SmogRank / Episodes / United States
North-eastern United States and Canada, 29 July to 9 August 2025
For 12 days, from 29 July to 9 August 2025, 292 cities in the United States and Canada had PM2.5 at least twice their usual for the time of year. The worst reading was Marquette, Michigan, United States: 112.0 µg/m³ on 30 July, about 14× its usual 8.1. Ended 9 August.
Day by day
How it spread
Every city it reached
| City | Days | Highest | Above usual |
|---|---|---|---|
| MarquetteMichigan, United States | 8 | 112.030 July | 14× |
| Rouyn-NorandaQuebec, Canada | 4 | 87.32 August | 12× |
| VirginiaMinnesota, United States | 9 | 111.031 July | 11× |
| BarabooWisconsin, United States | 8 | 78.631 July | 11× |
| MadisonWisconsin, United States | 8 | 82.431 July | 10× |
| GreendaleWisconsin, United States | 7 | 82.931 July | 10× |
| South MilwaukeeWisconsin, United States | 7 | 82.931 July | 10× |
| Winthrop HarborIllinois, United States | 6 | 77.531 July | 10× |
| ZionIllinois, United States | 6 | 77.531 July | 10× |
| SuperiorWisconsin, United States | 9 | 108.030 July | 10× |
| AppletonWisconsin, United States | 8 | 86.931 July | 10× |
| AltoonaWisconsin, United States | 6 | 86.831 July | 9.9× |
| Eau ClaireWisconsin, United States | 6 | 86.831 July | 9.8× |
| WaukeshaWisconsin, United States | 8 | 86.031 July | 9.7× |
| MilwaukeeWisconsin, United States | 8 | 91.131 July | 9.4× |
| CloquetMinnesota, United States | 8 | 73.231 July | 9.4× |
| Sault Ste. MarieOntario, Canada | 9 | 71.630 July | 9.3× |
| MankatoMinnesota, United States | 6 | 96.931 July | 9.1× |
| DuluthMinnesota, United States | 9 | 91.130 July | 9.1× |
| Green BayWisconsin, United States | 8 | 85.930 July | 9.1× |
| BlaineMinnesota, United States | 6 | 79.31 August | 9.1× |
| ManisteeMichigan, United States | 8 | 80.731 July | 8.7× |
| MolineIllinois, United States | 4 | 76.031 July | 8.6× |
| BrainerdMinnesota, United States | 5 | 75.731 July | 8.6× |
| RockfordIllinois, United States | 7 | 79.831 July | 8.3× |
| Parry SoundOntario, Canada | 7 | 62.03 August | 8.3× |
| Des PlainesIllinois, United States | 7 | 75.831 July | 8.2× |
| La VistaNebraska, United States | 2 | 48.51 August | 8.2× |
| CaryIllinois, United States | 7 | 75.031 July | 8.1× |
| ClintonIowa, United States | 4 | 73.931 July | 8.0× |
| MinneapolisMinnesota, United States | 6 | 80.71 August | 7.9× |
| Apple ValleyMinnesota, United States | 5 | 66.11 August | 7.9× |
| Greater SudburyOntario, Canada | 4 | 63.130 July | 7.9× |
| BellevueNebraska, United States | 2 | 49.51 August | 7.9× |
| Fort DodgeIowa, United States | 4 | 74.831 July | 7.8× |
| EastpointeMichigan, United States | 4 | 51.74 August | 7.8× |
| Cedar RapidsIowa, United States | 3 | 66.531 July | 7.7× |
| AllistonOntario, Canada | 7 | 53.83 August | 7.7× |
| North BayOntario, Canada | 4 | 53.030 July | 7.7× |
| OconomowocWisconsin, United States | 8 | 111.031 July | 7.6× |
| Detroit LakesMinnesota, United States | 5 | 69.931 July | 7.6× |
| ChicagoIllinois, United States | 6 | 69.731 July | 7.6× |
| Saint MichaelMinnesota, United States | 6 | 69.31 August | 7.6× |
| Sioux FallsSouth Dakota, United States | 3 | 45.11 August | 7.6× |
| TomahWisconsin, United States | 7 | 76.031 July | 7.5× |
| DavenportIowa, United States | 4 | 64.431 July | 7.5× |
| EriePennsylvania, United States | 5 | 53.34 August | 7.5× |
| MuscatineIowa, United States | 3 | 50.131 July | 7.5× |
| RochesterMinnesota, United States | 6 | 76.231 July | 7.4× |
| BurnsvilleMinnesota, United States | 6 | 75.11 August | 7.4× |
| SarniaOntario, Canada | 5 | 62.54 August | 7.4× |
| PeterboroughOntario, Canada | 6 | 52.53 August | 7.4× |
| BrookfieldIllinois, United States | 7 | 66.331 July | 7.3× |
| BellevilleOntario, Canada | 5 | 51.14 August | 7.3× |
| Saint PaulMinnesota, United States | 5 | 73.01 August | 7.2× |
| ShakopeeMinnesota, United States | 6 | 68.931 July | 7.2× |
| HudsonvilleMichigan, United States | 7 | 67.131 July | 7.2× |
| JenisonMichigan, United States | 7 | 67.131 July | 7.2× |
| LondonOntario, Canada | 5 | 63.14 August | 7.2× |
| MarshallMinnesota, United States | 5 | 61.51 August | 7.2× |
| ChathamOntario, Canada | 3 | 53.14 August | 7.2× |
| AberdeenSouth Dakota, United States | 4 | 41.11 August | 7.2× |
| Grand RapidsMichigan, United States | 5 | 73.231 July | 7.1× |
| LincolnwoodIllinois, United States | 7 | 72.031 July | 7.1× |
| Iowa CityIowa, United States | 3 | 64.931 July | 7.1× |
| BlairNebraska, United States | 3 | 48.41 August | 7.1× |
| Presque IsleMaine, United States | 1 | 41.43 August | 7.1× |
| Mount IvyNew York, United States | 1 | 35.55 August | 7.1× |
| New CityNew York, United States | 1 | 35.55 August | 7.1× |
| NewburghNew York, United States | 2 | 35.45 August | 7.1× |
| UticaNew York, United States | 4 | 35.47 August | 7.1× |
| Saint CloudMinnesota, United States | 5 | 63.71 August | 7.0× |
| AuroraIllinois, United States | 5 | 63.431 July | 7.0× |
| WarrenvilleIllinois, United States | 5 | 63.431 July | 7.0× |
| PierreSouth Dakota, United States | 3 | 40.131 July | 7.0× |
| West FargoNorth Dakota, United States | 5 | 67.231 July | 6.9× |
| NewmarketOntario, Canada | 8 | 60.23 August | 6.9× |
| BraidwoodIllinois, United States | 3 | 58.231 July | 6.9× |
| PittsfieldMassachusetts, United States | 3 | 44.75 August | 6.9× |
| BrantfordOntario, Canada | 6 | 59.54 August | 6.8× |
| Port HuronMichigan, United States | 5 | 58.84 August | 6.8× |
| BloomingtonIllinois, United States | 2 | 57.51 August | 6.8× |
| St. ThomasOntario, Canada | 5 | 55.64 August | 6.8× |
| SaguenayQuebec, Canada | 2 | 53.73 August | 6.8× |
| SyracuseNew York, United States | 7 | 45.44 August | 6.8× |
| HartfordVermont, United States | 4 | 40.95 August | 6.8× |
| BathurstNew Brunswick, Canada | 1 | 37.83 August | 6.8× |
| Franklin ParkIllinois, United States | 7 | 76.931 July | 6.7× |
| KitchenerOntario, Canada | 6 | 59.94 August | 6.7× |
| KingstonOntario, Canada | 4 | 47.24 August | 6.7× |
| VermillionSouth Dakota, United States | 3 | 41.81 August | 6.7× |
| BramptonOntario, Canada | 6 | 54.73 August | 6.6× |
| AlbanyNew York, United States | 5 | 49.85 August | 6.6× |
| BrookingsSouth Dakota, United States | 5 | 45.71 August | 6.6× |
| KearneyMissouri, United States | 2 | 44.61 August | 6.6× |
| LibertyMissouri, United States | 2 | 44.61 August | 6.6× |
| North AdamsMassachusetts, United States | 3 | 43.15 August | 6.6× |
| GreenfieldMassachusetts, United States | 2 | 40.45 August | 6.6× |
| WareMassachusetts, United States | 1 | 40.25 August | 6.6× |
| BenningtonVermont, United States | 3 | 39.25 August | 6.6× |
| TopekaKansas, United States | 2 | 62.01 August | 6.5× |
| East ChicagoIndiana, United States | 4 | 59.431 July | 6.5× |
| BarrieOntario, Canada | 8 | 57.93 August | 6.5× |
| GuelphOntario, Canada | 5 | 57.54 August | 6.5× |
| SouthfieldMichigan, United States | 5 | 56.14 August | 6.5× |
| JerseyvilleIllinois, United States | 1 | 53.01 August | 6.5× |
| OmahaNebraska, United States | 3 | 50.91 August | 6.5× |
| ColumbiaMissouri, United States | 3 | 72.51 August | 6.4× |
| OlatheKansas, United States | 2 | 64.01 August | 6.4× |
| New BaltimoreMichigan, United States | 5 | 56.34 August | 6.4× |
| MississaugaOntario, Canada | 5 | 51.73 August | 6.4× |
| BuffaloNew York, United States | 7 | 50.24 August | 6.4× |
| SpringfieldMassachusetts, United States | 2 | 45.25 August | 6.4× |
| North ChicopeeMassachusetts, United States | 2 | 39.35 August | 6.4× |
| BangorMaine, United States | 1 | 35.14 August | 6.4× |
| ElginIllinois, United States | 7 | 73.731 July | 6.3× |
| TorontoOntario, Canada | 7 | 57.93 August | 6.3× |
| RochesterNew York, United States | 7 | 46.04 August | 6.3× |
| RaymoreMissouri, United States | 2 | 45.01 August | 6.3× |
| DoltonIllinois, United States | 6 | 64.831 July | 6.2× |
| HamiltonOntario, Canada | 6 | 55.44 August | 6.2× |
| SavoyIllinois, United States | 2 | 52.31 August | 6.2× |
| DorvalQuebec, Canada | 4 | 44.24 August | 6.2× |
| White PlainsNew York, United States | 1 | 31.05 August | 6.2× |
| NorthbrookIllinois, United States | 3 | 60.731 July | 6.1× |
| HammondIndiana, United States | 6 | 60.431 July | 6.1× |
| LansingMichigan, United States | 5 | 59.731 July | 6.1× |
| MiltonOntario, Canada | 6 | 58.63 August | 6.1× |
| Kansas CityKansas, United States | 2 | 58.61 August | 6.1× |
| Michigan CityIndiana, United States | 5 | 56.931 July | 6.1× |
| Oak LawnIllinois, United States | 5 | 56.731 July | 6.1× |
| OakvilleOntario, Canada | 5 | 55.83 August | 6.1× |
| WaterdownOntario, Canada | 5 | 51.14 August | 6.1× |
| OttawaOntario, Canada | 5 | 45.23 August | 6.1× |
| EdmundstonNew Brunswick, Canada | 2 | 41.53 August | 6.1× |
| KeeneNew Hampshire, United States | 2 | 39.25 August | 6.1× |
| WindsorOntario, Canada | 5 | 59.84 August | 6.0× |
| MilfordMassachusetts, United States | 2 | 34.75 August | 6.0× |
| UxbridgeMassachusetts, United States | 2 | 34.75 August | 6.0× |
| PeoriaIllinois, United States | 3 | 61.51 August | 5.9× |
| Bay CityMichigan, United States | 6 | 51.44 August | 5.9× |
| BridgeviewIllinois, United States | 6 | 68.031 July | 5.8× |
| NapervilleIllinois, United States | 5 | 63.031 July | 5.8× |
| JolietIllinois, United States | 5 | 60.431 July | 5.8× |
| HartfordConnecticut, United States | 2 | 45.15 August | 5.8× |
| SherbrookeQuebec, Canada | 2 | 39.03 August | 5.8× |
| Saint-Jean-sur-RichelieuQuebec, Canada | 3 | 35.13 August | 5.8× |
| LaconiaNew Hampshire, United States | 2 | 29.04 August | 5.8× |
| KalamazooMichigan, United States | 7 | 61.631 July | 5.7× |
| WinnipegManitoba, Canada | 2 | 54.32 August | 5.7× |
| SpringfieldIllinois, United States | 2 | 53.31 August | 5.7× |
| YpsilantiMichigan, United States | 3 | 49.231 July | 5.7× |
| Des MoinesIowa, United States | 3 | 48.331 July | 5.7× |
| CornwallOntario, Canada | 4 | 41.44 August | 5.7× |
| ChanuteKansas, United States | 2 | 55.51 August | 5.6× |
| HollandMichigan, United States | 6 | 55.331 July | 5.6× |
| BeatriceNebraska, United States | 2 | 47.51 August | 5.6× |
| Kansas CityMissouri, United States | 2 | 47.01 August | 5.6× |
| PainesvilleOhio, United States | 2 | 36.24 August | 5.6× |
| FrederictonNew Brunswick, Canada | 1 | 30.24 August | 5.6× |
| DecaturIllinois, United States | 2 | 52.31 August | 5.5× |
| ChampaignIllinois, United States | 2 | 49.61 August | 5.5× |
| GranbyQuebec, Canada | 4 | 44.33 August | 5.5× |
| Calumet CityIllinois, United States | 5 | 56.031 July | 5.4× |
| St. CatharinesOntario, Canada | 7 | 41.54 August | 5.4× |
| DanburyConnecticut, United States | 2 | 40.25 August | 5.4× |
| MonctonNew Brunswick, Canada | 1 | 28.64 August | 5.4× |
| DetroitMichigan, United States | 5 | 56.04 August | 5.3× |
| TaylorMichigan, United States | 4 | 48.04 August | 5.3× |
| LeawoodKansas, United States | 2 | 44.11 August | 5.3× |
| Grand IslandNebraska, United States | 2 | 42.51 August | 5.3× |
| DrummondvilleQuebec, Canada | 3 | 36.43 August | 5.3× |
| LewistonMaine, United States | 1 | 32.24 August | 5.3× |
| Wood RiverIllinois, United States | 1 | 52.31 August | 5.2× |
| Lincoln ParkMichigan, United States | 3 | 49.84 August | 5.2× |
| BécancourQuebec, Canada | 3 | 34.73 August | 5.2× |
| WorcesterMassachusetts, United States | 2 | 34.05 August | 5.2× |
| Elmwood ParkIllinois, United States | 7 | 75.431 July | 5.1× |
| DearbornMichigan, United States | 5 | 53.64 August | 5.1× |
| AnkenyIowa, United States | 3 | 48.331 July | 5.1× |
| TecumsehMichigan, United States | 3 | 47.531 July | 5.1× |
| RedfordMichigan, United States | 4 | 46.44 August | 5.1× |
| ElkhartIndiana, United States | 5 | 46.131 July | 5.1× |
| ScrantonPennsylvania, United States | 4 | 41.25 August | 5.1× |
| WaterburyConnecticut, United States | 2 | 38.55 August | 5.1× |
| MontréalQuebec, Canada | 4 | 38.33 August | 5.1× |
| RutlandVermont, United States | 3 | 34.74 August | 5.1× |
| Rivière-des-Prairies–Pointe-aux-TremblesQuebec, Canada | 4 | 36.33 August | 5.0× |
| HaverhillMassachusetts, United States | 1 | 29.74 August | 5.0× |
| FraminghamMassachusetts, United States | 2 | 26.85 August | 5.0× |
| Saint JosephMissouri, United States | 2 | 48.61 August | 4.9× |
| WatertownSouth Dakota, United States | 4 | 45.21 August | 4.9× |
| South BendIndiana, United States | 3 | 44.731 July | 4.9× |
| Trois-RivièresQuebec, Canada | 3 | 37.23 August | 4.9× |
| DerryNew Hampshire, United States | 2 | 32.04 August | 4.9× |
| LondonderryNew Hampshire, United States | 2 | 32.04 August | 4.9× |
| WaterlooIowa, United States | 2 | 41.61 August | 4.8× |
| BrossardQuebec, Canada | 4 | 37.73 August | 4.8× |
| GaryIndiana, United States | 4 | 45.931 July | 4.7× |
| MiramichiNew Brunswick, Canada | 2 | 25.74 August | 4.7× |
| ShawiniganQuebec, Canada | 3 | 36.93 August | 4.6× |
| University CityMissouri, United States | 1 | 36.21 August | 4.6× |
| Cleveland HeightsOhio, United States | 2 | 34.34 August | 4.6× |
| State CollegePennsylvania, United States | 2 | 33.66 August | 4.6× |
| AugustaMaine, United States | 2 | 31.24 August | 4.6× |
| Upper AltonIllinois, United States | 1 | 48.11 August | 4.5× |
| PortageIndiana, United States | 5 | 46.131 July | 4.5× |
| East Saint LouisIllinois, United States | 1 | 46.01 August | 4.5× |
| QuébecQuebec, Canada | 3 | 37.03 August | 4.5× |
| WyomingMichigan, United States | 5 | 54.731 July | 4.4× |
| Sorel-TracyQuebec, Canada | 5 | 39.93 August | 4.4× |
| ArnoldMissouri, United States | 1 | 35.11 August | 4.4× |
| New HavenConnecticut, United States | 1 | 33.75 August | 4.4× |
| MendhamNew Jersey, United States | 1 | 32.55 August | 4.4× |
| RandolphNew Jersey, United States | 1 | 32.55 August | 4.4× |
| Fort LeeNew Jersey, United States | 1 | 31.45 August | 4.4× |
| Granite CityIllinois, United States | 1 | 47.61 August | 4.3× |
| LexingtonMassachusetts, United States | 3 | 38.65 August | 4.3× |
| ChesapeakeVirginia, United States | 1 | 34.97 August | 4.3× |
| Dodge CityKansas, United States | 1 | 30.72 August | 4.3× |
| PortsmouthNew Hampshire, United States | 1 | 28.54 August | 4.3× |
| L'Ancienne-LoretteQuebec, Canada | 2 | 38.93 August | 4.2× |
| ToledoOhio, United States | 4 | 38.44 August | 4.2× |
| CarlislePennsylvania, United States | 3 | 32.76 August | 4.2× |
| SchlusserPennsylvania, United States | 3 | 32.76 August | 4.2× |
| LowellMassachusetts, United States | 2 | 27.44 August | 4.2× |
| Columbia CityIndiana, United States | 3 | 40.21 August | 4.1× |
| MuncieIndiana, United States | 1 | 34.61 August | 4.0× |
| LafayetteIndiana, United States | 1 | 31.81 August | 4.0× |
| BridgeportConnecticut, United States | 1 | 31.35 August | 4.0× |
| LynnMassachusetts, United States | 1 | 25.74 August | 4.0× |
| Fort WayneIndiana, United States | 3 | 35.91 August | 3.9× |
| New York CityNew York, United States | 1 | 32.85 August | 3.9× |
| PortlandMaine, United States | 1 | 31.54 August | 3.9× |
| PoquosonVirginia, United States | 1 | 28.97 August | 3.9× |
| NorristownPennsylvania, United States | 1 | 27.95 August | 3.9× |
| St. LouisMissouri, United States | 1 | 37.71 August | 3.8× |
| DerbyKansas, United States | 2 | 36.91 August | 3.8× |
| HaysvilleKansas, United States | 2 | 36.91 August | 3.8× |
| LebanonPennsylvania, United States | 2 | 32.36 August | 3.8× |
| BostonMassachusetts, United States | 1 | 26.84 August | 3.8× |
| NepeanOntario, Canada | 7 | 57.630 July | 3.7× |
| Warrensville HeightsOhio, United States | 1 | 31.44 August | 3.7× |
| KokomoIndiana, United States | 1 | 30.51 August | 3.7× |
| AndersonIndiana, United States | 1 | 30.41 August | 3.7× |
| LincolnNebraska, United States | 1 | 27.32 August | 3.7× |
| LexingtonNorth Carolina, United States | 1 | 29.88 August | 3.6× |
| PatersonNew Jersey, United States | 1 | 28.55 August | 3.6× |
| HickoryNorth Carolina, United States | 1 | 28.48 August | 3.6× |
| Kennett SquarePennsylvania, United States | 2 | 27.25 August | 3.6× |
| YorkPennsylvania, United States | 1 | 29.26 August | 3.5× |
| ClemmonsNorth Carolina, United States | 1 | 27.48 August | 3.5× |
| HopewellVirginia, United States | 1 | 25.37 August | 3.5× |
| RoanokeVirginia, United States | 1 | 25.38 August | 3.5× |
| Ponca CityOklahoma, United States | 2 | 34.42 August | 3.4× |
| Beaver FallsPennsylvania, United States | 2 | 31.58 August | 3.4× |
| SteubenvilleOhio, United States | 2 | 31.08 August | 3.4× |
| BloomingtonIndiana, United States | 1 | 26.61 August | 3.4× |
| WilmingtonDelaware, United States | 1 | 26.05 August | 3.4× |
| PaulsboroNew Jersey, United States | 1 | 25.66 August | 3.4× |
| SewellNew Jersey, United States | 1 | 25.66 August | 3.4× |
| ClevelandOhio, United States | 3 | 34.54 August | 3.3× |
| HarrisburgPennsylvania, United States | 2 | 30.56 August | 3.3× |
| New HollandPennsylvania, United States | 2 | 29.46 August | 3.3× |
| LancasterPennsylvania, United States | 2 | 28.66 August | 3.3× |
| Winston-SalemNorth Carolina, United States | 1 | 28.08 August | 3.3× |
| Jersey CityNew Jersey, United States | 1 | 27.45 August | 3.3× |
| New BrunswickNew Jersey, United States | 1 | 25.15 August | 3.3× |
| MonessenPennsylvania, United States | 1 | 25.18 August | 3.3× |
| Natrona HeightsPennsylvania, United States | 2 | 28.67 August | 3.2× |
| YoungstownOhio, United States | 2 | 26.88 August | 3.2× |
| IndianapolisIndiana, United States | 1 | 33.11 August | 3.1× |
| HersheyPennsylvania, United States | 1 | 29.05 August | 3.1× |
| PennsaukenNew Jersey, United States | 1 | 26.65 August | 3.1× |
| LindenNew Jersey, United States | 1 | 26.15 August | 3.1× |
| AbingtonPennsylvania, United States | 1 | 25.75 August | 3.1× |
| Ann ArborMichigan, United States | 3 | 38.331 July | 3.0× |
| Kennedy TownshipPennsylvania, United States | 1 | 27.28 August | 3.0× |
| PittsburghPennsylvania, United States | 1 | 27.08 August | 3.0× |
| ElizabethNew Jersey, United States | 1 | 27.85 August | 2.9× |
| CamdenNew Jersey, United States | 1 | 27.35 August | 2.9× |
| PhiladelphiaPennsylvania, United States | 1 | 27.55 August | 2.8× |
| LimaOhio, United States | 1 | 26.51 August | 2.8× |
| Wake ForestNorth Carolina, United States | 2 | 33.08 August | 2.7× |
| Terre HauteIndiana, United States | 1 | 28.01 August | 2.7× |
| FishersIndiana, United States | 1 | 26.51 August | 2.7× |
| McCordsvilleIndiana, United States | 1 | 26.51 August | 2.7× |
| WarrenOhio, United States | 1 | 25.66 August | 2.6× |
| MiamiOklahoma, United States | 2 | 33.02 August | 2.5× |
| West MifflinPennsylvania, United States | 1 | 26.18 August | 2.5× |
| WestervilleOhio, United States | 1 | 25.91 August | 2.5× |
| MiddletownOhio, United States | 1 | 26.01 August | 2.2× |
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 and Canada
Number 5 of 173 episodes in the United States and Canada since our records began, by cities reached.
- Eastern United States and Canada, June and July 2023343
- Northern United States and Canada, July 2026327
- United States and Canada, July 2023322
- Eastern United States and Canada, May and June 2023317
- North-eastern United States and Canada, 29 July to 9 August 2025292
- Northern United States and Canada, May and June 2025247
- United States and Canada, June 2023195
- North-western United States and Canada, August 2023176
- North-western United States and Canada, 4 to 22 August 2026151
- Northern United States and Canada, July 2025139
- Northern United States and Canada, June 2025134
- North-western United States and Canada, July and August 2026118
Bars: cities reached; colour: the level of the episode's highest daily reading. All 173.
Use this page
SmogRank, North-eastern United States and Canada, 29 July to 9 August 2025: 292 cities with PM2.5 at twice their usual or more, 29 July to 9 August 2025, smogrank.com/episodes/2025-07-29-north-eastern-united-states-and-canada (accessed 5 October 2026).
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. Fire detections from NASA FIRMS; smoke maps from NOAA HMS.