Northern Ontario Region - Home

Air Quality Index Monitoring


What is the Air Quality Index?

The Air Quality Index (AQI) is an indicator of air quality, based on hourly pollutant measurements of some or all of the six most common air pollutants: sulphur dioxide, ozone, nitrogen dioxide, total reduced sulphur compounds, carbon monoxide and fine particulate matter.

Several state-of-the-art air monitoring stations, operated by the Ministry across the province, form the Air Quality Index (AQI) network.

The ministry takes real-time air quality data from its AQI monitoring sites to produce AQI readings for each location. AQI readings are reported to the public and news media hourly. The public can access the index values by calling the ministry's automatic telephone answering device (English recording:1-800-387-7768 or in Toronto 416-246-0411. French recording: 1-800-221-8852). The AQI can also be obtained from the ministry's Web site:

Here's how an AQI is determined:

  • At the end of each hour, the concentration of each pollutant that the AQI station monitors is converted into a number ranging from zero upwards, using a common scale, or index. The pollutant with the highest number at a given hour becomes the AQI reading. As the air quality changes, the AQI reading increases or decreases. The lower the AQI reading, the cleaner the air.

Here's what the readings mean:

  • If the air quality value is below 32, the air quality is considered relatively good.
  • If the AQI value is in the range of 32 to 49 (moderate category), there may be some adverse effects on very sensitive people.
  • An index value in the 50 to 99 range (poor category), may have some short-term adverse effects on the human or animal populations, or may cause significant damage to vegetation and property.
  • An AQI value of 100 or more (very poor category) may cause adverse effects on a large proportion of those exposed.
For Ontario Air Quality Monitoring Locations website.
Scenes from the Northern Ontario Region
Web Site Designed and Powered by