SmogRank / Episodes / United States
North-western United States, July 2024
For 4 days, from 26 to 29 July 2024, 23 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Lewiston, Idaho, United States: 109.9 µg/m³ on 26 July, about 12× its usual 8.8.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 23 in 1 country
Days 4 26 to 29 July 2024
Worst day 26 July 17 cities counted
Furthest above usual 13× Lewiston
Day by day
Play 26 July 17 cities at twice their usual or more
Missoula Pullman Coeur d'Alene Walla Walla Spokane Valley Spokane Conda Hermiston Tri-Cities Moses Lake Wenatchee Ellensburg Redmond The Dalles Gresham Auburn Milwaukie Renton Salmon Creek Vancouver Canby Portland Bellevue Columbia City Parkland Tigard Beaverton Tacoma Seattle Woodburn Shoreline Hillsboro Salem Longview Albany Bremerton Eugene Lacey Forest Grove Centralia McMinnville Corvallis Dallas Roseburg Aberdeen Casper Coos Bay Great Falls Rexburg Sunnyside Pendleton Helena Billings Sheridan Bozeman Moscow Bend Idaho Falls Yakima Butte Medford Ashland Pocatello Grants Pass Altamont Nampa Boise Meridian Twin Falls Lewiston 23 Jul 24 25 26 27 28 29 30 31 1 Aug 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
Nampa Nampa, 23 July: 99.7 µg/m³, 11× usual Nampa, 24 July: 42.7 µg/m³, 4.9× usual Nampa, 25 July: 39.6 µg/m³, 4.5× usual Nampa, 26 July: 49.3 µg/m³, 5.6× usual Nampa, 27 July: 66.7 µg/m³, 7.6× usual Nampa, 28 July: 42.5 µg/m³, 4.8× usual Nampa, 29 July: 48.6 µg/m³, 5.5× usual Nampa, 30 July: 20.3 µg/m³, 2.3× usual Nampa, 31 July: 15.4 µg/m³, 1.8× usual Nampa, 1 August: 14.1 µg/m³, 1.6× usual Meridian Meridian, 23 July: 93.6 µg/m³, 12× usual Meridian, 24 July: 30.0 µg/m³, 3.9× usual Meridian, 25 July: 38.1 µg/m³, 4.9× usual Meridian, 26 July: 46.2 µg/m³, 6.0× usual Meridian, 27 July: 68.8 µg/m³, 8.9× usual Meridian, 28 July: 47.7 µg/m³, 6.2× usual Meridian, 29 July: 52.2 µg/m³, 6.8× usual Meridian, 30 July: 21.5 µg/m³, 2.8× usual Meridian, 31 July: 14.3 µg/m³, 1.9× usual Meridian, 1 August: 14.9 µg/m³, 1.9× usual Boise Boise, 23 July: 70.1 µg/m³, 10× usual Boise, 24 July: 24.5 µg/m³, 3.6× usual Boise, 25 July: 34.8 µg/m³, 5.1× usual Boise, 26 July: 45.0 µg/m³, 6.6× usual Boise, 27 July: 55.8 µg/m³, 8.2× usual Boise, 28 July: 41.3 µg/m³, 6.1× usual Boise, 29 July: 47.7 µg/m³, 7.0× usual Boise, 30 July: 17.6 µg/m³, 2.6× usual Boise, 31 July: 11.7 µg/m³, 1.7× usual Boise, 1 August: 14.3 µg/m³, 2.1× usual Altamont Altamont, 23 July: 40.3 µg/m³, 5.7× usual Altamont, 24 July: 17.4 µg/m³, 2.5× usual Altamont, 25 July: 8.1 µg/m³, 1.1× usual Altamont, 26 July: 29.5 µg/m³, 4.2× usual Altamont, 27 July: 54.1 µg/m³, 7.6× usual Altamont, 28 July: 24.4 µg/m³, 3.4× usual Altamont, 29 July: 11.1 µg/m³, 1.6× usual Altamont, 30 July: 2.5 µg/m³, 0.4× usual Altamont, 31 July: 17.8 µg/m³, 2.5× usual Altamont, 1 August: 58.8 µg/m³, 8.3× usual Medford Medford, 23 July: 30.5 µg/m³, 5.3× usual Medford, 24 July: 15.6 µg/m³, 2.7× usual Medford, 25 July: 7.4 µg/m³, 1.3× usual Medford, 26 July: 29.3 µg/m³, 5.1× usual Medford, 27 July: 34.4 µg/m³, 5.9× usual Medford, 28 July: 10.3 µg/m³, 1.8× usual Medford, 29 July: 8.3 µg/m³, 1.4× usual Medford, 30 July: 2.3 µg/m³, 0.4× usual Medford, 31 July: 12.9 µg/m³, 2.2× usual Medford, 1 August: 32.7 µg/m³, 5.6× usual Grants Pass Grants Pass, 23 July: 29.3 µg/m³, 5.9× usual Grants Pass, 24 July: 10.5 µg/m³, 2.1× usual Grants Pass, 25 July: 6.2 µg/m³, 1.2× usual Grants Pass, 26 July: 35.5 µg/m³, 7.1× usual Grants Pass, 27 July: 16.0 µg/m³, 3.2× usual Grants Pass, 28 July: 5.6 µg/m³, 1.1× usual Grants Pass, 29 July: 4.6 µg/m³, 0.9× usual Grants Pass, 30 July: no reading Grants Pass, 31 July: 12.4 µg/m³, 2.5× usual Grants Pass, 1 August: 19.4 µg/m³, 3.9× usual Ashland Ashland, 23 July: 29.1 µg/m³, 5.0× usual Ashland, 24 July: 19.8 µg/m³, 3.4× usual Ashland, 25 July: 8.3 µg/m³, 1.4× usual Ashland, 26 July: 27.9 µg/m³, 4.8× usual Ashland, 27 July: 35.0 µg/m³, 6.0× usual Ashland, 28 July: 8.1 µg/m³, 1.4× usual Ashland, 29 July: 7.9 µg/m³, 1.4× usual Ashland, 30 July: 2.3 µg/m³, 0.4× usual Ashland, 31 July: 8.1 µg/m³, 1.4× usual Ashland, 1 August: 30.1 µg/m³, 5.2× usual Billings Billings, 23 July: 26.9 µg/m³, 3.7× usual Billings, 24 July: 22.4 µg/m³, 3.1× usual Billings, 25 July: 12.0 µg/m³, 1.7× usual Billings, 26 July: 14.7 µg/m³, 2.0× usual Billings, 27 July: 22.2 µg/m³, 3.1× usual Billings, 28 July: 22.0 µg/m³, 3.1× usual Billings, 29 July: 28.3 µg/m³, 3.9× usual Billings, 30 July: 24.5 µg/m³, 3.4× usual Billings, 31 July: 6.0 µg/m³, 0.8× usual Billings, 1 August: 7.5 µg/m³, 1.0× usual Sheridan Sheridan, 23 July: 26.0 µg/m³, 3.7× usual Sheridan, 24 July: 16.9 µg/m³, 2.4× usual Sheridan, 25 July: 19.0 µg/m³, 2.7× usual Sheridan, 26 July: 13.2 µg/m³, 1.9× usual Sheridan, 27 July: 14.2 µg/m³, 2.0× usual Sheridan, 28 July: 21.5 µg/m³, 3.1× usual Sheridan, 29 July: 28.9 µg/m³, 4.1× usual Sheridan, 30 July: 27.0 µg/m³, 3.9× usual Sheridan, 31 July: 9.4 µg/m³, 1.3× usual Sheridan, 1 August: 4.2 µg/m³, 0.6× usual Bend Bend, 23 July: 13.5 µg/m³, 2.2× usual Bend, 24 July: 53.1 µg/m³, 8.7× usual Bend, 25 July: 17.7 µg/m³, 2.9× usual Bend, 26 July: 13.5 µg/m³, 2.2× usual Bend, 27 July: 26.5 µg/m³, 4.3× usual Bend, 28 July: 61.2 µg/m³, 10× usual Bend, 29 July: 68.9 µg/m³, 11× usual Bend, 30 July: 19.2 µg/m³, 3.1× usual Bend, 31 July: 26.9 µg/m³, 4.4× usual Bend, 1 August: 13.7 µg/m³, 2.2× usual Lewiston Lewiston, 23 July: 20.6 µg/m³, 2.3× usual Lewiston, 24 July: 29.5 µg/m³, 3.4× usual Lewiston, 25 July: 24.7 µg/m³, 2.8× usual Lewiston, 26 July: 109.9 µg/m³, 12× usual Lewiston, 27 July: 58.0 µg/m³, 6.6× usual Lewiston, 28 July: 50.3 µg/m³, 5.7× usual Lewiston, 29 July: 18.8 µg/m³, 2.1× usual Lewiston, 30 July: 15.3 µg/m³, 1.7× usual Lewiston, 31 July: 9.4 µg/m³, 1.1× usual Lewiston, 1 August: 15.4 µg/m³, 1.8× usual Great Falls Great Falls, 23 July: 25.2 µg/m³, 1.9× usual Great Falls, 24 July: 27.6 µg/m³, 2.1× usual Great Falls, 25 July: 18.0 µg/m³, 1.4× usual Great Falls, 26 July: 15.8 µg/m³, 1.2× usual Great Falls, 27 July: 19.4 µg/m³, 1.5× usual Great Falls, 28 July: 21.3 µg/m³, 1.6× usual Great Falls, 29 July: 29.7 µg/m³, 2.3× usual Great Falls, 30 July: 15.5 µg/m³, 1.2× usual Great Falls, 31 July: 10.7 µg/m³, 0.8× usual Great Falls, 1 August: 12.1 µg/m³, 0.9× usual Yakima Yakima, 23 July: 6.1 µg/m³, 1.2× usual Yakima, 24 July: 17.5 µg/m³, 3.5× usual Yakima, 25 July: 58.4 µg/m³, 12× usual Yakima, 26 July: 26.8 µg/m³, 5.4× usual Yakima, 27 July: 22.0 µg/m³, 4.4× usual Yakima, 28 July: 24.1 µg/m³, 4.8× usual Yakima, 29 July: 40.1 µg/m³, 8.0× usual Yakima, 30 July: 5.4 µg/m³, 1.1× usual Yakima, 31 July: 8.6 µg/m³, 1.7× usual Yakima, 1 August: 13.2 µg/m³, 2.6× usual Sunnyside Sunnyside, 23 July: 19.3 µg/m³, 2.8× usual Sunnyside, 24 July: 17.6 µg/m³, 2.5× usual Sunnyside, 25 July: 40.6 µg/m³, 5.8× usual Sunnyside, 26 July: 18.0 µg/m³, 2.6× usual Sunnyside, 27 July: 25.5 µg/m³, 3.6× usual Sunnyside, 28 July: 20.7 µg/m³, 3.0× usual Sunnyside, 29 July: 22.2 µg/m³, 3.2× usual Sunnyside, 30 July: 7.5 µg/m³, 1.1× usual Sunnyside, 31 July: 6.7 µg/m³, 1.0× usual Sunnyside, 1 August: 12.6 µg/m³, 1.8× usual Twin Falls Twin Falls, 23 July: 12.0 µg/m³, 1.8× usual Twin Falls, 24 July: 18.6 µg/m³, 2.8× usual Twin Falls, 25 July: 6.3 µg/m³, 1.0× usual Twin Falls, 26 July: 62.0 µg/m³, 9.4× usual Twin Falls, 27 July: 65.0 µg/m³, 9.8× usual Twin Falls, 28 July: 36.5 µg/m³, 5.5× usual Twin Falls, 29 July: 42.1 µg/m³, 6.4× usual Twin Falls, 30 July: 22.1 µg/m³, 3.3× usual Twin Falls, 31 July: 16.2 µg/m³, 2.5× usual Twin Falls, 1 August: 12.4 µg/m³, 1.9× usual Butte Butte, 23 July: 15.2 µg/m³, 2.3× usual Butte, 24 July: 12.4 µg/m³, 1.9× usual Butte, 25 July: 12.9 µg/m³, 1.9× usual Butte, 26 July: 37.6 µg/m³, 5.6× usual Butte, 27 July: 37.7 µg/m³, 5.6× usual Butte, 28 July: 33.7 µg/m³, 5.0× usual Butte, 29 July: 30.7 µg/m³, 4.6× usual Butte, 30 July: 18.8 µg/m³, 2.8× usual Butte, 31 July: 3.1 µg/m³, 0.5× usual Butte, 1 August: 8.1 µg/m³, 1.2× usual Helena Helena, 23 July: 18.3 µg/m³, 2.0× usual Helena, 24 July: 21.3 µg/m³, 2.3× usual Helena, 25 July: 19.3 µg/m³, 2.1× usual Helena, 26 July: 35.8 µg/m³, 3.8× usual Helena, 27 July: 28.6 µg/m³, 3.1× usual Helena, 28 July: 31.0 µg/m³, 3.3× usual Helena, 29 July: 29.1 µg/m³, 3.1× usual Helena, 30 July: 16.9 µg/m³, 1.8× usual Helena, 31 July: 5.1 µg/m³, 0.5× usual Helena, 1 August: 8.2 µg/m³, 0.9× usual Pocatello Pocatello, 23 July: 18.2 µg/m³, 3.1× usual Pocatello, 24 July: 16.5 µg/m³, 2.8× usual Pocatello, 25 July: 10.6 µg/m³, 1.8× usual Pocatello, 26 July: 34.5 µg/m³, 5.8× usual Pocatello, 27 July: 25.5 µg/m³, 4.3× usual Pocatello, 28 July: 17.0 µg/m³, 2.9× usual Pocatello, 29 July: 35.5 µg/m³, 6.0× usual Pocatello, 30 July: 27.8 µg/m³, 4.7× usual Pocatello, 31 July: 17.3 µg/m³, 2.9× usual Pocatello, 1 August: 11.6 µg/m³, 2.0× usual Moscow Moscow, 23 July: 18.6 µg/m³, 2.3× usual Moscow, 24 July: 22.2 µg/m³, 2.7× usual Moscow, 25 July: 24.6 µg/m³, 3.0× usual Moscow, 26 July: 33.5 µg/m³, 4.1× usual Moscow, 27 July: 24.4 µg/m³, 3.0× usual Moscow, 28 July: 17.4 µg/m³, 2.1× usual Moscow, 29 July: 18.5 µg/m³, 2.3× usual Moscow, 30 July: 8.4 µg/m³, 1.0× usual Moscow, 31 July: 8.9 µg/m³, 1.1× usual Moscow, 1 August: 12.3 µg/m³, 1.5× usual Bozeman Bozeman, 23 July: 15.9 µg/m³, 2.2× usual Bozeman, 24 July: 19.3 µg/m³, 2.6× usual Bozeman, 25 July: 11.8 µg/m³, 1.6× usual Bozeman, 26 July: 27.8 µg/m³, 3.8× usual Bozeman, 27 July: 23.2 µg/m³, 3.2× usual Bozeman, 28 July: 22.9 µg/m³, 3.1× usual Bozeman, 29 July: 29.6 µg/m³, 4.1× usual Bozeman, 30 July: 23.3 µg/m³, 3.2× usual Bozeman, 31 July: 6.8 µg/m³, 0.9× usual Bozeman, 1 August: 6.4 µg/m³, 0.9× usual Pendleton Pendleton, 23 July: 9.1 µg/m³, 1.2× usual Pendleton, 24 July: 16.8 µg/m³, 2.3× usual Pendleton, 25 July: 15.1 µg/m³, 2.1× usual Pendleton, 26 July: 26.5 µg/m³, 3.6× usual Pendleton, 27 July: 18.6 µg/m³, 2.5× usual Pendleton, 28 July: 13.7 µg/m³, 1.9× usual Pendleton, 29 July: 10.5 µg/m³, 1.4× usual Pendleton, 30 July: 2.1 µg/m³, 0.3× usual Pendleton, 31 July: 4.4 µg/m³, 0.6× usual Pendleton, 1 August: 12.7 µg/m³, 1.7× usual Idaho Falls Idaho Falls, 23 July: 15.2 µg/m³, 2.5× usual Idaho Falls, 24 July: 14.2 µg/m³, 2.3× usual Idaho Falls, 25 July: 13.9 µg/m³, 2.3× usual Idaho Falls, 26 July: 26.4 µg/m³, 4.3× usual Idaho Falls, 27 July: 23.0 µg/m³, 3.8× usual Idaho Falls, 28 July: 17.8 µg/m³, 2.9× usual Idaho Falls, 29 July: 31.2 µg/m³, 5.1× usual Idaho Falls, 30 July: 23.9 µg/m³, 3.9× usual Idaho Falls, 31 July: 9.2 µg/m³, 1.5× usual Idaho Falls, 1 August: 9.0 µg/m³, 1.5× usual Rexburg Rexburg, 23 July: 13.0 µg/m³, 1.8× usual Rexburg, 24 July: 13.1 µg/m³, 1.8× usual Rexburg, 25 July: 9.0 µg/m³, 1.3× usual Rexburg, 26 July: no reading Rexburg, 27 July: 19.7 µg/m³, 2.7× usual Rexburg, 28 July: 18.0 µg/m³, 2.5× usual Rexburg, 29 July: 25.6 µg/m³, 3.6× usual Rexburg, 30 July: 21.9 µg/m³, 3.0× usual Rexburg, 31 July: 10.4 µg/m³, 1.4× usual Rexburg, 1 August: 10.0 µg/m³, 1.4× usual 23 Jul 24 25 26 27 28 29 30 31 1 Aug 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
Lewiston Idaho, United States 3 26 July 8.8 12× Meridian Idaho, United States 4 23 July 7.7 12× Yakima Washington, United States 1 25 July 5.0 12× Nampa Idaho, United States 4 23 July 8.8 11× Bend Oregon, United States 1 29 July 6.1 11× Boise Idaho, United States 4 23 July 6.8 10× Twin Falls Idaho, United States 4 27 July 6.6 9.8× Altamont Oregon, United States 2 1 August 7.1 8.3× Grants Pass Oregon, United States 1 26 July 4.0 7.1× Ashland Oregon, United States 2 27 July 5.8 6.0× Pocatello Idaho, United States 3 29 July 5.9 6.0× Medford Oregon, United States 2 27 July 5.8 5.9× Sunnyside Washington, United States 1 25 July 7.0 5.8× Butte Montana, United States 4 27 July 6.7 5.6× Idaho Falls Idaho, United States 2 29 July 6.1 5.1× Moscow Idaho, United States 1 26 July 8.1 4.1× Sheridan Wyoming, United States 1 29 July 7.0 4.1× Bozeman Montana, United States 2 29 July 7.3 4.1× Billings Montana, United States 1 29 July 7.2 3.9× Helena Montana, United States 4 26 July 9.3 3.8× Pendleton Oregon, United States 1 26 July 7.3 3.6× Rexburg Idaho, United States 1 29 July 7.2 3.6× Great Falls Montana, United States 1 29 July 13.1 2.3×
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
Number 48 of 131 episodes in the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 280 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 261 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 240 North-eastern United States and Canada, June 2025 196 North-eastern United States and Canada, June 2023 161 North-eastern United States and Canada, July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States, June 2025 104 North-western United States and Canada, August 2026 99 North-eastern United States and Canada, February 2026 96 North-western United States, July 2024 23 Bars: cities reached; colour: the level of the episode's highest daily reading. All 131 .
Use this page SmogRank, North-western United States, July 2024: 23 cities with PM2.5 at twice their usual or more, 26 to 29 July 2024, smogrank.com/episodes/2024-07-north-western-united-states (accessed 3 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.
