Monitoring Air Quality

Mobile Air Quality Index (AQI) Unit
Mobile Air Quality Index (AQI) Unit

The Air Quality Index (AQI) is a rating scale for outdoor air in Ontario. The lower the AQI, the better the air quality.

Based on data from its network of air monitoring stations, the Ministry of the Environment reports an AQI for many communities across Ontario to all major media outlets and the Ministry web site hourly.

Six key air pollutants are monitored by the ministry as part of the AQI:

These pollutants were chosen because they have an adverse effect on humans and the environment at high levels.

The air monitoring data are sent to a computer centre at the ministry. Data are compared to ambient air quality standards for each of the six air pollutants. These scientifically-based standards, which are updated from time to time, indicate the maximum safe level for a pollutant. Above this level, the pollutant begins to have an undesirable impact on people and the environment.

The monitoring data are converted into the AQI scale. The scale ranges from 0-15 (very good) to 100+ (very poor).

Sample AQI reading

An AQI is calculated for each of the six pollutants. It is simpler and easier now to describe the relative impacts of the pollutants on human health and the environment.

The pollutant with the highest AQI number, therefore, has the greatest impact. It becomes the "overall" AQI for a particular location. Say, for example, the AQI for ozone is 20, and this happens to be the highest out of the six pollutants. It is then reported as the overall AQI or quality of air for a particular location. Specifically, it would be reported as an "AQI of 20, reason: ozone."

For current AQI information, please call the AQI Reporting System line at: (416) 246-0411 in the Toronto area or 1 (800) 387-7768 toll free.
For AQI Information in French, call 1 (800) 221-8852