The federal Air Quality Health Index (AQHI) is a health protection communication tool designed to help the public make decisions to protect their health by limiting short-term exposure to air pollution and adjusting activities during increased levels of air pollution. It is based on the cumulative health effects of three common air pollutants: ozone, nitrogen dioxide, and fine particulate matter. It is measured on a scale from 1 to 10+, the lower the number, the lower the risk. Each risk category has accompanying health messaging footnote 1 . The health messages associated with the AQHI are outlined in the table below.

Air Quality Health Index categories and health messages
Health RiskAir Quality Health IndexHealth messages
At risk population footnote 2		Health messages
General population
Low1-3Enjoy your usual outdoor activities.Ideal air quality for outdoor activities.
Moderate4-6Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms.No need to modify your usual activities unless you experience symptoms such as coughing and throat irritation.
High7-10Reduce 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 highAbove 10Avoid 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.

Source: Environment and Climate Change Canada.

Air Quality Health Index annual results

  • Based on the AQHI categories, in 2022, Ontario reported low risk air quality 94.40% of the time, moderate risk 5.57% of the time, high risk 0.03% of the time and very high risk 0.002% of the time.
  • The percentage distribution of hourly AQHI readings for each of the 38 monitoring sites by AQHI value and the number of high risk AQHI days is detailed in the Appendix: 2022 Air Quality Health Index summary

Footnotes

  • footnote[1] Back to paragraph In May 2024, the ministry enhanced Ontario’s AQHI public reporting program by adopting a PM2.5 trigger into the AQHI formulation to better reflect elevated levels of PM2.5 and enable Ontarians to make informed decisions to protect their health during wildfire smoke events.
  • footnote[2] Back to paragraph People with heart or breathing problems are at greater risk. Follow your doctor’s usual advice about exercising and managing your condition.