SmogRank / Episodes / United States
North-western United States and Canada, 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
Regina Regina, 17 May: 160.0 µg/m³, 30× usual Regina, 18 May: 12.3 µg/m³, 2.3× usual Regina, 19 May: 14.5 µg/m³, 2.7× usual Regina, 20 May: 29.4 µg/m³, 5.5× usual Regina, 21 May: 17.1 µg/m³, 3.2× usual Regina, 22 May: 27.2 µg/m³, 5.1× usual Regina, 23 May: no reading Regina, 24 May: 18.0 µg/m³, 3.4× usual Regina, 25 May: 17.2 µg/m³, 3.2× usual Swift Current Swift Current, 17 May: 151.0 µg/m³, 28× usual Swift Current, 18 May: 27.0 µg/m³, 5.0× usual Swift Current, 19 May: 19.3 µg/m³, 3.6× usual Swift Current, 20 May: 154.0 µg/m³, 29× usual Swift Current, 21 May: 82.0 µg/m³, 15× usual Swift Current, 22 May: 40.1 µg/m³, 7.4× usual Swift Current, 23 May: 8.2 µg/m³, 1.5× usual Swift Current, 24 May: 20.8 µg/m³, 3.9× usual Swift Current, 25 May: 10.0 µg/m³, 1.9× usual Saskatoon Saskatoon, 17 May: 138.0 µg/m³, 21× usual Saskatoon, 18 May: 15.6 µg/m³, 2.4× usual Saskatoon, 19 May: 15.3 µg/m³, 2.4× usual Saskatoon, 20 May: 105.0 µg/m³, 16× usual Saskatoon, 21 May: 23.3 µg/m³, 3.6× usual Saskatoon, 22 May: 38.4 µg/m³, 5.9× usual Saskatoon, 23 May: 33.4 µg/m³, 5.1× usual Saskatoon, 24 May: 15.9 µg/m³, 2.4× usual Saskatoon, 25 May: 14.8 µg/m³, 2.3× usual Prince Albert Prince Albert, 17 May: 134.0 µg/m³, 19× usual Prince Albert, 18 May: 11.7 µg/m³, 1.7× usual Prince Albert, 19 May: 20.3 µg/m³, 2.9× usual Prince Albert, 20 May: 101.0 µg/m³, 14× usual Prince Albert, 21 May: 16.3 µg/m³, 2.3× usual Prince Albert, 22 May: 38.2 µg/m³, 5.5× usual Prince Albert, 23 May: 29.0 µg/m³, 4.1× usual Prince Albert, 24 May: 9.6 µg/m³, 1.4× usual Prince Albert, 25 May: 14.1 µg/m³, 2.0× usual Calgary Calgary, 17 May: 130.5 µg/m³, 21× usual Calgary, 18 May: 50.8 µg/m³, 8.1× usual Calgary, 19 May: 25.6 µg/m³, 4.1× usual Calgary, 20 May: 98.0 µg/m³, 16× usual Calgary, 21 May: 47.9 µg/m³, 7.6× usual Calgary, 22 May: 52.8 µg/m³, 8.4× usual Calgary, 23 May: 1.3 µg/m³, 0.2× usual Calgary, 24 May: 4.8 µg/m³, 0.8× usual Calgary, 25 May: 19.0 µg/m³, 3.0× usual Airdrie Airdrie, 17 May: 130.0 µg/m³, 26× usual Airdrie, 18 May: 31.2 µg/m³, 6.2× usual Airdrie, 19 May: 47.4 µg/m³, 9.5× usual Airdrie, 20 May: 184.0 µg/m³, 37× usual Airdrie, 21 May: 89.1 µg/m³, 18× usual Airdrie, 22 May: 53.1 µg/m³, 11× usual Airdrie, 23 May: 1.0 µg/m³, 0.2× usual Airdrie, 24 May: 4.7 µg/m³, 0.9× usual Airdrie, 25 May: 20.7 µg/m³, 4.1× usual Red Deer Red Deer, 17 May: 129.5 µg/m³, 22× usual Red Deer, 18 May: 15.0 µg/m³, 2.5× usual Red Deer, 19 May: 34.3 µg/m³, 5.8× usual Red Deer, 20 May: 191.0 µg/m³, 32× usual Red Deer, 21 May: 175.5 µg/m³, 30× usual Red Deer, 22 May: 110.8 µg/m³, 19× usual Red Deer, 23 May: 2.8 µg/m³, 0.5× usual Red Deer, 24 May: 9.3 µg/m³, 1.6× usual Red Deer, 25 May: 24.5 µg/m³, 4.2× usual Edmonton Edmonton, 17 May: 91.0 µg/m³, 13× usual Edmonton, 18 May: 20.4 µg/m³, 2.9× usual Edmonton, 19 May: 102.0 µg/m³, 15× usual Edmonton, 20 May: 309.5 µg/m³, 44× usual Edmonton, 21 May: 273.0 µg/m³, 39× usual Edmonton, 22 May: 122.0 µg/m³, 17× usual Edmonton, 23 May: 31.9 µg/m³, 4.6× usual Edmonton, 24 May: 14.3 µg/m³, 2.0× usual Edmonton, 25 May: 34.5 µg/m³, 4.9× usual St. Albert St. Albert, 17 May: 77.6 µg/m³, 14× usual St. Albert, 18 May: 14.8 µg/m³, 2.7× usual St. Albert, 19 May: 78.0 µg/m³, 14× usual St. Albert, 20 May: 231.0 µg/m³, 42× usual St. Albert, 21 May: 195.0 µg/m³, 35× usual St. Albert, 22 May: 84.7 µg/m³, 15× usual St. Albert, 23 May: 17.9 µg/m³, 3.3× usual St. Albert, 24 May: 5.9 µg/m³, 1.1× usual St. Albert, 25 May: 24.7 µg/m³, 4.5× usual Lethbridge Lethbridge, 17 May: 71.8 µg/m³, 14× usual Lethbridge, 18 May: 22.7 µg/m³, 4.5× usual Lethbridge, 19 May: 37.9 µg/m³, 7.6× usual Lethbridge, 20 May: 69.0 µg/m³, 14× usual Lethbridge, 21 May: 25.1 µg/m³, 5.0× usual Lethbridge, 22 May: 3.2 µg/m³, 0.6× usual Lethbridge, 23 May: 4.4 µg/m³, 0.9× usual Lethbridge, 24 May: 6.3 µg/m³, 1.3× usual Lethbridge, 25 May: 14.7 µg/m³, 2.9× usual Sherwood Park Sherwood Park, 17 May: 50.8 µg/m³, 10× usual Sherwood Park, 18 May: 11.1 µg/m³, 2.2× usual Sherwood Park, 19 May: 67.1 µg/m³, 13× usual Sherwood Park, 20 May: 204.0 µg/m³, 41× usual Sherwood Park, 21 May: 119.0 µg/m³, 24× usual Sherwood Park, 22 May: 53.8 µg/m³, 11× usual Sherwood Park, 23 May: 11.6 µg/m³, 2.3× usual Sherwood Park, 24 May: 3.4 µg/m³, 0.7× usual Sherwood Park, 25 May: 22.0 µg/m³, 4.4× usual Medicine Hat Medicine Hat, 17 May: 46.8 µg/m³, 9.4× usual Medicine Hat, 18 May: 15.2 µg/m³, 3.0× usual Medicine Hat, 19 May: 28.7 µg/m³, 5.7× usual Medicine Hat, 20 May: 104.0 µg/m³, 21× usual Medicine Hat, 21 May: 74.7 µg/m³, 15× usual Medicine Hat, 22 May: 19.6 µg/m³, 3.9× usual Medicine Hat, 23 May: 1.6 µg/m³, 0.3× usual Medicine Hat, 24 May: 4.5 µg/m³, 0.9× usual Medicine Hat, 25 May: 8.4 µg/m³, 1.7× usual Billings Billings, 17 May: 30.4 µg/m³, 6.1× usual Billings, 18 May: 33.6 µg/m³, 6.7× usual Billings, 19 May: 23.5 µg/m³, 4.7× usual Billings, 20 May: 24.8 µg/m³, 5.0× usual Billings, 21 May: 27.4 µg/m³, 5.5× usual Billings, 22 May: 12.2 µg/m³, 2.4× usual Billings, 23 May: 6.6 µg/m³, 1.3× usual Billings, 24 May: 4.2 µg/m³, 0.8× usual Billings, 25 May: 4.0 µg/m³, 0.8× usual Helena Helena, 17 May: 30.0 µg/m³, 4.3× usual Helena, 18 May: 72.5 µg/m³, 10× usual Helena, 19 May: 73.8 µg/m³, 11× usual Helena, 20 May: 34.8 µg/m³, 5.0× usual Helena, 21 May: 19.9 µg/m³, 2.8× usual Helena, 22 May: 5.1 µg/m³, 0.7× usual Helena, 23 May: 4.5 µg/m³, 0.6× usual Helena, 24 May: 5.6 µg/m³, 0.8× usual Helena, 25 May: 4.5 µg/m³, 0.6× usual Gillette Gillette, 17 May: no reading Gillette, 18 May: 55.1 µg/m³, 11× usual Gillette, 19 May: 23.5 µg/m³, 4.7× usual Gillette, 20 May: 21.3 µg/m³, 4.3× usual Gillette, 21 May: 49.0 µg/m³, 9.8× usual Gillette, 22 May: 44.7 µg/m³, 8.9× usual Gillette, 23 May: 16.8 µg/m³, 3.4× usual Gillette, 24 May: 13.1 µg/m³, 2.6× usual Gillette, 25 May: 4.9 µg/m³, 1.0× usual Sheridan Sheridan, 17 May: 24.8 µg/m³, 5.0× usual Sheridan, 18 May: 38.8 µg/m³, 7.8× usual Sheridan, 19 May: 24.1 µg/m³, 4.8× usual Sheridan, 20 May: 21.8 µg/m³, 4.4× usual Sheridan, 21 May: 40.3 µg/m³, 8.1× usual Sheridan, 22 May: 31.4 µg/m³, 6.3× usual Sheridan, 23 May: 13.9 µg/m³, 2.8× usual Sheridan, 24 May: 14.2 µg/m³, 2.8× usual Sheridan, 25 May: 7.6 µg/m³, 1.5× usual Great Falls Great Falls, 17 May: 23.1 µg/m³, 3.0× usual Great Falls, 18 May: 31.3 µg/m³, 4.1× usual Great Falls, 19 May: 41.2 µg/m³, 5.4× usual Great Falls, 20 May: 47.7 µg/m³, 6.2× usual Great Falls, 21 May: 32.2 µg/m³, 4.2× usual Great Falls, 22 May: 10.2 µg/m³, 1.3× usual Great Falls, 23 May: 8.2 µg/m³, 1.1× usual Great Falls, 24 May: 8.4 µg/m³, 1.1× usual Great Falls, 25 May: 8.5 µg/m³, 1.1× usual Idaho Falls Idaho Falls, 17 May: 6.5 µg/m³, 1.3× usual Idaho Falls, 18 May: 18.6 µg/m³, 3.7× usual Idaho Falls, 19 May: 29.0 µg/m³, 5.8× usual Idaho Falls, 20 May: 27.0 µg/m³, 5.4× usual Idaho Falls, 21 May: 19.7 µg/m³, 3.9× usual Idaho Falls, 22 May: 9.8 µg/m³, 2.0× usual Idaho Falls, 23 May: 5.2 µg/m³, 1.0× usual Idaho Falls, 24 May: 5.1 µg/m³, 1.0× usual Idaho Falls, 25 May: 7.1 µg/m³, 1.4× usual Salt Lake City Salt Lake City, 17 May: 8.0 µg/m³, 1.4× usual Salt Lake City, 18 May: 5.9 µg/m³, 1.0× usual Salt Lake City, 19 May: 15.6 µg/m³, 2.6× usual Salt Lake City, 20 May: 26.6 µg/m³, 4.5× usual Salt Lake City, 21 May: 17.6 µg/m³, 3.0× usual Salt Lake City, 22 May: 11.0 µg/m³, 1.9× usual Salt Lake City, 23 May: 5.7 µg/m³, 1.0× usual Salt Lake City, 24 May: 6.0 µg/m³, 1.0× usual Salt Lake City, 25 May: 5.9 µg/m³, 1.0× usual Bountiful Bountiful, 17 May: 7.7 µg/m³, 1.4× usual Bountiful, 18 May: 6.6 µg/m³, 1.2× usual Bountiful, 19 May: 16.1 µg/m³, 2.9× usual Bountiful, 20 May: 25.8 µg/m³, 4.7× usual Bountiful, 21 May: 17.4 µg/m³, 3.2× usual Bountiful, 22 May: 10.3 µg/m³, 1.9× usual Bountiful, 23 May: 4.7 µg/m³, 0.9× usual Bountiful, 24 May: 5.7 µg/m³, 1.0× usual Bountiful, 25 May: 5.0 µg/m³, 0.9× usual West Jordan West Jordan, 17 May: 9.3 µg/m³, 1.5× usual West Jordan, 18 May: 6.5 µg/m³, 1.0× usual West Jordan, 19 May: 15.1 µg/m³, 2.4× usual West Jordan, 20 May: 25.7 µg/m³, 4.1× usual West Jordan, 21 May: 18.3 µg/m³, 2.9× usual West Jordan, 22 May: 9.6 µg/m³, 1.5× usual West Jordan, 23 May: 4.8 µg/m³, 0.8× usual West Jordan, 24 May: 8.0 µg/m³, 1.3× usual West Jordan, 25 May: 6.9 µg/m³, 1.1× usual Millcreek Millcreek, 17 May: 11.7 µg/m³, 1.6× usual Millcreek, 18 May: 6.0 µg/m³, 0.8× usual Millcreek, 19 May: 15.2 µg/m³, 2.0× usual Millcreek, 20 May: 25.4 µg/m³, 3.4× usual Millcreek, 21 May: 18.9 µg/m³, 2.5× usual Millcreek, 22 May: 11.2 µg/m³, 1.5× usual Millcreek, 23 May: 6.0 µg/m³, 0.8× usual Millcreek, 24 May: 6.5 µg/m³, 0.9× usual Millcreek, 25 May: 7.2 µg/m³, 1.0× usual Magna Magna, 17 May: 7.8 µg/m³, 1.6× usual Magna, 18 May: 6.2 µg/m³, 1.2× usual Magna, 19 May: 14.2 µg/m³, 2.8× usual Magna, 20 May: 25.1 µg/m³, 5.0× usual Magna, 21 May: 18.1 µg/m³, 3.6× usual Magna, 22 May: 9.7 µg/m³, 1.9× usual Magna, 23 May: 3.6 µg/m³, 0.7× usual Magna, 24 May: 5.5 µg/m³, 1.1× usual Magna, 25 May: 4.9 µg/m³, 1.0× usual Spanish Fork Spanish Fork, 17 May: 7.8 µg/m³, 1.3× usual Spanish Fork, 18 May: 5.6 µg/m³, 1.0× usual Spanish Fork, 19 May: 17.9 µg/m³, 3.1× usual Spanish Fork, 20 May: 25.0 µg/m³, 4.3× usual Spanish Fork, 21 May: 15.5 µg/m³, 2.7× usual Spanish Fork, 22 May: 11.4 µg/m³, 2.0× usual Spanish Fork, 23 May: 6.2 µg/m³, 1.1× usual Spanish Fork, 24 May: 4.4 µg/m³, 0.8× usual Spanish Fork, 25 May: 6.1 µg/m³, 1.1× usual 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× Regina Saskatchewan, Canada 1 17 May 5.3 30× Swift Current Saskatchewan, Canada 2 20 May 5.4 29× Saskatoon Saskatchewan, Canada 1 17 May 6.5 21× Medicine Hat Alberta, Canada 2 20 May 4.0 21× Calgary Alberta, Canada 3 17 May 6.3 21× Prince Albert Saskatchewan, Canada 1 17 May 7.0 19× Lethbridge Alberta, Canada 2 17 May 4.1 14× Gillette Wyoming, United States 1 18 May 3.8 11× Helena Montana, United States 1 19 May 7.0 11× Sheridan Wyoming, United States 1 21 May 3.8 8.1× Billings Montana, United States 1 18 May 3.7 6.7× Great Falls Montana, United States 2 20 May 7.7 6.2× Idaho Falls Idaho, United States 1 19 May 3.8 5.8× 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 5.9 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. 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 16 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-western United States and Canada, May 2023 24 Bars: cities reached; colour: the level of the episode's highest daily reading. All 45 .
Use this page SmogRank, North-western United States and Canada, 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-united-states-and-canada-2 (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.
