About the indicator

Ground-level ozone, or O3, is an air pollutant that can negatively affect human health and the environment. O3 is found both in the lower and upper atmosphere of the Earth. In the lower atmosphere and at ground-level, exposure to O3 is harmful to humans as it irritates the respiratory system. In the upper atmosphere, O3 occurs naturally and protects the Earth from the sun’s harmful ultraviolet radiation.

O3 is not emitted directly into the atmosphere by humans, but forms through chemical reactions with precursor gases in the presence of heat and sunlight. Precursor gases, such as nitrogen dioxide and volatile organic compounds, are emitted by human activities in urban and industrial centres, and natural sources such as wildfires. Higher levels of O3 can also be transported to the ground from the ozone-rich upper atmosphere under suitable weather conditions.

O3 is a major component of smog which is a mixture of gases and particles emitted into the air by human activities. Smog forms haze, reduces visibility, and negatively affects human health.

O3 is part of the Air Quality Health Index (AQHI) that reports on health risks associated with local air quality across Alberta in real-time.

This indicator reports on the concentration of O3 from 2000 to 2020 and compares it to Alberta’s Ambient Air Quality Objectives (AAAQO), which set thresholds for air pollutants to protect human and ecosystem health. This indicator also discusses ongoing management of O3 levels in Alberta under the Canadian Ambient Air Quality Standards (CAAQS).

How condition of environment indicators for air are used

This condition of environment indicator reports on the current state and trends in Alberta’s air across the province. The air indicators were selected, prepared and reported on to meet this purpose.

Other types of reporting, such as CAAQS reporting (through Alberta’s Air Zone Reports) or compliance reporting near an industrial facility have different purposes and requirements. Therefore, other reporting may use different data sets, data analysis methods, or time-periods and are not directly comparable to the condition of environment reporting. For further details, visit:


Levels of O3 in Alberta are strongly influenced by natural atmospheric fluctuations, with high levels of background O3 in the spring.

Human activities also contribute higher levels of O3, particularly during summertime smog air pollution episodes.

Alberta is taking action to manage O3 levels under the Canadian Ambient Air Quality Standards.

  • Variation across Alberta

    • Figure 1 (PNG, 88 KB) shows that O3 levels vary across the province.
    • High levels of O3 can be observed near major population centres due to summertime smog episodes and in areas of the province affected by wildfire smoke.
    • High O3 levels are also common in regions such as the foothills due to natural background levels.
  • Changes over time

    • Figure 2 (PNG, 12 KB) shows that from 2000 to 2020, no significant temporal trend was observed for annual peak concentrations of O3 averaged across all long-term air monitoring stations in Alberta.
    • Figure 2.5 (PNG, 29 KB) shows that:
      • From 2000 to 2020, no significant trend was detected for peak O3 concentrations across Alberta’s major population centres.
      • In 2016, high O3 levels in Fort McMurray were caused by smoke from the Horse River Wildfire that entered the community and had major impacts on air quality.
    • Variability between years is driven by varying background levels of O3 that occur naturally.
  • Seasonal variation

    • Figure 3 (JPG, 67 KB) shows that the highest O3 concentrations occur between March and May because of high natural background O3 levels during spring.
    • Natural background levels of O3 tend to be highest at higher elevations in Alberta’s foothills.
    • Seasonal variation in O3 for 2020 is shown in Figure 3 using boxplots of monthly average O3 concentrations at all long-term air monitoring stations. Figure 3.5 (PNG, 6 KB) provides an explanation of the information shown in the boxplot.
  • Comparison to provincial objectives

    • Alberta’s Ambient Air Quality Objectives (AAAQOs) provide maximum acceptable thresholds for over 30 airborne compounds to protect human and ecosystem health. All industrial facilities must be designed and operated to ensure ambient air quality remains below these thresholds. When air quality exceeds an AAAQO, the Alberta government assesses the cause and determines whether corrective action is required.
    • In 2020, there were two exceedances of the one-hour daily maximum Alberta objective, related to summertime air pollution. The objective for O3 is 76 ppb for one-hour daily maximum periods based on the protection of human health.
  • Comparison to national standards

    • To drive improvement of air quality across Canada, the Canadian Ambient Air Quality Standards (CAAQS) have been developed for the following air pollutants:
      Analyses against the Canadian standards specifically assess human-caused air quality issues that can be controlled through local management actions while events outside the control of jurisdictions, such as wildfire smoke, are not included.
    • O3 levels approach the Canadian standards in several regions of the province due to urban and industrial emissions.
    • In the 2017-2019 assessment, 2 areas of the province were at the Orange Level – Actions for Preventing CAAQS Exceedances. Work is ongoing to manage elevated O3 levels in the summer and prevent exceedances through air quality management plans. The remaining areas of the province were at the Yellow Level – Actions for Preventing Air Quality Deterioration and Green Level – Actions for Keeping Clean Areas Clean. For details, see the Canadian Ambient Air Quality Standards under 'Management plans'.
    • Annual reporting of Alberta’s air quality against Canadian Ambient Air Quality Standards is available in Alberta’s Air Zone Reports.
Peak O3 concentrations across Alberta for 2020

Figure 1. Peak O3 concentrations across Alberta for 2020

View large image: Figure 1 (PNG, 88 KB)

Trend in peak O3 concentrations over time

Figure 2. Trends in peak O3 concentrations over time

View large image: Figure 2 (PNG, 12 KB)

Figure 3. Seasonal variation in O3 for 2020

Figure 3. Seasonal variation in O3 for 2020

View large image  (JPG, 67 KB)

Alberta Air Data Warehouse
Access long-term air quality monitoring data for Alberta.

Air Monitoring
Information on air monitoring in Alberta.

Alberta Air Zone Reports
Annual reporting of Alberta’s air quality against Canadian Ambient Air Quality Standards.

Ambient Air Quality Objectives (AAAQOs)
Review the provincial standards used to evaluate air quality in Alberta.

Canadian Ambient Air Quality Standards 
Alberta’s ambient air monitoring data and management levels are assessed annually against national standards.

Condition of the Environment Report – Air Component (PDF, 397 KB)
Information on data analysis methods and tools.

Environment and land use planning
Learn more about how air quality in Alberta is managed through regional land use planning.

Contact Alberta's Environmental Science Program or the Office of the Chief Scientist:

Email: [email protected]

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