SmogRank / Episodes / Canada
North-western Canada and United States, August and September 2023
For 7 days, from 31 August to 6 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 Prince Albert, Saskatchewan, Canada: 354.0 µg/m³ on 3 September, about 33× its usual 10.8.
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 7 31 August to 6 September 2023
Worst day 4 September 17 cities counted
Furthest above usual 33× Prince Albert
Day by day
Play 4 September 17 cities at twice their usual or more
Bozeman Butte Rexburg Missoula Idaho Falls Conda Pocatello Twin Falls Helena Casper Great Falls Lethbridge Rapid City Red Deer Airdrie St. Albert Calgary Sherwood Park Medicine Hat Billings Gillette Sheridan Edmonton Regina Swift Current Saskatoon Prince Albert 28 Aug 29 30 31 1 Sep 2 3 4 5 6 7 8 9 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
Regina Regina, 28 August: 74.1 µg/m³, 8.2× usual Regina, 29 August: 68.8 µg/m³, 7.6× usual Regina, 30 August: 60.0 µg/m³, 6.7× usual Regina, 31 August: 10.8 µg/m³, 1.2× usual Regina, 1 September: 59.9 µg/m³, 6.7× usual Regina, 2 September: 81.8 µg/m³, 9.1× usual Regina, 3 September: 108.0 µg/m³, 12× usual Regina, 4 September: 176.0 µg/m³, 20× usual Regina, 5 September: 38.2 µg/m³, 4.2× usual Regina, 6 September: 58.0 µg/m³, 6.4× usual Regina, 7 September: 40.7 µg/m³, 4.5× usual Regina, 8 September: 20.2 µg/m³, 2.2× usual Regina, 9 September: 15.2 µg/m³, 1.7× usual Prince Albert Prince Albert, 28 August: 64.8 µg/m³, 6.0× usual Prince Albert, 29 August: 88.3 µg/m³, 8.2× usual Prince Albert, 30 August: 52.7 µg/m³, 4.9× usual Prince Albert, 31 August: 20.2 µg/m³, 1.9× usual Prince Albert, 1 September: 98.1 µg/m³, 9.1× usual Prince Albert, 2 September: 93.8 µg/m³, 8.7× usual Prince Albert, 3 September: 354.0 µg/m³, 33× usual Prince Albert, 4 September: 171.0 µg/m³, 16× usual Prince Albert, 5 September: 10.6 µg/m³, 1.0× usual Prince Albert, 6 September: 26.8 µg/m³, 2.5× usual Prince Albert, 7 September: 32.3 µg/m³, 3.0× usual Prince Albert, 8 September: 23.0 µg/m³, 2.1× usual Prince Albert, 9 September: 16.2 µg/m³, 1.5× usual Edmonton Edmonton, 28 August: 61.9 µg/m³, 5.5× usual Edmonton, 29 August: 46.6 µg/m³, 4.1× usual Edmonton, 30 August: 47.0 µg/m³, 4.2× usual Edmonton, 31 August: 51.9 µg/m³, 4.6× usual Edmonton, 1 September: 76.3 µg/m³, 6.8× usual Edmonton, 2 September: 121.0 µg/m³, 11× usual Edmonton, 3 September: 201.0 µg/m³, 18× usual Edmonton, 4 September: 103.0 µg/m³, 9.1× usual Edmonton, 5 September: 62.7 µg/m³, 5.5× usual Edmonton, 6 September: 63.2 µg/m³, 5.6× usual Edmonton, 7 September: 25.1 µg/m³, 2.2× usual Edmonton, 8 September: 20.4 µg/m³, 1.8× usual Edmonton, 9 September: 21.0 µg/m³, 1.9× usual Swift Current Swift Current, 28 August: 52.2 µg/m³, 6.9× usual Swift Current, 29 August: 49.2 µg/m³, 6.5× usual Swift Current, 30 August: 21.0 µg/m³, 2.8× usual Swift Current, 31 August: 11.6 µg/m³, 1.5× usual Swift Current, 1 September: 46.8 µg/m³, 6.2× usual Swift Current, 2 September: 75.0 µg/m³, 9.9× usual Swift Current, 3 September: 68.3 µg/m³, 9.0× usual Swift Current, 4 September: 205.0 µg/m³, 27× usual Swift Current, 5 September: 47.3 µg/m³, 6.2× usual Swift Current, 6 September: 58.0 µg/m³, 7.6× usual Swift Current, 7 September: 21.6 µg/m³, 2.8× usual Swift Current, 8 September: 8.9 µg/m³, 1.2× usual Swift Current, 9 September: 6.0 µg/m³, 0.8× usual Saskatoon Saskatoon, 28 August: 48.0 µg/m³, 4.9× usual Saskatoon, 29 August: 48.9 µg/m³, 5.0× usual Saskatoon, 30 August: 55.8 µg/m³, 5.8× usual Saskatoon, 31 August: 18.5 µg/m³, 1.9× usual Saskatoon, 1 September: 113.0 µg/m³, 12× usual Saskatoon, 2 September: 105.0 µg/m³, 11× usual Saskatoon, 3 September: 270.0 µg/m³, 28× usual Saskatoon, 4 September: 175.0 µg/m³, 18× usual Saskatoon, 5 September: 13.3 µg/m³, 1.4× usual Saskatoon, 6 September: 32.6 µg/m³, 3.4× usual Saskatoon, 7 September: 22.8 µg/m³, 2.4× usual Saskatoon, 8 September: 17.1 µg/m³, 1.8× usual Saskatoon, 9 September: 15.9 µg/m³, 1.6× usual Red Deer Red Deer, 28 August: 33.7 µg/m³, 3.5× usual Red Deer, 29 August: 28.6 µg/m³, 2.9× usual Red Deer, 30 August: 27.5 µg/m³, 2.8× usual Red Deer, 31 August: 44.0 µg/m³, 4.5× usual Red Deer, 1 September: 40.3 µg/m³, 4.2× usual Red Deer, 2 September: 49.0 µg/m³, 5.1× usual Red Deer, 3 September: 111.7 µg/m³, 12× usual Red Deer, 4 September: 107.4 µg/m³, 11× usual Red Deer, 5 September: 72.4 µg/m³, 7.5× usual Red Deer, 6 September: 23.4 µg/m³, 2.4× usual Red Deer, 7 September: 8.3 µg/m³, 0.9× usual Red Deer, 8 September: 12.3 µg/m³, 1.3× usual Red Deer, 9 September: 10.4 µg/m³, 1.1× usual Sherwood Park Sherwood Park, 28 August: 30.5 µg/m³, 3.8× usual Sherwood Park, 29 August: 21.0 µg/m³, 2.6× usual Sherwood Park, 30 August: 20.8 µg/m³, 2.6× usual Sherwood Park, 31 August: 26.4 µg/m³, 3.3× usual Sherwood Park, 1 September: 47.1 µg/m³, 5.9× usual Sherwood Park, 2 September: 61.1 µg/m³, 7.6× usual Sherwood Park, 3 September: 114.0 µg/m³, 14× usual Sherwood Park, 4 September: 50.0 µg/m³, 6.3× usual Sherwood Park, 5 September: 33.8 µg/m³, 4.2× usual Sherwood Park, 6 September: 29.4 µg/m³, 3.7× usual Sherwood Park, 7 September: 11.4 µg/m³, 1.4× usual Sherwood Park, 8 September: 8.5 µg/m³, 1.1× usual Sherwood Park, 9 September: 11.1 µg/m³, 1.4× usual St. Albert St. Albert, 28 August: 30.1 µg/m³, 3.7× usual St. Albert, 29 August: 23.1 µg/m³, 2.9× usual St. Albert, 30 August: 23.8 µg/m³, 2.9× usual St. Albert, 31 August: 28.4 µg/m³, 3.5× usual St. Albert, 1 September: 45.4 µg/m³, 5.6× usual St. Albert, 2 September: 59.6 µg/m³, 7.4× usual St. Albert, 3 September: 104.0 µg/m³, 13× usual St. Albert, 4 September: 51.1 µg/m³, 6.3× usual St. Albert, 5 September: 36.8 µg/m³, 4.5× usual St. Albert, 6 September: 30.3 µg/m³, 3.7× usual St. Albert, 7 September: 10.5 µg/m³, 1.3× usual St. Albert, 8 September: 9.1 µg/m³, 1.1× usual St. Albert, 9 September: 13.4 µg/m³, 1.7× usual Medicine Hat Medicine Hat, 28 August: 29.0 µg/m³, 4.0× usual Medicine Hat, 29 August: 21.0 µg/m³, 2.9× usual Medicine Hat, 30 August: 1.7 µg/m³, 0.2× usual Medicine Hat, 31 August: 21.5 µg/m³, 2.9× usual Medicine Hat, 1 September: 15.0 µg/m³, 2.1× usual Medicine Hat, 2 September: 7.4 µg/m³, 1.0× usual Medicine Hat, 3 September: 24.0 µg/m³, 3.3× usual Medicine Hat, 4 September: 109.0 µg/m³, 15× usual Medicine Hat, 5 September: 78.6 µg/m³, 11× usual Medicine Hat, 6 September: 32.0 µg/m³, 4.4× usual Medicine Hat, 7 September: 6.9 µg/m³, 0.9× usual Medicine Hat, 8 September: 7.2 µg/m³, 1.0× usual Medicine Hat, 9 September: 5.4 µg/m³, 0.7× usual Calgary Calgary, 28 August: 23.2 µg/m³, 2.1× usual Calgary, 29 August: 22.0 µg/m³, 2.0× usual Calgary, 30 August: 25.0 µg/m³, 2.2× usual Calgary, 31 August: 42.6 µg/m³, 3.8× usual Calgary, 1 September: 23.7 µg/m³, 2.1× usual Calgary, 2 September: 10.7 µg/m³, 1.0× usual Calgary, 3 September: 62.7 µg/m³, 5.6× usual Calgary, 4 September: 143.0 µg/m³, 13× usual Calgary, 5 September: 82.9 µg/m³, 7.4× usual Calgary, 6 September: 16.8 µg/m³, 1.5× usual Calgary, 7 September: 8.3 µg/m³, 0.7× usual Calgary, 8 September: 9.8 µg/m³, 0.9× usual Calgary, 9 September: 10.3 µg/m³, 0.9× usual Airdrie Airdrie, 28 August: 17.4 µg/m³, 2.3× usual Airdrie, 29 August: 17.4 µg/m³, 2.3× usual Airdrie, 30 August: 17.8 µg/m³, 2.4× usual Airdrie, 31 August: 30.5 µg/m³, 4.1× usual Airdrie, 1 September: 17.3 µg/m³, 2.3× usual Airdrie, 2 September: 6.5 µg/m³, 0.9× usual Airdrie, 3 September: 58.5 µg/m³, 7.8× usual Airdrie, 4 September: 93.7 µg/m³, 12× usual Airdrie, 5 September: 50.9 µg/m³, 6.8× usual Airdrie, 6 September: 9.5 µg/m³, 1.3× usual Airdrie, 7 September: 6.2 µg/m³, 0.8× usual Airdrie, 8 September: 8.0 µg/m³, 1.1× usual Airdrie, 9 September: 8.4 µg/m³, 1.1× usual Lethbridge Lethbridge, 28 August: 12.3 µg/m³, 1.4× usual Lethbridge, 29 August: 14.0 µg/m³, 1.6× usual Lethbridge, 30 August: 4.5 µg/m³, 0.5× usual Lethbridge, 31 August: 25.8 µg/m³, 3.0× usual Lethbridge, 1 September: 14.1 µg/m³, 1.6× usual Lethbridge, 2 September: 3.4 µg/m³, 0.4× usual Lethbridge, 3 September: 18.1 µg/m³, 2.1× usual Lethbridge, 4 September: 83.9 µg/m³, 9.8× usual Lethbridge, 5 September: 47.3 µg/m³, 5.5× usual Lethbridge, 6 September: 14.2 µg/m³, 1.7× usual Lethbridge, 7 September: 3.5 µg/m³, 0.4× usual Lethbridge, 8 September: 11.4 µg/m³, 1.3× usual Lethbridge, 9 September: 8.1 µg/m³, 0.9× usual Great Falls Great Falls, 28 August: 16.3 µg/m³, 1.4× usual Great Falls, 29 August: 12.5 µg/m³, 1.1× usual Great Falls, 30 August: 8.8 µg/m³, 0.8× usual Great Falls, 31 August: 12.3 µg/m³, 1.1× usual Great Falls, 1 September: 21.4 µg/m³, 1.8× usual Great Falls, 2 September: 15.8 µg/m³, 1.4× usual Great Falls, 3 September: 10.3 µg/m³, 0.9× usual Great Falls, 4 September: 78.1 µg/m³, 6.7× usual Great Falls, 5 September: 57.5 µg/m³, 4.9× usual Great Falls, 6 September: 11.9 µg/m³, 1.0× usual Great Falls, 7 September: 10.2 µg/m³, 0.9× usual Great Falls, 8 September: 10.6 µg/m³, 0.9× usual Great Falls, 9 September: 9.5 µg/m³, 0.8× usual Billings Billings, 28 August: 5.4 µg/m³, 0.8× usual Billings, 29 August: 5.5 µg/m³, 0.8× usual Billings, 30 August: 6.6 µg/m³, 1.0× usual Billings, 31 August: 3.7 µg/m³, 0.5× usual Billings, 1 September: 8.2 µg/m³, 1.2× usual Billings, 2 September: 4.1 µg/m³, 0.6× usual Billings, 3 September: 3.4 µg/m³, 0.5× usual Billings, 4 September: 57.6 µg/m³, 8.3× usual Billings, 5 September: 115.0 µg/m³, 17× usual Billings, 6 September: 29.4 µg/m³, 4.3× usual Billings, 7 September: 5.9 µg/m³, 0.9× usual Billings, 8 September: 8.5 µg/m³, 1.2× usual Billings, 9 September: 6.2 µg/m³, 0.9× usual Helena Helena, 28 August: 8.9 µg/m³, 1.1× usual Helena, 29 August: 6.4 µg/m³, 0.8× usual Helena, 30 August: 4.8 µg/m³, 0.6× usual Helena, 31 August: 5.0 µg/m³, 0.6× usual Helena, 1 September: 11.3 µg/m³, 1.4× usual Helena, 2 September: 13.3 µg/m³, 1.7× usual Helena, 3 September: 6.6 µg/m³, 0.8× usual Helena, 4 September: 31.1 µg/m³, 3.9× usual Helena, 5 September: 35.1 µg/m³, 4.4× usual Helena, 6 September: 7.2 µg/m³, 0.9× usual Helena, 7 September: 6.1 µg/m³, 0.8× usual Helena, 8 September: 6.8 µg/m³, 0.9× usual Helena, 9 September: 6.1 µg/m³, 0.8× usual Sheridan Sheridan, 28 August: 3.1 µg/m³, 0.6× usual Sheridan, 29 August: 2.9 µg/m³, 0.6× usual Sheridan, 30 August: 7.0 µg/m³, 1.3× usual Sheridan, 31 August: 7.1 µg/m³, 1.4× usual Sheridan, 1 September: 3.4 µg/m³, 0.7× usual Sheridan, 2 September: 3.0 µg/m³, 0.6× usual Sheridan, 3 September: 2.2 µg/m³, 0.4× usual Sheridan, 4 September: 30.3 µg/m³, 5.8× usual Sheridan, 5 September: 91.5 µg/m³, 18× usual Sheridan, 6 September: 21.0 µg/m³, 4.0× usual Sheridan, 7 September: 3.1 µg/m³, 0.6× usual Sheridan, 8 September: 3.6 µg/m³, 0.7× usual Sheridan, 9 September: 4.2 µg/m³, 0.8× usual Gillette Gillette, 28 August: 6.4 µg/m³, 1.2× usual Gillette, 29 August: 7.7 µg/m³, 1.5× usual Gillette, 30 August: 6.9 µg/m³, 1.3× usual Gillette, 31 August: 6.0 µg/m³, 1.2× usual Gillette, 1 September: 6.0 µg/m³, 1.2× usual Gillette, 2 September: 3.9 µg/m³, 0.8× usual Gillette, 3 September: 4.3 µg/m³, 0.8× usual Gillette, 4 September: 26.9 µg/m³, 5.2× usual Gillette, 5 September: 90.4 µg/m³, 17× usual Gillette, 6 September: 43.7 µg/m³, 8.4× usual Gillette, 7 September: 9.9 µg/m³, 1.9× usual Gillette, 8 September: 9.5 µg/m³, 1.8× usual Gillette, 9 September: 11.1 µg/m³, 2.1× usual Rapid City Rapid City, 28 August: 10.3 µg/m³, 1.5× usual Rapid City, 29 August: 13.9 µg/m³, 2.0× usual Rapid City, 30 August: 11.6 µg/m³, 1.6× usual Rapid City, 31 August: 8.3 µg/m³, 1.2× usual Rapid City, 1 September: 15.3 µg/m³, 2.2× usual Rapid City, 2 September: 7.0 µg/m³, 1.0× usual Rapid City, 3 September: 6.7 µg/m³, 0.9× usual Rapid City, 4 September: 8.8 µg/m³, 1.2× usual Rapid City, 5 September: 73.6 µg/m³, 10× usual Rapid City, 6 September: 67.6 µg/m³, 9.5× usual Rapid City, 7 September: 29.3 µg/m³, 4.1× usual Rapid City, 8 September: 12.6 µg/m³, 1.8× usual Rapid City, 9 September: 17.0 µg/m³, 2.4× usual Casper Casper, 28 August: 4.1 µg/m³, 0.8× usual Casper, 29 August: 5.0 µg/m³, 1.0× usual Casper, 30 August: 3.9 µg/m³, 0.8× usual Casper, 31 August: 7.7 µg/m³, 1.5× usual Casper, 1 September: 2.9 µg/m³, 0.6× usual Casper, 2 September: 1.6 µg/m³, 0.3× usual Casper, 3 September: 1.9 µg/m³, 0.4× usual Casper, 4 September: 2.9 µg/m³, 0.6× usual Casper, 5 September: 26.8 µg/m³, 5.4× usual Casper, 6 September: 16.9 µg/m³, 3.4× usual Casper, 7 September: 2.6 µg/m³, 0.5× usual Casper, 8 September: 3.1 µg/m³, 0.6× usual Casper, 9 September: 6.2 µg/m³, 1.2× usual 28 Aug 30 1 Sep 3 5 7 9 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
Prince Albert Saskatchewan, Canada 5 3 September 10.8 33× Saskatoon Saskatchewan, Canada 5 3 September 9.7 28× Swift Current Saskatchewan, Canada 6 4 September 7.6 27× Regina Saskatchewan, Canada 6 4 September 9.0 20× Edmonton Alberta, Canada 6 3 September 11.3 18× Sheridan Wyoming, United States 2 5 September 5.2 18× Gillette Wyoming, United States 2 5 September 5.2 17× Billings Montana, United States 2 5 September 6.9 17× Medicine Hat Alberta, Canada 3 4 September 7.3 15× Sherwood Park Alberta, Canada 6 3 September 8.0 14× St. Albert Alberta, Canada 6 3 September 8.1 13× Calgary Alberta, Canada 4 4 September 11.2 13× Airdrie Alberta, Canada 4 4 September 7.5 12× Red Deer Alberta, Canada 6 3 September 9.7 12× Rapid City South Dakota, United States 1 5 September 7.1 10× Lethbridge Alberta, Canada 3 4 September 8.6 9.8× Great Falls Montana, United States 2 4 September 11.7 6.7× Casper Wyoming, United States 1 5 September 3.4 5.4× Helena Montana, United States 2 5 September 7.9 4.4×
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 19 of 45 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, 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-western Canada and United States, August and September 2023 19 Bars: cities reached; colour: the level of the episode's highest daily reading. All 45 .
Use this page SmogRank, North-western Canada and United States, August and September 2023: 19 cities with PM2.5 at twice their usual or more, 31 August to 6 September 2023, smogrank.com/episodes/2023-08-north-western-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.
