Ontario's AQHI is soaring. Here's what the numbers mean
Wildfires and intense heat have created some of the worst air quality on the planet.
Wildfire smoke drifting southward, combined with high temperatures, have created some of the worst air quality in the world over parts of Ontario.
By Wednesday morning, Toronto had taken the top spot on the list of worst air quality among major global cities.
Neighbouring cities fared just as bad, with soaring air quality numbers in Newmarket, Tiverton, and Kitchener, to name a few:
And don't forget the hazy skies
Several Ontario communities are reporting hazy skies Wednesday as a result of the numerous wildfires burning in Ontario and Quebec.
In some places, like Owen Sound and Kingston, the sky has taken on an orangey hue.
"Smoke particles scatter the light from the sun, giving the sky a milky or reddish appearance. The more particles there are suspended in the atmosphere, the stronger the effect," explains Weather Network meteorologist Michael Carter.
The Toronto skyline from the east end of the city on July 15, 2026 (Jason Gorber)
"They also absorb some of the sunlight, which can make the sunlight appear dim and also can cause a cooling effect on the air temperature."
Hazy skies in Owen Sound, Ont. on July 15, 2026 (April Walker)
What is air quality?
When air quality is good, conditions are typically clear. "Poor" air is laden with pollutants, chemicals, and, in the cases mentioned above, particles from wildfires.
The AQHI
In 2005 the Air Quality Health Index, or AQHI, was created, a collaborative effort that came about with the help of experts from ECCC, Health Canada, provincial government, and other experts. This reading informs Canadians about health risks in the air.
The Air Quality Index (AQI) is a tool used by many government agencies to communicate to the public how polluted the air is and how polluted it may become over 48 hours.
The newer AQHI takes into account the health effects and environmental concerns associated with varying concentrations of pollution, two factors the AQI does not. AQHI measures the impact of air quality on your health using a scale of 1-10, with 10 or more representing the highest risk.
To date, the highest AQHI rating in Canada was recorded on Historic AQHI reading in Canada in August 2017 when wildfires in Kamloops, B.C. pushed the AQHI rating to 49, with concentrations of fine particulate matter averaging around 684.5 micrograms per cubic metre at one point in the downtown area - more than double the daily average that's considered hazardous in China.
Orange skies at the 403/401 highway interchange in Mississauga on July 15, 2026 (Fraser McDonald)
Understanding AQHI ratings
Low: 1 - 3
An AQHI rating between 1 and 3 represents ideal air quality for outdoor activities, according to the Government of Canada. For the general population, no precautions are required.
Moderate: 4 - 6
People with respiratory conditions or certain environmental allergies may need to reduce or reschedule strenuous outdoor activities when a moderate AQHI is in effect. For others, it is generally safe to assume outdoor activities unless symptoms like coughing or throat irritation appear.
High: 7 - 10 and very high: above 10
Children and the elderly are advised to limit time outdoors when a high or very high AQHI rating is in effect.
The Weather Network has AQHI ratings on its city pages, making it easy to check air quality in real-time:
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*Header image: A hazy sky over Toronto July 15, 2026. (Jason Gorber)