By Julia · weather-canada.com editorial team · Published · 4 min read
Wildfire smoke is hard to write about honestly, because the most dramatic evidence is a photograph of an orange sky and the most reliable evidence is a network of monitoring stations that this article does not use. What we have is a model: the CAMS global atmospheric composition system, served by Open-Meteo, which estimates fine particles (PM2.5) hour by hour. It covers August 2022 to December 2025. This article reads it as carefully as it can and says what it cannot do.
The reading rules are short. The values are modelled, not measured; the grid is coarse, tens of kilometres; and a model does not know why the particles are there. When we count a day at 25 micrograms per cubic metre or more, the daily mean of the hourly values, that threshold is our own round number, not a regulatory limit. It is a way to count unusual days, nothing more.
One year stands out: 2023
For 2023, 2024 and 2025, the full years in the data, here are the days at or above that threshold in each of nine cities.
| City | 2023 | 2024 | 2025 | Highest daily mean (µg/m³) and date |
|---|---|---|---|---|
| Yellowknife | 59 | 17 | 12 | 266 · Aug 9, 2023 |
| Edmonton | 51 | 18 | 15 | 169 · Jan 4, 2023 |
| Calgary | 24 | 9 | 7 | 66 · Jul 15, 2023 |
| Winnipeg | 12 | 6 | 21 | 57 · Jun 1, 2025 |
| Toronto | 54 | 16 | 21 | 87 · Jun 8, 2023 |
| Montréal | 17 | 10 | 14 | 95 · Jun 6, 2023 |
| Ottawa | 11 | 0 | 10 | 71 · Jun 29, 2023 |
| Vancouver | 19 | 2 | 18 | 49 · Sep 5, 2025 |
| Halifax | 7 | 0 | 3 | 58 · Sep 30, 2023 |
Open-Meteo air-quality API (CAMS global model), August 2022 – December 2025; modelled PM2.5, not a monitoring station.
In eight of nine cities, 2023 has the most such days. Added together, the nine cities have 254 of them in 2023, 78 in 2024 and 121 in 2025. Toronto went from 54 in 2023 to 16 in 2024; Yellowknife from 59 to 17; Ottawa from 11 to zero. The one city where 2023 was not the worst is Winnipeg, with 12 days in 2023 and 21 in 2025.
Natural Resources Canada, in its summary of the 2023 season, reports more than 6,000 fires and about 15 million hectares burned, against a normal of roughly 2.5 million hectares a year. Our model does not measure fires; it measures particles. But the two pictures agree in shape: one year well above its neighbours, and it is the year the fire statistics single out.
The north has the worst days and the cleanest median
Yellowknife has the highest values in the dataset: 266 µg/m³ on August 9, 2023, followed by 218 on August 31 and 207 on September 13. It has 39 days at 50 µg/m³ or more since August 2022. Yet its median day, over the same period, is the cleanest of the nine cities, at 3.3 µg/m³. Vancouver's median is the highest, at 10.8, the everyday background of a large urban area. That contrast is the real shape of smoke exposure: not a constant haze, but short episodes laid on top of clean air.
The south shows the same story with lower peaks. Montréal's highest day is June 6, 2023 at 95 µg/m³, Toronto's June 8, 2023 at 87 and Ottawa's June 29, 2023 at 71. Calgary's is July 15, 2023 at 66.5 µg/m³. Halifax peaks at 58 on September 30, 2023. In Winnipeg the highest values are in 2025: 57 on June 1, then 53 on June 11 and 52 on July 29.
The calendar of the bad days
YellowknifeEdmontonTorontoVancouver
Open-Meteo air-quality API (CAMS global model), August 2022 – December 2025; modelled PM2.5, not a monitoring station.
The chart sums the three calendar years by month. In Yellowknife, every one of the 88 days at 25 or above falls between May and September, with the weight in July (27 days), August (29) and September (21). Toronto's season is earlier: 20 days in May, 29 in June, 18 in July. Vancouver's is late summer: 14 days in August and 6 in September, some two months after Toronto's peak. Its highest day in the whole series, September 5, 2025 at 48.6 µg/m³, fits that calendar.
The warning in the data
Since August 2022, Edmonton shows 36 days at or above 25 µg/m³ outside May to September, and its single highest daily value, 169 µg/m³ on January 4, 2023, falls in the middle of winter. Vancouver has 26 such days outside the warm season, and its second and third highest values of the series, 44 µg/m³ on October 18, 2022 and 43 on November 16, 2022, are in autumn. These are not fire-season dates. The model cannot tell us what put those particles in the air, and neither can we. The lesson is practical: a high value on a map is not automatically smoke, and a count like the one above overstates the smoke total in the cities that also have winter episodes.
What to do with this
Use the model for what it does well, which is the seasonality: for a trip to the north in July to September, or to Ontario in late spring, build in flexibility, and check the Air Quality Health Index from Environment and Climate Change Canada on the day, because it is built on measured values. A smoke day is a good day to move exercise indoors and a bad day to schedule a run. For the other half of the Canadian summer, the heat itself, read summer heat and humidex. For the decade of temperatures that frames this one, ten years of Canadian weather.
Period of the data cited: 2023–2025 (CAMS model, data from August 2022).