Population exposure to outdoor air pollutants

Key results

• In the most recent reporting period (2020 to 2022), 74% of Canadians lived in areas where outdoor concentrations of air pollutants were less than or equal to the standards.
• This represents a decrease from the 85% established for the previous period (2019 to 2021), largely due to ground-level ozone standard exceedances in southern Ontario, and to the 2022 wildfires in British Columbia and in the United States that caused fine particulate matter standards to be exceeded in Alberta and British Columbia^{Footnote 4} 
• This result is better than in 12 of the 16 reporting periods

Percentage of Canadians living in areas where outdoor concentrations of air pollutants were less than or equal to the 2020 Canadian Ambient Air Quality Standards, Canada, 2005 to 2022

Note: Except for the annual standards for nitrogen dioxide and sulphur dioxide, the 2020 Canadian Ambient Air Quality Standards use 3-year average concentrations. For this reason, the bar chart portrays percentage values over 3-year periods. The annual standards for nitrogen dioxide and sulphur dioxide use a single annual concentration for the 3-year reporting period. For example, for the 2020 to 2022 reporting period, the annual concentrations for 2022 were used for the annual standards for nitrogen dioxide and sulphur dioxide.
Source: Environment and Climate Change Canada (2024) Air Quality Research Division. Health Canada (2024) Air Quality Risk Assessment Division.

The indicator uses a total of 7 standards^{Footnote 5}  related to 4 air pollutants (fine particulate matter [PM_2.5], ground-level ozone [ozone], nitrogen dioxide [NO₂] and sulphur dioxide [SO₂]). All 7 of these standards must be met for the population of a given area to be counted as less than or equal to the standards.

During the 2020 to 2022 reporting period, Ontario and British Columbia recorded the highest number of communities with standard exceedances, at 16 and 14 communities, respectively. Prince Edward Island, Nova Scotia, Manitoba, Yukon and Nunavut had no exceedances. These results may also be influenced by the number, density and placement of monitoring stations.^{Footnote 6}  For detailed information on geographical areas where exceedances were observed, please refer to Annex B.

Over that period, exceedances of the 8-hour ozone standard affected the largest proportion of the Canadian population, at 19.0%, compared to the other standards. Of the 17 communities showing exceedances of the ozone standard, 16 communities are in southern Ontario where air quality is influenced by the flow of air pollutants from the United States as well as local and regional emissions from transportation and industrial sources.

Long term results by pollutant

• O₃ (8-hour): Between the 2005 to 2007 and 2020 to 2022 reporting periods, this was one of the most frequently exceeded standards. The proportion of the population living in areas where CAAQS exceedances occurred decreased significantly from 33.5% for the 2005 to 2007 reference period to 19.0% for the 2020 to 2022 period.^{Footnote 7}
• PM_2.5 (annual): From the 2005 to 2007 to the 2012 to 2014 reporting periods, the proportion of the population living in areas exceeding the annual standard for PM_2.5 increased steadily from 3.9% to 15.8%. A decrease was then observed up to the latest (2020 to 2022) reporting period, which had a proportion of 1.5%. This improvement can be attributed to fewer large cities having exceedances in the latter reporting periods; for example, no exceedances of this standard were recently recorded in Montreal or Hamilton.
• PM_2.5 (24-hour): Between the 2005 to 2007 and 2015 to 2017 reporting periods, there has been an overall decline in exceedances of the 24-hour standard for PM_2.5. The high proportion of population affected by exceedances in the reporting periods from 2016 to 2018 (12.2%), 2017 to 2019 (11.4%), and 2018 to 2020 (19.7%) can be attributed to the influence of smoke from large wildfires in the western United States and in British Columbia, which greatly affected air quality in large communities in Alberta and British Columbia. In the most recent reporting period (2020 to 2022), this proportion was 6.9%.
• NO₂ (1-hour and annual): Between the 2005 to 2007 and 2020 to 2022 reporting periods, the proportion of the population living in areas exceeding one of the standards for NO₂ decreased from around 12% to 0%.
• SO₂ (1-hour and annual): Exceedances of the standards for SO₂ had minimal influence on the indicator. For the 2020 to 2022 reporting period, exceedance of one of the standards were recorded for 2 communities in Quebec, 1 community in New Brunswick, 1 community in Ontario and 1 community in Saskatchewan, totalling 0.25% of the Canadian population. These exceedances tend to be limited to areas near major sources of SO₂. Despite its low influence on the indicator, SO₂ (specifically the 1-hour standard) remains a concern in some communities because of its impacts on the environment and populations close to sulphur-emitting facilities.

About the indicator

What the indicator measures

This indicator tracks the percentage of the Canadian population living in areas where concentrations of outdoor air pollutants from all sources were less than or equal to the 2020 CAAQS.^{Footnote 3}   The indicator uses the following 2020 standards (see Table 1 for more details).

• fine particulate matter (PM_2.5): 24-hour and annual
• ground-level ozone (O₃): 8-hour
• nitrogen dioxide (NO₂): 1-hour and annual
• sulphur dioxide (SO₂): 1-hour and annual

Why this indicator is important

Canadians are exposed to air pollutants on a daily basis, and this exposure can result in adverse health effects over the short- and long-term. Exposure to some air pollutants, even at low levels, has been linked to increased heart and respiratory problems, leading to increased hospitalization, emergency room visits and premature death. The Government of Canada estimates that each year 47 premature deaths per 100 000 Canadians can be linked to air pollution for a total of 17 400 premature deaths per year. The total economic valuation of the health impacts attributable to air pollution in Canada is $146 billion per year (based on 2020 currency).^{Footnote 8} Footnote

Ground-level ozone and PM_2.5 are two of the most widespread air pollutants and are key components of smog that lead to reduced visibility. Exposure to ozone and PM_2.5 can cause adverse health effects even at low levels. Exposure to ozone can cause throat irritation, coughing, shortness of breath and aggravation of existing conditions such as asthma. Over time, exposure to ozone may lead to development of asthma, reduced lung function and other lung conditions. Exposure to PM_2.5 can lead to onset or development of respiratory and cardiovascular adverse effects, such as asthma attacks, chronic bronchitis, heart attacks and may lead to the development of lung cancer.

Exposure to SO₂ and NO₂ can irritate the lungs, reduce lung function, and aggravate respiratory conditions, especially in people with asthma. Long-term exposure to NO₂ may lead to the development of allergies and asthma. Exposure to PM_2.5, ozone and NO₂ are all known to cause adverse health effects at low concentrations.

Most CAAQS pollutants (PM_2.5, ozone, and NO₂) are considered to be non-threshold pollutants. There is no identified safe level of exposure to these pollutants.^{Footnote 8}  A larger proportion of the Canadian population meeting the CAAQS is generally associated with lower overall levels of pollution exposure. Nevertheless, this proportion of the population is not considered to be "safe" from the adverse impacts of air pollution, but only at reduced health risk compared to populations exposed to higher concentrations of air pollution.

Besides their direct effects on human health, these pollutants also have adverse environmental impacts. NO₂ contributes to the formation of ozone and PM_2.5 and has major impacts on acid deposition ("acid rain") and eutrophication (excessive nutrients in a body of water leading to algal blooms and low oxygen that impact the aquatic system). Similarly, SO₂ is also a major contributor to acid deposition and contributes to formation of PM_2.5. When deposited into the environment, PM_2.5 can also damage vegetation and human-made structures. Ground-level ozone 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.

Improved air quality has been linked to reduced rates of heart attacks, hospital visits, allergy, and child asthma attacks, and prevents lost school and workdays. Cleaner air can also reduce damage to crops, forests, surface waters and infrastructure such as buildings and bridges.^{Footnote 9}

Related initiatives

This indicator tracks progress on the 2022 to 2026 Federal Sustainable Development Strategy, supporting the target: Increase the percentage of the population across Canada living in areas where air pollutant concentrations are less than or equal to the Canadian Ambient Air Quality Standards from 60%^{Footnote 10}   in 2005 to 85% in 2030. The most recent data available shows that, between the 2005 to 2007 and the 2020 to 2022 reporting periods, the percentage of Canadians living in areas where outdoor concentrations of air pollutants were less than or equal to the 2020 Canadian Ambient Air Quality Standards increased from 63% to 74%.

In addition, the indicator contributes to the Sustainable Development Goals of the 2030 Agenda for Sustainable Development. It is linked to Goal 11, Sustainable Cities and Communities and Target 11.6, "By 2030, reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management."

Related indicators

The Air health trends indicator provides an overview of the change in health risk over time associated with short-term exposure to air pollution in Canada.

The Air quality indicators track ambient concentrations of PM_2.5, ozone, SO₂, NO₂ and volatile organic compounds (VOCs) at the national and regional level and at local monitoring stations.

The Human exposure to harmful substances indicators track the concentrations of 4 substances (mercury, lead, cadmium and bisphenol A) in Canadians.

The Air pollutant emissions indicators track emissions from human activities of 6 key air pollutants: sulphur oxides (SO_X), nitrogen oxides (NO_X), volatile organic compounds (VOCs), ammonia (NH₃), carbon monoxide (CO) and fine particulate matter (PM_2.5). Black carbon, which is a component of PM_2.5, is also reported. For each air pollutant, data are provided at the national, provincial/territorial and facility level and by major sources.

Data sources and methods

Data sources

The indicator is calculated from air pollutant concentration data and population statistics.

The air pollutant concentration data are taken from Environment and Climate Change Canada's Canada-wide Air Quality Database. The population data were retrieved from Statistics Canada's demographic statistics.

Methods

The indicator is calculated by comparing the spatially averaged pollutant concentration for each geographical area with the respective 2020 Canadian Ambient Air Quality Standards (CAAQS, the standards). The total population of all geographical areas where the average concentrations for all pollutants are less than or equal to the respective standards are compared to the national population.

Caveats and limitations

From 2020 to 2022, approximately 65.6% of the population lived in areas covered by selected air quality monitoring stations that meet the data completeness criteria. Refer to Annex A for a list of geographical areas used in the indicator. The indicator assumes that the remainder of the population lives in areas where outdoor concentrations of ozone, fine particulate matter, sulphur dioxide and nitrogen dioxide are less than or equal to their 2020 standards.^{Footnote 13}

Populations in rural and northern regions of the country have relatively less coverage, as monitoring stations tend to be situated near urban areas with high population density.

Due to the unpredictable variability in extreme weather events such as wildfires, results may fluctuate significantly from one reporting period to another.

Resources

References

Canadian Council of Ministers of the Environment (2012) Guidance document on achievement determination for Canadian Ambient Air Quality Standards for fine particulate matter and ozone (PDF; 264 kB). Retrieved on December 4, 2024.

Canadian Council of Ministers of the Environment (2014) Air Quality Management System. Retrieved on December 4, 2024.

Canadian Council of Ministers of the Environment (2017) State of the Air. Retrieved on December 4, 2024.

Canadian Council of Ministers of the Environment (2019) Guidance document on air zone management (PDF; 225 kB). Retrieved on December 4, 2024.

Canadian Council of Ministers of the Environment (2020) Guidance document on achievement determination for Canadian Ambient Air Quality Standards for nitrogen dioxide (PDF; 616 kB). Retrieved on December 4, 2024.

Canadian Council of Ministers of the Environment (2020) Guidance document on achievement determination for Canadian Ambient Air Quality Standards for sulphur dioxide (PDF; 586 kB). Retrieved on December 4, 2024.

Environment and Climate Change Canada (2020) National Air Pollution Surveillance Program. Retrieved on December 4, 2024.

Government of Canada (2023) Outdoor air pollution and health. Retrieved on December 4, 2024.

Health Canada (2016) Human health risk assessment for ambient nitrogen dioxide. Retrieved on January 21, 2025.

Health Canada (2016) Human health risk assessment for sulphur dioxide : analysis of ambient exposure to and health effects of sulphur dioxide in the Canadian population. Retrieved on January 21, 2025.

Health Canada (2022) Canadian health science assessment for fine particulate matter (PM2.5). Retrieved on January 21, 2025.

Related information

Canadian Smog Science Assessment Highlights and Key Messages

Smog: causes and effects

Annex A. Geographical areas used to calculate the indicator

Annex B. Geographical areas with exceedances from the standars for the 2020-2022 reporting period

Annex A. Geographical areas used to calculate the indicator

Annex B. Geographical areas with exceedances from the standards for the 2020-2022 reporting period