SmogRank / Episodes / United States

Utah and Idaho, United States, 4 to 5 September 2024

For 2 days, from 4 to 5 September 2024, 12 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Meridian, Idaho, United States: 84.8 µg/m³ on 5 September, about 14× its usual 6.2.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached12in 1 country
Days24 to 5 September 2024
Worst day4 September12 cities counted
Furthest above usual14×Meridian

Day by day

4 September 12 cities at twice their usual or more
Idaho FallsHerrimanWest JordanCondaHighlandRexburgOremSpanish ForkRock SpringsSpanish SpringsMillcreekWest Valley CityBountifulMagnaSalt Lake CityNorth OgdenTooeleNampaPocatelloTwin FallsBoiseMeridian
1 Sep2345678
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

Twin FallsTwin Falls, 1 September: 15.5 µg/m³Twin Falls, 2 September: 11.2 µg/m³Twin Falls, 3 September: 34.7 µg/m³Twin Falls, 4 September: 49.3 µg/m³, 9.7× its usual 5.1Twin Falls, 5 September: 30.5 µg/m³, 6.0× its usual 5.1Twin Falls, 6 September: 17.0 µg/m³Twin Falls, 7 September: 18.0 µg/m³Twin Falls, 8 September: 16.5 µg/m³MeridianMeridian, 1 September: 47.0 µg/m³Meridian, 2 September: 15.6 µg/m³Meridian, 3 September: 26.2 µg/m³Meridian, 4 September: 38.4 µg/m³, 6.2× its usual 6.2Meridian, 5 September: 84.8 µg/m³, 14× its usual 6.2Meridian, 6 September: 31.4 µg/m³Meridian, 7 September: 23.6 µg/m³Meridian, 8 September: 14.1 µg/m³BoiseBoise, 1 September: 48.6 µg/m³Boise, 2 September: 14.8 µg/m³Boise, 3 September: 26.2 µg/m³Boise, 4 September: 36.0 µg/m³, 6.7× its usual 5.4Boise, 5 September: 53.5 µg/m³, 10× its usual 5.3Boise, 6 September: 26.2 µg/m³Boise, 7 September: 18.8 µg/m³Boise, 8 September: 11.0 µg/m³PocatelloPocatello, 1 September: 10.4 µg/m³Pocatello, 2 September: 6.6 µg/m³Pocatello, 3 September: 11.4 µg/m³Pocatello, 4 September: 35.8 µg/m³, 7.2× its usual 4.9Pocatello, 5 September: 18.4 µg/m³Pocatello, 6 September: 9.4 µg/m³Pocatello, 7 September: 8.0 µg/m³Pocatello, 8 September: 8.6 µg/m³NampaNampa, 1 September: 48.8 µg/m³Nampa, 2 September: 13.0 µg/m³Nampa, 3 September: 23.6 µg/m³Nampa, 4 September: 31.2 µg/m³, 4.4× its usual 7.1Nampa, 5 September: 48.2 µg/m³, 6.9× its usual 7.0Nampa, 6 September: 20.0 µg/m³Nampa, 7 September: 12.8 µg/m³Nampa, 8 September: 13.9 µg/m³TooeleTooele, 1 September: 9.3 µg/m³Tooele, 2 September: 10.6 µg/m³Tooele, 3 September: 5.2 µg/m³Tooele, 4 September: 30.7 µg/m³, 5.6× its usual 5.5Tooele, 5 September: 23.7 µg/m³Tooele, 6 September: 13.3 µg/m³Tooele, 7 September: 11.5 µg/m³Tooele, 8 September: 14.0 µg/m³Salt Lake CitySalt Lake City, 1 September: 10.2 µg/m³Salt Lake City, 2 September: 6.4 µg/m³Salt Lake City, 3 September: 5.1 µg/m³Salt Lake City, 4 September: 28.3 µg/m³, 4.9× its usual 5.8Salt Lake City, 5 September: 19.2 µg/m³Salt Lake City, 6 September: 10.4 µg/m³Salt Lake City, 7 September: 11.2 µg/m³Salt Lake City, 8 September: 10.4 µg/m³MagnaMagna, 1 September: 10.6 µg/m³Magna, 2 September: 5.9 µg/m³Magna, 3 September: 5.6 µg/m³Magna, 4 September: 27.5 µg/m³, 4.9× its usual 5.6Magna, 5 September: 17.3 µg/m³Magna, 6 September: 6.6 µg/m³Magna, 7 September: 8.9 µg/m³Magna, 8 September: 10.9 µg/m³MillcreekMillcreek, 1 September: 11.8 µg/m³Millcreek, 2 September: 7.1 µg/m³Millcreek, 3 September: 7.3 µg/m³Millcreek, 4 September: 27.5 µg/m³, 3.8× its usual 7.3Millcreek, 5 September: 21.1 µg/m³Millcreek, 6 September: 12.1 µg/m³Millcreek, 7 September: 12.8 µg/m³Millcreek, 8 September: 12.4 µg/m³North OgdenNorth Ogden, 1 September: 8.4 µg/m³North Ogden, 2 September: 6.4 µg/m³North Ogden, 3 September: 3.9 µg/m³North Ogden, 4 September: 26.6 µg/m³, 5.3× its usual 4.6North Ogden, 5 September: 9.9 µg/m³North Ogden, 6 September: 8.4 µg/m³North Ogden, 7 September: 9.2 µg/m³North Ogden, 8 September: 9.5 µg/m³BountifulBountiful, 1 September: 7.6 µg/m³Bountiful, 2 September: 5.4 µg/m³Bountiful, 3 September: 5.8 µg/m³Bountiful, 4 September: 26.1 µg/m³, 4.7× its usual 5.5Bountiful, 5 September: 9.4 µg/m³Bountiful, 6 September: 7.6 µg/m³Bountiful, 7 September: 10.2 µg/m³Bountiful, 8 September: 10.3 µg/m³West Valley CityWest Valley City, 1 September: 11.3 µg/m³West Valley City, 2 September: 6.0 µg/m³West Valley City, 3 September: 4.1 µg/m³West Valley City, 4 September: 25.9 µg/m³, 4.2× its usual 6.1West Valley City, 5 September: 18.4 µg/m³West Valley City, 6 September: 9.1 µg/m³West Valley City, 7 September: 10.2 µg/m³West Valley City, 8 September: 10.8 µg/m³1 Sep2345678
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
MeridianIdaho, United States2 84.85 September6.214×
BoiseIdaho, United States2 53.55 September5.310×
Twin FallsIdaho, United States2 49.34 September5.19.7×
PocatelloIdaho, United States1 35.84 September4.97.2×
NampaIdaho, United States2 48.25 September7.06.9×
TooeleUtah, United States1 30.74 September5.55.6×
North OgdenUtah, United States1 26.64 September4.65.3×
Salt Lake CityUtah, United States1 28.34 September5.84.9×
MagnaUtah, United States1 27.54 September5.64.9×
BountifulUtah, United States1 26.14 September5.54.7×
West Valley CityUtah, United States1 25.94 September6.14.2×
MillcreekUtah, United States1 27.54 September7.33.8×

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 84 of 130 episodes in the United States since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading. All 130.

Use this page

SmogRank, Utah and Idaho, United States, 4 to 5 September 2024: 12 cities with PM2.5 at twice their usual or more, 4 to 5 September 2024, smogrank.com/episodes/2024-09-04-utah-and-idaho-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.