SmogRank / Episodes / Canada

South-eastern Canada, March 2026

For 1 day, on 4 March 2026, 14 cities in Canada and the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Hamilton, Ontario, Canada: 37.6 µg/m³ on 4 March, about 6.3× its usual 6.0.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached14in 2 countries
Days14 March 2026
Worst day4 March14 cities counted
Furthest above usual6.7×Waterdown

Day by day

4 March 14 cities at twice their usual or more
St. CatharinesGuelphBrantfordBuffaloPeterboroughErieSt. ThomasRochesterBellevillePainesvilleSarniaChathamPort HuronKingstonCleveland HeightsShaker HeightsClevelandSyracuseEastpointeHamtramckWindsorDetroitRoyal OakSouthfieldDearbornLincoln ParkTaylorOttawaGatineauFlintUticaBay CityYpsilantiAnn ArborOregonScrantonToledoPerrysburgCornwallLansingNewburghRedfordTorontoBramptonNepeanBarrieMiltonNewmarketKitchenerOakvilleMississaugaLondonAllistonHamiltonWaterdown
1 Mar234567
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

HamiltonHamilton, 1 March: 2.5 µg/m³, 0.4× usualHamilton, 2 March: 5.3 µg/m³, 0.9× usualHamilton, 3 March: 14.0 µg/m³, 2.3× usualHamilton, 4 March: 37.6 µg/m³, 6.3× usualHamilton, 5 March: 18.5 µg/m³, 3.1× usualHamilton, 6 March: 8.7 µg/m³, 1.5× usualHamilton, 7 March: 5.9 µg/m³, 1.0× usualWaterdownWaterdown, 1 March: 2.8 µg/m³, 0.5× usualWaterdown, 2 March: 4.4 µg/m³, 0.8× usualWaterdown, 3 March: 13.0 µg/m³, 2.4× usualWaterdown, 4 March: 36.4 µg/m³, 6.7× usualWaterdown, 5 March: 16.4 µg/m³, 3.0× usualWaterdown, 6 March: 7.8 µg/m³, 1.4× usualWaterdown, 7 March: 6.4 µg/m³, 1.2× usualLondonLondon, 1 March: 2.5 µg/m³, 0.5× usualLondon, 2 March: 4.8 µg/m³, 0.9× usualLondon, 3 March: 15.4 µg/m³, 2.8× usualLondon, 4 March: 30.6 µg/m³, 5.6× usualLondon, 5 March: 16.7 µg/m³, 3.0× usualLondon, 6 March: 12.5 µg/m³, 2.3× usualLondon, 7 March: 5.6 µg/m³, 1.0× usualTorontoToronto, 1 March: 3.3 µg/m³, 0.5× usualToronto, 2 March: 5.7 µg/m³, 0.9× usualToronto, 3 March: 15.1 µg/m³, 2.5× usualToronto, 4 March: 30.6 µg/m³, 5.0× usualToronto, 5 March: 15.3 µg/m³, 2.5× usualToronto, 6 March: 9.6 µg/m³, 1.6× usualToronto, 7 March: 10.8 µg/m³, 1.8× usualOakvilleOakville, 1 March: 2.8 µg/m³, 0.5× usualOakville, 2 March: 4.4 µg/m³, 0.8× usualOakville, 3 March: 13.9 µg/m³, 2.6× usualOakville, 4 March: 30.4 µg/m³, 5.6× usualOakville, 5 March: 17.7 µg/m³, 3.3× usualOakville, 6 March: 7.5 µg/m³, 1.4× usualOakville, 7 March: 6.9 µg/m³, 1.3× usualMiltonMilton, 1 March: 2.8 µg/m³, 0.5× usualMilton, 2 March: 5.6 µg/m³, 1.0× usualMilton, 3 March: 16.7 µg/m³, 3.0× usualMilton, 4 March: 29.3 µg/m³, 5.3× usualMilton, 5 March: 16.7 µg/m³, 3.0× usualMilton, 6 March: 8.1 µg/m³, 1.5× usualMilton, 7 March: 6.4 µg/m³, 1.2× usualKitchenerKitchener, 1 March: 2.4 µg/m³, 0.5× usualKitchener, 2 March: 5.2 µg/m³, 1.0× usualKitchener, 3 March: 11.6 µg/m³, 2.2× usualKitchener, 4 March: 28.7 µg/m³, 5.4× usualKitchener, 5 March: 16.6 µg/m³, 3.1× usualKitchener, 6 March: 9.1 µg/m³, 1.7× usualKitchener, 7 March: 5.8 µg/m³, 1.1× usualAllistonAlliston, 1 March: 2.3 µg/m³, 0.5× usualAlliston, 2 March: 4.5 µg/m³, 0.9× usualAlliston, 3 March: 12.3 µg/m³, 2.5× usualAlliston, 4 March: 28.4 µg/m³, 5.7× usualAlliston, 5 March: 12.2 µg/m³, 2.4× usualAlliston, 6 March: 8.3 µg/m³, 1.7× usualAlliston, 7 March: 5.5 µg/m³, 1.1× usualNewmarketNewmarket, 1 March: no readingNewmarket, 2 March: no readingNewmarket, 3 March: 13.9 µg/m³, 2.6× usualNewmarket, 4 March: 28.4 µg/m³, 5.4× usualNewmarket, 5 March: 10.9 µg/m³, 2.1× usualNewmarket, 6 March: 8.5 µg/m³, 1.6× usualNewmarket, 7 March: 7.5 µg/m³, 1.4× usualMississaugaMississauga, 1 March: 2.8 µg/m³, 0.6× usualMississauga, 2 March: 4.4 µg/m³, 0.9× usualMississauga, 3 March: 13.6 µg/m³, 2.7× usualMississauga, 4 March: 28.1 µg/m³, 5.6× usualMississauga, 5 March: 17.1 µg/m³, 3.4× usualMississauga, 6 March: 7.6 µg/m³, 1.5× usualMississauga, 7 March: 9.0 µg/m³, 1.8× usualNepeanNepean, 1 March: 1.4 µg/m³, 0.3× usualNepean, 2 March: 2.6 µg/m³, 0.5× usualNepean, 3 March: 19.3 µg/m³, 3.6× usualNepean, 4 March: 27.2 µg/m³, 5.1× usualNepean, 5 March: 8.9 µg/m³, 1.7× usualNepean, 6 March: 11.6 µg/m³, 2.2× usualNepean, 7 March: 20.4 µg/m³, 3.8× usualRedfordRedford, 1 March: 7.2 µg/m³, 0.6× usualRedford, 2 March: 10.4 µg/m³, 0.9× usualRedford, 3 March: 22.2 µg/m³, 1.9× usualRedford, 4 March: 27.0 µg/m³, 2.3× usualRedford, 5 March: 19.7 µg/m³, 1.7× usualRedford, 6 March: 25.7 µg/m³, 2.2× usualRedford, 7 March: 9.9 µg/m³, 0.8× usualBarrieBarrie, 1 March: 3.5 µg/m³, 0.7× usualBarrie, 2 March: 6.3 µg/m³, 1.2× usualBarrie, 3 March: 9.9 µg/m³, 1.9× usualBarrie, 4 March: 26.5 µg/m³, 5.1× usualBarrie, 5 March: 13.2 µg/m³, 2.5× usualBarrie, 6 March: 7.7 µg/m³, 1.5× usualBarrie, 7 March: 6.3 µg/m³, 1.2× usualBramptonBrampton, 1 March: 2.5 µg/m³, 0.5× usualBrampton, 2 March: 4.5 µg/m³, 0.9× usualBrampton, 3 March: 14.0 µg/m³, 2.8× usualBrampton, 4 March: 25.1 µg/m³, 5.0× usualBrampton, 5 March: 14.7 µg/m³, 2.9× usualBrampton, 6 March: 11.1 µg/m³, 2.2× usualBrampton, 7 March: 8.7 µg/m³, 1.7× usual1 Mar234567
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
WaterdownOntario, Canada1 36.44 March5.46.7×
HamiltonOntario, Canada1 37.64 March6.06.3×
AllistonOntario, Canada1 28.44 March4.55.7×
OakvilleOntario, Canada1 30.44 March5.45.6×
MississaugaOntario, Canada1 28.14 March5.05.6×
LondonOntario, Canada1 30.64 March5.55.6×
KitchenerOntario, Canada1 28.74 March5.35.4×
NewmarketOntario, Canada1 28.44 March5.35.4×
MiltonOntario, Canada1 29.34 March5.55.3×
NepeanOntario, Canada1 27.24 March5.35.1×
BarrieOntario, Canada1 26.54 March5.25.1×
BramptonOntario, Canada1 25.14 March4.75.0×
TorontoOntario, Canada1 30.64 March6.15.0×
RedfordMichigan, United States1 27.04 March11.72.3×

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 Canada and the United States

Number 56 of 106 episodes in Canada and the United States since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading. All 106.

Use this page

SmogRank, South-eastern Canada, March 2026: 14 cities with PM2.5 at twice their usual or more, 4 March 2026, smogrank.com/episodes/2026-03-south-eastern-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.