SmogRank / Episodes / United States
Utah and Idaho, United States, February 2023
For 5 days, from 1 to 5 February 2023, 12 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was West Jordan, Utah, United States: 52.7 µg/m³ on 4 February, about 7.9× its usual 6.7. Ended 5 February.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 12 in 1 country
Days 5 1 to 5 February 2023
Worst day 4 February 8 cities counted
Furthest above usual 10× North Ogden
Day by day
Play 4 February 8 cities at twice their usual or more
Stansbury park Highland Cedar Hills Spanish Fork Pocatello Roosevelt Idaho Falls Vernal Twin Falls Rock Springs Lander Riverton Grand Junction Garden City Orem Bountiful Preston Tooele Herriman Millcreek Smithfield West Valley City Salt Lake City Magna West Jordan North Ogden 29 Jan 30 31 1 Feb 2 3 4 5 6 7 8 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
Smithfield Smithfield, 29 January: 1.8 µg/m³ Smithfield, 30 January: 7.6 µg/m³ Smithfield, 31 January: 21.8 µg/m³ Smithfield, 1 February: 41.6 µg/m³, 6.7× its usual 6.2 Smithfield, 2 February: no reading Smithfield, 3 February: no reading Smithfield, 4 February: no reading Smithfield, 5 February: no reading Smithfield, 6 February: no reading Smithfield, 7 February: no reading Smithfield, 8 February: no reading West Jordan West Jordan, 29 January: 3.8 µg/m³ West Jordan, 30 January: 6.2 µg/m³ West Jordan, 31 January: 13.4 µg/m³ West Jordan, 1 February: 30.5 µg/m³, 4.6× its usual 6.7 West Jordan, 2 February: 39.4 µg/m³, 5.8× its usual 6.8 West Jordan, 3 February: 47.6 µg/m³, 7.0× its usual 6.8 West Jordan, 4 February: 52.7 µg/m³, 7.9× its usual 6.7 West Jordan, 5 February: 27.7 µg/m³, 4.2× its usual 6.6 West Jordan, 6 February: 7.8 µg/m³ West Jordan, 7 February: 10.5 µg/m³ West Jordan, 8 February: 11.6 µg/m³ Magna Magna, 29 January: 2.6 µg/m³ Magna, 30 January: 3.7 µg/m³ Magna, 31 January: 11.4 µg/m³ Magna, 1 February: 29.3 µg/m³, 5.7× its usual 5.1 Magna, 2 February: 32.3 µg/m³, 6.2× its usual 5.2 Magna, 3 February: 40.4 µg/m³, 7.6× its usual 5.3 Magna, 4 February: 38.9 µg/m³, 7.5× its usual 5.2 Magna, 5 February: 28.6 µg/m³, 5.7× its usual 5.0 Magna, 6 February: 8.2 µg/m³ Magna, 7 February: 6.2 µg/m³ Magna, 8 February: 10.7 µg/m³ Salt Lake City Salt Lake City, 29 January: 3.4 µg/m³ Salt Lake City, 30 January: 3.7 µg/m³ Salt Lake City, 31 January: 11.1 µg/m³ Salt Lake City, 1 February: 27.6 µg/m³, 4.8× its usual 5.7 Salt Lake City, 2 February: 35.9 µg/m³, 6.2× its usual 5.8 Salt Lake City, 3 February: 41.1 µg/m³, 7.1× its usual 5.8 Salt Lake City, 4 February: 42.3 µg/m³, 7.4× its usual 5.7 Salt Lake City, 5 February: 29.0 µg/m³, 5.3× its usual 5.5 Salt Lake City, 6 February: 5.5 µg/m³ Salt Lake City, 7 February: 5.5 µg/m³ Salt Lake City, 8 February: 10.3 µg/m³ Bountiful Bountiful, 29 January: 3.5 µg/m³ Bountiful, 30 January: 5.5 µg/m³ Bountiful, 31 January: 12.9 µg/m³ Bountiful, 1 February: 27.1 µg/m³, 4.9× its usual 5.5 Bountiful, 2 February: no reading Bountiful, 3 February: no reading Bountiful, 4 February: no reading Bountiful, 5 February: no reading Bountiful, 6 February: no reading Bountiful, 7 February: no reading Bountiful, 8 February: no reading Preston Preston, 29 January: 2.3 µg/m³ Preston, 30 January: 6.5 µg/m³ Preston, 31 January: 13.0 µg/m³ Preston, 1 February: 26.4 µg/m³, 5.3× its usual 4.7 Preston, 2 February: no reading Preston, 3 February: no reading Preston, 4 February: no reading Preston, 5 February: no reading Preston, 6 February: no reading Preston, 7 February: no reading Preston, 8 February: no reading Millcreek Millcreek, 29 January: no reading Millcreek, 30 January: no reading Millcreek, 31 January: no reading Millcreek, 1 February: no reading Millcreek, 2 February: 41.0 µg/m³, 5.1× its usual 8.1 Millcreek, 3 February: 46.5 µg/m³, 5.7× its usual 8.1 Millcreek, 4 February: 51.1 µg/m³, 6.4× its usual 8.0 Millcreek, 5 February: 30.0 µg/m³, 3.8× its usual 7.8 Millcreek, 6 February: 9.3 µg/m³ Millcreek, 7 February: 13.2 µg/m³ Millcreek, 8 February: 14.3 µg/m³ North Ogden North Ogden, 29 January: 2.0 µg/m³ North Ogden, 30 January: no reading North Ogden, 31 January: no reading North Ogden, 1 February: 0.9 µg/m³ North Ogden, 2 February: 37.7 µg/m³, 7.4× its usual 5.1 North Ogden, 3 February: 47.7 µg/m³, 9.4× its usual 5.1 North Ogden, 4 February: 51.7 µg/m³, 10× its usual 5.1 North Ogden, 5 February: 30.0 µg/m³, 6.0× its usual 4.7 North Ogden, 6 February: 5.8 µg/m³ North Ogden, 7 February: 6.1 µg/m³ North Ogden, 8 February: 8.9 µg/m³ West Valley City West Valley City, 29 January: no reading West Valley City, 30 January: no reading West Valley City, 31 January: no reading West Valley City, 1 February: no reading West Valley City, 2 February: 33.9 µg/m³, 5.3× its usual 6.4 West Valley City, 3 February: 40.1 µg/m³, 6.3× its usual 6.4 West Valley City, 4 February: 42.3 µg/m³, 6.7× its usual 6.3 West Valley City, 5 February: 26.5 µg/m³, 4.2× its usual 6.3 West Valley City, 6 February: 5.1 µg/m³ West Valley City, 7 February: 6.5 µg/m³ West Valley City, 8 February: 8.5 µg/m³ Orem Orem, 29 January: 2.9 µg/m³ Orem, 30 January: 8.2 µg/m³ Orem, 31 January: 16.1 µg/m³ Orem, 1 February: 17.0 µg/m³ Orem, 2 February: 26.0 µg/m³, 4.1× its usual 6.4 Orem, 3 February: 21.6 µg/m³ Orem, 4 February: 20.1 µg/m³ Orem, 5 February: 9.7 µg/m³ Orem, 6 February: no reading Orem, 7 February: 10.8 µg/m³ Orem, 8 February: 11.2 µg/m³ Tooele Tooele, 29 January: 2.9 µg/m³ Tooele, 30 January: 3.8 µg/m³ Tooele, 31 January: 6.6 µg/m³ Tooele, 1 February: 11.9 µg/m³ Tooele, 2 February: 19.4 µg/m³ Tooele, 3 February: 27.3 µg/m³, 5.5× its usual 4.0 Tooele, 4 February: 26.7 µg/m³, 5.3× its usual 4.0 Tooele, 5 February: 19.6 µg/m³ Tooele, 6 February: 1.0 µg/m³ Tooele, 7 February: 3.0 µg/m³ Tooele, 8 February: 3.5 µg/m³ Herriman Herriman, 29 January: 1.5 µg/m³ Herriman, 30 January: 4.7 µg/m³ Herriman, 31 January: 9.6 µg/m³ Herriman, 1 February: 23.8 µg/m³ Herriman, 2 February: 21.0 µg/m³ Herriman, 3 February: 20.9 µg/m³ Herriman, 4 February: 27.9 µg/m³, 5.6× its usual 3.9 Herriman, 5 February: 5.9 µg/m³ Herriman, 6 February: 3.8 µg/m³ Herriman, 7 February: 6.3 µg/m³ Herriman, 8 February: 7.1 µg/m³ 29 Jan 31 1 Feb 2 4 6 8 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
North Ogden Utah, United States 4 4 February 5.1 10× West Jordan Utah, United States 5 4 February 6.7 7.9× Magna Utah, United States 5 3 February 5.3 7.6× Salt Lake City Utah, United States 5 4 February 5.7 7.4× West Valley City Utah, United States 4 4 February 6.3 6.7× Smithfield Utah, United States 1 1 February 6.2 6.7× Millcreek Utah, United States 4 4 February 8.0 6.4× Herriman Utah, United States 1 4 February 3.9 5.6× Tooele Utah, United States 2 3 February 4.0 5.5× Preston Idaho, United States 1 1 February 4.7 5.3× Bountiful Utah, United States 1 1 February 5.5 4.9× Orem Utah, United States 1 2 February 6.4 4.1×
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
Number 105 of 151 episodes in the United States since our records began, by cities reached.
Eastern United States and Canada, June and July 2023 343 Northern United States and Canada, July 2026 327 United States and Canada, July 2023 322 Eastern United States and Canada, May and June 2023 317 North-eastern United States and Canada, 29 July to 9 August 2025 292 Northern United States and Canada, May and June 2025 247 United States and Canada, June 2023 195 North-western United States and Canada, August 2023 176 North-western United States and Canada, 4 to 22 August 2026 151 Northern United States and Canada, July 2025 139 Northern United States and Canada, June 2025 134 North-western United States and Canada, July and August 2026 118 Utah and Idaho, United States, February 2023 12 Bars: cities reached; colour: the level of the episode's highest daily reading. All 151 .
Use this page SmogRank, Utah and Idaho, United States, February 2023: 12 cities with PM2.5 at twice their usual or more, 1 to 5 February 2023, smogrank.com/episodes/2023-02-utah-and-idaho-united-states (accessed 5 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.
