About the indicator
Ground-level ozone, or O3, is an air pollutant that can negatively affect human health and the environment. 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 (VOCs), are emitted by human activities in urban and industrial centres and by natural sources such as wildfires. Vegetation is another major source of natural VOCs.
This indicator reports on the concentration of O3 from 2000 to 2021 and compares it to Alberta’s Ambient Air Quality Objectives (AAAQOs), which set thresholds for air pollutants to protect human and ecosystem health. This indicator also discusses ongoing management of O3 concentrations in Alberta under the Canadian Ambient Air Quality Standards (CAAQS).
- 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.
- Higher levels of O3 can 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 negatively affects human health and forms haze which reduces visibility.
- 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.
- Condition of the Environment Report – Air Component (PDF, 77 KB)
Summary of key results
Last updated: April 2023
- O3 concentrations in Alberta are strongly influenced by natural atmospheric fluctuations with high levels of background O3 in the spring. These natural fluctuations are driven by several factors, such as seasonal patterns in meteorology and long-range transport of ozone precursors.
- Human activities also contribute to elevated concentrations of O3, particularly during summer smog episodes.
- Alberta is taking action to manage O3 concentrations under the CAAQS.
Variation across Alberta
- Peak O3 concentrations vary across the province (Figure 1).
- Elevated O3 concentrations can be observed near major population centres due to summer smog episodes and in areas of the province affected by wildfire smoke.
- Elevated O3 concentrations are common in regions such as the foothills that are at higher elevations and have increased forest cover (which results in higher natural VOC emissions).
- Many factors influence the variation in O3 concentration across Alberta, including meteorological conditions that influence O3 formation and transport (for example, solar radiation and wind speed), concentration of O3 precursors (VOCs, NO2), among others.
Figure 1. Peak O3 concentrations across Alberta for 2021
Changes over time
From 2000 to 2021, no significant temporal trend was observed for annual peak concentrations of O3 averaged across all long-term air monitoring stations in Alberta or for Alberta’s major population centres (Figure 2).
- Variability between years is driven by varying background levels of O3 that occur naturally, as well as the extent of summer smog episodes and wildfire smoke events.
- In 2016, high O3 concentrations in Fort McMurray were caused by smoke from the Horse River Wildfire that entered the community and had major impacts on air quality.
Figure 2. Trends in annual peak O3 concentrations over time at large population centres.
Chart data table
|Year||Provincial Average||10th Percentile||90th Percentile||Calgary||Edmonton||Fort McMurray||Grande Prairie||Lethbridge||Medicine Hat||Red Deer||CAAQS|
- The highest O3 concentrations occur between March and August because of high natural background O3 levels during spring and summer smog episodes (Figure 3).
Figure 3. Monthly variation in O3 for 2021, shown using bar plots of the median monthly value across all long-term air monitoring stations. Whiskers extend from the top of the bar to the maximum monthly value across all stations.
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 remain below these thresholds. When air quality exceeds an AAAQO, the Alberta government assesses the cause and determines whether corrective action is required.
- In 2021, there were 29 exceedances of the one-hour daily maximum AAAQO for O3, related to summer smog, wildfire smoke and smoke from brush pile burning. The summer smog AAAQO exceedances occurred in late June and early July due to hot, humid and stagnant weather conditions under a ridge of high pressure (resulting in a heat dome), which caused pollutants at the surface to build up over time. The objective for O3 is 76 ppb for one-hour daily maximum periods based on the protection of human health.
- Over the previous 4 years (2017 to 2020), the number of AAAQO exceedances ranged from 2 exceedances in 2020 to 19 exceedances in 2019. The low number in 2020 was due to less wildfire smoke and summer smog episodes that year.
Comparison to national standards
- To guide management in air quality across Canada, the Canadian Ambient Air Quality Standards (CAAQS) have been developed for the following air pollutants: fine particulate matter (PM2.5), nitrogen dioxide (NO2), ground level ozone (O3) and sulphur dioxide (SO2).
- Analyses against the CAAQS specifically assess human-caused air quality issues that can be controlled through management actions while events outside the control of jurisdictions, such as wildfire smoke, are not included.
- O3 concentrations approach the CAAQS in several regions of the province due to urban and industrial emissions.
- Annual reporting of Alberta’s air quality against the CAAQS is available in Alberta’s
Air Zone Reports.
- In the 2018-2020 assessment, one area of the province (the North Saskatchewan Region) was at the Orange Level – Actions for Preventing CAAQS Exceedances. The remaining areas of the province were at the Yellow Level – Actions for Preventing Air Quality Deterioration.
- Work is ongoing to manage elevated O3 concentrations in the summer and prevent exceedances through air quality management plans. For details, see the Canadian Ambient Air Quality Standards under ‘Management plans’.
Was this page helpful?
Your submissions are monitored by our web team and are used to help improve the experience on Alberta.ca.