Air quality

Fine particulate matter

Fine particulate matter (PM_2.5) is emitted to the air and can also be formed in the air through the interactions of other pollutants, such as nitrogen oxides, sulphur oxides, ammonia and volatile organic compounds. The particles can be in solid or liquid form. Fine particulate matter is one of the major components of smog. When inhaled deeply into the lungs, even small amounts of PM_2.5 can cause adverse health effects. Exposure to PM_2.5 can lead to respiratory and cardiovascular effects, such as asthma attacks, chronic bronchitis, heart attacks as well as lung cancer. Fine particulate matter can also damage vegetation and structures, contribute to haze and reduce visibility.

Average concentrations of fine particulate matter
Peak concentrations of fine particulate matter

National average fine particulate matter concentrations^{Footnote 4} 

Key results

Between 2005 and 2019,

• no trend was detected in the national average PM_2.5 concentrations
• national average concentrations remained below the 2020 standard^{Footnote 5}  of 8.8 micrograms per cubic metre (µg/m³) for all years; however, concentrations at some monitoring stations exceeded the standard in some years

National average fine particulate matter concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national average PM_2.5 concentration indicator is based on the annual average of the daily 24-hour average concentrations recorded at 145 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average PM_2.5 concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national average PM_2.5 concentration was 6.1 µg/m³, which was 17% (1.3 µg/m³) lower than in 2018. In 2018, the higher concentrations can be attributed in part to wildfire activity in western Canada. From 2005 to 2019, national concentrations decreased by 9% (0.6 µg/m³).

Changes in average PM_2.5 concentrations may be related to changes in the quantity of emissions and to annual variations in weather conditions. Weather conditions influence the formation, dispersion and regional transport of PM_2.5 as well as transboundary movement of PM_2.5, such as from the United States. The variations observed in average PM_2.5 concentrations were also influenced by the progressive introduction of monitoring equipment that uses newer measurement technologies.

From the mid-2000s to 2013, new PM_2.5 monitoring equipment was progressively introduced across Canada to replace older monitoring equipment. These new instruments measure an additional portion (semi-volatile) of the PM_2.5 mass not captured by the older instruments. Concentrations measured with the new monitors may not be directly comparable with measurements from years in which older instruments were used.

Regional average fine particulate matter concentrations

Key results

• Between 2005 and 2019,
  • increasing trends were detected for average PM_2.5 concentrations in the British Columbia region
  • a decreasing trend was detected in the southern Quebec region
  • no trends were detected for the Atlantic Canada, southern Ontario, and the Prairies and northern Ontario regions
• Since 2005, average PM_2.5 concentrations have remained below the 2020 standard^{Footnote 5} of 8.8 µg/m³ across all regions of Canada, with the exception of British Columbia in 2018; however, concentrations at some monitoring stations in 4 regions exceeded the standard in various years

Regional average fine particulate matter concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional average PM_2.5 concentration indicator is based on the annual average of the daily 24-hour average concentrations recorded at 11 monitoring stations in Atlantic Canada, 36 in southern Quebec, 39 in southern Ontario, 33 in the Prairies and northern Ontario region, and 24 in British Columbia. There were not enough stations to report results for the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standards is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average PM_2.5 concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the southern Ontario region had the highest regional average PM_2.5 concentration, at 6.4 µg/m³. The southern Quebec and British Columbia regions each reported a concentration of 6.2 µg/m³.The Prairies and northern Ontario region followed with a concentration of 6.1 µg/m³. The Atlantic Canada region had the lowest regional average concentration, at 5.0 µg/m³.

All 5 regions had lower concentrations in 2019 than in 2018. Between 2018 and 2019, the British Columbia and Prairies and northern Ontario regions had the largest reductions in concentrations, with decreases of 33% (3.0 µg/m³) and 31% (2.7 µg/m³), respectively. The average PM_2.5 concentration peaked in these 2 regions in 2018 primarily due to increased wildfire activity. British Columbia was also affected by wildfire activity in 2017. From 2018 to 2019, the southern Ontario, southern Quebec and Atlantic Canada regions had reductions of 6%, 5% and 2%, respectively.

Between 2005 and 2019,

• a decreasing trend of 0.1 µg/m³ per year was detected for the southern Quebec region
  • concentrations decreased by 28% (2.4 µg/m³)
• an increasing trend of 0.2 µg/m³ per year was detected for British Columbia
  • concentrations increased by 14% (0.8 µg/m³)
• no trends were detected for the Atlantic Canada, southern Ontario and the Prairies and northern Ontario regions

Average fine particulate matter concentrations in urban areas

Key results

In 2019, among the selected urban areas

• Windsor and Charlottetown had the highest average PM_2.5 concentrations
• Whitehorse,^{Footnote 6} Regina and Yellowknife had the lowest concentrations

Average fine particulate matter concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: * The concentration presented in the figure for Whitehorse was from 2018. Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Average PM_2.5 concentrations in Canadian urban areas differ from one location to another and from year to year. These differences are partly due to differences in emissions of pollutants, variations in weather conditions that influence PM_2.5 formation, dispersion and regional transport and variations in transboundary flows of pollution, primarily from the United States. Exceptional events, such as wildfires, can also impact average PM_2.5 concentrations measured in urban areas.

Average fine particulate matter concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore average PM_2.5 concentrations at specific monitoring stations.

In 2019, average PM_2.5 concentrations were recorded at 205 monitoring stations across Canada. Average PM_2.5 concentrations varied across monitoring stations.

• 6 stations recorded concentrations above 8.8 µg/m³
  • A single station in each New Brunswick, Quebec and Ontario and 3 stations located in British Columbia had concentrations between 8.9 µg/m³ and 10.6 µg/m³
• 11 stations recorded below 4.0 µg/m³. Of these stations, 2 were located in Newfoundland and Labrador, 1 each in Quebec and Ontario, 2 were in Manitoba, 3 were in Alberta and 2 were located in British Columbia

Average fine particulate matter concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program

National peak fine particulate matter concentrations^{Footnote 7} 

Key results

Between 2005 and 2019,

• no trend was detected in the peak PM_2.5 concentrations
• national peak concentrations remained below the 2020 standard^{Footnote 5}  of 27 µg/m³ for all years except 2018; however, concentrations at some monitoring stations exceeded the standard in some years

National peak fine particulate matter concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national peak PM_2.5 concentration indicator is based on the annual 98th percentile of the daily 24-hour average concentrations recorded at 147 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak PM_2.5 concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national peak PM_2.5 concentration was 17.1 µg/m³, which was 43% (12.9 µg/m³) lower than in 2018. In 2017 and 2018, the higher concentrations can be attributed primarily to wildfire activity in western Canada. From 2005 to 2019, national concentrations decreased by 29% (7.1 µg/m³).

Changes in peak PM_2.5 concentrations may be related to changes in the quantity of emissions and to annual variations in weather conditions. Weather conditions influence the formation, dispersion and regional transport of PM_2.5 as well as transboundary movement of PM_2.5, such as from the United States. The variations observed in peak PM_2.5 concentrations were also influenced by the progressive introduction of monitoring equipment that uses newer measurement technologies.

From the mid-2000s to 2013, new PM_2.5 monitoring equipment was progressively introduced across Canada to replace older monitoring equipment. These new instruments measure an additional portion (semi-volatile) of the PM_2.5 mass not captured by the older instruments. Concentrations measured with the new monitors may not be directly comparable with measurements from years in which older instruments were used.

Regional peak fine particulate matter concentrations

Key results

• Between 2005 and 2019,
  • increasing trends were detected for peak PM_2.5 concentrations in the Prairies and northern Ontario and British Columbia regions
  • decreasing trends were detected in the Atlantic Canada, southern Quebec and southern Ontario regions
  • no trend was detected for the northern territories region
• Since 2005, regional peak PM_2.5 concentrations have exceeded the 2020 standard^{Footnote 5}  of 27 µg/m³ at least once in all regions of Canada, with the exception of Atlantic Canada. Further, with the exception of Atlantic Canada, concentrations at some monitoring stations in all other regions exceeded the standard in various years

Regional peak fine particulate matter concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional peak PM_2.5 concentration indicator is based on the annual 98th percentile of the daily 24-hour average concentrations recorded at 11 monitoring stations in Atlantic Canada, 36 in southern Quebec, 39 in southern Ontario, 33 in the Prairies and northern Ontario region, 25 in British Columbia and 3 in the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak PM_2.5 concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the Prairies and northern Ontario region had the highest regional peak PM_2.5 concentration, at 20.6 µg/m³. The Atlantic Canada region had the lowest regional peak concentration, at 10.9 µg/m³.

The regional peak concentration was lower in 2019 than in 2018 in all regions except in the northern territories region. Between 2018 and 2019, the British Columbia and Prairies and northern Ontario regions had the largest reductions in concentrations, with decreases of 70% (38.3 µg/m³) and 56% (26.6 µg/m³), respectively. The average PM_2.5 concentration peaked in these 2 regions in 2018 in part due to increased wildfire activity. British Columbia was also affected by wildfire activity in 2017. From 2018 to 2019, the southern Quebec, southern Ontario and Atlantic Canada regions had concentration reductions of 10%, 7% and 2%, respectively. The northern territories region was the only region reporting an increase between 2018 and 2019, at 66% (7.5 µg/m³).

Between 2005 and 2019,

• an increasing trend of 1.4 µg/m³ per year was detected for the Prairies and northern Ontario region
  • concentrations increased by 68% (8.3 µg/m³)
• an increasing trend of 0.5 µg/m³ per year was detected for British Columbia
  • concentrations increased by 7% (1.0 µg/m³).
• a decreasing trend of 0.6 µg/m³ per year was detected for the southern Quebec region
  • concentrations decreased by 53% (18.3 µg/m³)
• a decreasing trend of 0.6 µg/m³ per year was detected for the southern Ontario region
  • concentrations decreased by 48% (15.6 µg/m³)
• a decreasing trend of 0.3 µg/m³ per year was detected for the Atlantic Canada region
  • concentrations decreased by 26% (3.9 µg/m³)
• no trend was detected for the northern territories region

Regional peak PM_2.5 concentrations tend to exceed the standard in years with increased wildfire activity.

Peak fine particulate matter concentrations in urban areas

Key results

In 2019, among the selected urban areas

• Whitehorse and Edmonton had the highest peak PM_2.5 concentrations
• Halifax and St. John's had the lowest concentrations

Peak fine particulate matter concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Peak PM_2.5 concentrations in Canadian urban areas differ from one location to another and from year to year. These differences are partly due to differences in emissions of pollutants, variations in weather conditions that influence PM_2.5 formation, dispersion and regional transport, as well as variations in transboundary flows of pollution, primarily from the United States. Exceptional events, such as wildfires, can also have a significant influence on the peak PM_2.5 concentrations in urban areas.

Peak fine particulate matter concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore peak PM_2.5 concentrations at specific monitoring stations.

In 2019, peak PM_2.5 concentrations were recorded at 207 monitoring stations across Canada. The highest peak PM_2.5 concentrations were generally recorded at monitoring stations in western Canada.

• 8 stations recorded concentrations above 27.0 µg/m³, ranging from 27.7 µg/m³ to 34.5 µg/m³. Of these stations, 4 were in Alberta, 2 were in British Columbia and 1 each in Yukon and the Northwest Territories
• 18 stations recorded concentrations below 10.0 µg/m³. Of these stations, 4 were located in Newfoundland and Labrador, 1 was in Prince Edward Island, 4 were in Nova Scotia, 1 each in New Brunswick, Quebec and Alberta, 2 were in Manitoba and 4 were located in British Columbia

Peak fine particulate matter concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Ground-level ozone

Ozone (O₃) in the upper atmosphere (10 to 50 kilometres above the earth's surface) protects the earth from the sun's harmful ultraviolet radiation. In the lower atmosphere and at ground level, O₃ is harmful to human health. It can lead to throat irritation, coughing, shortness of breath and reduced lung function, and also aggravate existing conditions, such as asthma or other chronic lung diseases. Ground-level O₃ can also impact vegetation, decrease the productivity of some crops and may contribute to forest decline. It can also damage synthetic materials and textiles, cause cracks in rubber, accelerate fading of dyes and speed deterioration of some paints and coatings. Ozone is not directly emitted, but is formed in the lower atmosphere when precursor gases such as nitrogen oxides and volatile organic compounds react in sunlight. Ground-level O₃ is a major component of smog, along with fine particulate matter. 

Average concentrations of ozone
Peak concentrations of ozone

National average ground-level ozone concentrations^{Footnote 8}

Key results

Between 2005 and 2019,

• no trend was detected in the national average O₃ concentrations
• national average concentrations remained stable

National average ozone concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national average O₃ concentration indicator is based on the annual average of the daily maximum 8‑hour average concentrations recorded at 171 monitoring stations across Canada. The shaded area shows the 10th and 90th percentile bounds of average O₃ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2019, the national average O₃ concentration was 33 parts per billion (ppb), which was 3% (1 ppb) lower than in 2018. From 2005 to 2019, national concentrations were relatively unchanged.

Regional average ground-level ozone concentrations

Key results

• Between 2005 and 2019,
  • an increasing trend was detected for average O₃ concentrations in the southern Quebec region
  • no trends were detected for any other region
• Since 2005, regional average O₃ concentrations have remained fairly steady in all regions of Canada; however, concentrations at some monitoring stations fluctuated over the years

Regional average ozone concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional average O₃ concentration indicator is based on the annual average of the daily maximum 8‑hour average concentrations recorded at 21 monitoring stations in Atlantic Canada, 41 in southern Quebec, 42 in southern Ontario, 34 in the Prairies and northern Ontario region, 30 in British Columbia and 3 in the northern territories region. The shaded area shows the 10th and 90th percentile bounds of average O₃ concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2019, the southern Ontario region had the highest regional average O₃ concentration, at 36 ppb. The Atlantic Canada and southern Quebec regions each had a concentration of 34 ppb, while the Prairies and northern Ontario and northern territories regions reported concentrations of 33 ppb and 32 ppb, respectively. The British Columbia region had the lowest regional average concentration, at 27 ppb.

The regional average concentration was lower in 2019 than in 2018 in all regions except in the northern territories region. Between 2018 and 2019, the Prairies and northern Ontario and British Columbia regions had the largest reduction in concentrations, with decreases of 5% (2 ppb) each. These decreases are likely due in part to reduced wildfire activity in western Canada in 2019. In addition to contributing to PM_2.5 concentrations, widfires also contribute to higher ozone levels. From 2018 to 2019, the southern Quebec region had a 3% reduction, while the southern Ontario and Atlantic Canada regions each had a 2% reduction. The northern territories region was the only region reporting an increase between 2018 and 2019. Concentrations in the region increased 2% (1 ppb).

Between 2005 and 2019, an increasing trend of 0.2 ppb per year was detected for the southern Quebec region. From 2005 to 2019, concentrations in southern Quebec increased by 1% (less than 1 ppb).

Average ground-level ozone concentrations in urban areas

Key results

In 2019, among the selected urban areas

• St. Catharines – Niagara Falls and London had the highest average O₃ concentrations
• Winnipeg, Vancouver and St. John's had the lowest concentrations

Average ozone concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Ground level ozone is a secondary pollutant that forms in the air through the chemical interactions of precursors. Annual average O₃ concentrations in Canadian urban areas differ from one location to another and from year to year. These differences are partly due to variations in local emissions of O₃ precursors (mostly NO_X and VOCs), variations in weather conditions that influence O₃ formation and variations in transboundary flows of pollution, primarily from the United States.

Average ground-level ozone concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore average O₃ concentrations at specific monitoring stations.

In 2019, average O₃ concentrations were recorded at 217 monitoring stations across Canada. Of these stations:

• 1 station located in Ontario had a concentration of 41 ppb
• 9 stations had concentrations below 25 ppb. Of these stations, 1 was located in Manitoba, the remaining 8 stations were all located in British Columbia

Average ozone concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

National peak ground-level ozone concentrations^{Footnote 9} 

Key results

Between 2005 and 2019,

• a decreasing trend was detected in the peak O₃ concentrations
• national peak concentrations remained below the 2020 standard^{Footnote 5}  of 62 ppb after 2007; however, concentrations at some monitoring stations exceeded the standard each year

National peak ozone concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national peak O₃ concentration indicator is based on the annual 4th‑highest of the daily maximum 8-hour average concentrations recorded at 171 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak O₃ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2019, the national peak O₃ concentration was 53 ppb, which was 10% (6 ppb) lower than in 2018. Between 2005 and 2019, a decreasing trend of 0.5 ppb per year was detected. From 2005 to 2019, national concentrations decreased by 15% (10 ppb). Reductions in Canadian and American emissions of ground-level O₃ precursor gases (nitrogen oxides [NO_X] and volatile organic compounds [VOCs]) are an important factor in this downward trend.

Regional peak ground-level ozone concentrations

Key results

• Between 2005 and 2019,
  • decreasing trends were detected for peak O₃ concentrations in the Atlantic Canada, southern Quebec and southern Ontario regions
  • no trends were detected for the Prairies and northern Ontario, British Columbia and northern territories regions
•  Since 2005, regional peak O₃ concentrations remained below the 2020 standard^{Footnote 5}  of 62 ppb in all regions, with the exception of southern Quebec and southern Ontario. Further, with the exception of the northern territories region, concentrations at some monitoring stations in all other regions regularly exceeded the standard

Regional peak ozone concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional peak O₃ indicator is based on the annual 4th‑highest of the daily maximum 8-hour average concentrations recorded at 21 monitoring stations in Atlantic Canada, 41 in southern Quebec, 42 in southern Ontario, 34 in the Prairies and northern Ontario region, 30 in British Columbia and 3 in the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak O₃ concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2019, the southern Ontario region had the highest regional peak O₃ concentrations at 59 ppb. British Columbia and the northern territories region had the lowest peak O₃ concentration level, each reporting 46 ppb.

The regional average concentration was lower in 2019 than in 2018 in all regions. Between 2018 and 2019, the British Columbia region had the largest reduction in concentrations, with a decrease of 15% (8 ppb). This decrease is likely due in part to reduced wildfire activity in western Canada in 2019. From 2018 to 2019, the southern Ontario and southern Quebec regions had reductions of 12% (8 ppb) and 11% (6 ppb), respectively. The Atlantic Canada and northern territories regions each had a 6% reduction in concentrations, while concentrations for the Prairies and northern Ontario region decreased by 5% over the same period.

Between 2005 and 2019,

• a decreasing trend of 1.0 ppb per year was detected for the southern Ontario region
  • concentrations decreased by 28% (23 ppb)
• a decreasing trend of 0.6 ppb per year was detected for the southern Quebec region
  • concentrations decreased by 23% (15 ppb)
• a decreasing trend of 0.4 ppb per year was detected for the Atlantic Canada region
  • concentrations decreased by 7% (4 ppb)
• no trends were detected for the northern territories, British Columbia, and Prairies and northern Ontario regions

From 2005 to 2018, southern Ontario was the only region where regional peak O₃ concentrations were consistently above the 2020 standard. In 2019, concentrations dropped below the standard.

Peak ground-level ozone concentrations in urban areas

Key results

In 2019, among the selected urban areas

• Windsor and Edmonton had the highest peak O₃ concentrations
• Winnipeg, Charlottetown, Vancouver and Yellowknife had the lowest concentrations

Peak ozone concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Ground level ozone is a secondary pollutant that forms in the air through the chemical interactions of precursors. Peak ozone concentrations in Canadian urban areas differ from one location to another and from year to year. These differences are partly due to variations in local emissions of O₃ precursors (mostly NO_X and VOCs), variations in weather conditions that influence O₃ formation and variations in transboundary flows of pollution, primarily from the United States.

Peak ground-level ozone concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore peak O₃ concentrations at specific monitoring stations.

In 2019, peak O₃ concentrations were recorded at 217 monitoring stations across Canada.

• 24 stations had concentrations over 62 ppb. Of these stations, 8 were located in Ontario and the remainder were located in Alberta
• 18 stations recorded concentrations below 45 ppb. Of these stations, 1 was located in Newfoundland and Labrador, 1 was located in Prince Edward Island, 1 was located in Manitoba, 13 were located in British Columbia and 2 were located in the Northwest Territories

Peak ozone concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program

Nitrogen dioxide

Nitrogen dioxide (NO₂) plays an important role in the formation of ozone in the atmosphere and it is also a precursor to fine particulate matter. It belongs to a group of substances called nitrogen oxides (NO_X).^{Footnote 10}  Nitrogen oxides are emitted into the atmosphere from high-temperature combustion processes such as vehicle engines, power plants and industrial processes. The main sources of nitrogen oxides in Canada are transportation, the oil and gas industry and the use of fossil fuels for electricity generation and heating. Exposure to NO₂ can result in adverse health effects; it can irritate the lungs, decrease lung function and increase susceptibility to allergens for people with asthma. Long-term exposure to NO₂ may contribute to allergies and the development of asthma. It also contributes to acid rain and eutrophication of environmental ecosystems.

Average concentrations of nitrogen dioxide
Peak concentrations of nitrogen dioxide

National average nitrogen dioxide concentrations^{Footnote 11 Footnote 12}

Key results

Between 2005 and 2019,

• a decreasing trend was detected in the average NO₂ concentrations
• national average concentrations remained below the 2020 standard^{Footnote 5}  of 17 parts per billion (ppb) for all years; however, concentrations at some monitoring stations exceeded the standard from 2005 to 2007

National average nitrogen dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national average NO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 119 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average NO₂ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national average NO₂ concentration was 7.2 ppb, which was 4% (0.3 ppb) lower than in 2018. Between 2005 and 2019, a decreasing trend of 0.3 ppb per year was detected. From 2005 to 2019, national concentrations decreased by 38% (4.4 ppb). This trend is mainly attributable to 2 factors:

• the adoption of new regulations that led to the gradual introduction of new technologies and clean fuel for vehicles and the introduction of progressively more stringent emission regulations for vehicles and engines by the federal government
• lower emissions from fossil-fuel-fired (for example, coal-fired) power-generating utilities as a result of better emission control technologies and closures of some coal-fired power plants 

Regional average nitrogen dioxide concentrations

Key results

• Between 2005 and 2019, decreasing trends were detected for all 5 regions
• Since 2005, regional average NO₂ concentrations remained below the 2020 standard^{Footnote 5}  of 17 ppb in all regions; however, concentrations at some monitoring stations in southern Quebec, southern Ontario and British Columbia exceeded the standard in earlier years

Regional average nitrogen dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional average NO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 7 monitoring stations in Atlantic Canada, 14 in southern Quebec, 30 in southern Ontario, 37 in the Prairies and northern Ontario region and 29 in British Columbia. There were not enough stations to report results for the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average NO₂ concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, British Columbia had the highest regional average NO₂ concentration, at 8.9 ppb. The southern Quebec region followed with a concentration of 8.0 ppb. The southern Ontario and Prairies and northern Ontario regions reported concentrations of 7.4 ppb and 6.6 ppb, respectively. The Atlantic Canada region had the lowest regional average concentration, at 2.9 ppb.

All 5 regions had lower or similar concentrations in 2019 than in 2018. Between 2018 and 2019, the southern Quebec region had the largest reduction in concentrations, with a decrease of 7% (0.6 ppb). The Prairies and northern Ontario and Atlantic Canada regions reported decreases of 6% and 5%, respectively. British Columbia and southern Ontario had reductions of 2% and 1%, respectively.

Between 2005 and 2019, decreasing trends were detected in each region. A decreasing trend of:

• 0.4 ppb per year was detected for the southern Ontario region
  • concentrations decreased by 52% (8.1 ppb)
• 0.4 ppb per year was detected for the southern Quebec region
  • concentrations decreased by 45% (6.5 ppb)
• 0.3 ppb per year was detected for British Columbia
  • concentrations decreased by 29% (3.7 ppb)
• 0.2 ppb per year was detected for the Prairies and northern Ontario region
  • concentrations decreased by 25% (2.2 ppb)
• 0.1 ppb per year was detected for the Atlantic Canada region
  • concentrations decreased by 44% (2.3 ppb)

Average nitrogen dioxide concentrations in urban areas

Key results

In 2019, among the selected urban areas^{Footnote 13} 

• Calgary, Vancouver, Toronto and Edmonton had the highest average NO₂ concentrations
• St. John's, Yellowknife and Charlottetown had the lowest concentrations

Average nitrogen dioxide concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: * The concentration presented in the figure for Whitehorse was from 2018. Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Average NO₂ concentrations in selected Canadian urban areas differ from one location to another and from year to year. Urban areas in proximity to important sources of NO₂, such as large road networks and highways, may explain the differences between cities.

Average nitrogen dioxide concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore average NO₂ concentrations at specific monitoring stations.

In 2019, average NO₂ concentrations were recorded at 179 monitoring stations across Canada. Average NO₂ concentrations were lower in eastern and northern areas of Canada.

• 2 stations located in British Columbia and Ontario recorded concentrations above 17.0 ppb (17.9 ppb and 18.5 ppb)
• 47 stations had concentrations below 4.0 ppb
  • 4 stations recorded concentrations below 1.0 ppb; these were located in Newfoundland and Labrador, Prince Edward Island (2 stations) and Nova Scotia

Average nitrogen dioxide concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program

National peak nitrogen dioxide concentrations^{Footnote 14} 

Key results

Between 2005 and 2019,

• a decreasing trend was detected in the peak NO₂ concentrations
• national peak concentrations remained below the 2020 standard^{Footnote 5}  of 60 ppb for all years; however, concentrations at some monitoring stations exceeded the standard in 2005

National peak nitrogen dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national peak NO₂ concentration indicator is based on the annual 98th percentile of the daily maximum 1-hour average concentrations recorded at 120 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak NO₂ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national peak NO₂ concentration was 37.0 ppb, which was 3% lower than in 2018. Between 2005 and 2019, a decreasing trend of 0.7 ppb per year was detected. From 2005 to 2019, national concentrations decreased by 23% (10.9 ppb). This trend is mainly attributable to 2 factors:

• the adoption of new regulations that led to the gradual introduction of new technologies and clean fuel for vehicles and the introduction of progressively more stringent emission regulations for vehicles and engines by the federal government
• lower emissions from fossil-fuel-fired (for example, coal-fired) power-generating utilities as a result of better emission control technologies and closures of some coal-fired power plants

Regional peak nitrogen dioxide concentrations

Key results

• Between 2005 and 2019, decreasing trends were detected for all 5 regions
• Since 2005, regional peak NO₂ concentrations remained below the 2020 standard^{Footnote 5} of 60 ppb in all regions; however, with the exception of British Columbia, concentrations at some monitoring stations exceeded the standard in earlier years

Regional peak nitrogen dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional peak NO₂ concentration indicator is based on the annual 98th percentile of the daily maximum 1-hour average concentrations recorded at 8 monitoring stations in Atlantic Canada, 14 in southern Quebec, 30 in southern Ontario, 37 in the Prairies and northern Ontario region and 29 in British Columbia. There were not enough stations to report results for the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak NO₂ concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, southern Quebec had the highest regional peak NO₂ concentration, at 42.1 ppb. The southern Ontario region followed with a concentration of 40.8 ppb. The Prairies and northern Ontario region and British Columbia reported concentrations of 36.2 ppb and 35.5 ppb, respectively. The Atlantic Canada region had the lowest regional peak concentration, at 26.2 ppb.

With the exception of southern Ontario, all regions had lower concentrations in 2019 than in 2018. Between 2018 and 2019, the Atlantic Canada region had the largest reduction in concentrations, with a decrease of 13% (3.8 ppb). The Prairies and northern Ontario and southern Quebec regions reported decreases of 9% (3.5 ppb) and 2% (0.7 ppb), respectively. British Columbia reported a decrease of 1% (0.5 ppb). Between 2018 and 2019, southern Ontario reported an increase of 4% (1.7 ppb).

Between 2005 and 2019, decreasing trends were detected in each region. A decreasing trend of:

• 1.0 ppb per year was detected for southern Ontario
  • concentrations in southern Ontario decreased by 31% (18.7 ppb)
• 0.7 ppb per year was detected the Atlantic Canada region
  • concentrations decreased by 35% (13.8 ppb)
• 0.7 ppb per year was detected for the southern Quebec region
  • concentrations decreased by 27% (15.5 ppb)
• 0.5 ppb per year was detected for the Prairies and northern Ontario region
  • concentrations decreased by 15% (6.6 ppb)
• 0.5 ppb per year was detected for British Columbia
  • concentrations decreased by 15% (6.5 ppb)

Peak nitrogen dioxide concentrations in urban areas

Key results

In 2019, among the selected urban areas^{Footnote 6} 

• Calgary, Edmonton and Toronto had the highest peak NO₂ concentrations
• St. John's, Oshawa and Halifax had the lowest concentrations

Peak nitrogen dioxide concentrations, selected Canadian urban areas, 2019

How this indicator was calculated

Note: * The concentration presented in the figure for Whitehorse was from 2018. Population centres were used to define the urban areas used for this indicator. The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. Refer to the section on data completeness criteria for more information. All concentrations available since 2005 for each urban areas are presented in the data table for this figure.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Peak NO₂ concentrations in selected Canadian urban areas differs from one location to another and from year to year. Urban areas in proximity to important sources of NO₂, such as large road network and highways, may explain the differences between cities.

Peak nitrogen dioxide concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore peak NO₂ concentrations at specific monitoring stations.

In 2019, peak NO₂ concentrations were recorded at 178 monitoring stations across Canada. Of these stations:

• 1 station in Alberta recorded a concentration above 60.0 ppb (62.7 ppb)
• 58 stations had concentrations below 30.0 ppb
  • 5 stations had concentrations below 10.0 ppb; these were located in Newfoundland and Labrador, Prince Edward Island (2 stations), Nova Scotia and Alberta

Peak nitrogen dioxide concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Sulphur dioxide

Sulphur dioxide (SO₂) is emitted when a fuel or raw material containing sulphur is burned or used in industrial processes such as metal ore smelting. The main sources of sulphur oxide emissions in Canada are the combustion of fuel for electricity generation and heating, processes in the non-ferrous smelting and refining industry, and the oil and gas industry. Sulphur dioxide emissions contribute to acid deposition and are a major precursor to fine particulate matter. High concentrations of SO₂ can adversely affect the respiratory systems of humans and animals. It can irritate the lungs, reduce lung function and increase susceptibility to allergens in people with asthma. Sulphur dioxide can also damage vegetation and materials.

Average concentrations of sulphur dioxide
Peak concentrations of sulphur dioxide

National average sulphur dioxide concentrations^{Footnote 12}

Key results

Between 2005 and 2019,

• a decreasing trend was detected in the average SO₂ concentrations
• national average concentrations remained below the 2020 standard^{Footnote 5}  of 5 parts per billion (ppb) for all years; however, concentrations at some monitoring stations were above the standard in 2005

National average sulphur dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national average SO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 80 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average SO₂ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national average SO₂ concentration was 0.7 parts per billion (ppb), which was 1% lower than in 2018. Between 2005 and 2019, a decreasing trend of 0.1 ppb per year was detected. From 2005 to 2019, national concentrations decreased by 64% (1.3 ppb). This trend is mainly attributable to reductions in sulphur oxide (SO_X) emissions in Canada resulting from technological upgrades and closures of non-ferrous metal smelters (including aluminium smelters) and pulp and paper facilities, the phase-out of coal-fired electricity, better emission control technologies within the oil and gas sector and the implementation of federal regulations related to sulphur content in fuels.

Regional average sulphur dioxide concentrations

Key results

• Between 2005 and 2019, decreasing trends were detected for all 5 regions
• Since 2005, regional average SO₂ concentrations remained below the 2020^{Footnote 5}  standard of 5 ppb in all regions; however, with the exception of British Columbia and the Prairies and northern Ontario regions, concentrations at some monitoring stations exceeded the standard

Regional average sulphur dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional average SO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 4 monitoring stations in Atlantic Canada, 9 in southern Quebec, 10 in southern Ontario, 32 in the Prairies and northern Ontario region and 23 in British Columbia. There were not enough stations to report results for the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of average SO₂ concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, southern Quebec and southern Ontario had the highest regional average SO₂ concentration, each reporting 1.2 ppb. Atlantic Canada and British Columbia followed with concentrations of 0.9 ppb and 0.7 ppb, respectively. The Prairies and northern Ontario region had the lowest regional average concentration, at 0.5 ppb.

Atlantic Canada and southern Ontario had lower concentrations in 2019 than in 2018. Between 2018 and 2019, the Atlantic Canada region had the largest reduction in concentrations, with a decrease of 17% (0.2 ppb), while the southern Quebec and southern Ontario regions reported 16% (0.2 ppb) and 13% (0.2 ppb) reductions, repectively. British Columbia reported a 10% (0.1 ppb) increase over the same period. The average SO₂ concentration in the Prairies and northern Ontario region was relatively unchanged between 2018 and 2019.

Between 2005 and 2019, decreasing trends were detected in each region. A decreasing trend of:

• 0.2 ppb per year was detected for southern Ontario
  • concentrations decreased by 70% (2.7 ppb)
• 0.1 ppb per year was detected for the remaining regions (Atlantic Canada, southern Quebec, the Prairies and northern Ontario region and British Columbia)
  • concentrations in Atlantic Canada and southern Quebec decreased by 66% (1.7 ppb) and 71% (2.9 ppb), respectively
  • concentrations in the Prairies and northern Ontario region decreased by 59% (0.7 ppb)
  • concentrations in British Columbia decreased by 48% (0.7 ppb)

Average sulphur dioxide concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore average SO₂ concentrations at specific monitoring stations.

In 2019, average SO₂ concentrations were recorded at 124 monitoring stations across Canada. Of these stations:

• 2 stations recorded concentrations above 5.0 ppb
  • 1 station in Quebec and 1 in British Columbia reported concentrations of 5.5 ppb and 7.5 ppb, respectively
• 79 stations had concentrations below 0.5 ppb
  • 13 stations recorded concentrations of 0.1 ppb. Of these stations, 1 was located in each Newfoundland and Labrador, Quebec, Manitoba and Saskatchewan, 5 were located in Alberta, 3 were in British Columbia and 1 station was located in the Northwest Territories

Average sulphur dioxide concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

National peak sulphur dioxide concentrations^{Footnote 15}

Key results

Between 2005 and 2019,

• a decreasing trend was detected in the peak SO₂ concentrations
• national peak concentrations remained below the 2020 standard^{Footnote 5}  of 70 ppb for all years; however, concentrations at some monitoring stations were above the standard in most years

National peak sulphur dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national peak SO₂ concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 81 monitoring stations across Canada. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak SO₂ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national peak SO₂ concentration was 20.3 ppb, which was 11% lower than in 2018. Between 2005 and 2019, a decreasing trend of 2.4 ppb per year was detected. From 2005 to 2019, national concentrations decreased by 64% (36.0 ppb). This trend is mainly attributable to reductions in sulphur oxide (SO_X) emissions in Canada and the United States resulting from technological upgrades and closures of non-ferrous metal smelters, the phase-out of coal-fired electricity, better emission control technologies within the oil and gas sector and the implementation of federal regulations related to sulphur content in fuels.

Regional peak sulphur dioxide concentrations

Key results

• Between 2005 and 2019, decreasing trends were detected for all 5 regions
• Since 2007, regional peak SO₂ concentrations remained below the 2020 standard^{Footnote 5}  of 70 ppb in all regions; however, concentrations Atlantic Canada, southern Quebec and southern Ontario exceeded the standards in 2005 and 2006. Concentrations at some monitoring stations exceeded the standard in all regions

Regional peak sulphur dioxide concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The regional peak SO₂ concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 5 monitoring stations in Atlantic Canada, 9 in southern Quebec, 10 in southern Ontario, 32 in the Prairies and northern Ontario region and 23 in British Columbia. There were not enough stations to report results for the northern territories region. The horizontal dashed line represents the 2020 Canadian Ambient Air Quality Standard (CAAQS). The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only and should not be used for evaluating overall air quality in Canada. While the standards are usually based on a 3-year average, the indicator is calculated as a 1-year average. The shaded area shows the 10th and 90th percentile bounds of peak SO₂ concentrations across monitoring stations in Canada. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, southern Quebec had the highest regional peak SO₂ concentration, at 32.7 ppb. Southern Ontario, Atlantic Canada and the Prairies and northern Ontario region followed with concentrations of 32.4 ppb, 20.8 ppb and 17.5 ppb, respectively. British Columbia had the lowest regional peak concentration, at 16.3 ppb.

With the exception of southern Quebec, all regions had lower concentrations in 2019 than in 2018. Between 2018 and 2019, the Atlantic Canada region had the largest reduction in concentrations, with a decrease of 35% (11.0 ppb). Southern Ontario, British Columbia and the Prairies and northern Ontario region reported decreases of 12% (4.4 ppb), 17% (3.4 ppb) and 7% (1.2 ppb), respectively over the same period. Southern Quebec reported a 12% (3.4 ppb) increase in concentrations in from 2018 to 2019.

Between 2005 and 2019, decreasing trends were detected in each region. A decreasing trend of:

• 3.7 ppb per year was detected for Atlantic Canada
  • concentrations decreased by 74% (58.9 ppb)
• 2.8 ppb per year was detected for southern Ontario
  • concentrations decreased by 61% (50.4 ppb)
• 2.6 ppb was detected for both the southern Quebec and Prairies and northern Ontario regions
  • concentrations in the southern Quebec and the Prairies and northern Ontario regions decreased by 56% (42.1 ppb) and 69% (39.8 ppb), respectively
• 1.8 ppb was detected for British Columbia
  • concentrations decreased by 56% (20.8 ppb)

Peak sulphur dioxide concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore peak SO₂ concentrations at specific monitoring stations.

In 2019, peak SO₂ concentrations were recorded at 124 monitoring stations across Canada.

• 7 stations recorded concentrations above 70 ppb, ranging from 82.4 ppb to 147.0 ppb. Of these stations, 1 was located in New Brunswick, 2 were in Quebec, 1 each in Ontario, Saskatchewan, Alberta and British Columbia
• 35 stations had concentrations below 5 ppb
  • 4 stations recorded concentrations of less than 1.0 ppb. Of these, a single station was located in both Newfoundland and Labrador and Saskatchewan and 2 were located in the Northwest Territories

Peak sulfur dioxide concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Volatile organic compounds

Volatile organic compounds (VOCs) are carbon-containing gases and vapours that are found in many common products such as gasoline and solvents^{Footnote 16} Volatile organic compounds are emitted from the oil and gas industry, solvent usage and transportation. Some VOCs can cause cancer and other serious health problems. Short-term exposure to high-levels of some VOCs can result in fatigue, nausea, dizziness, headaches, breathing problems and irritation of the eyes, nose and throat. Volatile organic compounds contribute to the formation of fine particulate matter (PM_2.5) and ozone (O₃), which are the main components of smog.

National average volatile organic compound concentrations^{Footnote 17} 

Between 2005 and 2019, a decreasing trend was detected in the national average VOC concentrations

National average volatile organic compound concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The national average VOC concentration indicator is based on the annual average of the daily time-integrated concentrations (24 hour for urban stations and 4 hour for rural stations) recorded at 30 monitoring stations across Canada. The shaded area shows the 10th and 90th percentile bounds of average VOC concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the national average VOC concentration was 63.6 parts per billion carbon (ppbC), which was 3% (1.9 ppbC) higher than in 2018. Between 2005 and 2019, a decreasing trend of 3.2 ppbC per year was detected. Over this period, national concentrations decreased by 33% (31.9 ppbC). This is consistent with the reduction in VOC emissions from cars and trucks, which is attributable to the introduction of new technologies, cleaner fuels and more stringent emissions standards and from reduction measures related to the production and use of paints, solvents and cleaners.

Regional average volatile organic compound concentrations

Key results

• Between 2005 and 2019, decreasing trends were detected for all 5 regions
• Average VOC concentrations varied by region and by monitoring station within each region

Regional average volatile organic compound concentrations, Canada, 2005 to 2019

How this indicator was calculated

Note: The average VOC concentration indicator is based on the annual average of the daily time-integrated concentrations (24 hour for urban stations and 4 hour for rural stations) recorded at 4 monitoring stations in Atlantic Canada, 5 in southern Quebec, 9 in southern Ontario, 5 in the Prairies and northern Ontario region and 7 in British Columbia. There were not enough stations to report results for the northern territories region. The shaded area shows the 10th and 90th percentile bounds of average VOC concentrations across monitoring stations in each region. For more information, consult the Air quality indicator definitions in the Methods section.
Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

In 2019, the Prairies and northern Ontario region had the highest regional average VOC concentration, at 96.3 ppbC. Atlantic Canada, British Columbia and southern Quebec followed with concentrations of 94.1 ppbC, 89.3 ppbC and 36.0 ppbC, respectively. The southern Ontario region had the lowest regional average concentration, at 27.3 ppbC.

With the exception of Atlantic Canada, all other regions had lower concentrations in 2019 than in 2018. Between 2018 and 2019, the southern Quebec region had the largest reduction in concentrations, with a decrease of 10% (4.2 ppbC). Southern Ontario, the Prairies and northern Ontario region and British Columbia reported decreases of 9% (2.7 ppbC), 4% (3.7 ppbC) and 3% (2.7 ppbC), respectively over the same period. The Atlantic Canada region reported a 63% (36.4 ppbC) increase in concentrations from 2018 to 2019.

Between 2005 and 2019, decreasing trends were detected in each region. A decreasing trend of:

• 3.5 ppbC per year was detected for the Atlantic Canada region and British Columbia
  • concentrations for the Atlantic Canada region and British Columbia decreased by 31% (43.2 ppbC) and 7% (6.7 ppbC), respectively
• 3.3 ppbC per year was detected for the southern Quebec region
  • concentrations decreased by 58% (50.4 ppbC)
• 2.9 ppbC per year was detected for the Prairies and northern Ontario region
  • concentrations decreased by 28% (38.1 ppbC)
• 1.6 ppbC was detected for the southern Ontario region
  • concentrations decreased by 51% (28.5 ppbC)

Average volatile organic compounds concentrations at monitoring stations

The National Air Pollution Surveillance program measures air pollutant concentrations at monitoring stations across Canada.

The Canadian Environmental Sustainability Indicators provide access to this information through an interactive map. The map allows you to explore average VOC concentrations at specific monitoring stations.

In 2019, average VOC concentrations were recorded at 37 monitoring stations across Canada.

• 5 stations recorded concentrations above 100 ppbC, ranging from 112.3 ppbC to 301.8 ppbC. Of these stations, 1 station was located in New Brunswick, Quebec and Alberta and 2 stations were in British Columbia
• 4 stations had concentrations below 20.0 ppbC. Of these, 1 station was located in New Brunswick, 2 were in Ontario and 1 was located in British Columbia

Average volatile organic compounds concentrations by monitoring station, Canada, 2019

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2022) National Air Pollution Surveillance Program.

Air quality monitoring stations are spread across the country, but are more concentrated in urban areas. The indicators for fine particulate matter (PM_2.5), ground-level ozone (O₃), sulphur dioxide (SO₂), nitrogen dioxide (NO₂) and volatile organic compounds (VOCs) are provided nationally and by region. The regions used for these indicators are listed and shown in the following table and map. See Annex A for the full list of stations used to calculate the national and regional indicators.

Regions used for the regional Air quality indicators

The Air quality indicators are also reported for the larger urban areas in Canada and the capitals of the provinces and territories when data are available. An urban area follows the definition of the Statistic Canada's census metropolitan area and census agglomeration. Refer to Annex F for the full list of stations used to calculate the urban area indicators. Ambient levels of PM_2.5, O₃, SO₂, NO₂ and VOCs by monitoring station are also shown in the Canadian Environmental Sustainability Indicators' interactive indicator maps.

Data quality assurance and quality control for the National Air Pollutant Surveillance program

Monitoring agencies contributing to the National Air Pollution Surveillance program all strive to adhere to established quality assurance and quality control standards, which are developed by Environment and Climate Change Canada in consultation with the provincial, territorial and regional governments participating in the program.

Ensuring data quality involves identifying the appropriate data quality objectives and methodologies that can be used to meet these objectives. The key data quality objectives for the National Air Pollution Surveillance program are:

• representativeness, referring to the degree to which data measurements represent a pollutant concentration of interest
• comparability, a measure of confidence with which one data set or method can be compared to another at other participating National Air Pollutant Surveillance program sites across Canada
• accuracy, the assessment of the overall agreement of a measurement with a known value
  • accuracy can include assessments of agreement among repeated measurements (precision) and measures of positive or negative systematic errors (bias)
• completeness, the assessment as to whether enough information is being collected to ensure confidence in conclusions or decisions made on the basis of data

Routine assessments of network operations provide assurance that the monitoring systems and data processing procedures produce an acceptable level of data quality to meet National Air Pollution Surveillance guidelines and to identify areas where improvements may be required. Three (3) main streams of audits and assessment are used in the National Air Pollution Surveillance network:

• performance and systems audits, which are conducted externally either by an Environment and Climate Change Canada auditor or by another agency separate from the monitoring agency
  • these audits are performed using independently verified reference standards and provide an unbiased quantitative assessment to defend the quality of the data
• interagency measurement program, which involves analysis by the monitoring agency of an unknown sample concentration provided by Environment and Climate Change Canada
  •  these tests help verify instrument accuracy and help determine data comparability across sites
• data quality assessments, which involve the statistical analysis of environmental data to determine if collected and reported data meet network and data quality objectives

Additional audits and assessments are performed by Environment and Climate Change Canada's air quality laboratories in Ottawa for the analysis of integrated VOC samples. Consult the National Air Pollution Surveillance Monitoring and Quality Assurance and Quality Control Guidelines (PDF; 2.8 MB) report for more information.

Note: ^[A] Units: µg/m³ = micrograms per cubic metre, ppb = parts per billion, ppbC = parts per billion carbon.

Average indicators are used to capture prolonged or repeated exposures over longer periods or chronic exposure while peak indicators are used to capture immediate or acute short-term exposures.

Canadian Ambient Air Quality Standards

In October 2012, the ministers of the environment, with the exception of Quebec,^{Footnote 20}  agreed to begin implementing the Air Quality Management System. This system provides a comprehensive, cross-Canada framework for collaborative action to further protect human health and the environment through continuous improvement of air quality. Under the system, the Canadian Ambient Air Quality Standards (CAAQS, the standards) are drivers for air quality across the country. The CAAQS are health- and environment-based air quality objectives for pollutant concentrations in outdoor air. Together with the management levels, ^{Footnote 21}  the CAAQS act as a benchmark to support continuous improvement of air quality. The standards are not "pollute-up-to levels" and the Air Quality Management System encourages governments to take action to improve air quality, considering that some pollutants can affect human health even at concentrations below the standards.

Under the Canadian Environmental Protection Act, 1999, the 2020 CAAQS were established:

• for PM_2.5 and O₃ in May 2013
• for SO₂ in October 2017
• for NO₂ in December 2017

The 2020 Canadian Ambient Air Quality Standards are presented in the table below. Calculation of the Air quality indicators mostly follows the same data-handling conventions as those used in calculating the concentrations to use for comparison to the standards. Formal comparison to the standards to determine if concentrations exceed a standard can only be done using ambient concentrations as measured at individual monitoring stations and not using national or regional average concentrations. As such, comparisons of the indicator values (such as the national and regional average concentrations) to the standards are provided for illustrative purposes only and not for assessing whether the standards are achieved. Indicator values that are below a standard do not imply that concentrations at individual monitoring stations are also below the standard. Furthermore, the indicators are not adjusted for exceptional events (such as wildfires) or for pollution from transboundary flows.

Data collection and validation

Data obtained from National Air Pollution Surveillance monitoring stations are converted to a format compatible with the Canada-wide Air Quality Database. All data in the Canada-wide Air Quality Database have a comparable level of quality because jurisdictions adhere to established quality assurance and quality control procedures as outlined in the National Air Pollution Surveillance Monitoring and Quality Assurance/Quality Control Guidelines (PDF; 2.8 MB). These procedures include site and sampling system design, use of monitoring methods that meet defined minimum performance specifications, operation, maintenance and calibrations, and data validation techniques. National Air Pollution Surveillance monitoring organizations are responsible for submitting quality-assured data, as per the specifications in the Guidelines, to the Canada-wide Air Quality Database. Data submitted to the National Air Pollution Surveillance database are in the hour-ending format (that is, minute data collected between 01:01 and 02:00 are averaged and reported as the 02:00 hour).

Data completeness criteria

The following criteria are used to determine which stations have sufficient hourly and daily measurements in each year to be considered valid for inclusion in the indicators.

Fine particulate matter (PM_2.5)

For the annual (calendar year) average PM_2.5 indicator:

• a daily 24-hour average concentration was considered valid if at least 75% (18 hours) of the 1‑hour concentrations were available on a given day
• an annual average concentration was considered valid if at least 75% of the daily average concentrations were available for the year and at least 60% of the daily average concentrations were available in each quarter^{Footnote 22}   of a calendar year

For the peak (98th percentile) 24-hour (calendar day) PM_2.5 indicator:

• a daily 24-hour average concentration was considered valid if at least 75% (18 hours) of the 1-hour concentrations were available on a given day
• a 98th percentile of the daily average concentration was considered valid if at least 75% of the daily average concentrations were available for the year and at least 60% of the daily average concentrations were available in each quarter^{Footnote 22}   of a calendar year
• a station was also included if it exceeded the 24-hour standard of 28.0 micrograms per cubic metre (µg/m³), even if the above data completeness criteria were not satisfied

Ground-level ozone (O₃)

For the annual average O₃ indicator:

• rolling (or moving) 8-hour average concentrations were calculated for each hour of the day from the 1-hour average concentrations, resulting in up to 24 8-hour average concentrations per day
• to be valid a rolling 8-hour average concentration must have at least 6 1-hour average concentrations
• a daily maximum 8-hour average concentration was considered valid if at least 75% (18) of the 8-hour rolling average concentrations were available in the day
• the annual maximum 8-hour average concentration was considered valid if at least 75% of all daily maximum 8-hour average concentrations were available for the period from April 1 to September 30

For the peak (4th-highest) 8-hour O₃ indicator:

• rolling (or moving) 8-hour average concentrations were calculated for each hour of the day from the 1-hour average concentrations, resulting in up to 24 8-hour average concentrations per day
• to be valid a rolling 8-hour average concentration must have at least 6 1-hour average concentrations
• a daily maximum 8-hour average concentration was considered valid if at least 75% (18) of the 8-hour rolling average concentrations were available in the day
• the annual 4th-highest daily maximum 8-hour average concentration was considered valid if there were at least 75% of all daily maximum 8-hour average concentrations in the period from April 1 to September 30
• a station was also included if it exceeded the 8-hour standard of 63 parts per billion (ppb), even if the above data completeness criteria were not satisfied

Nitrogen dioxide (NO₂)

For the annual (calendar year) average NO₂ indicator:

• an annual average concentration was considered valid if at least 75% of all the 1-hour average concentrations were available for the year and at least 60% were available in each quarter

For the peak (98th percentile) 1-hour NO₂ indicator:

• the daily maximum 1-hour average concentration was considered valid if at least 75% (18) of the hourly concentrations were available on a given day
• the 98th percentile of the daily maximum 1-hour average concentrations was considered valid if at least 75% of the daily maximum 1-hour average concentrations for the year were available and at least 60% in each quarter were available
• a station was also included if it exceeded the 1-hour standard of 60 ppb, even if the above data completeness criteria were not satisfied

Sulphur dioxide (SO₂)

For the annual (calendar year) average SO₂ indicator:

• an annual average concentration was considered valid if at least 75% of all the 1-hour average concentrations were available for the year and at least 60% were available in each quarter

For the peak (99th percentile) 1-hour SO₂ indicator:

• the daily maximum 1-hour average concentration was considered valid if at least 75% (18 hours) of the hourly concentrations were available on a given day
• the annual 99th percentile of the daily maximum 1-hour average concentrations was considered valid if at least 75% of all the daily maximum 1-hour average concentrations for the year were available and at least 60% in each quarter were available
• a station was also included if it exceeded the 1-hour standard of 70 ppb, even if the above data completeness criteria were not satisfied

Volatile organic compounds (VOCs)

There are fewer data available for VOCs and therefore the data completeness criteria for this indicator are different. At urban monitoring stations, VOC samples are usually collected over a 24-hour period once every 6 days; conversely at rural stations, samples are collected over a 4-hour sampling period (12:00 to 16:00) once every 3 days.^{Footnote 23} 

For the annual (calendar year) average VOC indicator:

• a daily average concentration was considered valid if data for a consecutive period of 24 hours (± 1 hour) at an urban station and for a consecutive 4 hours (± 0.5 hours) at a rural station were available on a given day and a quarter (3 months) had at least 5 samples
• a station was only included if there were 3 valid quarters in the year

After the data completeness criteria have been met, the pollutant concentrations are calculated for the selected stations.

Pollutant-specific calculations

Fine particulate matter

Fine particulate matter concentrations are expressed in micrograms per cubic metre (µg/m³). The PM_2.5 average and peak (98th percentile) 24-hour indicators are based on the 24-hour daily average concentrations (daily average) for the whole year. The daily average value for PM_2.5 is measured from midnight to midnight.

For a given station, the average indicator is calculated by summing all valid daily averages and dividing by the number of valid days. The peak (98th percentile) 24-hour indicator is obtained by determining the 98th percentile value of all 24-hour daily values for a given year. The 98th percentile value corresponds to the concentration for which 98% of all the daily 24-hour values are less than or equal to it and 2% are greater than or equal to it. For example, the 98th percentile value of 25 µg/m³ at a given station means that 98% of all daily 24-hour average concentrations are less than or equal to 25 µg/m³ and only 2% are greater than or equal to 25 µg/m³. In a year with a complete dataset, the 98th percentile corresponds to the 8th highest value. The following table provides the rank of the 98th percentile value based on the number of available daily measurements.^{Footnote 24} 

The urban area, regional and national indicators (average and peak [98th percentile] 24-hour) for PM_2.5 are calculated by averaging the station-level annual average and station-level annual peak values for all stations that met the completeness criteria within either the urban area, the region or Canada as a whole.

Ground-level ozone

Ozone concentrations are expressed in parts per billion (ppb). There are 24 consecutive 8-hour average concentrations (8-hour rolls) that can possibly be calculated for each day. The highest value of the 24 8‑hour average concentrations per day is the daily maximum. An illustration of the calculation running 8-hour average concentrations and the selection of the daily maximum is provided in the figure below.

Calculation of the ground-level ozone daily maximum 8-hour average concentration

For each station, the average O₃ indicator is calculated by taking the average of the daily maximum 8‑hour (ending) averages for the period from January 1 to December 31. The urban area, regional and national averages for O₃ are obtained by averaging the station-level annual averages for selected stations within the urban area, the region or Canada as a whole.

For each station, the peak (4th-highest) 8-hour O₃ indicator is based on the 4th-highest of the daily maximum 8-hour average concentrations measured over a given year. All of the daily maximum 8-hour average concentrations are ordered in an array from highest to lowest, with equal values repeated as often as they occur. Each value is assigned a rank. For a given year, the 4th-highest ranking value in the array is identified as the annual peak (4th-highest) 8-hour O₃ concentration for that station.

The urban area, regional and national peak O₃ indicators are obtained by averaging all 4th-highest values from all stations that met the completeness criteria within either the urban area, the region or Canada as a whole.

Nitrogen dioxide

Nitrogen dioxide concentrations are expressed in parts per billion (ppb). The NO₂ average indicator is based on the annual average of all 1-hour concentrations while the peak (98th percentile) 1-hour indicator is based on the annual 98th percentile of the daily maximum 1-hour average concentrations. The daily maximum 1‑hour average value for NO₂ is measured from midnight to midnight.

For a given station, the average indicator is calculated by summing all valid 1-hour averages and dividing by the number of total hours. The peak (98th percentile) 1-hour indicator is obtained by determining the 98th percentile value of all daily maximum 1-hour average for a given year. The 98th percentile value corresponds to the concentration for which 98% of all the daily maximum values are less than or equal to it and 2% is greater than or equal to it. For example, the 98th percentile value of 25 ppb at a given station means that 98% of all daily maximum 1-hour average concentrations are less than or equal to 25 ppb and only 2% are greater than or equal to 25 ppb.

The national, regional and urban area indicators (average and peak [98th percentile] 1-hour) for NO₂ are calculated by averaging the station-level annual average and station-level annual peak values for all stations that met the completeness criteria within either the urban area, the region or Canada as a whole.

Sulphur dioxide

Sulphur dioxide concentrations are expressed in parts per billion (ppb). The SO₂ average indicator is based on the annual average of the 1-hour concentrations while the peak (99th percentile) 1-hour indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations. The daily maximum 1‑hour average value for SO₂ is measured from midnight to midnight.

For a given station, the average indicator is calculated by summing all valid 1-hour averages and dividing by the number of total hours. The peak (99th percentile) 1-hour indicator is obtained by determining the 99th percentile value of all daily maximum 1-hour concentrations for a given year. The 99th percentile value corresponds to the concentration for which 99% of all the daily maximum 1-hour concentrations are less than or equal to and 1% are greater than or equal to it. For example, the 99th percentile value of 65 ppb at a given station means that 99% of all daily maximum 1-hour average concentrations are less than or equal to 65 ppb and only 1% are greater than or equal to 65 ppb. In a year with a complete dataset, the 99th percentile corresponds to the 4th highest value. The following table provides the rank of the 99th percentile value based on the number of available daily measurements.

The national and regional indicators (average and peak [99th percentile] 1-hour) for SO₂ are calculated by averaging the station-level annual average and station-level annual peak values for all stations that met the completeness criteria within the region or throughout Canada.

Volatile organic compounds

Volatile organic compounds are reported as a daily sum of individual compounds, as described in Annex D. The number of compounds included in the reported sum may slightly vary subject to the analytical validity of the individual compound concentrations. Urban VOC station indicators are calculated from the average of daily total VOC concentrations (24-hour time-integrated concentrations) while rural VOC station indicators are calculated from the average of daily 4-hour total VOC concentrations (time‑integrated samples collected from 12:00 to 16:00). The daily 24-hour average concentrations are based on measurements taken from midnight to midnight. For a station, the average indicator is calculated by taking the average of the daily total concentrations for a given year.

The national and regional indicators for VOCs are obtained by averaging the station-level annual averages from all stations that met the completeness criteria within the region and throughout Canada.

While the concentration unit for individual VOCs is usually expressed as micrograms per cubic metre (µg/m³), parts per billion carbon (ppbC) are used in this indicator to assess the quantity of mixed VOC species.

Station selection criteria for inclusion in national and regional indicators (time‑series)

Station-level indicators were calculated for the years 2005 to 2019 for all air pollutants. Each station was then assessed for its suitability (sufficient data, no large gaps at the beginning or end) for inclusion in the national and regional time series. The specific criteria are as follows:

• for the national and regional time series, a station is included if it satisfies the data completeness criteria for at least 11 of the 15 years
• stations are included if data are available for at least 1 of 3 years at the beginning or end of the time series
  • this measure avoids the use of data from stations that were commissioned or decommissioned at the beginning or end of the time series

In addition to the time series selection criteria, a minimum of 3 monitoring stations are required to calculate the indicator for a region, for a given year's trend.

Station selection results

The following table indicates the number of monitoring stations that satisfied the selection criteria (data completeness and time series) for the 2019 reporting year and were thus included in the time series for the national and regional Air quality indicators. Further details on the stations selected are available in Annex A.

Note: The sum of the regional stations may not match the national station numbers because a minimum of 3 monitoring stations are required to calculate the indicator for a region. Where there were not enough stations in the northern territories region, results from stations located in this region (Yukon and the Northwest Territories) were only included in the national totals.

Local (station-level) indicators for O₃, PM_2.5, SO₂, NO₂ and VOCs are also presented in the Canadian Environmental Sustainability Indicators' interactive indicator maps. All stations displayed on the map satisfy the data completeness criteria.

Imputation

Stations that do not have enough measurements to meet the 15-year time series criteria are excluded from the national and regional indicators. However, in some cases, monitoring stations are located close enough to others to allow data from neighbouring stations to be used to supplement missing data. Stations that were moved but remain relatively close to their previous location were also included. Annex B provides details on the stations that were used for imputation in the calculation of the time series.

Monitoring equipment

Fine particulate matter monitoring equipment

Six (6) types of monitoring equipment are used to monitor ambient PM_2.5 concentrations:

• older technology: Rupprecht & Patashnick tapered element oscillating microbalance (TEOM) monitor
• current technology: Thermo Scientific TEOM 1400a with the Series 8500C Filter Dynamics Measurement System (FDMS) monitor
• current technology: Met One BAM-1020 Beta Attenuation Mass monitor
• current technology: Thermo Scientific 5030 or 5030i SHARP (Synchronized Hybrid Ambient Real-time Particulate) monitor
• current Technology: GRIMM Environmental Dust Monitor model EDM 180
• current technology: Teledyne Advanced Pollution Instrumentation Model T640 PM mass monitor

The current technologies have been approved by the United States Environmental Protection Agency as Class III Federal Equivalent Methods and have been deployed across the National Air Pollution Surveillance network replacing older TEOM instruments that have been found to exclude a portion of the PM_2.5 mass from measurement. Further details on this technological transition are available in Annex C.

Ground-level ozone monitoring equipment

Ozone measurements are made using ultraviolet photometry. Sample air passes through a beam of light from an ultraviolet lamp, which is absorbed by O₃. The amount of ultraviolet light absorbed is proportional to the amount of O₃ in the sample.

Nitrogen dioxide monitoring equipment

Nitrogen dioxide is calculated by subtraction following the measurement of total of nitrogen oxides (NO_X) and nitrogen monoxide (NO). Nitrogen monoxide (NO) concentrations are determined photometrically by measuring the light intensity from the chemiluminescent reaction of NO mixed with excess O₃. The chemiluminescence method detects only NO, therefore, NO₂ must first be converted to NO for measurement purposes. Sample flow is either directed through a converter to reduce NO₂ to NO, or it bypasses the converter to allow detection of only NO. The sample stream with reduced NO₂ is a measurement of NO plus NO₂, which is expressed as NO_X (that is, NO_X = NO₂ + NO). The difference between NO_X and NO detection is taken as the NO₂ concentration (that is, NO₂ = NO_X - NO).

Sulphur dioxide monitoring equipment

Sulphur dioxide measurements are made using pulse-fluorescence ultraviolet adsorption instruments. This technology is based on the principle that SO₂ molecules absorb ultraviolet light at one wavelength and emit ultraviolet light at a different wavelength. The intensity of the emitted light is proportional to the number of SO₂ molecules in the sample gas.

Volatile organic compound monitoring equipment

A combined gas chromatography-flame ionization detector system is used for quantification of VOCs containing 2 carbons, while a combined gas chromatography-mass selective detector system operating in selected ion monitoring mode is used for quantification of VOCs containing 3 to 12 carbons. Approximately 120 VOCs (including a number of biogenic species such as isoprene and pinenes) are targeted for quantification in the samples, but not all VOCs are detectable in each sample. The total concentration of VOCs in parts per billion carbon is calculated from the total mass of 77 of these species when detectable in the sample. The list of VOCs targeted for quantification is provided in Annex D. 
Air samples are collected in either 6-litre or 3.2-litre stainless steel canisters. The canisters are then shipped to the Environment and Climate Change Canada analysis laboratory in Ottawa.

Statistical analysis

Non-parametric statistical tests were carried out on temporal concentration data to detect the presence of a linear trend and, if present, to determine the orientation (positive or negative) and magnitude of the rate of change (slope). The standard Mann-Kendall trend test was used to detect trend presence and orientation, while the Sen's pairwise slope method was used to estimate the slope. Both tests were applied to the national and regional data for PM_2.5, O₃, NO₂, SO₂ and VOCs. A trend was reported when the Mann-Kendall test indicated the presence of a trend at the 95% confidence level over the 15-year time series. Results of the tests are available in Annex F, with "Significant" expressing the presence and level of confidence of a trend and "Q" the slope.

Percentile bounds

A percentile is a statistical measure used to indicate the value below which a percentage of the data falls. For example, the 10th percentile is the value below which 10% of the data may be found. Likewise, the 90th percentile is the value below which 90% of the data may be found.

A percentile range is the difference between 2 determined percentiles. The 10th to 90th percentile range is the most common and is referred to as the 10th to 90th percentile bounds in the Air quality indicators. If sufficient data values are available, the bounds capture 80% of the data. When few data values are available, the calculated percentile range may vary greatly from one year to the next or may not be visible for a given year. This can be observed in the results for the northern territories region or for some regions in the regional VOC indicator.

Calculation of the urban area indicators

The urban areas used in the indicators are defined by population centres determined by Statistics Canada. A population centre is an area consisting of a population of at least 1 000 and a population density of 400 persons or more per square kilometre, based on population counts from the current Census of Population. All areas outside the population centres are classified as rural areas.

All the monitoring stations located within the population centre are considered in the calculation only if they meet the same data completeness criteria used for the national and regional indicators. Refer to the section on data completeness criteria for more information.

Annual ambient levels from all monitoring stations found within the urban area are averaged. The average is a simple arithmetic average and is not weighted by the population covered by each station. This calculation is repeated for each indicator.

The indicators only report 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when sufficient data was available. Data for the SO₂ and VOC indicators were considered too sparse to allow for appropriate urban area comparisons. For a complete list of the urban areas and monitoring stations found in these urban areas, consult Annex G.

Revisions to station selections

Monitoring stations are selected based on the 15-year time series criteria for the calculation of the Air quality indicators. As this is a rolling 15-year time period, the number of stations selected may vary from 1 iteration of the indicators to the next and may change the historical trends. Caution should be exercised when comparing different iterations of the Air quality indicators.

The following table shows the number of stations removed, added, relocated or combined for fine particulate matter (PM_2.5), ground-level ozone (O₃), nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and volatile organic compound (VOC) indicators. 

Note: ^[A] These stations no longer respect the data completeness and time series criteria as single or combined trend stations and were removed from the calculation of the national and regional indicators for the whole time series. ^[B] These stations were included in the calculation of the national and regional indicators. Annex B provides details on the stations that were used for imputation.

Regional air quality indicators

The number of available monitoring stations and pollutants measured varies from region to region. In certain years, regions that have close to the minimum number of monitoring stations required may report an unusual value if a particular monitoring station did not meet the completeness criteria for that year. This is especially true when the value obtained is an outlier from those obtained at other stations (value overshadows all other stations in the region). For this reason, the regional indicator may be subject to annual fluctuations in some regions (for example, the northern territories).

Effect of new fine particulate matter measurement technologies

Since 2005, the Rupprecht & Patashnick tapered element oscillating microbalance (TEOM) monitors used in the National Air Pollution Surveillance program have gradually been replaced by newer monitoring technologies (federal equivalency method-approved instruments). Many studies conducted in Canada, the United States and other countries have found that the TEOM monitors under-report concentrations compared with the newer monitors, especially when the air contains a large proportion of semi-volatile particulate matter. This may be the case during cooler seasons when the air contains a greater proportion of ammonium nitrate and semi-volatile organic compounds.

Some of the year-to-year variations in the PM_2.5 air quality indicator may be due, in part, to the introduction of the newer monitoring technologies across the National Air Pollution Surveillance Network rather than to changes in actual ambient concentrations only. As such, trends in PM_2.5 concentrations may not be a true reflection of the changes that have occurred over the time period concerned  (see Annex C).