SmogRank / Episodes / United States

North-eastern United States and Canada, April 2023

For 1 day, on 15 April 2023, 9 cities in the United States and Canada had PM2.5 at least twice their usual for the time of year. The worst reading was Port Huron, Michigan, United States: 29.6 µg/m³ on 15 April, about 5.8× its usual 5.1.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached9in 2 countries
Days115 April 2023
Worst day15 April9 cities counted
Furthest above usual5.8×Port Huron

Day by day

15 April 9 cities at twice their usual or more
BrantfordPainesvilleHamiltonClevelandWarrenHermitageYoungstownAkronSt. CatharinesMedinaCantonBarrieKenmoreCheektowagaRedfordTaylorPittsburghWilkinsburgYpsilantiFlintWest MifflinMcKeesportToledoBay CityPeterboroughJohnstownRochesterAltoonaLansingLimaState CollegeBellevilleKalamazooGrand RapidsJenisonKingstonElkhartHollandLebanonSouth BendScrantonKokomoReadingAllentownDearbornDetroitLondonSt. ThomasBuffaloErieSarniaKitchenerPort Huron
12 Apr131415161718
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

Port HuronPort Huron, 12 April: 9.7 µg/m³, 1.9× usualPort Huron, 13 April: 14.0 µg/m³, 2.7× usualPort Huron, 14 April: 17.1 µg/m³, 3.4× usualPort Huron, 15 April: 29.6 µg/m³, 5.8× usualPort Huron, 16 April: 16.8 µg/m³, 3.3× usualPort Huron, 17 April: 2.9 µg/m³, 0.6× usualPort Huron, 18 April: 2.5 µg/m³, 0.5× usualKitchenerKitchener, 12 April: 10.7 µg/m³, 2.1× usualKitchener, 13 April: 15.1 µg/m³, 3.0× usualKitchener, 14 April: 19.3 µg/m³, 3.9× usualKitchener, 15 April: 29.0 µg/m³, 5.8× usualKitchener, 16 April: 23.5 µg/m³, 4.7× usualKitchener, 17 April: 3.6 µg/m³, 0.7× usualKitchener, 18 April: 2.8 µg/m³, 0.6× usualSarniaSarnia, 12 April: 10.0 µg/m³, 2.0× usualSarnia, 13 April: 13.4 µg/m³, 2.7× usualSarnia, 14 April: 15.0 µg/m³, 3.0× usualSarnia, 15 April: 27.0 µg/m³, 5.4× usualSarnia, 16 April: 14.0 µg/m³, 2.8× usualSarnia, 17 April: 2.5 µg/m³, 0.5× usualSarnia, 18 April: 2.5 µg/m³, 0.5× usualDetroitDetroit, 12 April: 12.0 µg/m³, 1.9× usualDetroit, 13 April: 15.9 µg/m³, 2.5× usualDetroit, 14 April: 22.6 µg/m³, 3.6× usualDetroit, 15 April: 26.5 µg/m³, 4.2× usualDetroit, 16 April: 13.6 µg/m³, 2.2× usualDetroit, 17 April: 4.0 µg/m³, 0.6× usualDetroit, 18 April: 5.0 µg/m³, 0.8× usualErieErie, 12 April: 8.5 µg/m³, 1.7× usualErie, 13 April: 14.3 µg/m³, 2.9× usualErie, 14 April: 16.2 µg/m³, 3.2× usualErie, 15 April: 25.4 µg/m³, 5.1× usualErie, 16 April: 11.4 µg/m³, 2.3× usualErie, 17 April: 3.3 µg/m³, 0.7× usualErie, 18 April: no readingSt. ThomasSt. Thomas, 12 April: 11.3 µg/m³, 2.2× usualSt. Thomas, 13 April: 15.1 µg/m³, 2.9× usualSt. Thomas, 14 April: 19.0 µg/m³, 3.7× usualSt. Thomas, 15 April: 25.1 µg/m³, 4.8× usualSt. Thomas, 16 April: 17.8 µg/m³, 3.4× usualSt. Thomas, 17 April: 2.6 µg/m³, 0.5× usualSt. Thomas, 18 April: 3.8 µg/m³, 0.7× usualBuffaloBuffalo, 12 April: 11.1 µg/m³, 2.1× usualBuffalo, 13 April: 14.0 µg/m³, 2.7× usualBuffalo, 14 April: 19.3 µg/m³, 3.7× usualBuffalo, 15 April: 25.0 µg/m³, 4.8× usualBuffalo, 16 April: 20.5 µg/m³, 3.9× usualBuffalo, 17 April: 3.5 µg/m³, 0.7× usualBuffalo, 18 April: 4.8 µg/m³, 0.9× usualLondonLondon, 12 April: 10.0 µg/m³, 1.9× usualLondon, 13 April: 13.5 µg/m³, 2.5× usualLondon, 14 April: 15.6 µg/m³, 2.9× usualLondon, 15 April: 25.0 µg/m³, 4.7× usualLondon, 16 April: 14.3 µg/m³, 2.7× usualLondon, 17 April: 2.6 µg/m³, 0.5× usualLondon, 18 April: 3.5 µg/m³, 0.7× usualDearbornDearborn, 12 April: 13.3 µg/m³, 2.0× usualDearborn, 13 April: 16.1 µg/m³, 2.4× usualDearborn, 14 April: 23.4 µg/m³, 3.5× usualDearborn, 15 April: 25.0 µg/m³, 3.8× usualDearborn, 16 April: 16.4 µg/m³, 2.5× usualDearborn, 17 April: 5.2 µg/m³, 0.8× usualDearborn, 18 April: 4.9 µg/m³, 0.7× usual12 Apr131415161718
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
Port HuronMichigan, United States1 29.615 April5.15.8×
KitchenerOntario, Canada1 29.015 April4.75.8×
SarniaOntario, Canada1 27.015 April4.75.4×
EriePennsylvania, United States1 25.415 April4.75.1×
St. ThomasOntario, Canada1 25.115 April5.24.8×
BuffaloNew York, United States1 25.015 April5.24.8×
LondonOntario, Canada1 25.015 April5.34.7×
DetroitMichigan, United States1 26.515 April6.34.2×
DearbornMichigan, United States1 25.015 April6.63.8×

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 39 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-eastern United States and Canada, April 2023: 9 cities with PM2.5 at twice their usual or more, 15 April 2023, smogrank.com/episodes/2023-04-north-eastern-united-states-and-canada (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.