Air Quality Index and Atmospheric Hazards

Air Quality Index (AQI)

Ontario's air quality index (AQI) is an indicator of air quality throughout the province.  In Ontario, the AQI is based on hourly pollutant measurements of the six most common air contaminants: ground level ozone, fine particulate matter, sulphur dioxide, nitrogen dioxide , carbon monoxide and total reduced sulphur compounds.

The AQI is calculated from a series of equations which relate the air quality measurements to levels at which health or environmental impacts are known to occur.  Each air pollutant uses a slightly different equation, which results in a sub-index for that pollutant.  The pollutant with the highest sub-index becomes the overall AQI.

The main reason for using an AQI instead of the pollutant concentration is because it is much easier to compare the effects from different air pollutants if they are on a common scale related to their potential impacts on health or the environment. 

A multi-stakeholder committee consisting of the Ontario Ministry of the Environment (MOE), Environment Canada and Health Canada is currently working to develop an improved index which will take into consideration more than the one dominant air pollutant in the final AQI and will be based on the health impacts of each pollutant at the ambient concentration measured.  This will be more protective of health as research has shown that there can be increased effects when more than one pollutant is elevated.

Atmospheric Hazards

The Atmospheric Hazards Web site presents background material and searchable map data for atmospheric risks and hazards, including air quality (see the website's "Health" section), from naturally occurring events in Ontario. It was created by Environment Canada and Emergency Management Ontario, to assist municipalities in conducting hazard identification and risk assessments as required by Ontario's Emergency Management Act.