Air Quality in Ontario 2023 Report

Air quality highlights

• Overall, air quality in Ontario has improved over time as both ambient concentrations of common air pollutants and emissions to air have decreased. Over the last 10 years, concentrations have decreased by 28% for nitrogen dioxide, by 12% for fine particulate matter (PM_2.5) and by 42% for sulphur dioxide on average across the province (see table below).
• In 2023, Ontario reported air quality in the low-risk category 92% of the time, based on the Air Quality Health Index (AQHI).
• Transboundary influences, from both the United States (U.S.) and beyond, account for a significant portion of Ontario’s ozone when ozone levels are elevated.
• Ozone and fine particulate matter, the main components of smog, remain as pollutants of concern from a regional perspective. Sulphur dioxide and benzene remain a concern at the local level in some communities.
• In 2023, there were exceedances of the provincial Ambient Air Quality Criteria, or the Canadian Ambient Air Quality Standard, or both, for ground-level ozone, fine particulate matter and sulphur dioxide in some communities.
• Decreasing trends were observed for some traffic-related pollutants including black carbon and nitrate in fine particulate matter, while others showed no trend.
• 2023 marked an unprecedented wildfire season: Ontario issued 13 air quality alerts - Special Air Quality Statements (SAQS) – which covered 55 days. Seven of these SAQS were issued due to forecasts of elevated PM_2.5 concentrations from wildfire smoke, accounting for 49 of those 55 days.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as wildfires, and the long-range transport of air pollutants from the United States and elsewhere. Long-term trends are thus a better reflection of any improvements or a deterioration in air quality over time versus year over year changes.