What is air quality

Air quality describes the state of the air around us. Good air quality means clean, unpolluted air.

Poor air quality happens when pollutants reach concentrations that are of concern to human health and/or the environment.

Poor air quality comes from a number of factors, including emissions from various natural and man-made sources (e.g. forest fires, vehicles, power plants, industrial processes and residences), and is influenced by atmospheric and weather conditions.

Air pollution and your health

Clean air is critical for human health and the health of the environment.

Air pollution can:

  • make it harder to breathe
  • irritate your lungs and airways
  • worsen chronic diseases such as heart disease, chronic bronchitis, emphysema and asthma

Each person reacts differently to air pollution. Children, seniors and those with diabetes, heart or lung disease are most sensitive to the effects of air pollution.

Negative health effects can increase as air pollution worsens. Symptoms can increase if you are exposed to air pollution for a long time or breathe in a lot of it.

Monitoring air quality

Ontario has a network of 38 ambient (outside) air monitoring stations across the province that collect data and report on key pollutants that are indicators of overall air quality.

Ambient air monitoring stations are established in communities across Ontario so the data we gather represents the exposure of the general population. However, some neighbourhoods that are located near local sources, such as industrial facilities, might have higher concentrations of pollutants than what our monitoring stations measure.

This information is shared with the public through our Air Quality Health Index (AQHI) hourly. The Air Quality Health Index represents the relative risk of a mixture of common air pollutants that are known to harm human health.

We provide AQHI readings and forecasts, air pollution data, as well as information on what to do when a Special Air Quality Statement or Smog and Air Health Advisory is issued.

We publish an annual air quality report that provides information about the state of air quality provincewide and examines 10-year trends for key pollutants.

Status of our air quality

Our air quality has improved significantly over the past 10 years.

Since 2011, levels of smog-causing pollutants in the air have declined significantly, Ontario experienced a:

  • 50% decrease in sulphur dioxide
  • 25% decrease in nitrogen dioxide
  • 17% decrease in fine particulate matter
  • 13% decrease in ozone maximums

In 2020:

  • Ontario’s air was reported in the low risk category for 96% of the year
  • there were no smog advisories issued

For more information, read the 2020 Air Quality Report.

Reducing greenhouse gas emissions

Ontario has taken many steps to improve air quality. We were one of the first places in the world to eliminate coal as a fuel to generate electricity.

We are working with industries to help them cut their greenhouse gas (GHG) emissions by reducing and phasing out the use of coal in their operations.

In 2022, the province announced support for two Ontario steel facilities to replace their use of coal. This will result in significant GHG emission reductions—about 3 million tonnes a year per facility. That’s about the same as taking almost 2 million more cars off our roads.

Greening Ontario’s steel sector:

  • will significantly improve local air quality by reducing toxic pollutants such as benzo[a]pyrene, benzene and sulphur dioxide
  • represents a significant step in the fight against climate change

Progress since 2020

  • Continued to implement a strategy to address industrial emissions (such as the  Sarnia Air Action Plan and Hamilton Air Action Plan). We have enhanced oversight of industrial facilities, including:
    • enhanced inspections
    • reactive incident response
    • monitoring
    • communication with local stakeholders
  • Introduced a new regulation that sets strict emission limits for sulphur dioxide. This will significantly reduce emissions from petroleum facilities in Sarnia by approximately 90% by the end of 2028.
  • Initiated the Sarnia Area Environment Health Project to assess the risk of air pollution in the Sarnia area. The project is anticipated to be completed in spring or summer 2023.
  • Implemented the enhanced emissions testing program for commercial trucks and buses to further reduce pollutants in our air. This program will be integrated with the Ministry of Transportation’s annual safety Motor Vehicle Inspection Station Program in 2022.
  • Enhanced our Air Quality Health Index (AQHI) and roadside air monitoring networks by deploying new technology to the downtown Hamilton AQHI air monitoring station to better understand industrial and traffic related air pollution.
  • Worked with the federal government, Michigan, and the United States Environmental Protection Agency to better understand ozone formation and transport in our shared airshed.
  • Assessed the impacts of the COVID‑19 pandemic on air quality in Ontario by using data collected at our network of roadside air monitoring stations. The data showed that concentrations of common air pollutants associated with transportation and other major emissions sources generally decreased during the initial stages of the provincial declaration of an emergency in 2020.
  • Continued reporting on ambient and roadside air quality that confirms that:
    • Ontario’s actions to reduce airborne pollutants are working
    • regional air quality has been steadily improving in Ontario for many common air pollutants over the past 10 years
  • Created a regulation for nickel smelting and refining facilities in Sudbury to reduce sulphur dioxide emissions.
  • Created a regulation to reduce sulphur dioxide emissions from petroleum facilities in Ontario (including in Sarnia, Mississauga and Nanticoke).

Air quality reports