Understanding Air Quality Index

The best way to protect yourself from the adverse health effects of polluted air is to keep tabs on the Air Quality Index (AQI) in your area. Every day, cities across Canada measure the concentration of ozone in the air, and convert the reading to an AQI number on a scale of 0 to 500.

Air Quality Index

Weather Conditions

Health Advisory



Cool summer temperatures;

windy and/or cloudy;

recent rain or cool front




Mild summer temperatures;

light/moderate winds;

high pressure system, or partly cloudy skies

Unusually sensitive people, especially children or older people with respiratory disease, should limit outdoor activities.

Unhealthy for Sensitive Groups


Temperature upper 80s or above; light winds;

sunny skies

Sensitive people should limit prolonged outdoor exertion. Children may be more affected by high ozone levels than adults because their lungs and immune systems are still developing; they also breathe more rapidly and deeply than adults do, so more pollutants enter their lungs. Older people also must be careful because they tend to have heart and lung conditions and may be at higher risk for respiratory infections, such as the flu, bronchitis, and pneumonia.



Hazy, hot, and humidActive children and adults as well as people with respiratory diseases such as asthma should avoid prolonged outdoor exertion; everyone else, especially children and older adults, should limit prolonged outdoor exertion.

Very Unhealthy (Alert)


Continuous hot, stagnant weatherActive children and adults should avoid all outdoor exertion; everyone else, especially children, should minimize outdoor exertion and stay indoors with air conditioners running and windows and doors closed.

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