Air Quality Health Index (AQHI)

The AQHI was developed and implemented by Health Canada with the assistance of Environment and Climate Change Canada and all provinces. It derives a value based on the cumulative health effects of three pollutants – NO2, PM2.5 and ozone. The AQHI provides real-time air quality information using a scale of one through 10 or greater, with lower numbers representing better air quality, as depicted in Figure 24. Index values between one and three are considered low risk, four to six are moderate risk, seven to 10 are high risk and greater than 10 are very high risk. Table 2 outlines the health messages associated with the AQHI. The ministry website provides index values and corresponding categories and health messages.

Figure 24: AQHI Scale

Figure 24 is a graphic of the Air Quality Health Index scale which ranges from one to 10 plus.
Source: Environment & Climate Change Canada.

Table 2: Air Quality Health Index Categories and Health Messages
Health RiskAir Quality Health IndexHealth Messages – At Risk Populationfootnote *Health Messages – General Population
Low1-3Enjoy your usual outdoor activitiesIdeal 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 & Climate Change Canada

The AQHI also reflects exceedances of Ontario’s AAQC: 200 ppb for NO2, 80 ppb for ozone, 250 ppb for SO2, 30 ppm for CO, and 27 ppb for TRS compounds. If an hourly air pollutant concentration exceeds Ontario’s AAQC and the AQHI value is in the low or moderate risk categories (AQHI of 6 or less), then the AQHI is reported with the appropriate high risk value (AQHI of 7 or greater) to reflect the exceedance.

Based on the AQHI categories, in 2016, Ontario reported low risk air quality 93% of the time, moderate risk 6.7% of the time, and high risk less than 1% of the time; there were no very high risk hours reported. Table A20 of the Appendix provides the percentage distribution of hourly AQHI readings for each of the 39 monitoring sites by AQHI value and the number of high risk AQHI days.

Access to Air Quality Information

Near real-time and historic pollutant concentration data and AQHI values are available to the public (24 hours per day, 7 days a week) from across the province on the ministry’s web site. The public can also access index values via the Interactive Voice Response (IVR) system. (To access a recording in English or French, call 1-800-387-7768, or in Toronto, call 416-246-0411). The ministry’s web site also provides air quality forecasts throughout the day, based on regional meteorological conditions and current pollution levels in Ontario and bordering American states.

Air Quality Alerts

Ontario maintains a two-level air quality alert system in partnership with Environment and Climate Change Canada: The first level is a Special Air Quality Statement (SAQS), which informs the public of the potential for degrading air quality and is issued if an AQHI of 7 or greater is expected to last for 1 or 2 hours (i.e., “pop-up”). A SAQS is also issued for areas where forest fire smoke is expected to cause deteriorating air quality. The last major forest fire impact in Ontario was in July 2013 due to forest fire smoke that originated in northwestern Quebec, east of James Bay. In Ontario, potential impacts of forest fires are forecasted by determining prevalent meteorological conditions and observing air pollutants at AQHI air monitoring stations (Sofowote and Dempsey, 2015).

The second level is a Smog and Air Health Advisory (SAHA), issued when “high risk” AQHI levels (AQHI of 7 or greater) are expected to be persistent and continue for 3 hours or more. The SAQS does not constitute a SAHA, but serves as a notification for Ontarians, especially those at risk, to be aware of the air quality and adjust their activities if adverse health effects are observed.

Air quality alerts are issued via the Ministry of the Environment and Climate Change web site, Environment and Climate Change Canada’s web site, and through email air quality alert notifications. To subscribe for air quality alert notifications, please visit the ministry web site.

Ontario issued one SAHA in 2016 and 10 SAQS for regions across the province. The SAHA was issued for the City of Toronto where elevated ozone concentrations reached a maximum of 99 ppb. All 10 SAQS were issued as a result of elevated ozone concentrations across Ontario. Table A21 of the Appendix summarizes the number of SAQS and SAHA issued for Ontario in 2016.


  • footnote[*] 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.