SmogRank / Episodes / United States

North-western United States and Canada, May 2023

For 5 days, from 16 to 20 May 2023, 42 cities in the United States and Canada had PM2.5 at least twice their usual for the time of year. The worst reading was Regina, Saskatchewan, Canada: 160.0 µg/m³ on 17 May, about 30× its usual 5.3.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached42in 2 countries
Days516 to 20 May 2023
Worst day19 May29 cities counted
Furthest above usual30×Edmonton

Day by day

19 May 29 cities at twice their usual or more
PocatelloCondaTwin FallsNorth OgdenBoiseCoeur d'AleneMoscowMeridianBountifulSalt Lake CityNampaMagnaMillcreekWest JordanSpokane ValleyHerrimanTooeleHighlandSpokaneOremSpanish ForkWalla WallaPendletonPascoTri-CitiesHermistonMoses LakeGrand JunctionSunnysideWenatcheeCedar CityYakimaEllensburgThe DallesRedmondBendSpanish SpringsRenoCarson CityTruckeeSouth Lake TahoeParadiseLincolnFolsomRosevilleYuba CityArden-ArcadeSacramentoGaltModestoStocktonMantecaTracyRexburgPullmanGreat FallsIdaho FallsPentictonLewistonBillingsBozemanRock SpringsCasperMissoulaSheridanButteMedicine HatLaramieKelownaHelenaFort CollinsGilletteVernonColorado SpringsCheyenneSherwood ParkBoulderGreeleySt. AlbertLethbridgeEdmontonCranbrookThorntonDenverRapid CityKen CarylLongmontPrince AlbertKamloopsCalgarySaskatoonRed DeerAirdrieSwift CurrentRegina
13 May14151617181920212223
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

Prince AlbertPrince Albert, 13 May: 20.5 µg/m³, 3.0× usualPrince Albert, 14 May: 29.3 µg/m³, 4.3× usualPrince Albert, 15 May: 15.5 µg/m³, 2.3× usualPrince Albert, 16 May: 227.0 µg/m³, 33× usualPrince Albert, 17 May: 134.0 µg/m³, 20× usualPrince Albert, 18 May: 11.7 µg/m³, 1.7× usualPrince Albert, 19 May: 20.3 µg/m³, 3.0× usualPrince Albert, 20 May: 101.0 µg/m³, 15× usualPrince Albert, 21 May: 16.3 µg/m³, 2.4× usualPrince Albert, 22 May: 38.2 µg/m³, 5.6× usualPrince Albert, 23 May: 29.0 µg/m³, 4.3× usualRed DeerRed Deer, 13 May: 7.7 µg/m³, 1.4× usualRed Deer, 14 May: 7.7 µg/m³, 1.4× usualRed Deer, 15 May: 5.4 µg/m³, 0.9× usualRed Deer, 16 May: 134.5 µg/m³, 24× usualRed Deer, 17 May: 129.5 µg/m³, 23× usualRed Deer, 18 May: 15.0 µg/m³, 2.6× usualRed Deer, 19 May: 34.3 µg/m³, 6.0× usualRed Deer, 20 May: 191.0 µg/m³, 34× usualRed Deer, 21 May: 175.5 µg/m³, 31× usualRed Deer, 22 May: 110.8 µg/m³, 19× usualRed Deer, 23 May: 2.8 µg/m³, 0.5× usualCalgaryCalgary, 13 May: 9.2 µg/m³, 1.5× usualCalgary, 14 May: 8.1 µg/m³, 1.3× usualCalgary, 15 May: 16.8 µg/m³, 2.7× usualCalgary, 16 May: 112.5 µg/m³, 18× usualCalgary, 17 May: 130.5 µg/m³, 21× usualCalgary, 18 May: 50.8 µg/m³, 8.1× usualCalgary, 19 May: 25.6 µg/m³, 4.1× usualCalgary, 20 May: 98.0 µg/m³, 16× usualCalgary, 21 May: 47.9 µg/m³, 7.6× usualCalgary, 22 May: 52.8 µg/m³, 8.4× usualCalgary, 23 May: 1.3 µg/m³, 0.2× usualAirdrieAirdrie, 13 May: 9.6 µg/m³, 1.9× usualAirdrie, 14 May: 6.2 µg/m³, 1.2× usualAirdrie, 15 May: 4.0 µg/m³, 0.8× usualAirdrie, 16 May: 111.0 µg/m³, 22× usualAirdrie, 17 May: 130.0 µg/m³, 26× usualAirdrie, 18 May: 31.2 µg/m³, 6.2× usualAirdrie, 19 May: 47.4 µg/m³, 9.5× usualAirdrie, 20 May: 184.0 µg/m³, 37× usualAirdrie, 21 May: 89.1 µg/m³, 18× usualAirdrie, 22 May: 53.1 µg/m³, 11× usualAirdrie, 23 May: 1.0 µg/m³, 0.2× usualSaskatoonSaskatoon, 13 May: 21.5 µg/m³, 3.4× usualSaskatoon, 14 May: 16.3 µg/m³, 2.6× usualSaskatoon, 15 May: 11.8 µg/m³, 1.9× usualSaskatoon, 16 May: 97.9 µg/m³, 16× usualSaskatoon, 17 May: 138.0 µg/m³, 22× usualSaskatoon, 18 May: 15.6 µg/m³, 2.5× usualSaskatoon, 19 May: 15.3 µg/m³, 2.4× usualSaskatoon, 20 May: 105.0 µg/m³, 17× usualSaskatoon, 21 May: 23.3 µg/m³, 3.7× usualSaskatoon, 22 May: 38.4 µg/m³, 6.1× usualSaskatoon, 23 May: 33.4 µg/m³, 5.3× usualEdmontonEdmonton, 13 May: 8.3 µg/m³, 1.2× usualEdmonton, 14 May: 10.6 µg/m³, 1.5× usualEdmonton, 15 May: 8.3 µg/m³, 1.2× usualEdmonton, 16 May: 48.6 µg/m³, 6.9× usualEdmonton, 17 May: 91.0 µg/m³, 13× usualEdmonton, 18 May: 20.4 µg/m³, 2.9× usualEdmonton, 19 May: 102.0 µg/m³, 15× usualEdmonton, 20 May: 309.5 µg/m³, 44× usualEdmonton, 21 May: 273.0 µg/m³, 39× usualEdmonton, 22 May: 122.0 µg/m³, 17× usualEdmonton, 23 May: 31.9 µg/m³, 4.6× usualSt. AlbertSt. Albert, 13 May: 7.2 µg/m³, 1.3× usualSt. Albert, 14 May: 10.1 µg/m³, 1.8× usualSt. Albert, 15 May: 5.9 µg/m³, 1.1× usualSt. Albert, 16 May: 44.4 µg/m³, 8.1× usualSt. Albert, 17 May: 77.6 µg/m³, 14× usualSt. Albert, 18 May: 14.8 µg/m³, 2.7× usualSt. Albert, 19 May: 78.0 µg/m³, 14× usualSt. Albert, 20 May: 231.0 µg/m³, 42× usualSt. Albert, 21 May: 195.0 µg/m³, 35× usualSt. Albert, 22 May: 84.7 µg/m³, 15× usualSt. Albert, 23 May: 17.9 µg/m³, 3.3× usualGreat FallsGreat Falls, 13 May: 10.5 µg/m³, 1.3× usualGreat Falls, 14 May: 9.7 µg/m³, 1.2× usualGreat Falls, 15 May: 9.2 µg/m³, 1.2× usualGreat Falls, 16 May: 41.2 µg/m³, 5.2× usualGreat Falls, 17 May: 23.1 µg/m³, 2.9× usualGreat Falls, 18 May: 31.3 µg/m³, 4.0× usualGreat Falls, 19 May: 41.2 µg/m³, 5.2× usualGreat Falls, 20 May: 47.7 µg/m³, 6.0× usualGreat Falls, 21 May: 32.2 µg/m³, 4.1× usualGreat Falls, 22 May: 10.2 µg/m³, 1.3× usualGreat Falls, 23 May: 8.2 µg/m³, 1.0× usualLethbridgeLethbridge, 13 May: 8.2 µg/m³, 1.6× usualLethbridge, 14 May: 3.9 µg/m³, 0.8× usualLethbridge, 15 May: 5.0 µg/m³, 1.0× usualLethbridge, 16 May: 32.0 µg/m³, 6.4× usualLethbridge, 17 May: 71.8 µg/m³, 14× usualLethbridge, 18 May: 22.7 µg/m³, 4.5× usualLethbridge, 19 May: 37.9 µg/m³, 7.6× usualLethbridge, 20 May: 69.0 µg/m³, 14× usualLethbridge, 21 May: 25.1 µg/m³, 5.0× usualLethbridge, 22 May: 3.2 µg/m³, 0.6× usualLethbridge, 23 May: 4.4 µg/m³, 0.9× usualSherwood ParkSherwood Park, 13 May: 7.2 µg/m³, 1.4× usualSherwood Park, 14 May: 7.8 µg/m³, 1.6× usualSherwood Park, 15 May: 4.8 µg/m³, 1.0× usualSherwood Park, 16 May: 30.8 µg/m³, 6.2× usualSherwood Park, 17 May: 50.8 µg/m³, 10× usualSherwood Park, 18 May: 11.1 µg/m³, 2.2× usualSherwood Park, 19 May: 67.1 µg/m³, 13× usualSherwood Park, 20 May: 204.0 µg/m³, 41× usualSherwood Park, 21 May: 119.0 µg/m³, 24× usualSherwood Park, 22 May: 53.8 µg/m³, 11× usualSherwood Park, 23 May: 11.6 µg/m³, 2.3× usualReginaRegina, 13 May: 10.8 µg/m³, 2.0× usualRegina, 14 May: 10.7 µg/m³, 2.0× usualRegina, 15 May: 9.9 µg/m³, 1.9× usualRegina, 16 May: 18.4 µg/m³, 3.5× usualRegina, 17 May: 160.0 µg/m³, 30× usualRegina, 18 May: 12.3 µg/m³, 2.3× usualRegina, 19 May: 14.5 µg/m³, 2.7× usualRegina, 20 May: 29.4 µg/m³, 5.5× usualRegina, 21 May: 17.1 µg/m³, 3.2× usualRegina, 22 May: 27.2 µg/m³, 5.1× usualRegina, 23 May: no readingSwift CurrentSwift Current, 13 May: 13.1 µg/m³, 2.6× usualSwift Current, 14 May: 10.0 µg/m³, 2.0× usualSwift Current, 15 May: 9.1 µg/m³, 1.8× usualSwift Current, 16 May: 24.8 µg/m³, 5.0× usualSwift Current, 17 May: 151.0 µg/m³, 30× usualSwift Current, 18 May: 27.0 µg/m³, 5.4× usualSwift Current, 19 May: 19.3 µg/m³, 3.9× usualSwift Current, 20 May: 154.0 µg/m³, 31× usualSwift Current, 21 May: 82.0 µg/m³, 16× usualSwift Current, 22 May: 40.1 µg/m³, 8.0× usualSwift Current, 23 May: 8.2 µg/m³, 1.6× usualKamloopsKamloops, 13 May: 9.8 µg/m³, 2.0× usualKamloops, 14 May: 10.5 µg/m³, 2.1× usualKamloops, 15 May: 7.7 µg/m³, 1.5× usualKamloops, 16 May: 9.4 µg/m³, 1.9× usualKamloops, 17 May: 99.5 µg/m³, 20× usualKamloops, 18 May: 79.7 µg/m³, 16× usualKamloops, 19 May: 8.2 µg/m³, 1.6× usualKamloops, 20 May: 7.9 µg/m³, 1.6× usualKamloops, 21 May: 5.3 µg/m³, 1.1× usualKamloops, 22 May: 3.1 µg/m³, 0.6× usualKamloops, 23 May: 4.6 µg/m³, 0.9× usualCranbrookCranbrook, 13 May: 6.8 µg/m³, 1.4× usualCranbrook, 14 May: 5.6 µg/m³, 1.1× usualCranbrook, 15 May: 3.8 µg/m³, 0.8× usualCranbrook, 16 May: 5.6 µg/m³, 1.1× usualCranbrook, 17 May: 52.1 µg/m³, 10× usualCranbrook, 18 May: 75.6 µg/m³, 15× usualCranbrook, 19 May: 22.7 µg/m³, 4.5× usualCranbrook, 20 May: 11.0 µg/m³, 2.2× usualCranbrook, 21 May: 4.9 µg/m³, 1.0× usualCranbrook, 22 May: 3.2 µg/m³, 0.6× usualCranbrook, 23 May: 1.8 µg/m³, 0.4× usualVernonVernon, 13 May: 5.9 µg/m³, 1.2× usualVernon, 14 May: 6.2 µg/m³, 1.2× usualVernon, 15 May: 7.0 µg/m³, 1.4× usualVernon, 16 May: 6.4 µg/m³, 1.3× usualVernon, 17 May: 48.9 µg/m³, 9.8× usualVernon, 18 May: 60.7 µg/m³, 12× usualVernon, 19 May: 9.3 µg/m³, 1.9× usualVernon, 20 May: 7.1 µg/m³, 1.4× usualVernon, 21 May: 3.8 µg/m³, 0.8× usualVernon, 22 May: 1.3 µg/m³, 0.3× usualVernon, 23 May: 2.6 µg/m³, 0.5× usualMedicine HatMedicine Hat, 13 May: 5.2 µg/m³, 1.0× usualMedicine Hat, 14 May: 5.4 µg/m³, 1.1× usualMedicine Hat, 15 May: 4.7 µg/m³, 0.9× usualMedicine Hat, 16 May: 11.3 µg/m³, 2.3× usualMedicine Hat, 17 May: 46.8 µg/m³, 9.4× usualMedicine Hat, 18 May: 15.2 µg/m³, 3.0× usualMedicine Hat, 19 May: 28.7 µg/m³, 5.7× usualMedicine Hat, 20 May: 104.0 µg/m³, 21× usualMedicine Hat, 21 May: 74.7 µg/m³, 15× usualMedicine Hat, 22 May: 19.6 µg/m³, 3.9× usualMedicine Hat, 23 May: 1.6 µg/m³, 0.3× usualKelownaKelowna, 13 May: 6.7 µg/m³, 1.3× usualKelowna, 14 May: 8.9 µg/m³, 1.8× usualKelowna, 15 May: 7.4 µg/m³, 1.5× usualKelowna, 16 May: 5.1 µg/m³, 1.0× usualKelowna, 17 May: 39.5 µg/m³, 7.9× usualKelowna, 18 May: 52.1 µg/m³, 10× usualKelowna, 19 May: 12.2 µg/m³, 2.4× usualKelowna, 20 May: 8.6 µg/m³, 1.7× usualKelowna, 21 May: 5.5 µg/m³, 1.1× usualKelowna, 22 May: 1.6 µg/m³, 0.3× usualKelowna, 23 May: 0.6 µg/m³, 0.1× usualRapid CityRapid City, 13 May: 3.3 µg/m³, 0.6× usualRapid City, 14 May: 8.1 µg/m³, 1.6× usualRapid City, 15 May: 6.4 µg/m³, 1.2× usualRapid City, 16 May: 6.0 µg/m³, 1.2× usualRapid City, 17 May: 34.9 µg/m³, 6.7× usualRapid City, 18 May: 90.2 µg/m³, 17× usualRapid City, 19 May: 24.6 µg/m³, 4.7× usualRapid City, 20 May: 23.1 µg/m³, 4.4× usualRapid City, 21 May: 24.8 µg/m³, 4.8× usualRapid City, 22 May: 30.9 µg/m³, 5.9× usualRapid City, 23 May: 25.7 µg/m³, 4.9× usualBillingsBillings, 13 May: 5.3 µg/m³, 1.1× usualBillings, 14 May: 4.6 µg/m³, 0.9× usualBillings, 15 May: 7.5 µg/m³, 1.5× usualBillings, 16 May: 3.0 µg/m³, 0.6× usualBillings, 17 May: 30.4 µg/m³, 6.1× usualBillings, 18 May: 33.6 µg/m³, 6.7× usualBillings, 19 May: 23.5 µg/m³, 4.7× usualBillings, 20 May: 24.8 µg/m³, 5.0× usualBillings, 21 May: 27.4 µg/m³, 5.5× usualBillings, 22 May: 12.2 µg/m³, 2.4× usualBillings, 23 May: 6.6 µg/m³, 1.3× usualHelenaHelena, 13 May: 4.3 µg/m³, 0.6× usualHelena, 14 May: 4.6 µg/m³, 0.7× usualHelena, 15 May: 4.7 µg/m³, 0.7× usualHelena, 16 May: 13.7 µg/m³, 2.0× usualHelena, 17 May: 30.0 µg/m³, 4.3× usualHelena, 18 May: 72.5 µg/m³, 10× usualHelena, 19 May: 73.8 µg/m³, 11× usualHelena, 20 May: 34.8 µg/m³, 5.0× usualHelena, 21 May: 19.9 µg/m³, 2.8× usualHelena, 22 May: 5.1 µg/m³, 0.7× usualHelena, 23 May: 4.5 µg/m³, 0.6× usualPentictonPenticton, 13 May: 5.3 µg/m³, 1.1× usualPenticton, 14 May: 4.5 µg/m³, 0.9× usualPenticton, 15 May: 4.3 µg/m³, 0.9× usualPenticton, 16 May: 4.8 µg/m³, 1.0× usualPenticton, 17 May: 29.5 µg/m³, 5.9× usualPenticton, 18 May: 27.8 µg/m³, 5.6× usualPenticton, 19 May: 13.8 µg/m³, 2.8× usualPenticton, 20 May: 6.2 µg/m³, 1.2× usualPenticton, 21 May: 4.4 µg/m³, 0.9× usualPenticton, 22 May: 1.5 µg/m³, 0.3× usualPenticton, 23 May: 1.0 µg/m³, 0.2× usualBozemanBozeman, 13 May: 3.3 µg/m³, 0.7× usualBozeman, 14 May: 1.4 µg/m³, 0.3× usualBozeman, 15 May: 3.3 µg/m³, 0.7× usualBozeman, 16 May: 4.5 µg/m³, 0.9× usualBozeman, 17 May: 26.5 µg/m³, 5.3× usualBozeman, 18 May: 34.5 µg/m³, 6.9× usualBozeman, 19 May: 31.6 µg/m³, 6.3× usualBozeman, 20 May: 24.2 µg/m³, 4.8× usualBozeman, 21 May: 15.7 µg/m³, 3.1× usualBozeman, 22 May: 8.3 µg/m³, 1.7× usualBozeman, 23 May: 4.5 µg/m³, 0.9× usualGilletteGillette, 13 May: 2.3 µg/m³, 0.5× usualGillette, 14 May: 3.9 µg/m³, 0.8× usualGillette, 15 May: 6.2 µg/m³, 1.2× usualGillette, 16 May: 4.6 µg/m³, 0.9× usualGillette, 17 May: no readingGillette, 18 May: 55.1 µg/m³, 11× usualGillette, 19 May: 23.5 µg/m³, 4.7× usualGillette, 20 May: 21.3 µg/m³, 4.3× usualGillette, 21 May: 49.0 µg/m³, 9.8× usualGillette, 22 May: 44.7 µg/m³, 8.9× usualGillette, 23 May: 16.8 µg/m³, 3.4× usualButteButte, 13 May: 3.1 µg/m³, 0.6× usualButte, 14 May: no readingButte, 15 May: 2.9 µg/m³, 0.6× usualButte, 16 May: 4.1 µg/m³, 0.8× usualButte, 17 May: 17.6 µg/m³, 3.5× usualButte, 18 May: 42.1 µg/m³, 8.4× usualButte, 19 May: 46.4 µg/m³, 9.3× usualButte, 20 May: 22.1 µg/m³, 4.4× usualButte, 21 May: 11.4 µg/m³, 2.3× usualButte, 22 May: 3.9 µg/m³, 0.8× usualButte, 23 May: 1.8 µg/m³, 0.4× usualSheridanSheridan, 13 May: 6.3 µg/m³, 1.3× usualSheridan, 14 May: 6.2 µg/m³, 1.2× usualSheridan, 15 May: 5.7 µg/m³, 1.1× usualSheridan, 16 May: 7.3 µg/m³, 1.5× usualSheridan, 17 May: 24.8 µg/m³, 5.0× usualSheridan, 18 May: 38.8 µg/m³, 7.8× usualSheridan, 19 May: 24.1 µg/m³, 4.8× usualSheridan, 20 May: 21.8 µg/m³, 4.4× usualSheridan, 21 May: 40.3 µg/m³, 8.1× usualSheridan, 22 May: 31.4 µg/m³, 6.3× usualSheridan, 23 May: 13.9 µg/m³, 2.8× usualCasperCasper, 13 May: 1.3 µg/m³, 0.3× usualCasper, 14 May: 1.6 µg/m³, 0.3× usualCasper, 15 May: 1.3 µg/m³, 0.3× usualCasper, 16 May: 2.8 µg/m³, 0.6× usualCasper, 17 May: 4.9 µg/m³, 1.0× usualCasper, 18 May: 32.7 µg/m³, 6.5× usualCasper, 19 May: 36.7 µg/m³, 7.3× usualCasper, 20 May: 18.2 µg/m³, 3.6× usualCasper, 21 May: 12.3 µg/m³, 2.5× usualCasper, 22 May: 16.7 µg/m³, 3.3× usualCasper, 23 May: 6.7 µg/m³, 1.3× usualMissoulaMissoula, 13 May: 4.9 µg/m³, 1.0× usualMissoula, 14 May: 3.3 µg/m³, 0.7× usualMissoula, 15 May: 2.0 µg/m³, 0.4× usualMissoula, 16 May: 1.9 µg/m³, 0.4× usualMissoula, 17 May: 11.3 µg/m³, 2.3× usualMissoula, 18 May: 29.2 µg/m³, 5.8× usualMissoula, 19 May: 37.5 µg/m³, 7.5× usualMissoula, 20 May: 21.6 µg/m³, 4.3× usualMissoula, 21 May: 11.4 µg/m³, 2.3× usualMissoula, 22 May: 2.2 µg/m³, 0.4× usualMissoula, 23 May: 4.0 µg/m³, 0.8× usualCheyenneCheyenne, 13 May: 5.0 µg/m³, 1.0× usualCheyenne, 14 May: 3.8 µg/m³, 0.8× usualCheyenne, 15 May: 5.0 µg/m³, 1.0× usualCheyenne, 16 May: 6.3 µg/m³, 1.3× usualCheyenne, 17 May: 6.3 µg/m³, 1.3× usualCheyenne, 18 May: 29.0 µg/m³, 5.8× usualCheyenne, 19 May: 63.8 µg/m³, 13× usualCheyenne, 20 May: 35.1 µg/m³, 7.0× usualCheyenne, 21 May: 20.8 µg/m³, 4.2× usualCheyenne, 22 May: 27.2 µg/m³, 5.4× usualCheyenne, 23 May: 19.0 µg/m³, 3.8× usualRexburgRexburg, 13 May: 5.9 µg/m³, 0.9× usualRexburg, 14 May: 5.8 µg/m³, 0.9× usualRexburg, 15 May: 6.2 µg/m³, 1.0× usualRexburg, 16 May: 6.6 µg/m³, 1.0× usualRexburg, 17 May: 6.7 µg/m³, 1.1× usualRexburg, 18 May: 25.8 µg/m³, 4.1× usualRexburg, 19 May: 29.9 µg/m³, 4.7× usualRexburg, 20 May: 19.5 µg/m³, 3.1× usualRexburg, 21 May: 18.3 µg/m³, 2.9× usualRexburg, 22 May: 11.0 µg/m³, 1.7× usualRexburg, 23 May: 7.1 µg/m³, 1.1× usualLongmontLongmont, 13 May: 2.7 µg/m³, 0.5× usualLongmont, 14 May: 1.6 µg/m³, 0.3× usualLongmont, 15 May: 4.8 µg/m³, 1.0× usualLongmont, 16 May: 7.8 µg/m³, 1.6× usualLongmont, 17 May: 5.5 µg/m³, 1.1× usualLongmont, 18 May: 8.8 µg/m³, 1.8× usualLongmont, 19 May: 94.1 µg/m³, 19× usualLongmont, 20 May: 59.2 µg/m³, 12× usualLongmont, 21 May: 16.8 µg/m³, 3.4× usualLongmont, 22 May: 26.9 µg/m³, 5.4× usualLongmont, 23 May: 25.1 µg/m³, 5.0× usualKen CarylKen Caryl, 13 May: 3.6 µg/m³, 0.7× usualKen Caryl, 14 May: 2.1 µg/m³, 0.4× usualKen Caryl, 15 May: 3.7 µg/m³, 0.7× usualKen Caryl, 16 May: 4.6 µg/m³, 0.9× usualKen Caryl, 17 May: 5.0 µg/m³, 1.0× usualKen Caryl, 18 May: 4.5 µg/m³, 0.9× usualKen Caryl, 19 May: 88.0 µg/m³, 18× usualKen Caryl, 20 May: 56.9 µg/m³, 11× usualKen Caryl, 21 May: 13.5 µg/m³, 2.7× usualKen Caryl, 22 May: 35.4 µg/m³, 7.1× usualKen Caryl, 23 May: 32.5 µg/m³, 6.5× usualThorntonThornton, 13 May: 3.0 µg/m³, 0.6× usualThornton, 14 May: 1.6 µg/m³, 0.3× usualThornton, 15 May: 6.0 µg/m³, 1.2× usualThornton, 16 May: 8.2 µg/m³, 1.6× usualThornton, 17 May: 6.1 µg/m³, 1.2× usualThornton, 18 May: 8.5 µg/m³, 1.7× usualThornton, 19 May: 84.3 µg/m³, 17× usualThornton, 20 May: 61.3 µg/m³, 12× usualThornton, 21 May: 15.6 µg/m³, 3.1× usualThornton, 22 May: 28.7 µg/m³, 5.6× usualThornton, 23 May: 35.8 µg/m³, 7.0× usualDenverDenver, 13 May: 3.1 µg/m³, 0.6× usualDenver, 14 May: 2.6 µg/m³, 0.5× usualDenver, 15 May: 8.5 µg/m³, 1.7× usualDenver, 16 May: 6.3 µg/m³, 1.3× usualDenver, 17 May: 5.8 µg/m³, 1.2× usualDenver, 18 May: 8.1 µg/m³, 1.6× usualDenver, 19 May: 83.9 µg/m³, 17× usualDenver, 20 May: 59.6 µg/m³, 12× usualDenver, 21 May: 15.1 µg/m³, 3.0× usualDenver, 22 May: 31.3 µg/m³, 6.3× usualDenver, 23 May: 33.1 µg/m³, 6.6× usualGreeleyGreeley, 13 May: 1.4 µg/m³, 0.3× usualGreeley, 14 May: 0.9 µg/m³, 0.2× usualGreeley, 15 May: 4.3 µg/m³, 0.9× usualGreeley, 16 May: 9.1 µg/m³, 1.8× usualGreeley, 17 May: 5.6 µg/m³, 1.1× usualGreeley, 18 May: 8.1 µg/m³, 1.6× usualGreeley, 19 May: 69.9 µg/m³, 14× usualGreeley, 20 May: 44.7 µg/m³, 8.9× usualGreeley, 21 May: 22.1 µg/m³, 4.4× usualGreeley, 22 May: 21.9 µg/m³, 4.4× usualGreeley, 23 May: 14.3 µg/m³, 2.9× usualBoulderBoulder, 13 May: 2.9 µg/m³, 0.6× usualBoulder, 14 May: 2.3 µg/m³, 0.5× usualBoulder, 15 May: no readingBoulder, 16 May: 4.1 µg/m³, 0.8× usualBoulder, 17 May: 4.8 µg/m³, 1.0× usualBoulder, 18 May: 7.0 µg/m³, 1.4× usualBoulder, 19 May: 69.6 µg/m³, 14× usualBoulder, 20 May: 37.1 µg/m³, 7.4× usualBoulder, 21 May: 12.1 µg/m³, 2.4× usualBoulder, 22 May: 23.4 µg/m³, 4.7× usualBoulder, 23 May: 18.7 µg/m³, 3.7× usualFort CollinsFort Collins, 13 May: 0.4 µg/m³, 0.1× usualFort Collins, 14 May: 0.4 µg/m³, 0.1× usualFort Collins, 15 May: 2.3 µg/m³, 0.5× usualFort Collins, 16 May: 3.3 µg/m³, 0.7× usualFort Collins, 17 May: 1.6 µg/m³, 0.3× usualFort Collins, 18 May: 6.7 µg/m³, 1.3× usualFort Collins, 19 May: 53.9 µg/m³, 11× usualFort Collins, 20 May: 33.4 µg/m³, 6.7× usualFort Collins, 21 May: 12.8 µg/m³, 2.6× usualFort Collins, 22 May: 15.8 µg/m³, 3.2× usualFort Collins, 23 May: 13.5 µg/m³, 2.7× usualColorado SpringsColorado Springs, 13 May: 1.2 µg/m³, 0.2× usualColorado Springs, 14 May: 1.0 µg/m³, 0.2× usualColorado Springs, 15 May: 1.7 µg/m³, 0.3× usualColorado Springs, 16 May: 4.4 µg/m³, 0.9× usualColorado Springs, 17 May: 4.4 µg/m³, 0.9× usualColorado Springs, 18 May: 4.8 µg/m³, 1.0× usualColorado Springs, 19 May: 49.4 µg/m³, 9.9× usualColorado Springs, 20 May: 63.5 µg/m³, 13× usualColorado Springs, 21 May: 14.5 µg/m³, 2.9× usualColorado Springs, 22 May: 24.7 µg/m³, 4.9× usualColorado Springs, 23 May: 22.9 µg/m³, 4.6× usualLaramieLaramie, 13 May: 1.5 µg/m³, 0.3× usualLaramie, 14 May: 1.3 µg/m³, 0.3× usualLaramie, 15 May: 2.3 µg/m³, 0.5× usualLaramie, 16 May: 4.0 µg/m³, 0.8× usualLaramie, 17 May: 3.5 µg/m³, 0.7× usualLaramie, 18 May: 14.5 µg/m³, 2.9× usualLaramie, 19 May: 49.1 µg/m³, 9.8× usualLaramie, 20 May: 22.5 µg/m³, 4.5× usualLaramie, 21 May: 16.2 µg/m³, 3.2× usualLaramie, 22 May: 21.5 µg/m³, 4.3× usualLaramie, 23 May: 10.5 µg/m³, 2.1× usualRock SpringsRock Springs, 13 May: 2.6 µg/m³, 0.5× usualRock Springs, 14 May: 1.6 µg/m³, 0.3× usualRock Springs, 15 May: 3.5 µg/m³, 0.7× usualRock Springs, 16 May: 4.1 µg/m³, 0.8× usualRock Springs, 17 May: 5.6 µg/m³, 1.1× usualRock Springs, 18 May: 11.6 µg/m³, 2.3× usualRock Springs, 19 May: 36.4 µg/m³, 7.3× usualRock Springs, 20 May: 14.6 µg/m³, 2.9× usualRock Springs, 21 May: 11.4 µg/m³, 2.3× usualRock Springs, 22 May: 8.5 µg/m³, 1.7× usualRock Springs, 23 May: 6.8 µg/m³, 1.4× usualLewistonLewiston, 13 May: 5.7 µg/m³, 1.0× usualLewiston, 14 May: 2.1 µg/m³, 0.4× usualLewiston, 15 May: 4.8 µg/m³, 0.8× usualLewiston, 16 May: 6.9 µg/m³, 1.2× usualLewiston, 17 May: 9.9 µg/m³, 1.7× usualLewiston, 18 May: 23.5 µg/m³, 4.1× usualLewiston, 19 May: 34.8 µg/m³, 6.0× usualLewiston, 20 May: 26.2 µg/m³, 4.5× usualLewiston, 21 May: 11.5 µg/m³, 2.0× usualLewiston, 22 May: 5.3 µg/m³, 0.9× usualLewiston, 23 May: 4.4 µg/m³, 0.8× usualIdaho FallsIdaho Falls, 13 May: no readingIdaho Falls, 14 May: no readingIdaho Falls, 15 May: no readingIdaho Falls, 16 May: 8.5 µg/m³, 1.7× usualIdaho Falls, 17 May: 6.5 µg/m³, 1.3× usualIdaho Falls, 18 May: 18.6 µg/m³, 3.7× usualIdaho Falls, 19 May: 29.0 µg/m³, 5.8× usualIdaho Falls, 20 May: 27.0 µg/m³, 5.4× usualIdaho Falls, 21 May: 19.7 µg/m³, 3.9× usualIdaho Falls, 22 May: 9.8 µg/m³, 2.0× usualIdaho Falls, 23 May: 5.2 µg/m³, 1.0× usualPullmanPullman, 13 May: 3.7 µg/m³, 0.7× usualPullman, 14 May: 2.2 µg/m³, 0.4× usualPullman, 15 May: 2.8 µg/m³, 0.6× usualPullman, 16 May: 3.4 µg/m³, 0.7× usualPullman, 17 May: 5.8 µg/m³, 1.2× usualPullman, 18 May: 22.5 µg/m³, 4.5× usualPullman, 19 May: 25.4 µg/m³, 5.1× usualPullman, 20 May: 18.5 µg/m³, 3.7× usualPullman, 21 May: 6.4 µg/m³, 1.3× usualPullman, 22 May: 3.2 µg/m³, 0.6× usualPullman, 23 May: 3.2 µg/m³, 0.6× usual13 May1517192123
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.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

Every city it reached

CityDaysHighestUsualAbove usual
EdmontonAlberta, Canada3 309.520 May7.044×
St. AlbertAlberta, Canada3 231.020 May5.542×
Sherwood ParkAlberta, Canada3 204.020 May4.941×
AirdrieAlberta, Canada4 184.020 May4.537×
Red DeerAlberta, Canada3 191.020 May5.734×
Prince AlbertSaskatchewan, Canada1 227.016 May6.833×
Swift CurrentSaskatchewan, Canada1 154.020 May4.931×
ReginaSaskatchewan, Canada1 160.017 May5.330×
SaskatoonSaskatchewan, Canada1 138.017 May6.322×
Medicine HatAlberta, Canada2 104.020 May4.121×
CalgaryAlberta, Canada4 130.517 May6.321×
KamloopsBritish Columbia, Canada2 99.517 May4.620×
LongmontColorado, United States2 94.119 May5.019×
Ken CarylColorado, United States2 88.019 May3.518×
Rapid CitySouth Dakota, United States1 90.218 May5.217×
DenverColorado, United States2 83.919 May4.517×
ThorntonColorado, United States2 84.319 May5.117×
CranbrookBritish Columbia, Canada2 75.618 May4.515×
LethbridgeAlberta, Canada3 71.817 May4.114×
GreeleyColorado, United States2 69.919 May4.214×
BoulderColorado, United States2 69.619 May4.114×
CheyenneWyoming, United States3 63.819 May3.013×
Colorado SpringsColorado, United States2 63.520 May4.313×
VernonBritish Columbia, Canada2 60.718 May4.812×
GilletteWyoming, United States1 55.118 May3.611×
Fort CollinsColorado, United States2 53.919 May3.711×
HelenaMontana, United States2 73.819 May7.011×
KelownaBritish Columbia, Canada2 52.118 May3.810×
LaramieWyoming, United States1 49.119 May2.69.8×
ButteMontana, United States2 46.419 May4.09.3×
SheridanWyoming, United States1 40.321 May3.78.1×
MissoulaMontana, United States2 37.519 May2.67.5×
CasperWyoming, United States2 36.719 May2.57.3×
Rock SpringsWyoming, United States1 36.419 May3.67.3×
BozemanMontana, United States2 34.518 May4.76.9×
BillingsMontana, United States1 33.618 May3.76.7×
Great FallsMontana, United States3 47.720 May7.96.0×
LewistonIdaho, United States1 34.819 May5.86.0×
PentictonBritish Columbia, Canada2 29.517 May3.05.9×
Idaho FallsIdaho, United States1 29.019 May3.85.8×
PullmanWashington, United States1 25.419 May2.85.1×
RexburgIdaho, United States2 29.919 May6.34.7×

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 10 of 45 episodes in the United States and Canada since our records began, by cities reached.

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: 42 cities with PM2.5 at twice their usual or more, 16 to 20 May 2023, smogrank.com/episodes/2023-05-north-western-united-states-and-canada (accessed 2 October 2026).

Download top 10 (PNG)

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.