Protecting the air we breathe

The ministry is protecting Ontario’s air quality and ensuring we have strong environmental standards that protect human health and the environment. In doing so, the ministry is working to ensure cleaner air for all Ontarians by regulating air contaminants released by certain industrial and commercial facilities, limiting emissions from commercial trucks and buses, and better understanding the transboundary flow of air pollutants into Ontario.

Overall, ambient air quality confirms Ontario’s actions to reduce airborne pollutants are working and that regional air quality has been steadily improving in Ontario for many common air pollutants over the past 10 years.

While improvements have been made, we recognize more work needs to be done to ensure communities are protected from local sources of contaminants to air. The ministry will continue to hold facilities accountable, while working with municipalities, Indigenous communities, and industry to improve air quality and address unique challenges in communities with tailored solutions.

Learn more about what Ontario is doing to protect our air.

About this report

This report summarizes 10-year air quality trends and the state of ambient air quality in Ontario during 2020. It reports on the major sources of emissions to air, pollutant concentrations measured across the ministry’s Air Quality Health Index monitoring network, and Ontario’s performance against both provincial and federal ambient air quality criteria that were in effect in 2020. The ministry monitored ambient air quality in real time at 39 air monitoring stations in communities across Ontario in collaboration with the federal National Air Pollutant Surveillance (NAPS) program during 2020. This information was reported 24 hours a day, seven days a week, through the ministry’s public website.

The ministry’s Air Quality Health Index monitoring stations are generally representative of ambient air quality which reflects the contribution of all sources of air contaminants to air. These air monitoring stations are sited to be representative of general population exposure and thus do not necessarily reflect air quality at locations within a community that may be influenced by nearby local sources of air contaminants such as large industrial facilities or major transportation corridors. Concentrations of some air contaminants in neighborhoods located in close proximity to local sources such as an industrial facility may be higher than those measured at the ministry’s Air Quality Health Index monitoring stations.

There are local air quality monitoring networks operated by industrial associations in the communities of Hamilton (Hamilton Air Monitoring Network), Sarnia (Clean Air Sarnia and Area) and Sudbury (Greater Sudbury Air Quality) that provide additional air quality information for these communities.

Toronto North Air Quality Health Index Station
Two photographs showing the exterior (left) and interior (right) of the Toronto North Air Quality Health Index Station.

Air Quality Health Index monitoring stations

This is a map depicting the 39 Air Quality Health Index monitoring stations across Ontario that were in operation during 2020.


  • T: telemetry
  • NO2: nitrogen dioxide
  • PM2.5: fine particulate matter
  • O3: ground-level ozone
  • SO2: sulphur dioxide
  • CO: carbon monoxide
  • TRS: total reduced sulphur