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 key air contaminants listed above including volatile organic compounds such as benzene, toluene, ethylbenzene, xylene (BTEX) and 1,3-butadiene measured at the Ministry’s Air Quality Health Index air monitoring stations. Associated emission trends over the same 10-year period are also provided.

Nitrogen dioxide

Highlights

10-year trends

  • NO2 concentrations have decreased by 22%
  • NOx emissions have decreased by 28%

2019 results

10-year trends

Trend of NO2 annual means across Ontario, 2010-2019

This is a line graph showing the trend of nitrogen dioxide annual means from 2010 to 2019. The nitrogen dioxide annual mean concentrations across Ontario have decreased 22% 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 32 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 NOx emission trend, 2010-2019

This is a stacked column chart displaying the Ontario nitrogen oxides emissions trend from 2010 to 2019 indicating a decrease of approximately 28% or 105 kilotonnes, of which 51 kilotonnes was due to the road vehicles; 30 kilotonnes was due to the electricity utilities sector and 24 kilotonnes was due to other transportation sector (e.g. air, rail, marine transportation, and non-road vehicles/engines). Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

2019 results

Summary of annual NO2 results for 2019
Averaging time Low range High range Number of sites with AAQC exceedances
NO2
1-hour max		 17.2 ppb
at Grand Bend		 78.3 ppb
at Toronto East		 0
NO2
24-hour max		 9.8 ppb
at Port Stanley		 38.7 ppb
at Toronto West		 0
NO2
Annual mean		 2.49 ppb
at Grand Bend		 14.6 ppb
at Toronto West		 Not applicable

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 2019 NO2 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2019 nitrogen dioxide (NO2) annual statistics.

Ontario NOx emissions by sector, 2019

This is a pie chart depicting Ontario’s nitrogen oxides emissions by sector based on 2019 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

The transportation sector accounted for approximately 66% of total NOx emissions in 2019.

Fine particulate matter

Highlights

10-year trends

  • PM2.5 concentrations have decreased by 20%
  • PM2.5 emissions have decreased by 15%

2019 results

  • Thirteen AQHI air monitoring stations measured above the 24-hour PM2.5 reference level of 28 µg/m3 on at least one occasion.

10-year trends

Trend of PM2.5 annual means across Ontario, 2010-2019

This is a line graph showing the trend of fine particulate matter annual means from 2010 to 2019. The fine particulate matter annual mean concentrations across Ontario have decreased 20% 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 37 ambient air monitoring stations.
  • A correction factor was applied to PM2.5 concentrations measured by TEOM (2010-2012) to approximate SHARP-like measurements. PM2.5 concentrations measured by SHARP are reflected from 2013 and onward.
  • Ontario does not have an annual AAQC for PM2.5 and is instead compared against a 24-hour reference level of 28 µg/m3 based on the Canadian Ambient Air Quality Standards.

The 10-year trend for PM2.5 at individual AQHI air monitoring stations in Ontario is presented in the Appendix: 10-year trend for fine particulate matter (PM2.5).

Ontario PM2.5 emissions trend, 2010-2019

This is a stacked column chart displaying the Ontario fine particulate matter emissions trend from 2010 to 2019 indicating a decrease of approximately 15% or 9 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 2 kilotonnes was contributed by various industries. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

2019 results

Summary of annual PM2.5 results for 2019
Averaging time Low range High range Number of sites with AAQC exceedances
PM2.5
1-hour max		 29 µg/m3
at Petawawa		 91 µg/m 3
at Brantford		 Not applicable
PM2.5
24-hour max		 14 µg/m3
at Petawawa		 38 µg/m3
at Windsor West		 13
PM2.5
Annual mean		 3.8 µg/m3
at Petawawa		 9.1 µg/m3
at Windsor West		 Not applicable

A summary of the 2019 PM2.5 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2019 fine particulate matter (PM2.5) annual statistics.

Ontario PM2.5 emissions by sector, 2019

This is a pie chart depicting Ontario’s fine particulate matter emissions by sector based on 2019 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

Residential fuel combustion accounted for approximately 38% of the total PM2.5 emissions in 2019. The major contributor to residential emissions is fuel wood combustion in fireplaces and wood stoves.

Ground-level ozone

Highlights

10-year trends

  • No significant trends

2019 results

  • Five AQHI air monitoring stations measured ozone levels above the 1-hour AAQC of 80 ppb on at least one occasion

10-year trends

Trend of ozone means across Ontario, 2010-2019

This is a line graph showing the trend of ozone annual, summer and winter means from 2010 to 2019. 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 37 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.

Although there was no significant trend detected in ozone annual means, progressive reductions of NOx 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).

Similarly, there has been no significant trends in either the ozone summer or winter means over the past ten 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 2019.

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, 2010-2019

This is a line graph displaying the ozone annual means for urban and rural Ontario from 2010 to 2019.

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 NOx 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.

2019 results

Summary of annual O3 results for 2019
Averaging time Low range High range Number of sites with AAQC exceedances
Ozone 1-hour max 56 ppb
at Thunder Bay		 88 ppb
at Newmarket		 5
Ozone 24-hour max 40 ppb
at Oshawa		 56 ppb
at Port Stanley and Sarnia		 Not applicable
Ozone annual mean 21.8 ppb
at Toronto West		 32.3 ppb
at Port Stanley		 Not applicable

A summary of the 2019 ozone annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2019 ozone (O3) annual statistics.

Sulphur dioxide

Highlights

10-year trends

  • SO2 concentrations have decreased by 63%
  • SO2 emissions have decreased by 56%

2019 results

  • Five AQHI air monitoring stations measured sulphur dioxide levels above the 10-minute AAQC of 67 ppb on at least one occasion
  • Five AQHI air monitoring stations measured sulphur dioxide levels above the 1-hour AAQC of 40 ppb on at least one occasion
  • One AQHI air monitoring stations measured sulphur dioxide levels above the annual AAQC of 4 ppb

10-year trends

Trend of SO2 annual means across Ontario, 2010-2019

This is a line graph showing the trend of sulphur dioxide annual means from 2010 to 2019. The sulphur dioxide annual mean concentrations across Ontario have decreased 63% 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 9 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, 2010-2019

This is a stacked column chart displaying the Ontario sulphur dioxide emissions trend from 2010 to 2019 indicating a decrease of approximately 56% or 142 kilotonnes, of which 94 kilotonnes was due to the smelter sector and 38 kilotonnes was due to the electricity utilities sector.  Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

2019 results

Summary of annual SO2 results for 2019
Averaging time Low range High range Number of sites with AAQC exceedances
SO2 10-minutes max 4.8 ppb
at Ottawa Downtown		 344.2 ppb
at Sudbury		 5
SO2 1-hour max 2.7 ppb
at Ottawa Downtown		 123.7 ppb
at Hamilton Downtown		 5
SO2 24-hour max 0.6 ppb
at Ottawa Downtown		 45.9 ppb
at Hamilton Downtown		 Not applicable
SO2 Annual mean 0.15 ppb
at Toronto North		 4.75 ppb
at Hamilton Downtown		 1

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 2019 SO2 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2019 sulphur dioxide (SO2) annual statistics.

Ontario SO2 emissions by sector, 2019

This is a pie chart depicting Ontario’s sulphur dioxide emissions by sector based on 2019 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

Smelters in northern Ontario are the major sources of SO2 emissions in Ontario, accounting for approximately 37% of the provincial SO2 emissions in 2019.

Volatile organic compounds

Highlights

10-year trends

  • Benzene concentrations have decreased by 41%
  • Toluene concentrations have decreased by 54%
  • Ethylbenzene have decreased by 39%
  • m- and p-xylene have decreased by 39%
  • o-xylene have decreased by 34%
  • 1,3-butadiene have decreased by 55%

2019 results

  • Ontario’s AAQC for these volatile organic compounds (where applicable) were met except for one AQHI air monitoring station that measured benzene levels above the annual AAQC of 0.45 µg/m3.

10-year trends

VOCs are measured at eight AQHI air monitoring stations (Windsor West, Sarnia, London, Kitchener, Hamilton Downtown, Toronto North, Newmarket and Ottawa) by Environment and Climate Change Canada as part of a co-operative federal-provincial program under the NAPS Air Toxics Program. 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.

2019 results

Summary of annual VOC results for 2019
Averaging time Low range High range Number of sites with AAQC exceedances
Benzene 24-hour max 0.578 µg/m3
at London		 2.070 µg/m3
at Hamilton Downtown		 0
Benzene annual mean 0.250 µg/m3
at Newmarket		 0.568 µg/m3
at Hamilton Downtown		 1
Toluene 24-hour max 1.571 µg/m3
at Ottawa Downtown		 6.942 µg/m3
at Toronto North		 0
Toluene annual mean 0.418 µg/m3
at Newmarket		 1.390 µg/m3
at Toronto North		 Not applicable
Ethylbenzene 24-hour max 0.202 µg/m3
at Ottawa Downtown		 0.717 µg/m3
at Toronto North		 0
Ethylbenzene annual mean 0.064 µg/m3
at Ottawa Downtown		 0.157 µg/m3
at Toronto North		 Not applicable
m- and p-xylene 24-hour max 0.676 µg/m3
at Ottawa Downtown		 2.302 µg/m3
at Windsor West		  Not applicable
m- and p-xylene annual mean 0.186 µg/m3
at Ottawa Downtown		 0.500 µg/m3
at Toronto North		 Not applicable
o-xylene 24-hour max 0.279 µg/m3
at Ottawa Downtown		 0.814 µg/m3
at Hamilton Downtown		 Not applicable
o-xylene annual mean 0.068 µg/m3
at Newmarket		 0.156 µg/m3
at Toronto North		 Not applicable
1,3-butadiene 24-hour max 0.025 µg/m3
at London, Kitchener, Newmarket		 0.608 µg/m3
at Sarnia		 0
1,3-butadiene annual mean 0.025 µg/m3
at London, Kitchener, Newmarket		 0.054 µg/m3
at Sarnia		 0

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 2019 VOCs annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2019 benzene annual statistics, 2019 toluene annual statistics, 2019 ethylbenzene annual statistics, 2019 m- and p-xylene annual statistics, 2019 o-xylene annual statistics, and 2019 1,3-butadiene annual statistics.

Ontario VOC emissions by sector, 2019

This is a pie chart depicting Ontario’s volatile organic compound emissions by sector based on 2019 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2019, 2021).

Transportation sector accounted for 29% of VOC emissions in 2019; and general solvent use (e.g., degreasing, adhesives and sealants, consumer and commercial products) accounted for approximately 27% (APEI, 2020).

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.

Ontario’s Ambient Air Quality Criteria for common air pollutants
Contaminant 10 minutes AAQC
Assesses protection against acute effects		 1-hour AAQC
Assesses protection against acute effects		 8-hour AAQC
Assesses protection against acute effects		 24-hour AAQC
Assesses protection against chronic effects		 Annual AAQC
Assesses protection against chronic effects
NO2 N/A 200 ppb N/A 100 ppb N/A
PM2.5 N/A N/A N/A 28 μg/m3footnote 1 N/A
O3 N/A 80 ppb N/A N/A N/A
SO2 67 ppb 40 ppb N/A N/A 4 ppb
CO N/A 30 ppm 13 ppm N/A N/A
Benzene N/A N/A N/A 2.3 μg/m3 0.45 μg/m3
Toluene N/A N/A N/A 2,000 μg/m3footnote 2 N/A
Ethylbenzene 1,900 μg/m3 N/A N/A 1,000 μg/m3 N/A
1,3-Butadiene N/A N/A N/A 10 μg/m3 2 μg/m3

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.

Footnotes

  • footnote[1] Back to paragraph Ontario has adopted the 24-hour PM2.5 CAAQS value, in the absence of an AAQC, that could also be used “as is” for comparison to the 24-hour measurement of air quality data.
  • footnote[2] Back to paragraph Based on odour.