Roadside air monitoring in Ontario

Vehicles are a major source of air pollution in Ontario. Traffic-related air pollution is emitted from vehicle exhausts, fuel evaporation, and non-tailpipe sources such as brakes, tires and road dust. Elevated levels of traffic-related air pollution can be found up to 250 meters from a major road.

Exposure to traffic-related air pollutants has been linked to a wide range of adverse health outcomes, including respiratory and cardiovascular diseases, cancer, adverse birth and developmental outcomes, and premature mortality. Children, seniors, and people with pre-existing health conditions are more vulnerable to the adverse health effects from traffic-related pollution.

In 2015, Ontario, in collaboration with Environment and Climate Change Canada, established a dedicated roadside air monitoring network, the first of its kind in Canada, to better understand traffic-related air pollution in highly urbanized settings.  These three dedicated roadside air monitoring stations monitor common air pollutants as well as the traffic-related pollutants such as NO₂, PM_2.5, ultrafine particles, black carbon, metals, and major components of PM_2.5. The ministry has also designated 10 of its AQHI air monitoring stations located near major roads as roadside air monitoring stations to complement the dedicated roadside air monitoring network.

Roadside air monitoring stations

This is a map depicting the three dedicated and ten AQHI roadside air monitoring stations across Ontario that were in operation during 2023.

Note:

• Roadside air monitoring stations are located typically within approximately 100 m of a major roadway with daily traffic volumes greater than 10,000 vehicles per day.

Nitrogen dioxide

Combustion or burning of carbon-based materials (e.g., wood, gasoline) in air produces nitrogen oxides (NO_x), of which NO₂ is a component. The transportation sector is the main source of nitrogen dioxide in Ontario.

8-year trends

Trend of NO₂ annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of NO₂ annual mean concentrations across the roadside air monitoring network from 2016 to 2023. The NO₂ annual mean concentrations decreased by 20% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 12 roadside air monitoring stations.
• 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.

The 8-year trend for NO₂ at individual roadside air monitoring stations in Ontario is presented in the Appendix: 8-year trend for nitrogen dioxide.   
 

2023 results

A summary of the 2023 NO₂ annual statistics for individual roadside air monitoring stations is detailed in the Appendix: 2023 nitrogen dioxide (NO₂) annual statistics for the roadside air monitoring network.

Fine particulate matter

Fine particulate matter consists of primary and secondary PM_2.5. Primary PM_2.5 is emitted directly to the atmosphere. Major sources of primary PM_2.5 include residential fireplaces and wood stoves, motor vehicles, smelters, power plants, industrial facilities, and agricultural burning and wildfires. Secondary PM_2.5 is formed indirectly in the atmosphere through a series of complex chemical reactions of gaseous precursors such as nitrogen dioxide and sulphur dioxide.   
 

8-year trends

Trend of PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of PM_2.5 annual mean concentrations across the roadside air monitoring network from 2016 to 2023. There was no trend over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 12 roadside air monitoring stations.
• Ontario uses the annual PM_2.5 CAAQS “as is” for comparison to a single annual average of air quality data; this value, 8.8 µg/m³, is considered a Reference Level.
• 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.

The 8-year trend for PM_2.5 at individual roadside air monitoring stations in Ontario is presented in the Appendix: 8-year trend for fine particulate matter.   
 

2023 results

The wildfire smoke events in 2023 were unprecedented and caused widespread, elevated PM_2.5 concentrations across the province. Further information and analyses are provided in Wildfire smoke events in Ontario, 2023.

A summary of the 2023 PM_2.5 annual statistics for individual roadside air monitoring stations is detailed in the Appendix: 2023 fine particulate matter (PM_2.5) annual statistics for the roadside air monitoring network.

Ultrafine particles

Ultrafine particles are less than 0.1 µm in aerodynamic diameter and are mostly emitted from road traffic in urban environments. These tiny particles have larger surface areas per unit mass to absorb toxic chemicals and can also penetrate deep into the lungs.

8-year trends

Trend of ultrafine particles annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of ultrafine particles annual mean concentrations from 2016 to 2023. The ultrafine particles annual mean concentrations within the network have decreased by 18% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from three roadside air monitoring stations in Toronto.
• Ontario does not have an annual AAQC for ultrafine particles.
• 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.

The 8-year trend for ultrafine particles at individual roadside air monitoring stations in Ontario is presented in the Appendix: 8-year trend for ultrafine particles.

2023 results

A summary of the 2023 ultrafine particles annual statistics for individual roadside air monitoring stations is detailed in the Appendix: 2023 ultrafine particles annual statistics.

Black carbon

Black carbon is a sooty black material produced through incomplete combustion processes. It is emitted from anthropogenic (e.g., engines and coal-fired power plants) and natural sources (e.g., wildfires). Black carbon comprises a significant portion of fine particulate matter and is linked to both climate warming and adverse health effects.

8-year trends

Trend of black carbon annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of black carbon annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. The black carbon annual mean concentrations within the network have decreased by 33% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 8 roadside air monitoring stations.
• Ontario does not have an annual AAQC for black carbon.
• 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.

The 8-year trend for black carbon at individual roadside air monitoring stations in Ontario is presented in the Appendix: 8-year trend for black carbon.

2023 results

A summary of the 2023 black carbon annual statistics for individual roadside air monitoring stations is detailed in the Appendix: 2023 black carbon annual statistics.

Heavy metals in PM_2.5

Heavy metals are a loose term used to refer to naturally occurring trace elements, including metals that reside lower in the Periodic Table of Elements. Heavy metals in PM_2.5 are often associated with industrial processes, vehicle emissions, and various human activities. When inhaled, these airborne particles can accumulate in the body over time and have adverse health effects, particularly when exposure levels are high or prolonged. The ministry measures 24 heavy metals in PM_2.5, of which six select metals are presented below since they are often measured above their respective detection limits.

8-year trends

Trend of iron in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of iron in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. Iron in PM_2.5 annual mean concentrations increased by 48% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside air monitoring stations.
• Ontario does not have an annual AAQC for iron in PM_2.5.
• 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.

Trend of copper in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of copper in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. There was no trend over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside air monitoring stations.
• Ontario does not have an annual AAQC for copper in PM_2.5.
• 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.

Trend of manganese in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of manganese in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. Manganese in PM_2.5 annual mean concentrations decreased by 28% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside air monitoring stations.
• Ontario does not have an annual AAQC for manganese in PM_2.5.
• 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.  

Trend of lead in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of lead in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. Lead in PM_2.5 annual mean concentrations decreased by 26% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside air monitoring stations.
• Ontario does not have an annual AAQC for lead in PM_2.5.
• 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.

Trend of selenium in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of selenium in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. Selenium in PM_2.5 annual mean concentrations increased by 21% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside air monitoring stations.
• Ontario does not have an annual AAQC for selenium in PM_2.5.
• 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.

Trend of zinc in PM_2.5 annual means across the roadside air monitoring network, 2016-2023

This is a line graph showing the trend of zinc in PM_2.5 annual mean concentrations from 2016 to 2023 across the roadside air monitoring network. Zinc in PM_2.5 annual mean concentrations decreased by 35% over this 8-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The 8-year trend is based on data from 2 roadside research air monitoring stations.
• Ontario does not have an annual AAQC for zinc in PM_2.5.
• 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.

The 8-year trend for heavy metals at individual roadside air monitoring stations in Ontario is presented in the Appendix: 8-year trend for iron in PM_2.5; 8-year trend for copper in PM_2.5; 8-year trend for manganese in PM_2.5; 8-year trend for lead in PM_2.5; 8-year trend for selenium in PM_2.5; 8-year trend for zinc in PM_2.5.

2023 results

A summary of the 2023 heavy metals in PM_2.5 annual statistics for individual roadside air monitoring stations is detailed in the Appendix: 2023 iron in PM_2.5 annual statistics; 2023 copper in PM_2.5 annual statistics; 2023 manganese in PM_2.5 annual statistics; 2023 lead in PM_2.5 annual statistics; 2023 selenium in PM_2.5 annual statistics; and 2023 zinc in PM_2.5 annual statistics.

Major components in PM_2.5

Major components in PM_2.5, with the exception of black carbon and metals, are the parts of tiny particles that can change or evaporate when exposed to heat (also known as non-refractory species in PM_2.5).  In the air, these include organic compounds, sulphate, nitrate and ammonium compounds. Vehicle emissions and industry are major sources of these components which can affect human health.

The ministry monitors major components in PM_2.5 at the Toronto Hwy 401 air monitoring station, however, due to technical difficulties, there were insufficient data in 2023 to calculate a valid annual mean. The Toronto Hwy 401 air monitoring station measures five major components in PM_2.5, of which four components are presented since chloride is mostly below its detection limit.

8-year trends

Trend of organics in PM_2.5 at Toronto Hwy 401, 2016-2023

This is a line graph showing the trend of organics in PM_2.5 annual mean concentrations from 2016 to 2023 at the Toronto Hwy 401 roadside air monitoring station. There was no trend over this 8-year period.

Note:

• Ontario does not have an annual AAQC for organics in PM_2.5.
• 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.

Trend of sulphate in PM_2.5 at Toronto Hwy 401, 2016-2023

This is a line graph showing the trend of sulphate in PM_2.5 annual mean concentrations from 2016 to 2023 at the Toronto Hwy 401 roadside air monitoring station. There was no trend over this 8-year period.

Note:

• Ontario does not have an annual AAQC for sulphate in PM_2.5.
• 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.

Trend of nitrate in PM_2.5 at Toronto Hwy 401, 2016-2023

This is a line graph showing the trend of nitrate in PM_2.5 annual mean concentrations from 2016 to 2023 at the Toronto Hwy 401 roadside air monitoring station. Nitrate in PM_2.5 annual mean concentrations decreased by 25% over this 8-year period.

Note:

• Ontario does not have an annual AAQC for nitrate in PM_2.5.
• 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.

Trend of ammonium in PM_2.5 at Toronto Hwy 401, 2016-2023

This is a line graph showing the trend of ammonium in PM_2.5 annual mean concentrations from 2016 to 2023 at the Toronto Hwy 401 roadside air monitoring station. There was no trend over this 8-year period.

Note:

• Ontario does not have an annual AAQC for ammonium in PM_2.5.
• 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. 

Relative distribution of major components in PM_2.5 at Toronto Hwy 401, 2016-2023

This is a stacked column chart showing the relative distribution of major components in PM_2.5 based on annual mean concentrations from 2016 to 2023 at the Toronto Hwy 401 roadside air monitoring station. Relative contribution of PM_2.5 components varied from year to year with the organic component representing the largest contribution across all years; however, data reporting requirements were not met in 2023 to calculate annual mean concentrations.

The 8-year trends for the four major components in PM_2.5 monitored at the Toronto Hwy 401 roadside air monitoring station in Ontario are presented in the Appendix: 8-year trend for organics in PM_2.5; 8-year trend for sulphate in PM_2.5; 8-year trend for nitrate in PM_2.5; 8-year trend for ammonium in PM_2.5.

2023 results

A summary of the 2023 annual statistics for major components in PM_2.5 at the Windsor West and Toronto Hwy 401 roadside air monitoring stations is detailed in the Appendix: 2023 organics in PM_2.5 annual statistics; 2023 sulphate in PM_2.5 annual statistics; 2023 nitrate in PM_2.5 annual statistics, 2023 ammonium in PM_2.5 annual statistics.