This section presents the 10-year trends and annual results for key air contaminants listed below including volatile organic compounds such as benzene, toluene, ethylbenzene, xylene (BTEX) and 1,3-butadiene. Associated emission trends over the same 10-year period are also provided.

Nitrogen dioxide

Highlights

10-year trends

  • NO2 concentrations have decreased by 21%
  • NOx emissions have decreased by 26%

2018 results

10-year trends

Trend of NO2 annual means across Ontario, 2009-2018

This is a line graph showing the trend of nitrogen dioxide annual means from 2009 to 2018. The nitrogen dioxide annual mean concentrations across Ontario have decreased 21% 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 33 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, 2009-2018

This is a stacked column chart displaying the Ontario nitrogen oxides emissions trend from 2009 to 2018 indicating a decrease of approximately 26%. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

2018 results

Summary of annual NO2 results for 2018
Averaging time Low range High range Number of sites with AAQC exceedances
NO2
1-hour max		 21.2 ppb
at Port Stanley		 62.8 ppb
at Toronto W.		 0
NO2
24-hour max		 11.5 ppb
at Parry Sound		 39.2 ppb
at Toronto W.		 0
NO2
Annual mean		 2.86 ppb
at Parry Sound		 14.4 ppb
at Toronto W.		 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 2018 NO2 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2018 nitrogen dioxide (NO2) annual statistics.

Ontario NOx emissions by sector, 2018

This is a pie chart depicting Ontario’s nitrogen oxides emissions by sector based on 2018 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

The transportation sector accounted for approximately 66% of total NOx emissions in 2018.

Fine particulate matter

Highlights

10-year trends

  • PM2.5 concentrations have decreased by 11%
  • PM2.5 emissions have decreased by 10%

2018 results

  • Twenty AQHI air monitoring stations measured daily averages above the 24-hour PM2.5 reference level of 28 µg/m3

10-year trends

Trend of PM2.5 annual means across Ontario, 2009-2018

This is a line graph showing the trend of fine particulate matter annual means from 2009 to 2018. The fine particulate matter annual mean concentrations across Ontario have decreased 11% 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 PM2.5 concentrations measured by TEOM (2009-2012) 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.

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, 2009-2018

This is a stacked column chart displaying the Ontario fine particulate matter emissions trend from 2009 to 2018 indicating a decrease of approximately 10%. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

2018 results

Summary of annual PM2.5 results for 2018
Averaging time Low range High range Number of sites with AAQC exceedances
PM2.5
1-hour max		 37 µg/m3
at Ottawa Downtown and Kingston		 198 µg/m 3
at North Bay		 Not applicable
PM2.5
24-hour max		 21 µg/m3
at Chatham, Dorset, and Sault Ste. Marie		 52 µg/m3
at North Bay		 20
PM2.5
Annual mean		 3.6 µg/m3
at Petawawa		 9.2 µg/m3
at Hamilton Downtown		 Not applicable

A summary of the 2018 PM2.5 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2018 fine particulate matter (PM2.5) annual statistics.

Ontario PM2.5 emissions by sector, 2018

This is a pie chart depicting Ontario’s fine particulate matter emissions by sector based on 2018 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

Residential fuel combustion accounted for approximately 54% of the total PM2.5 emissions in 2018. 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

2018 results

  • Thirteen 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, 2009-2018

This is a line graph showing the trend of ozone annual, summer and winter means from 2009 to 2018. 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.

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 AAQC for ozone during the warmer months and remain a challenge in areas of the province. However, ozone concentrations during the winter months were well below Ontario’s ozone AAQC of 80 ppb in 2018.

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, 2009-2018

This is a line graph displaying the ozone annual means for urban and rural Ontario from 2009 to 2018.

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.

2018 results

Summary of annual O3 results for 2018
Averaging time Low range High range Number of sites with AAQC exceedances
Ozone 1-hour max 63 ppb
at North Bay and Thunder Bay		 104 ppb
at Tiverton		 13
Ozone 24-hour max 46 ppb
at Thunder Bay		 69 ppb
at Port Stanley		 Not applicable
Ozone annual mean 22.3 ppb
at Toronto W.		 32.3 ppb
at Port Stanley and Tiverton		 Not applicable

A summary of the 2018 ozone annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2018 ozone (O3) annual statistics.

Sulphur dioxide

Highlights

10-year trends

  • SO2 concentrations have decreased by 59%
  • SO2 emissions have decreased by 27%

2018 results

  • Six 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, 2009-2018

This is a line graph showing the trend of sulphur dioxide annual means from 2009 to 2018. The sulphur dioxide annual mean concentrations across Ontario have decreased 59% 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, 2009-2018

This is a stacked column chart displaying the Ontario sulphur dioxide emissions trend from 2009 to 2018 indicating a decrease of approximately 27%. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

2018 results

Summary of annual SO2 results for 2018
Averaging time Low range High range Number of sites with AAQC exceedances
SO2 10-minutes max 6.9 ppb
at Ottawa Downtown		 298.8 ppb
at Sudbury		 6
SO2 1-hour max 3.3 ppb
at Ottawa Downtown		 136.9 ppb
at Hamilton Downtown		 5
SO2 24-hour max 0.9 ppb
at Ottawa Downtown		 50.5 ppb
at Hamilton Downtown		 Not applicable
SO2 Annual mean 0.18 ppb
at Ottawa Downtown		 5.02 ppb
at Hamilton Downtown		 1

In 2018, Ontario updated the AAQC for sulphur dioxide, based on the latest available science and reference values established by Health Canada, to better protect human health and the environment.

A summary of the 2018 SO2 annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2018 sulphur dioxide (SO2) annual statistics.

Ontario SO2 emissions by sector, 2018

This is a pie chart depicting Ontario’s sulphur dioxide emissions by sector based on 2018 estimates for point/area/transportation sources.Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

Smelters in central Ontario are the major sources of SO2 emissions in Ontario, accounting for approximately 50% of the provincial SO2 emissions in 2018.

Volatile organic compounds

Highlights

10-year trends

  • Benzene concentrations have decreased by 27%
  • Toluene concentrations have decreased by 40%
  • Ethylbenzene have decreased by 32%
  • m- and p-xylene have decreased by 31%
  • o-xylene have decreased by 23%
  • 1,3-butadiene have decreased by 51%

2018 results

  • Ontario’s AAQC for these volatile organic compounds (where applicable) were met except for three AQHI air monitoring stations that measured benzene levels above the 24-hour AAQC of 2.3 µg/m3 and/or the annual AAQC of 4 µg/m3.

10-year trends

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

In 2018, 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 2009 and 2018 are included in this discussion.

Trend of benzene annual means across Ontario, 2009-2018

This is a line graph showing the trend of benzene annual mean from 2009 to 2018. The benzene annual mean concentrations across Ontario have decreased 27% 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, 2009-2018

This is a line graph showing the trend of toluene annual mean from 2009 to 2018. The toluene annual mean concentrations across Ontario have decreased 40% 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, 2009-2018

This is a line graph showing the trend of ethylbenzene annual mean from 2009 to 2018. The ethylbenzene annual mean concentrations across Ontario have decreased 32% 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, 2009-2018

This is a line graph showing the trend of xylene annual mean from 2009 to 2018. The m- and p-xylene and o-xylene annual mean concentrations across Ontario have decreased 31%, decreased 23%, 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, 2009-2018

This is a line graph showing the trend of 1,3-butadiene annual mean from 2009 to 2018. The 1,3-butadiene annual mean concentrations across Ontario have decreased 51% 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.

2018 results

Summary of annual VOC results for 2018
Averaging time Low range High range Number of sites with AAQC exceedances
Benzene  24-hour max 0.6 µg/m3
at London 		 4.4 µg/m3
at Hamilton Downtown 		 2 
Benzene annual mean 0.33 µg/m3
at London 		 0.64 µg/m3
at Hamilton Downtown 		 3 
Toluene 24-hour max 1.6 µg/m3
at Newmarket 		 5.1 µg/m3
at Sarnia 		 0 
Toluene annual mean 0.63 µg/m3
at Kitchener 		 1.13 µg/m3
at Windsor W. 		 Not applicable 
Ethylbenzene  24-hour max 0.2 µg/m3
at Ottawa Downtown 		 2.7 µg/m3
at Sarnia 		 0 
Ethylbenzene annual mean 0.09 µg/m3
at Ottawa Downtown 		 0.24 µg/m3
at Sarnia 		 Not applicable 
m- and p-xylene 24-hour max 0.6 µg/m3
at Ottawa Downtown  		 8.1 µg/m3
at Sarnia 		 Not applicable 
m- and p-xylene annual mean 0.23 µg/m3
at Ottawa Downtown 		 0.56 µg/m3
at Sarnia 		 Not applicable 
o-xylene  24-hour max 0.3 µg/m3
at Ottawa Downtown		 3.1 µg/m3
at Sarnia 		 Not applicable 
o-xylene annual mean 0.09 µg/m3
at Ottawa Downtown 		 0.22 µg/m3
at Sarnia 		 Not applicable 
1,3-butadiene 24-hour max 0.0 µg/m3
at Newmarket		 0.6 µg/m3
at Sarnia 		 0 
1,3-butadiene annual mean 0.02 µg/m3
at London		 0.08 µg/m3
at Sarnia 		 0 

A summary of the 2018 VOCs annual statistics for individual AQHI air monitoring stations is detailed in the Appendix: 2018 benzene annual statistics, 2018 toluene annual statistics, 2018 ethylbenzene annual statistics, 2018 m- and p-xylene annual statistics, 2018 o-xylene annual statistics, and 2018 1,3-butadiene annual statistics.

Ontario VOC emissions by sector, 2018

This is a pie chart depicting Ontario’s volatile organic compound emissions by sector based on 2018 estimates for point/area/transportation sources. Please note this chart excludes emissions from open and natural sources (Air Pollutant Emission Inventory 1990-2018, 2020).

General solvent use (e.g., degreasing, adhesives and sealants, consumer and commercial products) accounted for approximately 32% of VOC emissions in 2018 while the transportation sector, accounting for approximately 25% (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) is a concentration of a contaminant in air that is protective against adverse effects on health and/or the environment.

AAQCs are not regulatory values but are used to assess general (ambient) air quality resulting from all sources of a contaminant to air. AAQCs 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. Currently, there is no AAQCs for PM2.5, hence a reference level of 28 μg/m3 used in this Report is based on the 24-hour PM2.5 Canadian Ambient Air Quality Standard (CAAQS) in effect in 2018.

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/m3 footnote 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 ppb 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/m3 footnote 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