracuse Kingston Scranton Fredericton Saint John Rivière-des-Prairies–Pointe-aux-Trembles Cornwall L'Ancienne-Lorette Brossard Drummondville Waterbury Lynn Rutland Laconia Coventry Sherbrooke Portsmouth Providence Quincy Lowell North Chicopee Boston Granby Hartford Brockton Springfield Keene Lexington Haverhill Fall River Portland Greenfield Edmundston New London Worcester 27 Sep 28 29 30 1 Oct 2 3 4 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
Granby Granby, 27 September: 12.6 µg/m³, 2.5× usual Granby, 28 September: 17.5 µg/m³, 3.5× usual Granby, 29 September: 26.2 µg/m³, 5.2× usual Granby, 30 September: 33.0 µg/m³, 6.6× usual Granby, 1 October: 22.2 µg/m³, 4.4× usual Granby, 2 October: 11.1 µg/m³, 2.2× usual Granby, 3 October: 9.9 µg/m³, 2.0× usual Granby, 4 October: 11.4 µg/m³, 2.3× usual Edmundston Edmundston, 27 September: 9.3 µg/m³, 1.9× usual Edmundston, 28 September: 11.0 µg/m³, 2.2× usual Edmundston, 29 September: 13.1 µg/m³, 2.6× usual Edmundston, 30 September: 39.1 µg/m³, 7.8× usual Edmundston, 1 October: 26.4 µg/m³, 5.3× usual Edmundston, 2 October: 8.7 µg/m³, 1.7× usual Edmundston, 3 October: 9.6 µg/m³, 1.9× usual Edmundston, 4 October: 6.1 µg/m³, 1.2× usual Greenfield Greenfield, 27 September: 5.9 µg/m³, 1.2× usual Greenfield, 28 September: 9.1 µg/m³, 1.8× usual Greenfield, 29 September: 13.5 µg/m³, 2.7× usual Greenfield, 30 September: 36.5 µg/m³, 7.3× usual Greenfield, 1 October: 13.5 µg/m³, 2.7× usual Greenfield, 2 October: 9.0 µg/m³, 1.8× usual Greenfield, 3 October: 8.8 µg/m³, 1.8× usual Greenfield, 4 October: 8.8 µg/m³, 1.8× usual Keene Keene, 27 September: 5.9 µg/m³, 1.2× usual Keene, 28 September: 11.4 µg/m³, 2.3× usual Keene, 29 September: 17.9 µg/m³, 3.6× usual Keene, 30 September: 33.9 µg/m³, 6.8× usual Keene, 1 October: 16.2 µg/m³, 3.2× usual Keene, 2 October: 8.6 µg/m³, 1.7× usual Keene, 3 October: 8.2 µg/m³, 1.6× usual Keene, 4 October: 9.3 µg/m³, 1.9× usual Springfield Springfield, 27 September: 7.2 µg/m³, 1.4× usual Springfield, 28 September: 10.9 µg/m³, 2.2× usual Springfield, 29 September: 12.1 µg/m³, 2.4× usual Springfield, 30 September: 33.4 µg/m³, 6.7× usual Springfield, 1 October: 18.9 µg/m³, 3.8× usual Springfield, 2 October: 9.8 µg/m³, 2.0× usual Springfield, 3 October: 10.0 µg/m³, 2.0× usual Springfield, 4 October: 11.1 µg/m³, 2.2× usual Hartford Hartford, 27 September: 7.2 µg/m³, 1.4× usual Hartford, 28 September: 12.7 µg/m³, 2.5× usual Hartford, 29 September: 8.4 µg/m³, 1.7× usual Hartford, 30 September: 32.9 µg/m³, 6.6× usual Hartford, 1 October: 24.1 µg/m³, 4.8× usual Hartford, 2 October: 11.8 µg/m³, 2.4× usual Hartford, 3 October: 10.7 µg/m³, 2.1× usual Hartford, 4 October: 12.5 µg/m³, 2.5× usual North Chicopee North Chicopee, 27 September: 5.3 µg/m³, 1.1× usual North Chicopee, 28 September: 8.7 µg/m³, 1.7× usual North Chicopee, 29 September: 10.8 µg/m³, 2.2× usual North Chicopee, 30 September: 31.4 µg/m³, 6.3× usual North Chicopee, 1 October: 16.2 µg/m³, 3.2× usual North Chicopee, 2 October: 8.0 µg/m³, 1.6× usual North Chicopee, 3 October: 7.8 µg/m³, 1.6× usual North Chicopee, 4 October: 9.0 µg/m³, 1.8× usual Sherbrooke Sherbrooke, 27 September: 11.8 µg/m³, 2.4× usual Sherbrooke, 28 September: 15.5 µg/m³, 3.1× usual Sherbrooke, 29 September: 23.5 µg/m³, 4.7× usual Sherbrooke, 30 September: 29.9 µg/m³, 6.0× usual Sherbrooke, 1 October: 20.7 µg/m³, 4.1× usual Sherbrooke, 2 October: 9.5 µg/m³, 1.9× usual Sherbrooke, 3 October: 9.4 µg/m³, 1.9× usual Sherbrooke, 4 October: 10.0 µg/m³, 2.0× usual Laconia Laconia, 27 September: 5.2 µg/m³, 1.0× usual Laconia, 28 September: 11.1 µg/m³, 2.2× usual Laconia, 29 September: 14.7 µg/m³, 2.9× usual Laconia, 30 September: 29.7 µg/m³, 5.9× usual Laconia, 1 October: 15.6 µg/m³, 3.1× usual Laconia, 2 October: 6.5 µg/m³, 1.3× usual Laconia, 3 October: 6.7 µg/m³, 1.3× usual Laconia, 4 October: 9.2 µg/m³, 1.8× usual Rutland Rutland, 27 September: 7.6 µg/m³, 1.5× usual Rutland, 28 September: 13.2 µg/m³, 2.6× usual Rutland, 29 September: 18.7 µg/m³, 3.7× usual Rutland, 30 September: 29.7 µg/m³, 5.9× usual Rutland, 1 October: 11.2 µg/m³, 2.2× usual Rutland, 2 October: 8.0 µg/m³, 1.6× usual Rutland, 3 October: 9.6 µg/m³, 1.9× usual Rutland, 4 October: 10.8 µg/m³, 2.2× usual Waterbury Waterbury, 27 September: 7.3 µg/m³, 1.5× usual Waterbury, 28 September: 12.5 µg/m³, 2.5× usual Waterbury, 29 September: 5.6 µg/m³, 1.1× usual Waterbury, 30 September: 28.6 µg/m³, 5.7× usual Waterbury, 1 October: 16.8 µg/m³, 3.4× usual Waterbury, 2 October: 10.6 µg/m³, 2.1× usual Waterbury, 3 October: 9.6 µg/m³, 1.9× usual Waterbury, 4 October: 11.0 µg/m³, 2.2× usual Drummondville Drummondville, 27 September: 10.8 µg/m³, 2.2× usual Drummondville, 28 September: 16.8 µg/m³, 3.4× usual Drummondville, 29 September: 22.6 µg/m³, 4.5× usual Drummondville, 30 September: 28.1 µg/m³, 5.6× usual Drummondville, 1 October: 17.6 µg/m³, 3.5× usual Drummondville, 2 October: 9.1 µg/m³, 1.8× usual Drummondville, 3 October: 10.5 µg/m³, 2.1× usual Drummondville, 4 October: 12.0 µg/m³, 2.4× usual Cornwall Cornwall, 27 September: 12.5 µg/m³, 2.3× usual Cornwall, 28 September: 17.1 µg/m³, 3.1× usual Cornwall, 29 September: 21.3 µg/m³, 3.9× usual Cornwall, 30 September: 27.6 µg/m³, 5.0× usual Cornwall, 1 October: 15.2 µg/m³, 2.8× usual Cornwall, 2 October: 11.2 µg/m³, 2.0× usual Cornwall, 3 October: 10.6 µg/m³, 1.9× usual Cornwall, 4 October: 11.5 µg/m³, 2.1× usual Brossard Brossard, 27 September: 10.9 µg/m³, 2.1× usual Brossard, 28 September: 17.1 µg/m³, 3.4× usual Brossard, 29 September: 21.8 µg/m³, 4.3× usual Brossard, 30 September: 27.0 µg/m³, 5.3× usual Brossard, 1 October: 19.8 µg/m³, 3.9× usual Brossard, 2 October: 10.4 µg/m³, 2.0× usual Brossard, 3 October: 10.2 µg/m³, 2.0× usual Brossard, 4 October: 11.0 µg/m³, 2.2× usual L'Ancienne-Lorette L'Ancienne-Lorette, 27 September: 13.7 µg/m³, 2.7× usual L'Ancienne-Lorette, 28 September: 17.2 µg/m³, 3.4× usual L'Ancienne-Lorette, 29 September: 22.4 µg/m³, 4.5× usual L'Ancienne-Lorette, 30 September: 26.2 µg/m³, 5.2× usual L'Ancienne-Lorette, 1 October: 19.0 µg/m³, 3.8× usual L'Ancienne-Lorette, 2 October: 9.5 µg/m³, 1.9× usual L'Ancienne-Lorette, 3 October: 13.7 µg/m³, 2.7× usual L'Ancienne-Lorette, 4 October: 12.2 µg/m³, 2.4× usual Lexington Lexington, 27 September: 6.0 µg/m³, 1.2× usual Lexington, 28 September: 10.4 µg/m³, 2.1× usual Lexington, 29 September: 19.5 µg/m³, 3.9× usual Lexington, 30 September: 25.8 µg/m³, 5.2× usual Lexington, 1 October: 34.1 µg/m³, 6.8× usual Lexington, 2 October: 12.8 µg/m³, 2.6× usual Lexington, 3 October: 10.9 µg/m³, 2.2× usual Lexington, 4 October: 17.4 µg/m³, 3.5× usual Rivière-des-Prairie… Rivière-des-Prairies–Pointe-aux-Trembles, 27 September: 10.4 µg/m³, 2.0× usual Rivière-des-Prairies–Pointe-aux-Trembles, 28 September: 18.5 µg/m³, 3.5× usual Rivière-des-Prairies–Pointe-aux-Trembles, 29 September: 23.8 µg/m³, 4.5× usual Rivière-des-Prairies–Pointe-aux-Trembles, 30 September: 25.7 µg/m³, 4.8× usual Rivière-des-Prairies–Pointe-aux-Trembles, 1 October: 18.1 µg/m³, 3.4× usual Rivière-des-Prairies–Pointe-aux-Trembles, 2 October: 10.4 µg/m³, 2.0× usual Rivière-des-Prairies–Pointe-aux-Trembles, 3 October: 11.9 µg/m³, 2.2× usual Rivière-des-Prairies–Pointe-aux-Trembles, 4 October: 12.9 µg/m³, 2.4× usual Worcester Worcester, 27 September: 6.7 µg/m³, 1.3× usual Worcester, 28 September: 9.4 µg/m³, 1.9× usual Worcester, 29 September: 11.8 µg/m³, 2.4× usual Worcester, 30 September: no reading Worcester, 1 October: 40.1 µg/m³, 8.0× usual Worcester, 2 October: 10.7 µg/m³, 2.1× usual Worcester, 3 October: 9.3 µg/m³, 1.9× usual Worcester, 4 October: 12.0 µg/m³, 2.4× usual New London New London, 27 September: 6.4 µg/m³, 1.3× usual New London, 28 September: 10.9 µg/m³, 2.2× usual New London, 29 September: 7.8 µg/m³, 1.6× usual New London, 30 September: 24.0 µg/m³, 4.8× usual New London, 1 October: 39.7 µg/m³, 7.9× usual New London, 2 October: 18.0 µg/m³, 3.6× usual New London, 3 October: 9.3 µg/m³, 1.9× usual New London, 4 October: 12.6 µg/m³, 2.5× usual Portland Portland, 27 September: 7.5 µg/m³, 1.5× usual Portland, 28 September: 9.3 µg/m³, 1.9× usual Portland, 29 September: 11.7 µg/m³, 2.3× usual Portland, 30 September: 17.2 µg/m³, 3.4× usual Portland, 1 October: 36.1 µg/m³, 7.2× usual Portland, 2 October: 9.2 µg/m³, 1.8× usual Portland, 3 October: 11.2 µg/m³, 2.2× usual Portland, 4 October: 12.8 µg/m³, 2.6× usual Haverhill Haverhill, 27 September: 5.6 µg/m³, 1.1× usual Haverhill, 28 September: 7.5 µg/m³, 1.5× usual Haverhill, 29 September: 10.8 µg/m³, 2.2× usual Haverhill, 30 September: 15.4 µg/m³, 3.1× usual Haverhill, 1 October: 35.5 µg/m³, 7.1× usual Haverhill, 2 October: 10.7 µg/m³, 2.1× usual Haverhill, 3 October: 7.9 µg/m³, 1.6× usual Haverhill, 4 October: 10.2 µg/m³, 2.0× usual Fall River Fall River, 27 September: 6.4 µg/m³, 1.3× usual Fall River, 28 September: 11.0 µg/m³, 2.2× usual Fall River, 29 September: 12.3 µg/m³, 2.5× usual Fall River, 30 September: 23.0 µg/m³, 4.6× usual Fall River, 1 October: 35.3 µg/m³, 7.1× usual Fall River, 2 October: 15.5 µg/m³, 3.1× usual Fall River, 3 October: 9.9 µg/m³, 2.0× usual Fall River, 4 October: 12.3 µg/m³, 2.5× usual Brockton Brockton, 27 September: 6.6 µg/m³, 1.3× usual Brockton, 28 September: 9.0 µg/m³, 1.8× usual Brockton, 29 September: 13.0 µg/m³, 2.6× usual Brockton, 30 September: 23.9 µg/m³, 4.8× usual Brockton, 1 October: 33.4 µg/m³, 6.7× usual Brockton, 2 October: 14.3 µg/m³, 2.9× usual Brockton, 3 October: 9.1 µg/m³, 1.8× usual Brockton, 4 October: 11.0 µg/m³, 2.2× usual Boston Boston, 27 September: 6.5 µg/m³, 1.3× usual Boston, 28 September: 7.9 µg/m³, 1.6× usual Boston, 29 September: 14.1 µg/m³, 2.8× usual Boston, 30 September: 18.5 µg/m³, 3.7× usual Boston, 1 October: 31.8 µg/m³, 6.4× usual Boston, 2 October: 13.5 µg/m³, 2.7× usual Boston, 3 October: 9.3 µg/m³, 1.9× usual Boston, 4 October: 12.7 µg/m³, 2.5× usual Quincy Quincy, 27 September: 6.4 µg/m³, 1.3× usual Quincy, 28 September: 7.8 µg/m³, 1.6× usual Quincy, 29 September: 13.5 µg/m³, 2.7× usual Quincy, 30 September: 21.6 µg/m³, 4.3× usual Quincy, 1 October: 31.7 µg/m³, 6.3× usual Quincy, 2 October: 13.4 µg/m³, 2.7× usual Quincy, 3 October: 8.3 µg/m³, 1.7× usual Quincy, 4 October: 11.3 µg/m³, 2.3× usual Providence Providence, 27 September: 8.1 µg/m³, 1.6× usual Providence, 28 September: 11.0 µg/m³, 2.2× usual Providence, 29 September: 12.1 µg/m³, 2.4× usual Providence, 30 September: 21.5 µg/m³, 4.3× usual Providence, 1 October: 31.5 µg/m³, 6.3× usual Providence, 2 October: 16.1 µg/m³, 3.2× usual Providence, 3 October: 11.1 µg/m³, 2.2× usual Providence, 4 October: 13.5 µg/m³, 2.7× usual Lowell Lowell, 27 September: 6.0 µg/m³, 1.2× usual Lowell, 28 September: 8.4 µg/m³, 1.7× usual Lowell, 29 September: 13.1 µg/m³, 2.6× usual Lowell, 30 September: 19.5 µg/m³, 3.9× usual Lowell, 1 October: 31.3 µg/m³, 6.3× usual Lowell, 2 October: 11.0 µg/m³, 2.2× usual Lowell, 3 October: 7.8 µg/m³, 1.6× usual Lowell, 4 October: 11.3 µg/m³, 2.3× usual Portsmouth Portsmouth, 27 September: 5.9 µg/m³, 1.2× usual Portsmouth, 28 September: 8.5 µg/m³, 1.7× usual Portsmouth, 29 September: 11.7 µg/m³, 2.3× usual Portsmouth, 30 September: 12.1 µg/m³, 2.4× usual Portsmouth, 1 October: 30.8 µg/m³, 6.2× usual Portsmouth, 2 October: 9.3 µg/m³, 1.9× usual Portsmouth, 3 October: 8.0 µg/m³, 1.6× usual Portsmouth, 4 October: 10.6 µg/m³, 2.1× usual Coventry Coventry, 27 September: 9.6 µg/m³, 1.9× usual Coventry, 28 September: 13.0 µg/m³, 2.6× usual Coventry, 29 September: 10.9 µg/m³, 2.2× usual Coventry, 30 September: 21.5 µg/m³, 4.3× usual Coventry, 1 October: 29.8 µg/m³, 6.0× usual Coventry, 2 October: 13.3 µg/m³, 2.7× usual Coventry, 3 October: 8.2 µg/m³, 1.6× usual Coventry, 4 October: 9.8 µg/m³, 2.0× usual Lynn Lynn, 27 September: 5.7 µg/m³, 1.1× usual Lynn, 28 September: 7.3 µg/m³, 1.5× usual Lynn, 29 September: 10.8 µg/m³, 2.2× usual Lynn, 30 September: 14.2 µg/m³, 2.8× usual Lynn, 1 October: 29.0 µg/m³, 5.8× usual Lynn, 2 October: 11.3 µg/m³, 2.3× usual Lynn, 3 October: 7.7 µg/m³, 1.5× usual Lynn, 4 October: 9.9 µg/m³, 2.0× usual 27 Sep 28 29 30 1 Oct 2 3 4 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
Worcester Massachusetts, United States 1 1 October 4.2 8.0× New London Connecticut, United States 1 1 October 4.1 7.9× Edmundston New Brunswick, Canada 1 30 September 4.5 7.8× Greenfield Massachusetts, United States 1 30 September 4.3 7.3× Portland Maine, United States 1 1 October 4.6 7.2× Haverhill Massachusetts, United States 1 1 October 4.4 7.1× Fall River Massachusetts, United States 1 1 October 4.1 7.1× Lexington Massachusetts, United States 2 1 October 3.7 6.8× Keene New Hampshire, United States 1 30 September 4.4 6.8× Springfield Massachusetts, United States 1 30 September 5.0 6.7× Brockton Massachusetts, United States 1 1 October 4.6 6.7× Granby Quebec, Canada 1 30 September 4.8 6.6× Hartford Connecticut, United States 1 30 September 4.8 6.6× Boston Massachusetts, United States 1 1 October 4.7 6.4× Quincy Massachusetts, United States 1 1 October 4.3 6.3× Providence Rhode Island, United States 1 1 October 5.0 6.3× North Chicopee Massachusetts, United States 1 30 September 3.8 6.3× Lowell Massachusetts, United States 1 1 October 4.4 6.3× Portsmouth New Hampshire, United States 1 1 October 4.2 6.2× Sherbrooke Quebec, Canada 1 30 September 4.2 6.0× Coventry Rhode Island, United States 1 1 October 3.5 6.0× Laconia New Hampshire, United States 1 30 September 3.1 5.9× Rutland Vermont, United States 1 30 September 4.7 5.9× Lynn Massachusetts, United States 1 1 October 4.1 5.8× Waterbury Connecticut, United States 1 30 September 4.7 5.7× Drummondville Quebec, Canada 1 30 September 4.6 5.6× Brossard Quebec, Canada 1 30 September 5.1 5.3× L'Ancienne-Lorette Quebec, Canada 1 30 September 4.8 5.2× Cornwall Ontario, Canada 1 30 September 5.5 5.0× Rivière-des-Prairies–Pointe-aux-Trembles Quebec, Canada 1 30 September 5.3 4.8×
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 the United States and Canada
Number 13 of 45 episodes in the United States and Canada since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 279 North-eastern United States and Canada, May and June 2023 260 North-eastern United States and Canada, July 2023 241 North-eastern United States and Canada, June 2023 161 North-western United States and Canada, August 2023 110 North-eastern United States and Canada, July 2023 75 Western United States, September 2023 61 South-eastern United States, October 2023 47 North-eastern United States, July 2023 46 North-western United States and Canada, May 2023 42 Western United States, December 2023 32 Northern United States, January 2023 32 North-eastern United States and Canada, September and October 2023 30 Bars: cities reached; colour: the level of the episode's highest daily reading. All 45 .
Use this page SmogRank, North-eastern United States and Canada, September and October 2023: 30 cities with PM2.5 at twice their usual or more, 30 September to 1 October 2023, smogrank.com/episodes/2023-09-north-eastern-united-states-and-canada (accessed 2 October 2026).
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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.
