SmogRank / Episodes / Canada
North-western Canada and United States, September 2023
For 2 days, from 6 to 7 September 2023, 19 cities in Canada and the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Rapid City, South Dakota, United States: 67.6 µg/m³ on 6 September, about 9.5× its usual 7.1. Ended 7 September.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 19 in 2 countries
Days 2 6 to 7 September 2023
Worst day 6 September 18 cities counted
Furthest above usual 9.5× Rapid City
Day by day
Play 6 September 18 cities at twice their usual or more
Lewistown Great Falls Lethbridge Bozeman Helena Valley West Central Helena Sheridan Cody Butte Columbia Falls Calgary Airdrie Missoula Red Deer Riverton Lander Rexburg Casper Idaho Falls Conda Pocatello Rock Springs Preston Smithfield Laramie North Ogden Ranchettes Cheyenne Twin Falls Bountiful Salt Lake City Millcreek Magna Prince Albert Saskatoon Fort McMurray Sherwood Park St. Albert Grand Centre Lockwood Billings Medicine Hat Fort Saskatchewan Estevan Edmonton Regina Miles City Scottsbluff Havre Swift Current Gillette Rapid City 3 Sep 4 5 6 7 8 9 10 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
Rapid City Rapid City, 3 September: 6.7 µg/m³ Rapid City, 4 September: 8.8 µg/m³ Rapid City, 5 September: 73.6 µg/m³ Rapid City, 6 September: 67.6 µg/m³, 9.5× its usual 7.1 Rapid City, 7 September: 29.3 µg/m³ Rapid City, 8 September: 12.6 µg/m³ Rapid City, 9 September: 17.0 µg/m³ Rapid City, 10 September: 11.8 µg/m³ Edmonton Edmonton, 3 September: 201.0 µg/m³ Edmonton, 4 September: 103.0 µg/m³ Edmonton, 5 September: 62.7 µg/m³ Edmonton, 6 September: 63.2 µg/m³, 5.7× its usual 11.1 Edmonton, 7 September: 25.1 µg/m³, 2.3× its usual 11.0 Edmonton, 8 September: 20.4 µg/m³ Edmonton, 9 September: 21.0 µg/m³ Edmonton, 10 September: 11.6 µg/m³ Swift Current Swift Current, 3 September: 68.3 µg/m³ Swift Current, 4 September: 205.0 µg/m³ Swift Current, 5 September: 47.3 µg/m³ Swift Current, 6 September: 58.0 µg/m³, 7.8× its usual 7.4 Swift Current, 7 September: 21.6 µg/m³ Swift Current, 8 September: 8.9 µg/m³ Swift Current, 9 September: 6.0 µg/m³ Swift Current, 10 September: 8.3 µg/m³ Regina Regina, 3 September: 108.0 µg/m³ Regina, 4 September: 176.0 µg/m³ Regina, 5 September: 38.2 µg/m³ Regina, 6 September: 58.0 µg/m³, 6.6× its usual 8.8 Regina, 7 September: 40.7 µg/m³, 4.8× its usual 8.5 Regina, 8 September: 20.2 µg/m³ Regina, 9 September: 15.2 µg/m³ Regina, 10 September: 21.7 µg/m³ Miles City Miles City, 3 September: 7.4 µg/m³ Miles City, 4 September: 79.5 µg/m³ Miles City, 5 September: 111.0 µg/m³ Miles City, 6 September: 52.8 µg/m³, 6.9× its usual 7.7 Miles City, 7 September: 30.2 µg/m³ Miles City, 8 September: 15.0 µg/m³ Miles City, 9 September: 12.9 µg/m³ Miles City, 10 September: 10.4 µg/m³ Fort Saskatchewan Fort Saskatchewan, 3 September: 178.0 µg/m³ Fort Saskatchewan, 4 September: 84.1 µg/m³ Fort Saskatchewan, 5 September: 44.6 µg/m³ Fort Saskatchewan, 6 September: 50.8 µg/m³, 5.3× its usual 9.6 Fort Saskatchewan, 7 September: 17.4 µg/m³ Fort Saskatchewan, 8 September: 13.2 µg/m³ Fort Saskatchewan, 9 September: 13.8 µg/m³ Fort Saskatchewan, 10 September: 9.1 µg/m³ Gillette Gillette, 3 September: 4.3 µg/m³ Gillette, 4 September: 26.9 µg/m³ Gillette, 5 September: 90.4 µg/m³ Gillette, 6 September: 43.7 µg/m³, 8.2× its usual 5.3 Gillette, 7 September: 9.9 µg/m³ Gillette, 8 September: 9.5 µg/m³ Gillette, 9 September: 11.1 µg/m³ Gillette, 10 September: 4.5 µg/m³ Havre Havre, 3 September: 4.7 µg/m³ Havre, 4 September: 136.0 µg/m³ Havre, 5 September: 102.0 µg/m³ Havre, 6 September: 37.4 µg/m³, 7.5× its usual 4.8 Havre, 7 September: 9.5 µg/m³ Havre, 8 September: 6.7 µg/m³ Havre, 9 September: 5.8 µg/m³ Havre, 10 September: 5.6 µg/m³ Scottsbluff Scottsbluff, 3 September: 3.5 µg/m³ Scottsbluff, 4 September: 2.3 µg/m³ Scottsbluff, 5 September: 30.8 µg/m³ Scottsbluff, 6 September: 36.8 µg/m³, 7.4× its usual 4.3 Scottsbluff, 7 September: 19.5 µg/m³ Scottsbluff, 8 September: 5.8 µg/m³ Scottsbluff, 9 September: 12.6 µg/m³ Scottsbluff, 10 September: 4.7 µg/m³ Estevan Estevan, 3 September: 88.4 µg/m³ Estevan, 4 September: 83.9 µg/m³ Estevan, 5 September: 62.5 µg/m³ Estevan, 6 September: 34.8 µg/m³, 3.3× its usual 10.5 Estevan, 7 September: 58.4 µg/m³, 5.6× its usual 10.5 Estevan, 8 September: 20.3 µg/m³ Estevan, 9 September: 21.1 µg/m³ Estevan, 10 September: 18.2 µg/m³ Saskatoon Saskatoon, 3 September: 270.0 µg/m³ Saskatoon, 4 September: 175.0 µg/m³ Saskatoon, 5 September: 13.3 µg/m³ Saskatoon, 6 September: 32.6 µg/m³, 3.5× its usual 9.2 Saskatoon, 7 September: 22.8 µg/m³ Saskatoon, 8 September: 17.1 µg/m³ Saskatoon, 9 September: 15.9 µg/m³ Saskatoon, 10 September: 12.5 µg/m³ Medicine Hat Medicine Hat, 3 September: 24.0 µg/m³ Medicine Hat, 4 September: 109.0 µg/m³ Medicine Hat, 5 September: 78.6 µg/m³ Medicine Hat, 6 September: 32.0 µg/m³, 4.4× its usual 7.3 Medicine Hat, 7 September: 6.9 µg/m³ Medicine Hat, 8 September: 7.2 µg/m³ Medicine Hat, 9 September: 5.4 µg/m³ Medicine Hat, 10 September: 5.3 µg/m³ St. Albert St. Albert, 3 September: 104.0 µg/m³ St. Albert, 4 September: 51.1 µg/m³ St. Albert, 5 September: 36.8 µg/m³ St. Albert, 6 September: 30.3 µg/m³, 3.7× its usual 8.1 St. Albert, 7 September: 10.5 µg/m³ St. Albert, 8 September: 9.1 µg/m³ St. Albert, 9 September: 13.4 µg/m³ St. Albert, 10 September: 9.9 µg/m³ Billings Billings, 3 September: 3.4 µg/m³ Billings, 4 September: 57.6 µg/m³ Billings, 5 September: 115.0 µg/m³ Billings, 6 September: 29.4 µg/m³, 4.3× its usual 6.8 Billings, 7 September: 5.9 µg/m³ Billings, 8 September: 8.5 µg/m³ Billings, 9 September: 6.2 µg/m³ Billings, 10 September: 7.3 µg/m³ Lockwood Lockwood, 3 September: 3.4 µg/m³ Lockwood, 4 September: 57.6 µg/m³ Lockwood, 5 September: 115.0 µg/m³ Lockwood, 6 September: 29.4 µg/m³, 4.3× its usual 6.8 Lockwood, 7 September: 5.9 µg/m³ Lockwood, 8 September: 8.5 µg/m³ Lockwood, 9 September: 6.2 µg/m³ Lockwood, 10 September: 7.3 µg/m³ Sherwood Park Sherwood Park, 3 September: 114.0 µg/m³ Sherwood Park, 4 September: 50.0 µg/m³ Sherwood Park, 5 September: 33.8 µg/m³ Sherwood Park, 6 September: 29.4 µg/m³, 3.7× its usual 7.9 Sherwood Park, 7 September: 11.4 µg/m³ Sherwood Park, 8 September: 8.5 µg/m³ Sherwood Park, 9 September: 11.1 µg/m³ Sherwood Park, 10 September: 6.7 µg/m³ Prince Albert Prince Albert, 3 September: 354.0 µg/m³ Prince Albert, 4 September: 171.0 µg/m³ Prince Albert, 5 September: 10.6 µg/m³ Prince Albert, 6 September: 26.8 µg/m³, 2.5× its usual 10.9 Prince Albert, 7 September: 32.3 µg/m³, 3.0× its usual 10.9 Prince Albert, 8 September: 23.0 µg/m³ Prince Albert, 9 September: 16.2 µg/m³ Prince Albert, 10 September: 14.0 µg/m³ Grand Centre Grand Centre, 3 September: 292.0 µg/m³ Grand Centre, 4 September: 56.1 µg/m³ Grand Centre, 5 September: 4.9 µg/m³ Grand Centre, 6 September: 26.7 µg/m³, 3.2× its usual 8.4 Grand Centre, 7 September: 32.5 µg/m³, 4.0× its usual 8.2 Grand Centre, 8 September: 11.5 µg/m³ Grand Centre, 9 September: 11.3 µg/m³ Grand Centre, 10 September: 15.2 µg/m³ Fort McMurray Fort McMurray, 3 September: 259.0 µg/m³ Fort McMurray, 4 September: 26.2 µg/m³ Fort McMurray, 5 September: 6.0 µg/m³ Fort McMurray, 6 September: 21.5 µg/m³ Fort McMurray, 7 September: 44.8 µg/m³, 3.6× its usual 12.6 Fort McMurray, 8 September: 23.4 µg/m³ Fort McMurray, 9 September: 25.6 µg/m³ Fort McMurray, 10 September: 17.8 µg/m³ 3 Sep 4 5 6 7 8 9 10 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
Rapid City South Dakota, United States 1 6 September 7.1 9.5× Gillette Wyoming, United States 1 6 September 5.3 8.2× Swift Current Saskatchewan, Canada 1 6 September 7.4 7.8× Havre Montana, United States 1 6 September 4.8 7.5× Scottsbluff Nebraska, United States 1 6 September 4.3 7.4× Miles City Montana, United States 1 6 September 7.7 6.9× Regina Saskatchewan, Canada 2 6 September 8.8 6.6× Edmonton Alberta, Canada 2 6 September 11.1 5.7× Estevan Saskatchewan, Canada 2 7 September 10.5 5.6× Fort Saskatchewan Alberta, Canada 1 6 September 9.6 5.3× Medicine Hat Alberta, Canada 1 6 September 7.3 4.4× Billings Montana, United States 1 6 September 6.8 4.3× Lockwood Montana, United States 1 6 September 6.8 4.3× Grand Centre Alberta, Canada 2 7 September 8.2 4.0× St. Albert Alberta, Canada 1 6 September 8.1 3.7× Sherwood Park Alberta, Canada 1 6 September 7.9 3.7× Fort McMurray Alberta, Canada 1 7 September 12.6 3.6× Saskatoon Saskatchewan, Canada 1 6 September 9.2 3.5× Prince Albert Saskatchewan, Canada 2 7 September 10.9 3.0×
Daily means in µg/m³, over the days each city counted in this episode. Highest: its highest of those days. Usual: the city's median for the time of year of that day (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that, with a usual under 5 µg/m³ taken as 5.
Against other episodes in Canada and the United States
Number 72 of 173 episodes in Canada and the United States since our records began, by cities reached.
Eastern United States and Canada, June and July 2023 343 Northern United States and Canada, July 2026 327 United States and Canada, July 2023 322 Eastern United States and Canada, May and June 2023 317 North-eastern United States and Canada, 29 July to 9 August 2025 292 Northern United States and Canada, May and June 2025 247 United States and Canada, June 2023 195 North-western United States and Canada, August 2023 176 North-western United States and Canada, 4 to 22 August 2026 151 Northern United States and Canada, July 2025 139 Northern United States and Canada, June 2025 134 North-western United States and Canada, July and August 2026 118 North-western Canada and United States, September 2023 19 Bars: cities reached; colour: the level of the episode's highest daily reading. All 173 .
Use this page SmogRank, North-western Canada and United States, September 2023: 19 cities with PM2.5 at twice their usual or more, 6 to 7 September 2023, smogrank.com/episodes/2023-09-north-western-canada-and-united-states (accessed 5 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.
