Air quality

Fine particulate matter

Fine particulate matter (PM_2.5) is emitted directly 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. PM_2.5 is one of the major components of smog and one of the most widespread outdoor pollutants. Exposure to PM_2.5 can lead to the onset or development of adverse respiratory and cardiovascular effects, such as asthma attacks, chronic bronchitis, heart attacks as well as lung cancer.^{Footnote 5}  Fine particulate matter can also damage vegetation and structures, contribute to acidification and eutrophication^{Footnote 6}  of ecosystems, contribute to haze, and reduce visibility.

National average fine particulate matter concentrations

Key results

From 2006 to 2020,

• no significant trend was detected in the national average PM_2.5 concentrations
• national average concentrations remained below the 2020 standard of 8.8 µg/m³ for all years, but exceedances were recorded at some monitoring stations in particular in 2018

National average fine particulate matter concentrations, Canada, 2006 to 2020

How is this indicator 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 146 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average PM_2.5 concentration was 6.0 µg/m³, the lowest since 2009, and represented a 19.0% decrease compared to 2018, the highest concentration recorded.

Changes in average PM_2.5 concentrations are related not only to changes in the quantity of emissions of PM_2.5 and its precursors, but also to annual variations in weather conditions that 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 related to 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 (semi-volatile) portion of the PM_2.5 mass not captured by the older instruments. This should be considered when comparing measurements from newer monitors with those from years in which older instruments were used.

Regional average fine particulate matter concentrations

Key results

• From 2006 to 2020, 
  • an increasing trend was detected for average PM_2.5 concentrations in British Columbia
  • a decreasing trend was detected in the southern Quebec region
  • no trends were detected for the Atlantic Canada, the Prairies and northern Ontario, or southern Ontario regions
• Since 2006, average PM_2.5 concentrations have remained below the 2020 standard of 8.8 µg/m³ across all regions, with the exception of British Columbia in 2018; however, concentrations at some monitoring stations exceeded the standard in all regions, except for Atlantic Canada

Regional average fine particulate matter concentrations, Canada, 2006 to 2020

How is this indicator 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 12 monitoring stations in the Atlantic Canada region, 36 in the southern Quebec region, 38 in the southern Ontario region, 33 in the Prairies and northern Ontario region and 25 in British Columbia. There were not enough stations to report results for the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, British Columbia had the highest regional average PM_2.5 concentration, at 6.8 µg/m³. The southern Quebec and southern Ontario regions reported a concentration of 6.3 µg/m³ and 6.2 µg/m³, respectively. The Prairies and northern Ontario region and the Atlantic Canada region had the lowest regional average concentrations with 5.2 µg/m³ and 5.1 µg/m³, respectively.

Between 2019 and 2020, increases in concentrations were recorded as follows: 6.8% in British Columbia, 3.4% in the Atlantic Canada region and 1.3% in the southern Quebec region. In contrast, the Prairies and northern Ontario region and the southern Ontario region recorded reductions of 16.5% and 4.1%, respectively.

From 2006 to 2020:

• a decreasing trend of 0.1 µg/m³ per year was detected for the southern Quebec region
• an increasing trend of 0.2 µg/m³ per year was detected for British Columbia
• no trends were detected for the Atlantic Canada, southern Ontario, or the Prairies and northern Ontario regions

Average fine particulate matter concentrations in urban areas

Key results

In 2020, among the selected urban areas

• Quebec, QC had the highest average PM_2.5 concentration
• Yellowknife, NT had the lowest concentration

Average fine particulate matter concentrations, selected Canadian urban areas, 2020

How is this indicator calculated

Note: : The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) 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 PM_2.5 and precursor 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 users to explore average PM_2.5 concentrations at specific monitoring stations.

In 2020, average PM_2.5 concentrations were recorded at 213 monitoring stations across Canada. Average PM_2.5 concentrations varied across monitoring stations.

• 9 stations recorded concentrations above 8.8 µg/m³: 3 stations in Quebec and 6 in British Columbia had concentrations between 8.9 µg/m³ and 12.4 µg/m³
• 11 stations recorded below 4.0 µg/m³: 1 was located in Saskatchewan, 2 in Newfoundland and Labrador, 3 in British Columbia and 5 in Alberta

Average fine particulate matter concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

National average peak fine particulate matter concentrations

Key results

Between 2006 and 2020,

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

National average peak fine particulate matter concentrations, Canada, 2006 to 2020

How is this indicator calculated

Note: : The national average 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 comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average peak PM_2.5 concentration was 18.4 µg/m³, which was 6.4% (1.1 µg/m³) higher than in 2019. Between 2006 and 2020, national concentrations slightly decreased by 2.8% (0.5 µg/m³). The higher concentrations observed in 2017 and 2018 can be attributed primarily to wildfire activity in western Canada.

Changes in peak PM_2.5 concentrations are related not only to changes in the quantity of emissions but also to annual variations in weather conditions which influence the formation, dispersion, and regional transport of PM_2.5 as well as transboundary movement of PM_2.5 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 2000 to 2013, new PM_2.5 monitoring equipment was progressively introduced across Canada to replace older monitoring equipment. These new instruments measure an additional (semi-volatile) portion of the PM_2.5 mass not captured by the older instruments. This should be considered when comparing measurements from newer monitors with those from years in which older instruments were used .

Regional average peak fine particulate matter concentrations

Key results

• From 2006 to 2020,
  • increasing trends were detected for regional average peak PM_2.5 concentrations in the Prairies and northern Ontario region and in British Columbia
  • decreasing trends were detected in the Atlantic Canada, southern Quebec, and southern Ontario regions
  • no trend was detected for the northern territories region
• Since 2006, regional average peak PM_2.5 concentrations have exceeded the 2020 standard of 27 µg/m³ 3 times in both British Columbia and the Prairies and northern Ontario region, and once in both the southern Ontario and northern territories regions. The regional average peak concentrations remained below the standard for all years in the other regions

Regional average peak fine particulate matter concentrations, Canada, 2006 to 2020

How is this indicator calculated

Note: The regional average peak PM_2.5 concentration indicator is based on the annual 98th percentile of the daily 24-hour average concentrations recorded at 12 monitoring stations in the Atlantic Canada region, 36 in the southern Quebec region, 38 in the southern Ontario region, 33 in the Prairies and northern Ontario region, 25 in British Columbia and 3 in the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, British Columbia had the highest regional average peak PM_2.5 concentration, at 30.8 µg/m³. The Atlantic Canada region had the lowest average peak concentration, at 11.3 µg/m³.

Between 2019 and 2020, British Columbia, the southern Quebec and Atlantic Canada regions had recorded an increasing concentration with respectively 89.8% (14.6 µg/m³), 12.9% (2.1 µg/m³), 4.4% (0.5 µg/m³). In contrast, concentrations had decreased by 26.9% (5.7 µg/m³) in the Prairies and northern Ontario region, 21.3% (4.0 µg/m³) in the northern territories region and 8.7% (1.5 µg/m³) in southern Ontario region in the same time period.

From 2006 to 2020,

• an increasing trend of 0.9 µg/m³ per year was detected for the Prairies and northern Ontario region
• an increasing trend of 0.8 µg/m³ per year was detected for British Columbia
• a decreasing trend of 0.4 µg/m³ per year was detected for the southern Quebec and the southern Ontario regions
• a decreasing trend of 0.3 µg/m³ per year was detected for the Atlantic Canada region
• no trend was detected for the northern territories region

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

Average peak fine particulate matter concentrations in urban areas

Key results

In 2020, among the selected urban areas

• Victoria, BC had the highest average peak PM_2.5 concentration
• St. John's, NL had the lowest concentration

Average peak fine particulate matter concentrations, selected Canadian urban areas, 2020

How is this indicator calculated

Note: The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) 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 users to explore peak PM_2.5 concentrations at specific monitoring stations.

In 2020, peak PM_2.5 concentrations were recorded at 214 monitoring stations across Canada. The highest peak PM_2.5 concentrations were generally recorded at monitoring stations in western Canada.

• 32 stations recorded concentrations above 27 µg/m³, ranging from 27.1 µg/m³ to 64.4 µg/m³. Of these stations, 1 station was located in Alberta, 3 were in Quebec and 28 in British Columbia
• 16 stations recorded concentrations below 10 µg/m³. Of these stations, 4 were located in Nova Scotia, 3 in each British Columbia and Newfoundland and Labrador, 2 in New Brunswick, and 1 station was located in each Prince Edward Island, Saskatchewan, Alberta and Northwest Territories

Peak fine particulate matter concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

Ground-level ozone

Ozone (O₃) is a gas that, when present in the upper atmosphere (10 to 50 kilometres above the earth's surface), protects plant, animal, and human health from the sun's harmful ultraviolet radiation. In the lower atmosphere and at ground level, O₃ is a secondary pollutant formed when precursor gases such as nitrogen oxides and volatile organic compounds react in sunlight. Exposure to O₃ is harmful to human health and can cause throat irritation, coughing, shortness of breath and aggravation of existing conditions such as asthma. Over time, exposure to O₃ may lead to development of asthma, reduced lung function and other lung conditions.^{Footnote 5}  Ground-level O₃ can 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. Ground-level O₃ is a major component of smog, along with fine particulate matter.

National average ground-level ozone concentrationsFootnote

Key results

• From 2006 to 2020,
  • no trend was detected in the national average O₃ concentrations
  • national average concentrations remained stable
• In 2020, the national average O₃ concentration was 32.7 ppb, around 1.0% lower than 2019 level

National average ozone concentrations, Canada, 2006 to 2020

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 163 monitoring stations across Canada. There is no comparison with CAAQS given no standard exists for O₃. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Regional average ground-level ozone concentrations

Key results

From 2006 to 2020,

• an increasing trend was detected for average O₃ concentrations in the southern Quebec region
• no trends were detected for any other region

Regional average ozone concentrations, Canada, 2006 to 2020

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 18 monitoring stations in the Atlantic Canada region, 40 in the southern Quebec region, 41 in the southern Ontario region, 32 in the Prairies and northern Ontario region, and 30 in British Columbia. There were not enough stations to report results for the northern territories region. There is no comparison with CAAQS given no standard exists for O₃. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2020, the southern Ontario region had the highest regional average O₃ concentration, at 35.7 ppb. The Prairies and northern Ontario, the southern Quebec and the Atlantic Canada regions each had an average concentration around 33.0 ppb, followed by British Columbia with regional average concentrations of 27.3 ppb.

The regional average concentration was lower in 2020 than in 2019 in all regions except in British Columbia. The reduction recorded were between 1.9% (0.6 ppb) for the Prairies and northern Ontario region, the largest decrease in concentration, and 0.6% (0.2 ppb) for the southern Ontario region.

Between 2006 and 2020, an increasing trend of 0.2 ppb per year was detected for the southern Quebec region. Over that period, all other regions had no trend detected.

Average ground-level ozone concentrations in urban areas

Key results

In 2020, among the selected urban areas

• St. Catharines – Niagara Falls, ON had the highest average O₃ concentration
• Vancouver, BC had the lowest concentration

Average ozone concentrations, selected Canadian urban areas, 2020

How this indicator was calculated

Note: * The concentration is from 2017 and reported for information purposes, as no valid data was available for more recent years. The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

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 users to explore average O₃ concentrations at specific monitoring stations.

In 2020, average O₃ concentrations were recorded at 216 monitoring stations across Canada. Of these stations:

• 1 station located in Newfoundland and Labrador had a concentration above 40 ppb, with 44.0 ppb
• 6 stations had concentrations below 25 ppb, all of them were located in British Columbia

Average ozone concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

National average peak ground-level ozone concentrations

Key results

From 2006 to 2020,

• a decreasing trend was detected in the national average peak O₃ concentrations
• national average peak concentrations remained below the 2020 standard of 62 ppb since 2008, with, however, many exceedances recorded at some monitoring stations particularly in southern Ontario region

National average peak ozone concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The national average peak O₃ concentration indicator is based on the annual 4th-highest of the daily maximum 8-hour average concentrations recorded at 163 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2020, the national average peak O₃ concentration was 54.1 ppb, 0.9% higher than 2019 level. From 2006 to 2020, a decreasing trend of 0.5 ppb per year was detected. National concentrations decreased by 12.2% (7.5 ppb) between 2006 and 2020. Reductions in Canadian and American emissions of ground-level O₃ precursor gases (nitrogen oxides and volatile organic compounds) are an important factor in this downward trend.

Regional average peak ground-level ozone concentrations

Key results

• From 2006 to 2020,
  • decreasing trends were detected for regional average peak O₃ concentrations in the Atlantic Canada, southern Quebec, and southern Ontario regions
  • no trends were detected for the Prairies and northern Ontario region or British Columbia
• Since 2006,
  • both southern Quebec and southern Ontario regions have regional average peak concentrations that exceeded the 2020 standard of 62 ppb. In the southern Ontario region, except for 2019, regional average peak concentrations were consistently above the standard
  • other regional average peak O₃ concentrations remained below the standard, with exceedances measured at some monitoring stations

Regional average peak ozone concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The regional average peak O₃ indicator is based on the annual 4th-highest of the daily maximum 8-hour average concentrations recorded at 18 monitoring stations in the Atlantic Canada region, 40 in the southern Quebec region, 41 in the southern Ontario region, 32 in the Prairies and northern Ontario region, and 30 in British Columbia. There were not enough stations to report results for the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and methods section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

In 2020, the southern Ontario region had the highest regional average peak O₃ concentration at 63.3 ppb. British Columbia had the lowest average peak O₃ concentration at 47.2 ppb.

Between 2019 and 2020, the Prairies and northern Ontario region had the largest reduction in average concentration, with a decrease of 12.7% (7.4 ppb). This decrease is likely due in part to reduced wildfire activity in western Canada and fewer summer smog episodes in 2020. The Atlantic Canada region recorded a smaller decrease of 2.1% (1.0 ppb). On the other hand, the southern Ontario, southern Quebec region and British Columbia had increases of 8.0% (4.7 ppb), 7.0% (3.6 ppb) and 1.6% (0.7 ppb), respectively.

From 2006 to 2020,

• a decreasing trend of 0.9 ppb per year was detected for the southern Ontario region
• a decreasing trend of 0.5 ppb per year was detected for the Atlantic Canada region
• a decreasing trend of 0.4 ppb per year was detected for the southern Quebec region 
• no trends were detected for the British Columbia or Prairies and northern Ontario regions

Average peak ground-level ozone concentrations in urban areas

Key results

In 2020, among the selected urban areas

• Windsor, ON and Oshawa, ON had the highest average peak O₃ concentrations
• Yellowknife, NT had the lowest concentration

Average peak ozone concentrations, selected Canadian urban areas, 2020

How this indicator was calculated

Note: * The concentration is from 2017 and reported for information purposes, as no valid data was available for more recent years. The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program and the Canadian Air and Precipitation Monitoring Network.

Average peak 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.

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 users to explore peak O₃ concentrations at specific monitoring stations.

In 2020, peak O₃ concentrations were recorded at 216 monitoring stations across Canada.

• 33 stations had concentrations over 62 ppb. Most of them (30) were located in Ontario, the 3 remaining stations were in Quebec (2) and Newfoundland and Labrador (1)
• 21 stations recorded concentrations below 45 ppb. Of these stations, 11 were located in British Columbia, 5 in Newfoundland and Labrador, 2 in the Northwest Territories and 1 station was located in each Alberta, Nunavut and Prince Edward Island

Peak ozone concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program

Nitrogen dioxide

Nitrogen dioxide (NO₂) belongs to a group of substances called nitrogen oxides (NO_X). 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 the oil and gas, transportation, industry and off-road vehicles and mobile equipment. The majority of emitted NO_X is nitrogen monoxide (NO); however, once in the atmosphere NO reacts with volatile organic compounds and ozone to form NO₂. 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 lead to the development of allergies and asthma.^{Footnote 5}  NO₂ also has adverse environmental impacts. It contributes to the formation of O₃ and PM_2.5 and has major impacts on acid deposition (acid rain) and eutrophication of aquatic ecosystems.

National average nitrogen dioxide concentrations

Key results

From 2006 to 2020,

• a decreasing trend was detected in the average NO₂ concentration
• the national average concentrations remained well below the 2020 standard of 17.0 parts per billion (ppb) in this period; however, concentrations at few monitoring stations exceeded the standards

National average nitrogen dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The national average NO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 118 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average NO₂ concentration was 6.3 ppb, which was 13.0% (0.9 ppb) lower than in 2019. From 2006 to 2020, a decreasing trend of 0.3 ppb per year was detected. The national average concentration decreased by 41.0% (4.3 ppb) between 2006 and 2020. This trend is mainly attributable to 2 factors:

• lower emissions from vehicles and engines following the adoption of new technologies and clean fuel for vehicles and the introduction of progressively more stringent emission regulations by the federal government
• lower emissions from fossil-fuel-fired (for example, coal-fired) power-generating utilities from improved emission control technologies and the closures of some coal-fired power plants

Regional average nitrogen dioxide concentrations

Key results

• From 2006 to 2020, decreasing trends were detected for all 5 regions
• Since 2006, regional average NO₂ concentrations remained below the 2020 standard of 17.0 ppb in all regions; however, very few monitoring stations recorded concentrations exceeding standards

Regional average nitrogen dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The regional average NO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 8 monitoring stations in the Atlantic Canada region, 16 in the southern Quebec region, 30 in the southern Ontario region, 34 in the Prairies and northern Ontario region and 28 in British Columbia. There were not enough stations to report results for the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, British Columbia had the highest regional average NO₂ concentration, at 7.9 ppb. The southern Quebec region followed with a concentration of 6.7 ppb. The southern Ontario and Prairies and northern Ontario regions reported concentrations of 6.2 ppb and 6.0 ppb, respectively. The Atlantic Canada region had the lowest regional average concentration, at 2.7 ppb.

All 5 regions had lower concentrations in 2020 than in 2019. The southern Ontario region had the largest reduction proportion in average concentration, with a decrease of 16.6% (1.2 ppb). British Columbia, southern Quebec and Prairies and northern Ontario regions reported decreases of 13.3% (1.2 ppb), 12.1% (0.9 ppb) and 10.6% (0.7 ppb), respectively. The Atlantic Canada had the lowest reduction of 7.7% (0.2 ppb).

From 2006 to 2020, a decreasing trend of:

• 0.4 ppb per year was detected for the southern Ontario and the southern Quebec regions
• 0.2 ppb per year was detected for British Columbia and the Prairies and northern Ontario region
• 0.1 ppb per year was detected for the Atlantic Canada region

Average nitrogen dioxide concentrations in urban areas

Key results

In 2020, among the selected urban areas

• Calgary, AB had the highest average NO₂ concentration
• St. John's, NL had the lowest concentration

Average nitrogen dioxide concentrations, selected Canadian urban areas, 2020

How this indicator was calculated

Note: The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

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 users to explore average NO₂ concentrations at specific monitoring stations.

In 2020, average NO₂ concentrations were recorded at 186 monitoring stations across Canada. Average NO₂ concentrations were lower in eastern and northern areas of Canada.

• no stations had average concentrations above 17.0 ppb
• 61 stations had average concentrations below 4.0 ppb, with most of them in the Atlantic Canada region (22) and in the Prairies and north Ontario region (17)

Average nitrogen dioxide concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program

National average peak nitrogen dioxide concentrations

Key results

From 2006 to 2020,

• a decreasing trend was detected in the national average peak NO₂ concentration
• national average peak concentrations remained below the 2020 standard of 60 ppb for all years, however, concentrations at only a few monitoring stations exceeded the standard

National average peak nitrogen dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note:The national average peak NO₂ concentration indicator is based on the annual 98th percentile of the daily maximum 1-hour average concentrations recorded at 118 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average peak NO₂ concentration was 33.9 ppb, which was 9.3% lower than in 2019.

From 2006 to 2020, a decreasing trend of 0.6 ppb per year was detected. National average peak concentration decreased by 22.1% (9.6 ppb) between 2006 and 2020. This trend is mainly attributable to 2 factors:

• lower emissions from vehicles and engines following the adoption of new regulations and clean fuel for vehicles and the introduction of progressively more stringent emission regulations by the federal government
• lower emissions from fossil-fuel-fired (for example, coal-fired) power-generating utilities from improved emission control technologies and the closures of some coal-fired power plants

Regional average peak nitrogen dioxide concentrations

Key results

• From 2006 to 2020, decreasing trends were detected for all 5 regions 
• Since 2006, regional average peak NO₂ concentrations remained below the 2020 standard of 60 ppb in all regions; however, exceedances were recorded at a few monitoring stations in all regions except British Columbia

Regional average peak nitrogen dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The regional average 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 the Atlantic Canada region, 16 in the southern Quebec region, 30 in the southern Ontario region, 34 in the Prairies and northern Ontario region and 28 in British Columbia. There were not enough stations to report results for the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the southern Quebec region had the highest regional average peak NO₂ concentration, at 38.9 ppb. The Prairies and northern Ontario region followed with an average peak concentration of 35.2 ppb, the southern Ontario region with 34.7 ppb, and British Columbia with 31.6 ppb. The Atlantic Canada region had the lowest regional average peak concentration, at 26.8 ppb.

Except for the Atlantic Canada region, all regions had lower concentrations in 2020 than in 2019. The southern Ontario region had the largest reduction in average peak concentration between 2019 and 2020, with a decrease of 15.3% (6.3 ppb) followed by British Columbia with 12.4% (4.4 ppb). The southern Quebec region and the Prairies and northern Ontario region reported nearly the same lowest decrease rate of 5.4% (2.2 ppb and 2.0 ppb, respectively), while the Atlantic Canada region reported an increase of 5.5% (1.4 ppb).

From 2006 to 2020, a decreasing trend of:

• 0.9 ppb per year was detected for southern Ontario
• 0.6 ppb per year was detected the Atlantic Canada and the southern Quebec regions
• 0.5 ppb per year was detected for the Prairies and northern Ontario region
• 0.4 ppb per year was detected for British Columbia

Average peak nitrogen dioxide concentrations in urban areas

Key results

In 2020, among the selected urban areas

• Calgary, AB had the highest average peak NO₂ concentration
• Oshawa, ON and St. John's, NL had the lowest concentrations

Average peak nitrogen dioxide concentrations, selected Canadian urban areas, 2020

How this indicator was calculated

Note: The indicator only reports 25 urban areas for the most populated communities in Canada and the provincial and territorial capitals when data meeting the completeness criteria was available. All concentrations available since 2006 for each urban areas are presented in a separate data table.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

Urban areas in proximity to important sources of NO₂, such as large road network and highways, may explain the discrepancy between city’s concentrations.

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 users to explore peak NO₂ concentrations at specific monitoring stations.

In 2020, peak NO₂ concentrations were recorded at 186 monitoring stations across Canada. Of these stations:

• 1 station in Alberta recorded concentration above 60 ppb (65 ppb)
• 72 stations had concentrations below 30 ppb, 4 of them were below 10 ppb; these were located in Prince Edward Island (2 stations), Nova Scotia and New Brunswick

Peak nitrogen dioxide concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) 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 oil and gas industry, combustion of fossil fuel for electricity generation and processes in the non-ferrous smelting and refining industry. Sulphur dioxide emissions contribute to acid deposition and are a major precursor to fine particulate matter. Exposure to high concentrations of SO₂ can adversely affect the respiratory systems of humans and animals. SO₂ exposure can irritate the lungs, reduce lung function, and increase susceptibility to allergens in people with asthma. SO₂ can also damage vegetation and contributes to the deterioration of building materials such as paint or concrete.

National average sulphur dioxide concentrations

Key results

From 2006 to 2020,

• a decreasing trend was detected in the average SO₂ concentration
• national average concentrations remained below the 2020 standard of 5.0 ppb for all years, however, concentrations at a few monitoring stations exceeded the standard

National average sulphur dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The national average SO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 84 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average SO₂ concentration was 0.7 ppb, which was 2.0% lower than 2019 level. From 2006 to 2020, a decreasing trend of around 0.1 ppb per year was detected. National concentrations decreased by 61.7% (1.2 ppb) between 2006 and 2020. 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

• From 2006 to 2020, decreasing trends were detected for all 6 regions
• Since 2006, regional average SO₂ concentrations remained below the 2020 standard of 5.0 ppb in all regions, however, concentrations at a few monitoring stations exceeded the standard in all regions except the northern territories region

Regional average sulphur dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The regional average SO₂ concentration indicator is based on the annual average of the hourly concentrations recorded at 6 monitoring stations in the Atlantic Canada region, 9 in the southern Quebec region, 10 in the southern Ontario region, 32 in the Prairies and northern Ontario region, 24 in British Columbia and 3 in the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, southern Ontario and southern Quebec regions had the highest regional average SO₂ concentrations, with values of 1.2 ppb and 1.1 ppb, respectively. The Atlantic Canada region followed with a regional average concentration of 0.8 ppb. The Prairies and northern Ontario region and British Columbia had average concentrations of 0.6 ppb each. The northern territories region had the lowest regional average concentration, with 0.4 ppb.

The northern territories, the Prairies and northern Ontario and Atlantic Canada regions had higher concentrations in 2020 than in 2019, with increases of 120.0% (0.2 ppb), 21.4% (0.1 ppb) and 7.0% (0.1 ppb), respectively. The other regions recorded a decrease between 2019 and 2020. British Columbia had the largest reduction in concentrations, with a decrease of 17.4% (0.1 ppb), while the southern Ontario and southern Quebec regions reported decreases of 15.0% (0.2 ppb) and 6.3% (0.1 ppb), respectively.

From 2006 to 2020, a decreasing trend of:

• 0.2 ppb per year was detected for southern Ontario
• 0.1 ppb per year was detected for both British Columbia and southern Quebec regions 
• 0.07 ppb per year was detected for Atlantic Canada
• 0.04 ppb per year was detected for the Prairies and northern Ontario and the northern territories regions

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 users to explore annual average SO₂ concentrations at specific monitoring stations.

In 2020, average SO₂ concentrations were recorded at 123 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 5.4 ppb and 5.9 ppb, respectively.
• 74 stations had concentrations below 0.5 ppb. Most of these stations were located in Alberta (22) and British Columbia (21)

Average sulphur dioxide concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

National average peak sulphur dioxide concentrations

Key results

From 2006 to 2020,

• a decreasing trend was detected in the national average peak SO₂ concentration
• national average peak concentration remained below the 2020 standard of 70 ppb for all years, however, concentrations at some monitoring stations were above the standard

National average peak sulphur dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The national average peak SO₂ concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 84 monitoring stations across Canada. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the national average peak SO₂ concentration was 21.1 ppb, which was 4.9% higher than 2019 level. From 2006 to 2020, a decreasing trend of 2.1 ppb per year was detected. National concentrations decreased by 58.0% (29.1ppb) between 2006 and 2020. 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 average peak sulphur dioxide concentrations

Key results

• From 2006 to 2020, decreasing trends were detected for the 6 regions 
• Since 2007, regional average peak SO₂ concentrations remained below the 2020 standard of 70 ppb in all regions 
• Concentrations at a few monitoring stations exceeded the standard in all regions except northern territories region

Regional average peak sulphur dioxide concentrations, Canada, 2006 to 2020

How this indicator was calculated

Note: The regional average peak SO₂ concentration indicator is based on the annual 99th percentile of the daily maximum 1-hour average concentrations recorded at 6 monitoring stations in the Atlantic Canada region, 9 in the southern Quebec region, 10 in the southern Ontario region, 32 in the Prairies and northern Ontario region, 24 in British Columbia and 3 in the northern territories region. The comparison to the Canadian Ambient Air Quality Standard is provided for illustrative purposes only. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2020, the southern Quebec region had the highest regional average peak SO₂ concentration, at 32.5 ppb. The southern Ontario, the Atlantic Canada, the Prairies and northern Ontario regions, and British Columbia followed with concentrations of 29.4 ppb, 22.0 ppb, 20.9 ppb and 16.1 ppb, respectively. The northern territories region had recorded very low regional average peak concentration, at 1.0 ppb.

Between 2019 and 2020, the Prairies and northern Ontario, the Atlantic Canada and the northern territories regions reported the largest increase in average peak concentration of 19.1% (3.3 ppb), 18.6% (3.5 ppb) and 16.0% (0.1 ppb), respectively. At a lesser extent, British Columbia concentrations increased by 2.7% (0.4 ppb). By contrast, southern Ontario, and southern Quebec regions reported reductions in average peak concentrations, with decreases of 14.7% (5.1 ppb) and 0.6% (0.2 ppb), respectively.

From 2006 to 2020, a decreasing trend of:

• 2.6 ppb per year was detected for the Atlantic Canada region
• 2.5 ppb per year was detected for both the southern Ontario and southern Quebec regions
• 2.0 ppb per year was detected for the Prairies and northern Ontario region
• 1.9 ppb per year was detected for British Columbia
• 0.1 ppb per year was detected for the northern territories region

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 users to explore peak SO₂ concentrations at specific monitoring stations.

In 2020, peak SO₂ concentrations were recorded at 123 monitoring stations across Canada:

• 8 stations recorded concentrations above 70 ppb, ranging from 72.6 ppb to 206.8 ppb. Of these stations, 1 was located each in New Brunswick, Saskatchewan, British Columbia, and Ontario, 2 were each located in Quebec and Alberta
• 41 stations had concentrations below 5 ppb. Of these, 33 stations were located in western and northern Canada: British Columbia (18), Alberta (7), Saskatchewan (4) and Northern Territories (4)

Peak sulfur dioxide concentrations by monitoring station, Canada, 2020

Navigate data using the interactive map

How this indicator was calculated

Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

Volatile organic compounds^{Footnote 2}

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

The national and regional VOC indicators cover the period from 2006 to 2019 only as no station met the data completeness criteria for 2020.

National average volatile organic compound concentrations

Key results

• From 2006 to 2019, a decreasing trend was detected in the national average VOC concentrations

National average volatile organic compound concentrations, Canada, 2006 to 2019

How this indicator was calculated

Note: VOC sampling in 2020 was limited and no station met the data completeness criteria for that year. Therefore, no VOC concentration is being reported for 2020 in this indicator. 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. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2019, the national average VOC concentration was 65.5 parts per billion carbon (ppbC), which was 3.0% (1.9 ppbC) higher than in 2018. From 2006 to 2019, a decreasing trend of 3.5 ppbC per year was detected. Over this period, national concentrations decreased by 39.0% (41.5 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

• From 2006 to 2019, decreasing trends were detected for all 5 regions

Regional average volatile organic compound concentrations, Canada, 2006 to 2019

How this indicator was calculated

Note:VOC sampling in 2020 was limited and no station met the data completeness criteria for that year. Therefore, no VOC concentration is being reported for 2020 in this indicator. 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 the Atlantic Canada region, 6 in the southern Quebec region, 9 in the southern Ontario region, 5 in the Prairies and northern Ontario region and 6 in British Columbia. There were not enough stations to report results for the northern territories region. For more information, consult the Air quality indicator definitions in the Data sources and method section.
Source: Environment and Climate Change Canada (2023) National Air Pollution Surveillance Program.

In 2019, British Columbia had the highest regional average VOC concentration, at 102.4 ppbC. The Prairies and northern Ontario and the Atlantic Canada regions followed with concentrations of 96.3 ppbC and 94.1 ppbC, respectively. The southern Ontario region had the lowest regional average concentration, at 27.3 ppbC.

All regions had lower concentrations in 2019 than in 2018 except for the Atlantic Canada region. Between 2018 and 2019, the southern Quebec region had the largest reduction in concentrations, with a decrease of 17.3% (7.5 ppbC). The southern Ontario, British Columbia and Prairies and northern Ontario regions reported decreases of 9.0% (2.7 ppbC), 5.3% (5.7 ppbC) and 3.7% (3.7 ppbC), respectively, over the same period. The Atlantic Canada region reported a 63.2% (36.4 ppbC) increase in concentrations from 2018 to 2019. However, this increase could be explained by the low concentration in 2018 due to the absence of data from one station during that year.

From 2006 to 2019, a decreasing trend of:

• 5.3 ppbC per year was detected for British Columbia
• 3.4 ppbC per year was detected for the Atlantic Canada region
• 3.1 ppbC per year was detected for the southern Quebec region
• 2.8 ppbC per year was detected for the Prairies and northern Ontario region
• 1.1 ppbC was detected for the southern Ontario region

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 users 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 in each of New Brunswick, Quebec, and Alberta and 2 stations were in British Columbia
• 4 stations had concentrations below 20 ppbC. Of these, 1 station was located in each New Brunswick and British Columbia, 2 in Ontario

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 (2023) National Air Pollution Surveillance Program.

Air quality monitoring stations are located across the country but are more concentrated in urban areas and in Canada’s south. The indicators for PM_2.5, O₃, SO₂, NO₂ and VOCs are provided nationally and by region. The regions used for these indicators are listed and shown in the following table and map.

Regions used for the regional Air quality indicators

The Air quality indicators are also reported for the largest urban areas across Canada and the capitals of the provinces and territories when sufficient data are available. An urban area follows the definition of the Statistic Canada's population centre. Ambient levels of PM_2.5, O₃, SO₂, NO₂ and VOCs measured by monitoring station are also shown in the Canadian Environmental Sustainability Indicators interactive 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: the degree to which data measurements represent a pollutant concentration of interest
• Comparability: the 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 (see table below). Such assessment can include analysis 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 based on 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: conducted externally either by an ECCC 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: involves analysis by the monitoring agency of an unknown sample concentration provided by ECCC. These tests help verify instrument accuracy and help determine data comparability across sites
• Data quality assessments: 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 ECCC'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) for more information.

Note: 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 9}  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 improvements 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 10}  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
• SO₂ in October 2017
• 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 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 11}  of a calendar year

For the peak (98th percentile) 24-hour 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 of a calendar year
• a station was also included if the 98th percentile of the daily average concentration exceeded the 24-hour standard of 27 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. The 8-hour average concentrations are reported to the end hour.
• 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. The 8-hour average concentrations are reported to the end hour
• 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 the annual 4th-highest daily maximum 8-hour average concentration exceeded the 8-hour standard of 62 parts per billion (ppb), even if the above data completeness criteria were not satisfied

Nitrogen dioxide (NO₂)

For the annual 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
• a station was also included if the annual average concentration exceeded the 1-hour standard of 17.0 ppb, and at least 50% of the NO₂ 1-hour values are available in each calendar 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 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
• a station was also included if the annual average concentration exceeded the 1-hour standard of 5.0 ppb, and at least 50% of the SO₂ 1-hour values are available in each calendar quarter r

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 12} 

For the annual 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.

Note: ^[A] Since no station satisfied the data completeness criteria for 2020, VOC concentrations are presented up to 2019. In 2019, 37 stations met the criteria.

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 13} 

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 Figure 36.

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 average 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 B. 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 2006 to 2020 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) till 2020 reporting year and were thus included in the time series for the national and regional Air quality indicators. Further details are available in a list of selected stations.

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, NO₂, and SO₂ are also presented in the Canadian Environmental Sustainability Indicators interactive maps. All stations displayed on the map satisfy the data completeness criteria fro the year 2020.

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.

Monitoring equipment

Fine particulate matter monitoring equipment

Several types of equipment (Annex A) are used to monitor ambient PM_2.5 concentrations:

PM_2.5 Pre-Federal Equivalency Method (FEM) and Non-Federal Equivalency Method Instruments

• Non-FEM: Rupprecht & Patashnick tapered element oscillating microbalance (TEOM) monitor or TEOM® Series 1400/1400a with sample equilibrium system (SES) monitor
• Pre-FEM: Met One BAM-1020 Beta Attenuation Mass monitor (prior to 2008)
• Pre-FEM: Thermo Scientific TEOM 1400a with the Series 8500C Filter Dynamics Measurement System (FDMS) monitor (prior to 2010)
• Pre-FEM: Thermo Scientific 5030 SHARP (Synchronized Hybrid Ambient Realtime Particulate) monitor (prior to 2010)

PM_2.5 Designated Federal Equivalency Method (FEM) Instruments

• FEM: Thermo Scientific TEOM 1400a with the Series 8500C Filter Dynamics Measurement System (FDMS) monitor
• FEM: Met One BAM-1020 Beta Attenuation Mass monitor
• FEM: Thermo Scientific 5030 or 5030i SHARP (Synchronized Hybrid Ambient Realtime Particulate) monitor
• FEM: GRIMM Environmental Dust Monitor model EDM 180
• FEM: Teledyne Advanced Pollution Instrumentation Model T640 PM mass monitor

The Thermo Scientific TEOM 1400a with 8500C FDMS (2010), Met One BAM-1020 (2008), Thermo Scientific SHARP (2010), GRIMM 180 (2011) and Teledyne T640 (2016) monitors 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 non-FEM tapered element oscillating microbalance instruments, which in some circumstances may under report the PM_2.5 mass concentrations relative to the National Air Pollution Surveillance PM_2.5 Reference Method. Since 2005, the tapered element oscillating microbalance monitors have gradually been replaced by the federal equivalent methods monitors. The federal equivalent methods monitors measure a portion (semi-volatile) of the PM_2.5 mass not captured by the older instruments. Because of these measurement differences between the new and the old monitoring equipment, concentrations measured with the new monitors may not be directly comparable with the measurements from years in which older instruments were used.

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 B. 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 C, 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 centre 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. For more information on the stations considered, consult the list of stations used for the urban area indicators.

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.

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.

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 & Potashnick 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.