Toronto, Canada Air Quality & Smog

Dominant pollutants, when pollution and smog are worst, a notable historical episode, and the official monitoring agencies for Toronto, Canada — plus how to check the current reading. Toronto reports air quality on the Air Quality Health Index (AQHI) — our full guide explains how that scale works and how it compares to the US AQI.

Dominant pollutants

PM2.5, summer smog (ozone), NO₂.

Seasonal pattern: when smog is worst

Toronto historically suffered summer "smog days" from ozone and particulate, but air quality improved markedly after Ontario phased out coal-fired power, closing its last coal plant in 2014. The dominant modern hazard is episodic wildfire smoke — from northern Ontario and Quebec fires and, increasingly, transport from western Canada.

A notable air-quality episode

In June 2023, smoke from Quebec and Ontario wildfires pushed Toronto's AQHI to "Very High" (10+) for several days, briefly giving the city some of the worst air quality of any major metro worldwide.

The local index and who runs it

Toronto reports air quality using the Air Quality Health Index (AQHI), not the US AQI — so the same air can read as a different number than you may be used to. ECCC and Ontario jointly publish the AQHI and station readings through Air Quality Ontario, with special air-quality statements during smoke events.

• Environment and Climate Change Canada (ECCC)
• Ontario Ministry of the Environment (Air Quality Ontario)

How to check air quality in Toronto

For the official live reading, the agency portals above are the canonical source. To understand what the numbers mean, start with our guide to the Air Quality Health Index (AQHI) and the broader comparison of world air-quality indices. Smog Report puts glanceable air quality on your iPhone — widgets, Live Activities, Siri, and Apple Watch — free and with no account.

Common questions about Toronto air quality

Why does Toronto have air-quality and smog problems?

Toronto historically suffered summer "smog days" from ozone and particulate, but air quality improved markedly after Ontario phased out coal-fired power, closing its last coal plant in 2014. The dominant modern hazard is episodic wildfire smoke — from northern Ontario and Quebec fires and, increasingly, transport from western Canada.

What are the main air pollutants in Toronto?

Toronto's dominant pollutants are PM2.5, summer smog (ozone), NO₂. The reading on any given day is usually driven by whichever of these is highest.

Has Toronto had a major air-quality or smog event?

In June 2023, smoke from Quebec and Ontario wildfires pushed Toronto's AQHI to "Very High" (10+) for several days, briefly giving the city some of the worst air quality of any major metro worldwide.

What air-quality index does Toronto use?

Toronto reports air quality on the Air Quality Health Index (AQHI) (AQHI), not the US AQI — so the same air can read as a different number than you may be used to. For live, glanceable readings on your iPhone, the free Smog Report app auto-selects the right local index for wherever you are.

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