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World Air Quality Index

The World Air Quality Index project uses measurements of particulate matter, including PM 2.5, which are 2.5 microns or smaller, as well as ozone, nitrogen oxide, sulphur dioxide and carbon monoxide emissions.

Canada had an overall air quality rating of 154 on Tuesday morning, which is considered “unhealthy.�

Saskatoon, Saskatchewan had the worst air in the country, according to , with a reading of 223 as of 11 a.m., which is considered “very unhealthy.�

The province has been heavily impacted by wildfire smoke, including last weekend, when a Canadian Football League game in Regina between the Saskatchewan Roughriders and Calgary Stampeders was postponed from Friday to Saturday due to poor air quality.

‘Unhealthy’ ratings in Ontario

On July 15, Toronto had a  rating of 122, which is “unhealthy for sensitive groups.� Milton and Hamilton both had ratings of 132. Galetta, a community in rural western Ottawa, had Ontario’s worst air quality with a rating of 152 on Tuesday.

Heat alert continues

Ontario is also grappling with a on Tuesday, with a warning from Environment Canada of a “prolonged period of extreme heat and humidity.�

can expect a daytime high of 31 C on Tuesday and even higher temperatures for Wednesday, with a high of 33 C.

Meanwhile, Environment Canada issued a for southern Ontario on Tuesday, “due to the possibility of deteriorating air quality.� The alert covers Windsor, Toronto, York Region, Mississauga, Brampton, Halton Hills, Burlington and St. Catharines.

According to , most of Ontario returned to a “moderate� air quality risk on Tuesday, with air quality health index readings in the four to six range. Readings of eight and above are considered “high risk� or “very high risk.� Conditions have improved from Monday, when Toronto and parts of southern Ontario saw ratings in the 10 or 10+ range, indicating a “very high risk.�

Special air quality statement

“Elevated pollution levels are expected today,� Environment Canada warned in Tuesday’s special air quality statement.

“Weather conditions are expected to cause increasing levels of ozone,� Environment Canada added.

Moderate risk air quality health index (AQHI) values are expected on Tuesday with the potential for short-term high risk AQHI values due to ozone combining with residual wildfire smoke, the weather agency said.

What to do

When air pollution levels are high, residents of affected areas should limit time outdoors and consider reducing or rescheduling outdoor sports, activities and events, Environment Canada said in Tuesday’s advisory.

During periods of poor air quality, Canadians may experience symptoms such as eye, nose and throat irritation, headaches or a mild cough. More serious but less common symptoms include wheezing, chest pains or severe cough, Environment Canada added.

Adults aged 65 and older, pregnant people, infants and young children, people with an existing illness or chronic health condition, and people who work outdoors, should reduce or reschedule strenuous activities outdoors and seek medical attention if experiencing symptoms.

When indoors, residents should keep windows and doors closed as much as possible and prioritize keeping cool during heat events.

To protect your indoor air from outdoor air pollution, use an air filter in your ventilation system or a certified portable air cleaner.

Should you wear a mask?

In a , Dr. Kevan Mehta, a pediatric respirologist at McMaster Children’s Hospital in Hamilton, said fine particles known as PM 2.5 can impact the lungs and other systems of the body.

Families may choose to stay indoors during air quality advisories, but Mehta recommends a balanced approach. With hot and humid air conditions, anyone with breathing issues should weigh health and safety considerations when planning outdoor activities.

If you have a chronic breathing issue such as asthma, an N95 mask can filter out PM 2.5 irritants. Lower-grade masks may offer protection from larger particles, but they won’t filter out PM 2.5.

But given how difficult it can be to breathe in hot, humid air, Mehta doesn’t recommend using an N95 mask for an extended time outdoors, especially for children.