Air Rankings

Key Observations & Incidents

  1. Wildfire smoke drove major spikes
    • Smoke from wildfires in Manitoba, Saskatchewan, and northern Ontario drifted east and degraded air quality in Toronto multiple times in summer 2025.
    • On June 6, 2025, Toronto’s air quality was briefly ranked the worst in the world (or among the worst) due to smoke incursions.
    • By July 14, Toronto was again ranked the second‑most polluted major city globally at certain times, per IQAir rankings.
    • On August 4, Toronto’s air quality was among the worst globally, prompting special air quality statements.
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  2. Air Quality Health Index (AQHI) ratings and alerts
    • On August 4, 2025, in early morning, the AQHI for downtown Toronto was reported at 6 (“moderate risk”) and forecast to rise to 7 (“high risk”) during the day.
    • During smoke events in July, Environment Canada’s AQHI index in Toronto was reported at levels 5 (moderate risk) and forecasts indicated it could climb to 7 (high risk).
    • After the smoke cleared late July, the special air quality statement was lifted and the AQHI dropped to level 3 (low risk) according to Environment Canada.
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  3. Particulemater (PM₂.₅) / polluant concentration snapshots
    • On June 22 (at 17:00), Air Matters listed Toronto’s US‑style AQI as “Moderate,” with PM₂.₅ ≈ 17.3 µg/m³, O₃ ≈ 58.4 µg/m³, NO₂ ≈ 8.9 µg/m³, CO ≈ 125 µg/m³.
    • In general, during smoke episodes, PM₂.₅ concentrations in Toronto rose well above typical background levels (though I couldn’t find a reliable continuous time series).
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  4. Duration and frequency of degraded air quality
    • Several “special air quality statements” were issued over multiple days in mid‑July and early August, indicating that harmful smoke conditions persisted for stretches of time.
    • For example, the July 15 special statement was amid a multi‑day heat/smoke event, and forecasts suggested it might persist.

By late July, the air quality statement was ended as smoke cleared.

Interpretation & Caveats

  • No full seasonal aggregation found — I did not locate a publicly published report or dataset that gives mean, median, or percentile statistics (e.g. daily average PM₂.₅ over June–August 2025) for Toronto.
  • Bias toward extreme events — Most of the documented figures relate to peak smoke conditions or severe episodes, not “baseline summer” conditions.
  • Mix of indices and units — Reports use AQHI (Canada), AQI (US or global via IQAir), PM₂.₅ concentrations in µg/m³, etc. Care must be taken when comparing across them.

Temporal & spatial variability — Air quality during smoke events can vary significantly by hour and location (downwind, elevation, local weather). The reports reflect snapshots rather than full coverage.