Canada's Air

Canadians enjoy a good level of outdoor air quality. Emissions of air pollutants that cause smog and acid rain have decreased significantly during the past decades. These reductions have contributed to the reduction of the air pollutants that Canadians breathe every day – pollutants that can contribute to health issues such as asthma and cardiovascular diseases.

While significant progress has been made to reduce air pollution, poor air quality remains a serious issue in some areas of Canada. Canadians living in heavily populated and industrialized areas of the country may be exposed to potentially harmful levels of outdoor air pollutants, at concentrations that exceeded established standards. Air pollutants such as fine particulate matter and ground-level ozone, the major components of smog, can adversely affect the health of Canadians, especially small children, the elderly, and those with heart and lung conditions, even at low concentrations.

This website provides information on the Air Quality Management System, air quality across Canada, air pollution and its effects, and actions to improve the air that we breathe.

Air Quality Management System

  • In order to better protect human health and the environment, in 2012 ministers of the environment, with the exception of Québec, agreed to implement a new Air Quality Management System (AQMS) to guide work on air emissions across Canada.
  • AQMS is a comprehensive and collaborative approach by federal, provincial and territorial governments to reduce the emissions and ambient concentrations of various pollutants of concern.
  • AQMS provides a framework for collaborative action across Canada to further protect human health and the environment from harmful air pollutants through continuous improvement of air quality.

Although Québec supports the general objectives of the AQMS, it will not implement the system since it includes federal industrial emission requirements that duplicate Québec’s regulation. However, Québec is collaborating with jurisdictions on developing other elements of the system, notably air zones and airsheds.


Collaboration and Accountability

AQMS was built on a foundation of collaboration, accountability and transparency. Industry, non-governmental and Indigenous organizations worked with governments to develop AQMS, they continue to monitor implementation of AQMS and participate in its ongoing development and improvement, including actions to address mobile sources.

Monitoring and public reporting are critical to transparency, accountability and the effective implementation of the system. Provinces and territories, with assistance from the federal government, are responsible for monitoring air pollutants in their air zones and for reporting to their constituents about air quality and actions taken to implement AQMS. Provinces and territories will produce annual air zone reports that include information on achievement of the CAAQS, air quality issues and trends, and the air management level in each air zone.



Canadian Ambient Air Quality Standards (CAAQS) are developed as a key element of the Air Quality Management System to drive improvement of air quality across Canada. CAAQS have been developed for nitrogen dioxide (NO2), sulphur dioxide (SO2), fine particulate matter (PM2.5) and ozone (O3). Ongoing reviews of the CAAQS help ensure they reflect the latest scientific information. The CAAQS are established as air quality objectives under the Canadian Environmental Protection Act, 1999.


Air Zone Management

To assist with air quality management, provinces and territories have defined smaller geographic areas called air zones that divide their jurisdiction and that have unique air quality characteristics. These characteristics may include pollutant sources, topography, meteorological patterns, population density and other potential factors that influence ambient air concentrations.

Industrial Emissions Requirements

Base-level Industrial Emissions Requirements (BLIERs) are intended to ensure that all significant industrial sources in Canada, regardless of where facilities are located, meet a good base-level of performance. BLIERs are quantitative or qualitative emissions requirements proposed for new and existing major industrial sectors and some equipment types. BLIERs are focused on nitrogen oxides (NOx), sulphur dioxide (SO2), volatile organic compounds (VOCs) and particulate matter (PM).

Airshed Coordination

Six regional airsheds cover all of Canada and allow for coordination and joint action in resolving issues involving the movement of air pollutants across provincial/territorial boundaries and international borders. These airsheds were developed taking larger scale issues, such as the movement of large air masses, typical long-term meteorological conditions, topography and air zone boundaries into consideration.

Mobile Sources

AQMS includes work to address emissions from mobile sources. The work builds on the existing range of federal, provincial and territorial initiatives aimed at reducing emissions from the transportation sector.

Air Pollutants

The air pollutants included in this report are:

Particulate Matter (PM)

Particulate matter (PM), a major component of smog, consists of airborne particles in solid or liquid form. PM may be classified as primary or secondary, depending on the process that led to its formation. Primary PM is emitted directly into the atmosphere from a source, such as a smokestack or exhaust pipe, or from wind-blown soils or vehicle traffic on a dirt road. Secondary PM is formed in the atmosphere through a series of chemical and physical reactions involving gases such as sulphur oxides (SOx) and nitrogen oxides (NOx). PM exists in various sizes and the particles of most concern for human health are those with a diameter of less than 2.5 micrometres (PM2.5).

Ground-level ozone (O3)

Ground-level ozone (O3), is a colourless, odourless and highly irritating gas that forms close to the Earth’s surface. O3 is a major component of smog. In contrast to “primary” pollutants which are emitted directly into the atmosphere from a source, O3 is considered a “secondary” pollutant because it is formed through complex chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. While O3 at ground-level is a significant environmental and health concern, approximately 10 to 40 kilometres above the Earth's surface, there is a beneficial layer of stratospheric ozone which shields the earth from harmful ultraviolet radiation. Ozone is also a short-lived climate pollutant and also contributes to climate change.

Nitrogen dioxide (NO2)

Nitrogen dioxide (NO2) belongs to the oxides of nitrogen group of compounds (NOx) that are formed primarily through the burning of fossil fuels. While transportation sources represent over half of all emissions, energy production and industrial processes also emit significant amounts of NOx, mainly as Nitric Oxide (NO) and Nitrogen dioxide (NO2). NO2 at higher concentrations has a strong, harsh odour and can typically be seen over large cities as a brownish haze. Once formed, NO2 can combine with water molecules in the air to form compounds like nitric acid and nitrous acid. Ultimately, these compounds fall to earth through precipitation (such as rain, snow and fog) where they contribute to the acidification and eutrophication of ecosystems.

Sulphur dioxide (SO2)

Sulphur dioxide (SO2) is a colourless gas that smells like burnt matches. It belongs to a group of sulphur-containing gases called sulphur oxides (SOx). SO2 is emitted when fossil fuels or raw materials containing sulphur are burned or used in an industrial process like metal ore smelting or electric power generation. It can also be produced in large quantities during extraction and processing of fossil fuels. SO2 contributes to the formation of PM2.5 and smog, and when combined with water molecules in the air, it can form compounds like sulfuric acid, which eventually falls to earth as acid rain, snow and fog.

Volatile Organic Compounds (VOCs)

Volatile organic compounds (VOCs) are organic chemicals that easily turn to vapour under normal atmospheric conditions. When VOCs are exposed to sunlight, complex chemical reactions occur with NOx that lead to the production of O3 and fine particulate matter (PM2.5), two key components of smog. Smog is known to have adverse effects on human health and the environment. VOCs cover a wide range of chemicals including fumes from oil-based paint, household cleaning products, solvents and gasoline, as well as from some natural sources. Across Canada, the main human-related sources are related to the extraction of oil and gas, the use of paints and solvents, transportation, and home firewood burning.

Learn the difference between pollutant emissions and ambient concentrations:

Air emissions

Air emissions refer to the release of pollutants into the atmosphere from a source. A “source” can include industrial facilities, various types of transportation, home heating appliances and much more. Air emissions also come from natural sources, like forest fires and volcanoes. The quantity of emissions released from human activities vary depending on a number of factors, such as: changes in industrial output and processes, fuel types, pollutant reduction technologies and the economy.

Ambient concentrations

Ambient air concentrations refer to the amount of pollutants in a defined volume of air. These are usually expressed in parts per billion by volume (ppb) for gases and in micrograms per meter cubed for particulate matter. Ambient air quality reporting only considers outdoor air, with air monitoring stations located mostly in, or near, large communities where exposure takes place. Ambient air concentrations reflect and respond to changes in the quantity of emissions released and to changes in meteorology (wind speed, wind direction, temperature, precipitation, etc.).

Pollutant Sources

  • CARS

Effects on Human Health and the Environment

According to the World Health Organization (WHO) air pollution represents the biggest environmental risk to human health and can severely affect the environment. Even at low levels, air pollution has been clearly linked to increased heart and breathing problems, increased hospitalization and emergency room visits and premature death. Health Canada estimates air pollution contributes to about 15,300 deaths in Canada each year, as well as many non-fatal impacts, with a total economic cost of $120 billion annually.

Improved air quality reduces heart attacks and hospital visits, avoids hundreds of thousands of child asthma attacks, and prevents millions of lost school and work days in Canada alone. Cleaner air can also reduce damage to crops, forests, surface waters, and infrastructure such as buildings and bridges, and can help address climate change impacts since some air pollutants are also greenhouse gases or contribute to the formation of greenhouse gases.

Source: Health Canada, 2021. Health Impacts of Air Pollution in Canada: Estimates of morbidity and premature mortality outcomes – 2021 Report.

Fine Particulate Matter (PM2.5)

Health Effects - Exposures to fine particulate matter (PM2.5) can negatively impact the heart and lungs, and can leadto health issues like asthma attacks, chronic bronchitis, and heart attacks. Exposure to PM2.5 is also linked to increased emergency room visits and hospitalization due to respiratory and cardiovascular problems, as well as increased risk of premature mortality. Children and those with pre-existing cardiovascular and respiratory disease have greater sensitivity to effects.

Environmental Effects - Impacts on the environment can vary depending on the chemical make-up but, mostly, PM can cause changes to soil and water chemistry. This can adversely impact organisms and vegetation. PM2.5 can stain and damage stone and other materials, statues and monuments. PM2.5 also contributes to reduced visibility, which affects cities, airports, and wilderness areas, and can negatively impact tourism and the economy.

Ozone (O3)

Health Effects - Exposure to ozone (O3) can cause respiratory symptoms such as throat irritation, coughing, shortness of breath, and reduced lung function. Ozone exposure can also aggravate existing conditions like asthma or other chronic lung diseases. Sensitive populations such as children, and people suffering from respiratory or cardiovascular conditions are at higher risk, especially during summer months when ozone levels increase.

Environmental Effects - Ozone is absorbed directly by plants through pores in their leaves. Once inside the plant, O3 can damage leaves, reduce photosynthesis, impair reproduction and decrease agricultural crop yields. This can reduce the variety of plants in an ecosystem. While mostly known for its adverse effects on health and the environment, ozone is also a greenhouse gas that contributes to climate change.

Nitrogen dioxide (NO2)

Health Effects - Short-term exposure to NO2 can elicit a range of adverse respiratory effects including decreased lung function, increased respiratory symptoms, and airway inflammation, and cause aggravation of respiratory diseases, particularly asthma and chronic obstructive pulmonary disease. Long-term exposure to NO2 may contribute to allergic responses, asthma development and may increase susceptibility to respiratory infections. Inhalation of NO2 has also been linked to effects on the cardiovascular system, and some reproductive effects.

Environmental Effects - NO2 can affect ecosystems both directly and indirectly and contributes to the formation of ozone. Direct effects occur when plants absorb the NO2 through their leaves, which can lead to lesions and dead tissue, and to altered plant growth and yield. Indirect effects occur when NO2 (and other NOx) reacts with water and oxygen to form acid rain, or when an overabundance of nitrogen adversely affects an ecosystem.

Sulfur dioxide (SO2)

Health Effects - Exposure to SO2 can have negative impacts on respiratory health, including reduced lung function, increased respiratory symptoms, and airway inflammation. Persons with asthma, about 9% of the Canadian population, are especially vulnerable, along with sensitive populations such as children and those with pre-existing respiratory disease. Effects can also include increased emergency room visits and hospitalizations for respiratory causes.

Environmental Effects - SO2 can affect ecosystems both directly and indirectly, and contributes to the formation of PM2.5. Direct effects occur when plants absorb the SO2 through their leaves. Indirect effects occur when sulphur-containing compounds, like the sulfuric acid in acid rain, are deposited onto soil and water. Once absorbed by the plant, SO2 can interfere with photosynthesis and energy metabolism, and can cause decreased plant growth and yield. SO2 can damage materials and structures including objects of cultural importance like statues and monuments.

Volatile Organic Compounds (VOCs)

Health Effects - Adverse health effects from exposure to VOCs depends upon the nature of the chemical, the level of exposure, and the length of exposure. Many substances included in this grouping have little effect on health. For those that do, the effects can vary greatly, from irritation (eye, nose and throat), headaches, nausea, dizziness, and the worsening of asthma symptoms, to more severe effects like damage to the liver, kidneys, and central nervous system. Some VOCs, like benzene, are carcinogens, and long-term exposure to them can increase the risk of developing cancer.

Environmental Effects - VOCs contributes to the formation of PM2.5 and O3, which are the main ingredients of smog. Smog reduces visibility in many areas, including cities, airports and wilderness areas and can negatively impact tourism and the economy. PM2.5 and O3 can adversely affect vegetation by damaging leaves, reducing photosynthesis, impairing reproduction and growth, and decreasing crop yields.


CCME developed Canadian Ambient Air Quality Standards (CAAQS) for PM2.5, O3, SO2 and NO2. All CAAQS consist of three interrelated elements:

  • an averaging time period
  • a numerical value
  • the statistical form of the numerical standard.
Pollutant Averaging Time Numerical Value Statistical Form
2015 2020 2025
Fine Particulate Matter (PM2.5) 24-hour 28 μg/m3 27 μg/m3   The 3-year average of the annual 98th percentile of the daily 24-hour average concentrations
Annual 10.0 μg/m3 8.8 μg/m3   The 3-year average of the annual average of the daily 24-hour average concentrations
Ozone (O3) 8-hour 63 ppb 62 ppb 60 ppb The 3-year average of the annual 4th highest of the daily maximum 8-hour average ozone concentrations
Nitrogen dioxide (NO2) 1-hour - 60 ppb 42 ppb

The 3-year average of the annual 98th percentile of the daily maximum 1-hour average concentrations
Annual - 17.0 ppb 12.0 ppb The average over a single calendar year of all 1-hour average concentrations
Sulphur dioxide (SO2) 1-hour - 70 ppb 65 ppb The 3-year average of the annual 99th percentile of the SO2 daily maximum 1-hour average concentrations
Annual - 5.0 ppb 4.0 ppb The average over a single calendar year of all 1-hour average SO2 concentrations

Air Zones and Airsheds

Air zones and airsheds are used to manage air quality at the local and regional levels respectively.


Select an air-zone and follow the link above the map to learn more and to access air quality reports.

CAAQS Management Levels

CAAQS are supported by four colour-coded management levels. Each management level is determined by the amount of a pollutant within an air zone and provides recommended air quality management actions. If the amount of a pollutant within an air zone increases, the management actions become more stringent. This helps ensure that CAAQS are not treated as pollute-up-to levels and actions will be taken to keep clean areas clean.

When determining the CAAQS management levels, provinces and territories can consider the influence of human activities originating outside of the province or territory and of exceptional events such as forest fires.

Air quality management levels Management Levels for Fine Particulate Matter CAAQS Management Levels for the Ozone CAAQS Management Levels for Nitrogen dioxide CAAQS Management Levels for Sulphur dioxide CAAQS
24-hour (micrograms per cubic metre) Annual (micrograms per cubic metre) 8-hour (parts per billion) 1-hour (parts per billion) Annual (parts per billion) 1-hour (parts per billion) Annual (parts per billion)
2015 2020 2015 2020 2020 2025 2020 2025 2020 2025 2020 2025 2020 2025
Red >28 >27 >10.0 >8.8 >62 >60 >60 >42 >17.0 >12.0 >70 >65 >5.0 >4.0
Orange 20 to 28 20 to 27 6.5 to 10.0 6.5 to 8.8 57 to 62 57 to 60 32 to 60 32 to 42 7.1 to 17.0 7.1 to 12.0 51 to 70 51 to 65 3.1 to 5.0 3.1 to 4.0
Yellow 11 to 19 4.1 to 6.4 51 to 56 21 to 31 2.1 to 7.0 31 to 50 2.1 to 3.0
Green ≤10 ≤4.0 ≤50 ≤20 ≤2.0 ≤30 ≤2.0

CAAQS Achievement

This map shows CAAQS achievement across Canada. CAAQS achievement means that the measured air pollutant concentration* in an air zone does not exceed the CAAQS numerical value.

* The measurements used to determine CAAQS achievement can be influenced by human activities originating outside of the province or territory and by exceptional events such as forest fires. Jurisdictions may account for these sources when determining the management levels in the air zones. This information can be found in provincial and territorial air zone reports.


The achievement of 2020 CAAQS was determined by provinces and territories using ambient concentrations measured in the air zones for one of the following three-year periods: 2018-2020 or 2019-2021.


Select an air-zone and follow the link in its label above to learn more.

Sources of Pollutant Emissions in 2019

Emissions of air pollutants come from human activities and natural causes. This chart presents emissions from human-activities only. Percentages are measured against a Canada-wide total which excludes open sources (like road dust) and natural sources (like forest fires).

Source: Environment and Climate Change Canada, 2021. Air Pollutant Emissions Inventory

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Canada-Wide Air Pollutant Emissions Trends Over Time

Overall, air pollutant emissions have decreased since 1990. Governments, businesses and individual Canadians have all contributed to these achievements. This chart shows the percentage change in emissions from 1990 levels of four key air pollutants.

Source: Environment and Climate Change Canada, 2021. Air Pollutant Emissions Indicators

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