What is the Air Quality Health Index?

The Air Quality Health Index or "AQHI" is a scale designed to help you understand what the air quality around you means to your health.

It is a health protection tool that is designed to help you make decisions to protect your health by limiting short-term exposure to air pollution and adjusting your activity levels during increased levels of air pollution. It also provides advice on how you can improve the quality of the air you breathe.

This index pays particular attention to people who are sensitive to air pollution and provides them with advice on how to protect their health during air quality levels associated with low, moderate, high and very high health risks.

The AQHI communicates four primary things:

  1. Measures the air quality in relation to your health on a scale from 1 to 10. The higher the number, the greater the health risk associated with the air quality. When the amount of air pollution is very high, the number will be reported as 10+.
  2. Assigns a category that describes the level of health risk associated with the index reading (e.g. Low, Moderate, High, or Very High Health Risk).
  3. Provides health messages customized to each category for both the general population and the ‘at risk’ population.
  4. Shows current hourly AQHI readings and maximum forecast values for today, tonight and tomorrow.

The AQHI is designed to give you this information along with some suggestions on how you might adjust your activity levels depending on your individual health risk from air pollution.

How is the Air Quality Health Index calculated?

The formula developed to calculate the Air Quality Health Index is based on research conducted by Health Canada using health and air quality data collected in major cities across Canada.

The Air Quality Health Index represents the relative risk of a mixture of common air pollutants which are known to harm human health. Three pollutants were chosen as indicators of the overall outdoor air mixture:

For more information on how the AQHI has been modified for reporting in Ontario, please visit the Frequently Asked Questions.

What is the scale for the Air Quality Health Index

The Air Quality Health Index provides a number from 1 to 10+ to indicate the level of health risk associated with local air quality. Occasionally, when the amount of air pollution is abnormally high, the number may exceed 10.

The higher the number, the greater the health risk and our need to take precautions.

The index describes the level of health risk associated with this number as ‘low’, ‘moderate’, ‘high’ or ‘very high’, and suggests steps we can take to reduce our exposure.

Air Quality Health Index Categories, Values and Associated Colours
Air Quality Health Index Categories and Values
1
2
3
4
5
6
7
8
9
10
+
Low Risk
(1 - 3)
Moderate Risk
(4 - 6)
High Risk
(7 - 10)
Very High Risk
 
  • 1-3 Low health risk
  • 4-6 Moderate health risk
  • 7-10 High health risk
  • 10 + Very high health risk

Air Quality Health Index Categories and Health Messages

The table below provides the health messages for each category of the Air Quality Health Index for the "at risk" population and the general population.
Health Risk Air Quality Health Index Health Messages
At Risk Population* General Population
Low 1 - 3 Enjoy your usual outdoor activities. Ideal air quality for outdoor activities.
Moderate 4 - 6 Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms. No need to modify your usual outdoor activities unless you experience symptoms such as coughing and throat irritation.
High 7 - 10 Reduce or reschedule strenuous activities outdoors. Children and the elderly should also take it easy. Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms such as coughing and throat irritation.
Very High Above 10 Avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion. Reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation.

* People with heart or breathing problems are at greater risk. Follow your doctor's usual advice about exercising and managing your condition.