10-year trends and annual results

Concentrations of air contaminants measured at 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.

This section presents the 10-year trends and annual results for concentrations of key air contaminants listed below including volatile organic compounds such as benzene, toluene, ethylbenzene, xylene (BTEX) and 1,3-butadiene as measured at the Ministry’s Air Quality Health Index air monitoring stations. Emission trends for these key air contaminants from major emissions sources in Ontario such as industry, electricity utilities, transportation, and residential properties are also provided.

Nitrogen dioxide

10-year trends

Trend of NO₂ annual means across Ontario, 2012-2021

This is a line graph showing the trend of nitrogen dioxide annual means from 2012 to 2021. The nitrogen dioxide annual mean concentrations across Ontario have decreased 28% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 34 ambient air monitoring stations.
• Ontario does not have an annual AAQC for NO₂.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 10-year trend for NO₂ at individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for nitrogen dioxide (NO₂).

Ontario NO_x emission trend, 2012-2021

This is a stacked column chart displaying the Ontario NO_X emissions trend from 2012 to 2021 indicating a decrease of approximately 37% or 108 kilotonnes, of which 73 kilotonnes was due to the road vehicles. Sixteen kilotonnes was due to other transportation (e.g. air, marine, rail transportation, and non-road vehicles/engines) and 14 kilotonnes was due to the electricity utilities sector. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023). Ontario’s former emissions trading regulations (O. Reg. 397/01 and O. Reg. 194/05) and Drive Clean light duty vehicle program, and the phase-in of more stringent emission and vehicle standards for new vehicles have contributed to the reduction in nitrogen dioxide emissions over time.

2021 results

The highest NO₂ means were recorded in large, urbanized areas which are influenced by significant vehicular traffic, such as the Greater Toronto Area of southern Ontario.

A summary of the 2021 NO₂ annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2021 nitrogen dioxide (NO₂) annual statistics.

Ontario NO_x emissions by sector, 2021

This is a chart depicting Ontario’s NO_X emissions by sector based on 2021 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

The transportation sector accounted for approximately 56% of total NO_x emissions in 2021.

Fine particulate matter

10-year trends

Trend of PM_2.5 annual means across Ontario, 2012-2021

This is a line graph showing the trend of fine particulate matter annual means from 2012 to 2021. The fine particulate matter annual mean concentrations across Ontario have decreased 18% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 38 ambient air monitoring stations.
• A correction factor was applied to PM_2.5 concentrations measured by TEOM (2012) to approximate SHARP-like measurements. PM_2.5 concentrations measured by SHARP are reflected from 2013 and onward.
• The Ontario annual AAQC for PM_2.5 of 8.8 µg/m³ was introduced in 2020.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 10-year trend for PM_2.5 at individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for fine particulate matter (PM_2.5).

Ontario PM_2.5 emissions trend, 2012-2021

This is a stacked column chart displaying the Ontario PM_2.5 emissions trend from 2012 to 2021 indicating a decrease of approximately 12% or six kilotonnes, of which four kilotonnes was due to the transportation sector (e.g. road vehicles, air, marine, rail transportation, and non-road vehicles/engines) and two kilotonnes was contributed by various industries. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

The phase-in of more stringent emission and vehicle standards for new vehicles, Ontario’s closure of coal burning electricity generating utilities, and reduced emissions from industrial processes have contributed to the reduction in PM_2.5 emissions in Ontario.

2021 results

A summary of the 2021 PM_2.5 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2021 fine particulate matter (PM_2.5) annual statistics.

Wildfire smoke events in Ontario, 2021

Wildfire season typically occurs from early April to late October in Ontario. As wildfires burn through forests and grasslands, they produce dense smoke. It is difficult to predict when the fires will occur, how big they will be, how much smoke they will generate and what direction the smoke will travel. Wildfire smoke may be carried hundreds or thousands of kilometres from the fire zone (Environment and Climate Change Canada, 2023).

In 2021, Ontario experienced several wildfire smoke events, including one particular event that caused widespread, elevated PM_2.5 concentrations across the province on July 19, 2021. Smoke from active forest fires burning in eastern Manitoba and northwestern Ontario travelled through southern Ontario and caused deteriorating air quality and reduced visibility as the smoke descended to the ground-level. Hazy skies were obvious in some communities as smoke drifted across regions.

Forest fire smoke event on July 19, 2021

The smoke plumes from the active fires prompted the issuance of a Special Air Quality Statement (SAQS) for most of the province. On July 19, 2021, the Toronto Downtown AQHI air monitoring station reported both the highest 1-hour and 24-hour PM_2.5 concentration of 170 µg/m³ and 58.7 µg/m³, respectively. Twenty-four AQHI air monitoring stations, including Toronto Downtown, exceeded the PM_2.5 24-hour AAQC of 27 µg/m³ on July 19 due to the forest fire smoke. On July 20, a cold front moved across the province and increased winds allowed for good mixing and dispersion of pollutants, and improved air quality.

Ontario PM_2.5 emissions by sector, 2021

This is a chart depicting Ontario’s PM_2.5 emissions by sector based on 2021 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources, such as forest fires (Air Pollutant Emission Inventory 1990-2021, 2023).

Residential fuel combustion accounted for approximately 37% of the total PM_2.5 emissions in 2021. The major contributor to residential emissions is fuel wood combustion in fireplaces and wood stoves.

Ground-level ozone

10-year trends

Trend of ozone maximums across Ontario, 2012-2021

This is a line graph showing the trend of ozone one-hour maximums from 2012 to 2021. There was no significant trend detected for Ontario over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 38 ambient air monitoring stations.
• The Ontario one-hour AAQC for ozone is 80 ppb.

The 10-year trend of one-hour maximum ozone for individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for ozone (O₃) maximums.

Trend of ozone means across Ontario, 2012-2021

This is a line graph showing the trend of ozone annual, summer and winter means from 2012 to 2021. There were no significant trends detected for Ontario over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 38 ambient air monitoring stations.
• Summer: May - September; Winter: January - April, October - December.
• Ontario does not have an annual or seasonal AAQC for ozone.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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.

There has been no significant trend (increasing or decreasing) in annual and seasonal ozone means over the past 10 years.

Ozone levels continue to exceed Ontario’s 1-hour AAQC for ozone during the warmer months and remain a challenge in some areas of the province, such as southwestern Ontario. However, ozone concentrations during the winter months were well below Ontario’s ozone 1-hour AAQC of 80 ppb in 2021.

The 10-year trend of annual, summer and winter ozone for individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for ozone (O₃), 10-year trend for ozone (O₃) summer means, and 10-year trend for ozone (O₃) winter means.

Ozone annual means for urban and rural Ontario, 2012-2021

This is a line graph displaying the ozone annual means for urban and rural Ontario from 2012 to 2021.

Note:

• Urban S. are urban areas in southern Ontario - Windsor, London, Hamilton, Toronto.
• Urban N. are urban areas in northern Ontario - Thunder Bay, Sault Ste. Marie, Sudbury, North Bay.
• Rural areas in Ontario - Port Stanley, Tiverton, Parry Sound, Petawawa.
• Ontario does not have an annual AAQC for ozone.

Ozone annual mean concentrations in urban areas in southern Ontario have been more comparable to those of urban areas in northern Ontario in recent years.

Generally, ozone concentrations are higher in rural, transboundary-influenced sites on the northern shore of Lake Erie and the eastern shore of Lake Huron. Ozone concentrations are lower in urban areas because it is depleted (scavenged) by reacting with NO emitted by vehicles and other local combustion sources.

2021 results

A summary of the 2021 ozone annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2021 ozone (O₃) annual statistics.

Sulphur dioxide

10-year trends

Trend of SO₂ annual means across Ontario, 2012-2021

This is a line graph showing the trend of sulphur dioxide annual means from 2012 to 2021. The sulphur dioxide annual mean concentrations across Ontario have decreased 54% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 10 ambient air monitoring stations.
• The Ontario annual AAQC for SO₂ of 4 ppb was introduced in 2018.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 10-year trend for SO₂ at individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for sulphur dioxide (SO₂).

Ontario SO₂ emission trend, 2012-2021

This is a stacked column chart displaying the Ontario SO₂ emissions trend from 2012 to 2021 indicating a decrease of approximately 62% or 157 kilotonnes, of which 129 kilotonnes was due to the smelter sector and 10 kilotonnes was due to the electricity utilities sector. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

Emissions reductions at Ontario smelters through the implementation of site-specific standards under O. Reg. 419/05, Ontario’s closure of coal burning electricity generating utilities, Ontario’s former emissions trading regulations (O. Reg. 397/01 and O. Reg. 194/05), and low sulphur content in transportation fuels have contributed to the reduction in SO₂ emissions in Ontario.

2021 results

Concentrations of sulphur dioxide in neighborhoods that are 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 which are sited to be representative of general population exposure.

A summary of the 2021 SO₂ annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2021 sulphur dioxide (SO₂) annual statistics.

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. These data have not been integrated into this ministry report; however, they are being addressed with regulations which aim to decrease local concentrations of SO₂.

Ontario SO₂ emissions by sector, 2021

This is a chart depicting Ontario’s sulphur dioxide emissions by sector based on 2021 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

Smelters in northern Ontario are the major sources of SO₂ emissions in Ontario, accounting for approximately 37% of the provincial SO₂ emissions

Volatile organic compounds

Volatile organic compounds (VOC) are measured at select ambient air monitoring stations across Ontario as part of a co-operative federal-provincial program under the National Air Pollution Surveillance program.

Note: VOC samples were limited in 2021 as Environment and Climate Change Canada’s laboratories had restrictions due to COVID-19 measures put in place following Public Health guidelines. As a result, only three of six AQHI air monitoring stations were operational for VOC monitoring in 2021.

10-year trends

VOCs are measured at six AQHI air monitoring stations (Windsor West, Sarnia, London, Kitchener, Hamilton Downtown, and Newmarket), however only three (Windsor West, Sarnia and Hamilton Downtown) were operational for VOC monitoring in 2021 due to COVID-19 measures put in place following Public Health guidelines.

In 2021, 107 VOCs were analyzed and reported for each sample at each site. For the purposes of this report, commonly detected VOCs (benzene, toluene, ethylbenzene, xylene, and 1,3-butadiene) between 2012 and 2021 are included in this discussion.

Trend of benzene annual means across Ontario, 2012-2021

This is a line graph showing the trend of benzene annual means from 2012 to 2021. The benzene annual mean concentrations across Ontario have decreased 36% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 6 ambient air monitoring stations.
• The 2021 average is based on 3 ambient air monitoring stations.
• VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID-19 measures put in place following Public Health guidelines.
• The Ontario annual AAQC for benzene of 0.45 µg/m³ was introduced in 2016.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 toluene annual means across Ontario, 2012-2021

This is a line graph showing the trend of toluene annual means from 2012 to 2021. The toluene annual mean concentrations across Ontario have decreased 53% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 6 ambient air monitoring stations.
• The 2021 average is based on 3 ambient air monitoring stations.
• VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID-19 measures put in place following Public Health guidelines.
• Ontario does not have an annual AAQC for toluene.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 ethylbenzene annual means across Ontario, 2012-2021

This is a line graph showing the trend of ethylbenzene annual means from 2012 to 2021. The ethylbenzene annual mean concentrations across Ontario have decreased 39% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 6 ambient air monitoring stations.
• The 2021 average is based on 3 ambient air monitoring stations.
• VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID-19 measures put in place following Public Health guidelines.
• Ontario does not have an annual AAQC for ethylbenzene.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 xylene annual means across Ontario, 2012-2021

This is a line graph showing the trend of xylene annual means from 2012 to 2021. The m- and p-xylene and o-xylene annual mean concentrations across Ontario have decreased 39% and 33%, respectively, over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 6 ambient air monitoring stations.
• The 2021 average is based on 3 ambient air monitoring stations.
• VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID-19 measures put in place following Public Health guidelines.
• Ontario does not have an annual AAQC for xylene.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 1,3-butadiene annual means across Ontario, 2012-2021

This is a line graph showing the trend of 1,3-butadiene annual means from 2012 to 2021. The 1,3-butadiene annual mean concentrations across Ontario have decreased 53% over this 10-year period. To view the data for a specific location, please select the 'Stations' radio button and use the drop-down menu.

Note:

• The Ontario 10-year trend is based on data from 6 ambient air monitoring stations.
• The 2021 average is based on 3 ambient air monitoring stations.
• VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID-19 measures put in place following Public Health guidelines.
• The Ontario annual AAQC for 1,3-butadiene is 2.0 µg/m³.
• Air quality in Ontario can vary from year to year due to a variety of factors including pollutant emissions, weather, natural events such as forest fires, 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 10-year trend for VOCs at individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for benzene, 10-year trend for toluene, 10-year trend for ethylbenzene, 10-year trend for m- and p-xylene, 10-year trend for o-xylene, and 10-year trend for 1,3-butadiene.

Ontario VOC emission trend, 2012-2021

This is a stacked column chart displaying the Ontario VOC emissions trend from 2012 to 2021 indicating a decrease of approximately 25% or 87 kilotonnes, of which 47 kilotonnes was due to the transportation sector and 36 kilotonnes was due to the solvent use, surface coating and printing sectors. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

The introduction of more stringent vehicle and engine emission standards for new vehicles, the former Drive Clean light duty vehicle program and various regulations, Canadian Council of Ministers of the Environment VOC emissions guidelines and codes of practice for VOC emitting products and materials have contributed to the reduction in VOC emissions in Ontario.

2021 results

Concentrations of some VOCs in neighborhoods that are 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 which are sited to be representative of general population exposure.

A summary of the 2021 VOCs annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2021 benzene annual statistics, 2021 toluene annual statistics, 2021 ethylbenzene annual statistics, 2021 m- and p-xylene annual statistics, 2021 o-xylene annual statistics, and 2021 1,3-butadiene annual statistics.

Ontario VOC emissions by sector, 2021

This is a chart depicting Ontario’s VOC emissions by sector based on 2021 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2021, 2023).

General solvent use (e.g., degreasing, adhesives and sealants, consumer and commercial products) accounted for 27% of VOC emissions in 2021; and transportation sector accounted for 23% (Air Pollutant Emission Inventory 1990-2021, 2023).

Ontario Ambient Air Quality Criteria

Ambient air quality refers to general air quality resulting from all sources of contaminants to air. Ambient Air Quality Criteria (AAQC) are a concentration of a contaminant in air that is protective against adverse effects on health and/or the environment.

AAQC are not regulatory values but are used to assess general (ambient) air quality resulting from all sources (i.e., industrial and non-industrial sources) of a contaminant to air. AAQC are most commonly used in environmental assessments, special studies using ambient air monitoring data, assessment of general air quality in a community and annual reporting on air quality across the province.

Notes:

• ppb – parts (of contaminant) per billion (parts of air) – by volume.
• μg/m³ – micrograms (of contaminant) per cubic metre (of air) – by weight.
• ppm – parts (of contaminant) per million (parts of air) – by volume.
• ng/m³ - nanograms (of contaminant) per cubic metre (of air) – by weight.