About the indicator

Sulphur dioxide, or SO2, is an air pollutant that can have negative effects on human and ecosystem health. Exposure to SO2 can result in respiratory health problems. SO2 can also negatively affect vegetation when deposited onto land surfaces, for example through acid deposition, commonly known as acid rain.

The major source of SO2 is the burning of sulphur-containing materials, primarily from industrial sources, such as the extraction and processing of oil and gas and power generation. SO2 emissions can also lead to the formation of other air pollutants, such as fine particulate matter.

SO2 is part of Alberta’s 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 SO2 from 2000 to 2020 and compares it to Alberta’s Ambient Air Quality Objectives (AAAQO). The Alberta objectives set thresholds for air pollutants to protect human and ecosystem health. This indicator also discusses future management of SO2 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:

Results

The highest levels of SO2 in Alberta are found near large industrial facilities. Levels of SO2 have been decreasing throughout much of the province over the past 2 decades, due to improved technology and practices at industrial facilities.

  • Variation across Alberta

    • Figure 1 (PNG, 658 KB) shows that concentrations of SO2 are higher near major industrial sources, such as in Alberta’s oil sands region and the industrial heartland to the East of Edmonton.
  • Changes over time

    • Figure 2 (PNG, 18 KB) shows that between 2000 and 2020, Alberta saw an overall decrease of annual average concentrations of SO2 when averaged across all monitoring stations. This trend is consistent with trends across Canada as technology improves for industrial emissions sources.
    • Edmonton, Calgary and Fort McMurray saw decreasing trends in annual average SO2 levels. Grande Prairie, Lethbridge, and Red Deer saw no significant trends in SO2 levels. No trend estimate is available for Medicine Hat due to insufficient years of data.
    • Figure 2.5 (PNG, 122 KB) shows that at stations located near industrial facilities, there has also been a general decreasing trend in SO2 since 2000.
    • More recently, between 2011 and 2020, 4 out of 39 stations in the province saw increasing trends in SO2. Two stations are located near industrial facilities in the Lower Athabasca Region, where SO2 levels are managed through Alberta’s regulatory system and the Lower Athabasca Regional Plan. The other stations are regional monitoring stations in the North Saskatchewan Region and Upper Athabasca Region. Concentrations at all four stations remain below Alberta’s Ambient Air Quality Objectives (AAAQO).
  • Comparison to provincial objectives

    • Alberta’s Ambient Air Quality Objectives (AAAQO) 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, Alberta Environment and Parks assesses the cause and determines whether corrective action is required.
    • Figure 2 (PNG, 18 KB) shows that between 2000 and 2020, annual average concentrations of SO2 were well below the annual Alberta objective throughout the entire province. The annual objective of 8.0 parts per billion (ppb) for SO2 is based on the protection of ecosystems.
    • In 2020, there was one exceedance of the one-hour Alberta objective. The one-hour objective of 172 ppb for SO2 is based on the protection of human health.
    • Historically, exceedances of the one-hour objective have been observed at stations near industrial facilities known to emit SO2 in the oil sands region and the industrial heartland to the East of Edmonton.
  • Comparison to national standards

    • SO2 is a new indicator for the Canadian standards and will be reported on for the first time using data from 2018 to 2020.
    • Based on data from 2017 to 2019, SO2 levels are below the Canadian standards across the entire province. The Canadian standards have more stringent thresholds than the current Alberta objectives for SO2.
    • Management levels for the Canadian standards for SO2 will be assigned when the assessment of 2018 to 2020 data is complete. Information presented here is not an assessment of the achievement status of the Canadian standards.
    • Annual reporting of Alberta’s air quality against Canadian Ambient Air Quality Standards is available in Alberta’s Air Zone Reports.
Figure 1 - Annual average SO2 concentrations across Alberta for 2020

Figure 1. Annual average SO2 concentrations across Alberta for 2020

View large image: Figure 1 (PNG, 658 KB)

Figure 2 - Trends in annual average SO2 concentrations over time.

Figure 2. Trends in annual average SO2 concentrations over time. Trends are indicated in the legend (○ = no significant trend detected; ∆ = increasing trend; ∇ = decreasing trend; X = insufficient data).

View large image (PNG, 18 KB)

Focused study

Alberta Environment and Parks investigated concentrations of SO2 in the mineable oil sands region as part of the management response under the Air Quality Management Framework for the Lower Athabasca Region.

  • Levels of SO2 exceeded the Level 4 trigger for the upper range of hourly data in 2016 and 2017 under the Lower Athabasca Regional Plan (see the 2017 Status of Air Quality report).
  • The trigger exceedance was caused by episodes or spikes of SO2. These episodes typically lasted for several hours and occurred regularly throughout the year, starting in the middle of 2014.
  • The relationships between SO2 and weather conditions, such as wind-speed and wind direction, were explored.
  • The characteristics of the SO2 episodes suggest a source from nearby industrial operations but were not consistent with any known emission sources.
  • This work is part of a broader investigation in the Lower Athabasca Regional Plan Management Response.
Figure 3 – Upper range of the hourly data (calculated as the 99th percentile) for SO2 at the Lower Camp station in the Lower Athabasca Region from 2012-2020.

Figure 3. Upper range of the hourly data (calculated as the 99th percentile) for SO2 at the Lower Camp station in the Lower Athabasca Region from 2012 to 2020.

View large image: Figure 3 (PNG, 11 KB)

Related

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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