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 over the same 10-year period are also provided.

Concentrations of 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. VOC samples were not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID measures put in place following Public Health guidelines. As a result, only 10-year trend data based on 2019 measurements are provided in this report for context. For 2019 VOC results, please see the Air Quality in Ontario 2019 Report.

Nitrogen dioxide

10-year trends

Trend of NO₂ annual means across Ontario, 2011-2020

This is a line graph showing the trend of nitrogen dioxide annual means from 2011 to 2020. The nitrogen dioxide annual mean concentrations across Ontario have decreased 25% 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.

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, 2011-2020

This is a stacked column chart displaying the Ontario nitrogen oxides emissions trend from 2011 to 2020 indicating a decrease of approximately 36% or 129 kilotonnes, of which 72 kilotonnes was due to the road vehicles; 36 kilotonnes was due to other transportation sector (e.g., air, rail, marine transportation, and non-road vehicles/engines) and 12 kilotonnes was due to the electricity utilities sector. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022). 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.

2020 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 2020 NO₂ annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2020 nitrogen dioxide (NO₂) annual statistics.

Ontario NO_x emissions by sector, 2020

This is a pie chart depicting Ontario’s NO_x emissions by sector based on 2020 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022).

The transportation sector accounted for approximately 65% of total NO_x emissions in 2020.

Fine particulate matter

10-year trends

Trend of PM_2.5 annual means across Ontario, 2011-2020

This is a line graph showing the trend of fine particulate matter annual means from 2011 to 2020. The fine particulate matter annual mean concentrations across Ontario have decreased 17% 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 (2011-2012) 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 is 8.8 µg/m³.

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, 2011-2020

This is a stacked column chart displaying the Ontario PM_2.5 emissions trend from 2011 to 2020 indicating a decrease of approximately 18% or 11 kilotonnes, of which 6 kilotonnes was due to the transportation sector (e.g., road vehicles, air, rail marine transportation, and non-road vehicles/engines) and 3 kilotonnes was contributed by various industries. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022). 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 fine particulate matter emissions in Ontario.

2020 results

A summary of the 2020 PM_2.5 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2020 fine particulate matter (PM_2.5) annual statistics.

Ontario PM_2.5 emissions by sector, 2020

This is a pie chart depicting Ontario’s PM_2.5 emissions by sector based on 2020 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022).

Residential fuel combustion accounted for approximately 38% of the total PM_2.5 emissions in 2020. 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, 2011-2020

This is a line graph showing the trend of ozone one-hour maximums from 2011 to 2020. The ozone one-hour maximum concentrations across Ontario have decreased 13% 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.

Progressive reductions of NO_x emissions in Ontario and the U.S. have resulted in a decrease in maximum ozone concentrations and the duration of elevated ozone events in the province (OMOECC, 2018).

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, 2011-2020

This is a line graph showing the trend of ozone annual, summer and winter means from 2011 to 2020. 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.

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 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 2020.

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, 2011-2020

This is a line graph displaying the ozone annual means for urban and rural Ontario from 2011 to 2020.

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. This indicates that the decrease in ozone scavenging observed over the past 10 years due to local NO_x emission reductions has been greater in urban areas in southern Ontario than in northern Ontario.

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.

2020 results

A summary of the 2020 ozone annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2020 ozone (O₃) annual statistics.

Sulphur dioxide

10-year trends

Trend of SO₂ annual means across Ontario, 2011-2020

This is a line graph showing the trend of sulphur dioxide annual means from 2011 to 2020. The sulphur dioxide annual mean concentrations across Ontario have decreased 50% 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 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, 2011-2020

This is a stacked column chart displaying the Ontario SO₂ emissions trend from 2011 to 2020 indicating a decrease of approximately 57% or 148 kilotonnes, of which 103 kilotonnes was due to the smelter sector and 12 kilotonnes was due to the electricity utilities sector. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022). 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 sulphur dioxide emissions in Ontario.

2020 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 2020 SO₂ annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2020 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.

Ontario SO₂ emissions by sector, 2020

This is a pie chart depicting Ontario’s sulphur dioxide emissions by sector based on 2020 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022).

Smelters in northern Ontario are the major sources of SO₂ emissions in Ontario, accounting for approximately 54% of the provincial SO₂ emissions in 2020.

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 not collected in 2020 as Environment and Climate Change Canada’s laboratories were shut down due to COVID measures put in place following Public Health guidelines. As a result, only 10-year trend data based on 2019 measurements are provided in this report for context, however, VOC emissions estimates are presented to 2020. For 2019 VOC results, please see the Air Quality in Ontario 2019 Report.

10-year trends

VOCs are measured at eight AQHI air monitoring stations (Windsor West, Sarnia, London, Kitchener, Hamilton Downtown, Toronto North, Newmarket and Ottawa). Toronto North began monitoring VOCs in 2017 and therefore is not included in the 10-year trends.

In 2019, 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 2010 and 2019 are included in this discussion.

Trend of benzene annual means across Ontario, 2010-2019

This is a line graph showing the trend of benzene annual mean from 2010 to 2019. The benzene annual mean concentrations across Ontario have decreased 41% 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 7 ambient air monitoring stations.

Trend of toluene annual means across Ontario, 2010-2019

This is a line graph showing the trend of toluene annual mean from 2010 to 2019. The toluene 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 7 ambient air monitoring stations.
• Ontario does not have an annual AAQC for toluene.

Trend of ethylbenzene annual means across Ontario, 2010-2019

This is a line graph showing the trend of ethylbenzene annual mean from 2010 to 2019. 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 7 ambient air monitoring stations.
• Ontario does not have an annual AAQC for ethylbenzene.

Trend of xylene annual means across Ontario, 2010-2019

This is a line graph showing the trend of xylene annual mean from 2010 to 2019. The m- and p-xylene and o-xylene annual mean concentrations across Ontario have decreased 39%, and decreased 34%, 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 7 ambient air monitoring stations.
• Ontario does not have an annual AAQC for xylene.

Trend of 1,3-butadiene annual means across Ontario, 2010-2019

This is a line graph showing the trend of 1,3-butadiene annual mean from 2010 to 2019. The 1,3-butadiene annual mean concentrations across Ontario have decreased 55% over this 10-year period. Select another location from the drop-down menu to learn the percent change in air quality for other communities.

Note:

• The Ontario 10-year trend is based on data from 7 ambient air monitoring stations.

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.

2020 results

Ontario VOC emission trend, 2011-2020

This is a stacked column chart displaying the Ontario VOC emissions trend from 2011 to 2020 indicating a decrease of approximately 27% or 101 kilotonnes, of which 60 kilotonnes was due to the transportation sector and 34 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 1990-2020, 2022).

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.

Ontario VOC emissions by sector, 2020

This is a pie chart depicting Ontario’s volatile organic compound emissions by sector based on 2020 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2020, 2022).

Transportation sector accounted for 28% of VOC emissions in 2020; and general solvent use (e.g., degreasing, adhesives and sealants, consumer and commercial products) accounted for approximately 26% (Air Pollutant Emission Inventory 1990-2020, 2022).

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.