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The ministry has a network of 40 ambient (outside) air monitoring stations across the province that supply ministry staff with real-time air pollutant data. This data is relayed to the public via Ontario's Air Quality Index (AQI).

The AQI is used as an indicator of ambient air quality based on the following pollutants in our air:

• Ozone (O₃)
• Fine Particulate Matter (PM_2.5)
• Nitrogen Dioxide (NO₂)
• Carbon Monoxide (CO)
• Sulphur Dioxide (SO₂)
• Total Reduced Sulphur (TRS) Compounds

The AQI  is reported in real-time on www.airqualityontario.com, 24-hours a day, seven days a week, for 40 locations across the province.

The potential health and environmental impacts of the range of AQI values are shown in the following table (PDF).

Ozone and fine particulate matter

Ozone and fine particulate matter (PM2.5) are linked to respiratory issues, increased hospital admissions and premature deaths. Ozone also causes agricultural crop loss each year in Ontario, with visible leaf damage in many crops, garden plants and trees, especially during the summer months.

In 2000, the Canadian Council of Ministers of the Environment (CCME) developed Canada-wide standards for ozone and PM_2.5 because of these pollutants' adverse effects on human health and the environment.

Learn More

For more information about these pollutants, see:

• Ontario's Air Quality Index (fact sheet)
• Air Quality Ontario