SmogRank / Episodes / United States

Northern United States, September 2023

For 2 days, from 16 to 17 September 2023, 11 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Bismarck, North Dakota, United States: 68.2 µg/m³ on 16 September, about 12× its usual 5.8.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached11in 1 country
Days216 to 17 September 2023
Worst day17 September6 cities counted
Furthest above usual12×Bismarck

Day by day

17 September 6 cities at twice their usual or more
Grand IslandWatertownSaint JosephAnkenyDes MoinesSaint CloudShakopeeSaint MichaelBurnsvilleApple ValleyLibertyKansas CityMinneapolisBlaineSaint PaulRaymoreRochesterWaterlooRapid CityTopekaOlatheKansas CityBrookingsWest FargoSioux FallsOmahaLincolnBellevueAberdeenBismarck
13 Sep14151617181920
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

BismarckBismarck, 13 September: 7.3 µg/m³, 1.3× usualBismarck, 14 September: 16.5 µg/m³, 2.8× usualBismarck, 15 September: 61.3 µg/m³, 11× usualBismarck, 16 September: 68.2 µg/m³, 12× usualBismarck, 17 September: 19.0 µg/m³, 3.3× usualBismarck, 18 September: 22.8 µg/m³, 3.9× usualBismarck, 19 September: 15.8 µg/m³, 2.7× usualBismarck, 20 September: 46.7 µg/m³, 8.1× usualWest FargoWest Fargo, 13 September: 3.1 µg/m³, 0.5× usualWest Fargo, 14 September: 7.1 µg/m³, 1.1× usualWest Fargo, 15 September: 30.6 µg/m³, 4.8× usualWest Fargo, 16 September: 28.2 µg/m³, 4.4× usualWest Fargo, 17 September: 4.2 µg/m³, 0.7× usualWest Fargo, 18 September: 16.0 µg/m³, 2.5× usualWest Fargo, 19 September: 16.9 µg/m³, 2.6× usualWest Fargo, 20 September: 35.9 µg/m³, 5.6× usualAberdeenAberdeen, 13 September: 4.2 µg/m³, 0.8× usualAberdeen, 14 September: 5.2 µg/m³, 0.9× usualAberdeen, 15 September: 17.4 µg/m³, 3.2× usualAberdeen, 16 September: 41.8 µg/m³, 7.6× usualAberdeen, 17 September: 7.6 µg/m³, 1.4× usualAberdeen, 18 September: 17.9 µg/m³, 3.3× usualAberdeen, 19 September: 10.9 µg/m³, 2.0× usualAberdeen, 20 September: 25.6 µg/m³, 4.7× usualSioux FallsSioux Falls, 13 September: 4.0 µg/m³, 0.7× usualSioux Falls, 14 September: 5.2 µg/m³, 0.9× usualSioux Falls, 15 September: 7.6 µg/m³, 1.3× usualSioux Falls, 16 September: 27.3 µg/m³, 4.6× usualSioux Falls, 17 September: no readingSioux Falls, 18 September: no readingSioux Falls, 19 September: 11.2 µg/m³, 1.9× usualSioux Falls, 20 September: 6.8 µg/m³, 1.2× usualBrookingsBrookings, 13 September: 5.0 µg/m³, 0.8× usualBrookings, 14 September: 5.6 µg/m³, 0.9× usualBrookings, 15 September: 6.5 µg/m³, 1.0× usualBrookings, 16 September: 26.9 µg/m³, 4.1× usualBrookings, 17 September: 3.2 µg/m³, 0.5× usualBrookings, 18 September: 16.0 µg/m³, 2.5× usualBrookings, 19 September: 10.9 µg/m³, 1.7× usualBrookings, 20 September: 6.1 µg/m³, 0.9× usualOmahaOmaha, 13 September: 9.9 µg/m³, 1.4× usualOmaha, 14 September: 8.8 µg/m³, 1.2× usualOmaha, 15 September: 7.4 µg/m³, 1.0× usualOmaha, 16 September: 17.0 µg/m³, 2.3× usualOmaha, 17 September: 35.7 µg/m³, 4.9× usualOmaha, 18 September: 22.3 µg/m³, 3.1× usualOmaha, 19 September: 8.0 µg/m³, 1.1× usualOmaha, 20 September: 8.3 µg/m³, 1.1× usualBellevueBellevue, 13 September: 6.8 µg/m³, 1.1× usualBellevue, 14 September: 6.9 µg/m³, 1.1× usualBellevue, 15 September: 4.9 µg/m³, 0.8× usualBellevue, 16 September: 17.2 µg/m³, 2.8× usualBellevue, 17 September: 35.5 µg/m³, 5.7× usualBellevue, 18 September: 19.5 µg/m³, 3.1× usualBellevue, 19 September: 6.4 µg/m³, 1.0× usualBellevue, 20 September: 5.0 µg/m³, 0.8× usualLincolnLincoln, 13 September: no readingLincoln, 14 September: no readingLincoln, 15 September: no readingLincoln, 16 September: no readingLincoln, 17 September: 35.2 µg/m³, 5.7× usualLincoln, 18 September: 15.3 µg/m³, 2.5× usualLincoln, 19 September: 4.7 µg/m³, 0.8× usualLincoln, 20 September: 7.2 µg/m³, 1.2× usualKansas CityKansas City, 13 September: 12.4 µg/m³, 1.5× usualKansas City, 14 September: 10.4 µg/m³, 1.2× usualKansas City, 15 September: 10.9 µg/m³, 1.3× usualKansas City, 16 September: 8.1 µg/m³, 1.0× usualKansas City, 17 September: 31.5 µg/m³, 3.7× usualKansas City, 18 September: 28.8 µg/m³, 3.4× usualKansas City, 19 September: 11.4 µg/m³, 1.3× usualKansas City, 20 September: 7.9 µg/m³, 0.9× usualOlatheOlathe, 13 September: 9.1 µg/m³, 1.1× usualOlathe, 14 September: 8.8 µg/m³, 1.1× usualOlathe, 15 September: 24.1 µg/m³, 3.0× usualOlathe, 16 September: 7.7 µg/m³, 1.0× usualOlathe, 17 September: 28.4 µg/m³, 3.6× usualOlathe, 18 September: 26.8 µg/m³, 3.4× usualOlathe, 19 September: 12.5 µg/m³, 1.6× usualOlathe, 20 September: 8.6 µg/m³, 1.1× usualTopekaTopeka, 13 September: 8.8 µg/m³, 1.0× usualTopeka, 14 September: 9.6 µg/m³, 1.1× usualTopeka, 15 September: 9.4 µg/m³, 1.1× usualTopeka, 16 September: 6.8 µg/m³, 0.8× usualTopeka, 17 September: 27.1 µg/m³, 3.1× usualTopeka, 18 September: 25.0 µg/m³, 2.8× usualTopeka, 19 September: 7.9 µg/m³, 0.9× usualTopeka, 20 September: 8.4 µg/m³, 1.0× usual13 Sep14151617181920
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
BismarckNorth Dakota, United States1 68.216 September5.812×
AberdeenSouth Dakota, United States1 41.816 September5.57.6×
BellevueNebraska, United States1 35.517 September6.25.7×
LincolnNebraska, United States1 35.217 September6.25.7×
West FargoNorth Dakota, United States1 35.920 September6.45.6×
OmahaNebraska, United States1 35.717 September7.34.9×
Sioux FallsSouth Dakota, United States1 27.316 September5.94.6×
BrookingsSouth Dakota, United States1 26.916 September6.54.1×
Kansas CityKansas, United States1 31.517 September8.53.7×
OlatheKansas, United States1 28.417 September8.03.6×
TopekaKansas, United States1 27.117 September8.83.1×

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 30 of 41 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 41.

Use this page

SmogRank, Northern United States, September 2023: 11 cities with PM2.5 at twice their usual or more, 16 to 17 September 2023, smogrank.com/episodes/2023-09-northern-united-states-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.