SmogRank / Episodes / United States
North-western Canada and United States, May 2023
For 3 days, from 20 to 22 May 2023, 24 cities in the United States and Canada had PM2.5 at least twice their usual for the time of year. The worst reading was Edmonton, Alberta, Canada: 309.5 µg/m³ on 20 May, about 44× its usual 7.0.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 24 in 2 countries
Days 3 20 to 22 May 2023
Worst day 20 May 21 cities counted
Furthest above usual 44× Edmonton
Day by day
Play 20 May 21 cities at twice their usual or more
Bozeman Butte Rexburg Missoula Conda Casper Pocatello Rock Springs North Ogden Twin Falls Laramie Highland Herriman Orem Tooele Cheyenne Fort Collins Grand Junction Longmont Greeley Boulder Thornton Denver Ken Caryl Millcreek West Jordan Spanish Fork Salt Lake City Bountiful Magna Helena Idaho Falls Billings Regina Great Falls Sheridan Gillette Lethbridge Prince Albert Calgary Saskatoon Medicine Hat Swift Current Red Deer Airdrie Sherwood Park St. Albert Edmonton 17 May 18 19 20 21 22 23 24 25 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
Edmonton Edmonton, 17 May: 91.0 µg/m³ Edmonton, 18 May: 20.4 µg/m³ Edmonton, 19 May: 102.0 µg/m³ Edmonton, 20 May: 309.5 µg/m³, 44× its usual 7.0 Edmonton, 21 May: 273.0 µg/m³, 38× its usual 7.1 Edmonton, 22 May: 122.0 µg/m³, 17× its usual 7.2 Edmonton, 23 May: 31.9 µg/m³ Edmonton, 24 May: 14.3 µg/m³ Edmonton, 25 May: 34.5 µg/m³ St. Albert St. Albert, 17 May: 77.6 µg/m³ St. Albert, 18 May: 14.8 µg/m³ St. Albert, 19 May: 78.0 µg/m³ St. Albert, 20 May: 231.0 µg/m³, 42× its usual 5.5 St. Albert, 21 May: 195.0 µg/m³, 34× its usual 5.7 St. Albert, 22 May: 84.7 µg/m³, 14× its usual 5.9 St. Albert, 23 May: 17.9 µg/m³ St. Albert, 24 May: 5.9 µg/m³ St. Albert, 25 May: 24.7 µg/m³ Sherwood Park Sherwood Park, 17 May: 50.8 µg/m³ Sherwood Park, 18 May: 11.1 µg/m³ Sherwood Park, 19 May: 67.1 µg/m³ Sherwood Park, 20 May: 204.0 µg/m³, 41× its usual 5.0 Sherwood Park, 21 May: 119.0 µg/m³, 24× its usual 5.0 Sherwood Park, 22 May: 53.8 µg/m³, 11× its usual 5.0 Sherwood Park, 23 May: 11.6 µg/m³ Sherwood Park, 24 May: 3.4 µg/m³ Sherwood Park, 25 May: 22.0 µg/m³ Red Deer Red Deer, 17 May: 129.5 µg/m³ Red Deer, 18 May: 15.0 µg/m³ Red Deer, 19 May: 34.3 µg/m³ Red Deer, 20 May: 191.0 µg/m³, 32× its usual 5.9 Red Deer, 21 May: 175.5 µg/m³, 29× its usual 6.0 Red Deer, 22 May: 110.8 µg/m³, 18× its usual 6.1 Red Deer, 23 May: 2.8 µg/m³ Red Deer, 24 May: 9.3 µg/m³ Red Deer, 25 May: 24.5 µg/m³ Airdrie Airdrie, 17 May: 130.0 µg/m³ Airdrie, 18 May: 31.2 µg/m³ Airdrie, 19 May: 47.4 µg/m³ Airdrie, 20 May: 184.0 µg/m³, 37× its usual 4.6 Airdrie, 21 May: 89.1 µg/m³, 18× its usual 4.7 Airdrie, 22 May: 53.1 µg/m³, 11× its usual 4.8 Airdrie, 23 May: 1.0 µg/m³ Airdrie, 24 May: 4.7 µg/m³ Airdrie, 25 May: 20.7 µg/m³ Swift Current Swift Current, 17 May: 151.0 µg/m³ Swift Current, 18 May: 27.0 µg/m³ Swift Current, 19 May: 19.3 µg/m³ Swift Current, 20 May: 154.0 µg/m³, 29× its usual 5.4 Swift Current, 21 May: 82.0 µg/m³, 15× its usual 5.5 Swift Current, 22 May: 40.1 µg/m³ Swift Current, 23 May: 8.2 µg/m³ Swift Current, 24 May: 20.8 µg/m³ Swift Current, 25 May: 10.0 µg/m³ Saskatoon Saskatoon, 17 May: 138.0 µg/m³ Saskatoon, 18 May: 15.6 µg/m³ Saskatoon, 19 May: 15.3 µg/m³ Saskatoon, 20 May: 105.0 µg/m³, 16× its usual 6.5 Saskatoon, 21 May: 23.3 µg/m³ Saskatoon, 22 May: 38.4 µg/m³ Saskatoon, 23 May: 33.4 µg/m³ Saskatoon, 24 May: 15.9 µg/m³ Saskatoon, 25 May: 14.8 µg/m³ Medicine Hat Medicine Hat, 17 May: 46.8 µg/m³ Medicine Hat, 18 May: 15.2 µg/m³ Medicine Hat, 19 May: 28.7 µg/m³ Medicine Hat, 20 May: 104.0 µg/m³, 21× its usual 4.0 Medicine Hat, 21 May: 74.7 µg/m³, 15× its usual 4.2 Medicine Hat, 22 May: 19.6 µg/m³ Medicine Hat, 23 May: 1.6 µg/m³ Medicine Hat, 24 May: 4.5 µg/m³ Medicine Hat, 25 May: 8.4 µg/m³ Prince Albert Prince Albert, 17 May: 134.0 µg/m³ Prince Albert, 18 May: 11.7 µg/m³ Prince Albert, 19 May: 20.3 µg/m³ Prince Albert, 20 May: 101.0 µg/m³, 14× its usual 7.0 Prince Albert, 21 May: 16.3 µg/m³ Prince Albert, 22 May: 38.2 µg/m³ Prince Albert, 23 May: 29.0 µg/m³ Prince Albert, 24 May: 9.6 µg/m³ Prince Albert, 25 May: 14.1 µg/m³ Calgary Calgary, 17 May: 130.5 µg/m³ Calgary, 18 May: 50.8 µg/m³ Calgary, 19 May: 25.6 µg/m³ Calgary, 20 May: 98.0 µg/m³, 16× its usual 6.3 Calgary, 21 May: 47.9 µg/m³, 7.6× its usual 6.3 Calgary, 22 May: 52.8 µg/m³, 8.4× its usual 6.3 Calgary, 23 May: 1.3 µg/m³ Calgary, 24 May: 4.8 µg/m³ Calgary, 25 May: 19.0 µg/m³ Lethbridge Lethbridge, 17 May: 71.8 µg/m³ Lethbridge, 18 May: 22.7 µg/m³ Lethbridge, 19 May: 37.9 µg/m³ Lethbridge, 20 May: 69.0 µg/m³, 14× its usual 4.1 Lethbridge, 21 May: 25.1 µg/m³, 5.0× its usual 4.1 Lethbridge, 22 May: 3.2 µg/m³ Lethbridge, 23 May: 4.4 µg/m³ Lethbridge, 24 May: 6.3 µg/m³ Lethbridge, 25 May: 14.7 µg/m³ Great Falls Great Falls, 17 May: 23.1 µg/m³ Great Falls, 18 May: 31.3 µg/m³ Great Falls, 19 May: 41.2 µg/m³ Great Falls, 20 May: 47.7 µg/m³, 6.2× its usual 7.7 Great Falls, 21 May: 32.2 µg/m³, 4.2× its usual 7.7 Great Falls, 22 May: 10.2 µg/m³ Great Falls, 23 May: 8.2 µg/m³ Great Falls, 24 May: 8.4 µg/m³ Great Falls, 25 May: 8.5 µg/m³ Helena Helena, 17 May: 30.0 µg/m³ Helena, 18 May: 72.5 µg/m³ Helena, 19 May: 73.8 µg/m³ Helena, 20 May: 34.8 µg/m³, 5.0× its usual 7.0 Helena, 21 May: 19.9 µg/m³ Helena, 22 May: 5.1 µg/m³ Helena, 23 May: 4.5 µg/m³ Helena, 24 May: 5.6 µg/m³ Helena, 25 May: 4.5 µg/m³ Regina Regina, 17 May: 160.0 µg/m³ Regina, 18 May: 12.3 µg/m³ Regina, 19 May: 14.5 µg/m³ Regina, 20 May: 29.4 µg/m³, 5.5× its usual 5.3 Regina, 21 May: 17.1 µg/m³ Regina, 22 May: 27.2 µg/m³ Regina, 23 May: no reading Regina, 24 May: 18.0 µg/m³ Regina, 25 May: 17.2 µg/m³ Idaho Falls Idaho Falls, 17 May: 6.5 µg/m³ Idaho Falls, 18 May: 18.6 µg/m³ Idaho Falls, 19 May: 29.0 µg/m³ Idaho Falls, 20 May: 27.0 µg/m³, 5.4× its usual 3.8 Idaho Falls, 21 May: 19.7 µg/m³ Idaho Falls, 22 May: 9.8 µg/m³ Idaho Falls, 23 May: 5.2 µg/m³ Idaho Falls, 24 May: 5.1 µg/m³ Idaho Falls, 25 May: 7.1 µg/m³ Salt Lake City Salt Lake City, 17 May: 8.2 µg/m³ Salt Lake City, 18 May: 6.1 µg/m³ Salt Lake City, 19 May: 15.4 µg/m³ Salt Lake City, 20 May: 26.7 µg/m³, 4.5× its usual 6.0 Salt Lake City, 21 May: 17.4 µg/m³ Salt Lake City, 22 May: 10.7 µg/m³ Salt Lake City, 23 May: 5.7 µg/m³ Salt Lake City, 24 May: 6.2 µg/m³ Salt Lake City, 25 May: 5.1 µg/m³ Bountiful Bountiful, 17 May: 7.7 µg/m³ Bountiful, 18 May: 6.6 µg/m³ Bountiful, 19 May: 16.1 µg/m³ Bountiful, 20 May: 25.8 µg/m³, 4.7× its usual 5.5 Bountiful, 21 May: 17.4 µg/m³ Bountiful, 22 May: 10.3 µg/m³ Bountiful, 23 May: 4.7 µg/m³ Bountiful, 24 May: 5.7 µg/m³ Bountiful, 25 May: 5.0 µg/m³ West Jordan West Jordan, 17 May: 9.3 µg/m³ West Jordan, 18 May: 6.5 µg/m³ West Jordan, 19 May: 15.1 µg/m³ West Jordan, 20 May: 25.7 µg/m³, 4.1× its usual 6.3 West Jordan, 21 May: 18.3 µg/m³ West Jordan, 22 May: 9.6 µg/m³ West Jordan, 23 May: 4.8 µg/m³ West Jordan, 24 May: 8.0 µg/m³ West Jordan, 25 May: 6.9 µg/m³ Millcreek Millcreek, 17 May: 11.7 µg/m³ Millcreek, 18 May: 6.0 µg/m³ Millcreek, 19 May: 15.2 µg/m³ Millcreek, 20 May: 25.4 µg/m³, 3.4× its usual 7.5 Millcreek, 21 May: 18.9 µg/m³ Millcreek, 22 May: 11.2 µg/m³ Millcreek, 23 May: 6.0 µg/m³ Millcreek, 24 May: 6.5 µg/m³ Millcreek, 25 May: 7.2 µg/m³ Magna Magna, 17 May: 7.8 µg/m³ Magna, 18 May: 6.2 µg/m³ Magna, 19 May: 14.2 µg/m³ Magna, 20 May: 25.1 µg/m³, 5.0× its usual 5.0 Magna, 21 May: 18.1 µg/m³ Magna, 22 May: 9.7 µg/m³ Magna, 23 May: 3.6 µg/m³ Magna, 24 May: 5.5 µg/m³ Magna, 25 May: 4.9 µg/m³ Spanish Fork Spanish Fork, 17 May: 7.8 µg/m³ Spanish Fork, 18 May: 5.6 µg/m³ Spanish Fork, 19 May: 17.9 µg/m³ Spanish Fork, 20 May: 25.0 µg/m³, 4.3× its usual 5.8 Spanish Fork, 21 May: 15.5 µg/m³ Spanish Fork, 22 May: 11.4 µg/m³ Spanish Fork, 23 May: 6.2 µg/m³ Spanish Fork, 24 May: 4.4 µg/m³ Spanish Fork, 25 May: 6.1 µg/m³ Gillette Gillette, 17 May: no reading Gillette, 18 May: 55.1 µg/m³ Gillette, 19 May: 23.5 µg/m³ Gillette, 20 May: 21.3 µg/m³ Gillette, 21 May: 49.0 µg/m³, 9.8× its usual 3.8 Gillette, 22 May: 44.7 µg/m³ Gillette, 23 May: 16.8 µg/m³ Gillette, 24 May: 13.1 µg/m³ Gillette, 25 May: 4.9 µg/m³ Sheridan Sheridan, 17 May: 24.8 µg/m³ Sheridan, 18 May: 38.8 µg/m³ Sheridan, 19 May: 24.1 µg/m³ Sheridan, 20 May: 21.8 µg/m³ Sheridan, 21 May: 40.3 µg/m³, 8.1× its usual 3.8 Sheridan, 22 May: 31.4 µg/m³ Sheridan, 23 May: 13.9 µg/m³ Sheridan, 24 May: 14.2 µg/m³ Sheridan, 25 May: 7.6 µg/m³ Billings Billings, 17 May: 30.4 µg/m³ Billings, 18 May: 33.6 µg/m³ Billings, 19 May: 23.5 µg/m³ Billings, 20 May: 24.8 µg/m³ Billings, 21 May: 27.4 µg/m³, 5.5× its usual 3.7 Billings, 22 May: 12.2 µg/m³ Billings, 23 May: 6.6 µg/m³ Billings, 24 May: 4.2 µg/m³ Billings, 25 May: 4.0 µg/m³ 17 May 18 19 20 21 22 23 24 25 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
Edmonton Alberta, Canada 3 20 May 7.0 44× St. Albert Alberta, Canada 3 20 May 5.5 42× Sherwood Park Alberta, Canada 3 20 May 5.0 41× Airdrie Alberta, Canada 3 20 May 4.6 37× Red Deer Alberta, Canada 3 20 May 5.9 32× Swift Current Saskatchewan, Canada 2 20 May 5.4 29× Medicine Hat Alberta, Canada 2 20 May 4.0 21× Saskatoon Saskatchewan, Canada 1 20 May 6.5 16× Calgary Alberta, Canada 3 20 May 6.3 16× Prince Albert Saskatchewan, Canada 1 20 May 7.0 14× Lethbridge Alberta, Canada 2 20 May 4.1 14× Gillette Wyoming, United States 1 21 May 3.8 9.8× Sheridan Wyoming, United States 1 21 May 3.8 8.1× Great Falls Montana, United States 2 20 May 7.7 6.2× Regina Saskatchewan, Canada 1 20 May 5.3 5.5× Billings Montana, United States 1 21 May 3.7 5.5× Idaho Falls Idaho, United States 1 20 May 3.8 5.4× Helena Montana, United States 1 20 May 7.0 5.0× Magna Utah, United States 1 20 May 5.0 5.0× Bountiful Utah, United States 1 20 May 5.5 4.7× Salt Lake City Utah, United States 1 20 May 6.0 4.5× Spanish Fork Utah, United States 1 20 May 5.8 4.3× West Jordan Utah, United States 1 20 May 6.3 4.1× Millcreek Utah, United States 1 20 May 7.5 3.4×
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 the United States and Canada
Number 44 of 141 episodes in the United States and Canada since our records began, by cities reached.
Eastern United States and Canada, 25 June to 2 July 2023 280 North-eastern United States and Canada, July 2026 264 Eastern United States and Canada, May and June 2023 261 North-eastern United States and Canada, 30 July to 9 August 2025 241 Eastern United States and Canada, July 2023 240 North-eastern United States and Canada, 3 to 9 June 2025 196 Eastern United States and Canada, 14 to 19 June 2023 161 North-eastern United States and Canada, 12 to 16 July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States and Canada, 10 to 14 June 2025 104 North-western United States and Canada, 4 to 11 August 2026 99 North-eastern United States and Canada, 14 to 19 February 2026 96 North-western Canada and United States, May 2023 24 Bars: cities reached; colour: the level of the episode's highest daily reading. All 141 .
Use this page SmogRank, North-western Canada and United States, May 2023: 24 cities with PM2.5 at twice their usual or more, 20 to 22 May 2023, smogrank.com/episodes/2023-05-north-western-canada-and-united-states (accessed 4 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.
