Air indicators – Sulphur dioxide

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 plants or surrounding surfaces and can contribute to acidic deposition, commonly known as acid rain.

This indicator reports on the concentration of SO₂ from 2000 to 2024 and provides information on the variation across Alberta and how concentrations have changed over time. This indicator also compares SO₂ concentrations with Ambient Air Quality Objectives (AAAQOs), which set thresholds for air pollutants to protect human and ecosystem health.

Sulphur dioxide facts

• The major sources of SO₂ in Alberta are primarily 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.

Methods

For information on how the results in this indicator were calculated and for references, see: Condition of the Environment Report – Air Component

Summary of key results

Last updated: February 2026

• SO₂ concentrations have been decreasing throughout much of the province over the past 2 decades, due to improved emissions control technology and practices at industrial facilities. Recent examples include the phase-out of coal-powered electricity, efforts to reduce flaring and venting, and required increases to sulphur recovery and removal from industrial emissions.
• Over the past 2 decades, annual average concentrations of SO₂ were well below the annual AAAQO throughout Alberta. Historically, exceedances of the one-hour AAAQO have occurred at stations near industrial facilities.
• The highest concentrations of SO₂ in Alberta are found near large industrial facilities.

Variation across Alberta

• Concentrations of SO₂ are higher near major industrial sources such as in Alberta’s oil sands region and east of Edmonton (Figures 1a and 1b). 
   

Changes over time

• Between 2000 and 2024, Alberta saw a statistically significant decrease of annual average and peak concentrations of SO₂ when averaged across all monitoring stations (Figure 2). This trend is consistent with trends across Canada as technology improves for removal of SO₂ from industrial emission sources.
• Edmonton and Calgary saw statistically significant decreasing trends in annual average SO₂ concentrations. Other major population centres (Fort McMurray, Grande Prairie, Lethbridge, Medicine Hat and Red Deer) saw no statistically significant trends in annual average SO_2.
• Peak SO₂ concentrations decreased in Calgary and Fort McMurray. This decrease was statistically significant. No statistically significant trend in peak SO₂ was detected for other major population centres in Alberta. 
• Statistically significant decreasing trends in annual average and peak SO₂ were also detected at stations located near industrial facilities since 2000 (Figure 3). This decrease is due to improved emissions control technology and practices at industrial facilities.

Examining the trends over more recent years and for all stations across the province provides additional information on the changes over time for the indicator. Between 2015 and 2024, 6 out of 43 stations meeting data completeness criteria had statistically significant increasing trends in monthly average SO₂. 

• These stations, located in the Lower Athabasca Region where SO₂ levels are managed through Alberta’s regulatory system and the Lower Athabasca Regional Plan, include Fort Chipewyan, Fort McKay South, Anzac and Cold Lake South.
• The other 2 stations with increasing trends in monthly average SO₂ are community monitoring stations located in northwest Alberta: Beaverlodge and Grande Prairie.

Comparison to provincial objectives

Alberta's Ambient Air Quality Objectives  provide thresholds for over 30 airborne compounds to protect human and ecosystem health. The AAAQOs are used in the design of industrial facilities and to establish emissions requirements. The Alberta government tracks AAAQO exceedances and assesses the need for management action.

Figure 2 shows that between 2000 and 2024, annual average concentrations of SO₂ were well below the annual AAAQO throughout Alberta. The annual AAAQO of 8.0 parts per billion (ppb) for SO₂ is based on the protection of ecosystems.

In 2024, there were 4 exceedances of the one-hour AAAQO and 1 exceedance of the 24-hour AAAQO: 

• Three of the one-hour exceedances and the 24-hour exceedance occurred at the Lower Camp station, located near industrial facilities in northeastern Alberta.
• One exceedance occurred at the Scotford South station, located in the industrial heartland northeast of Edmonton. 
• Historically, exceedances of the AAAQO have been observed at stations near industrial facilities that emit SO₂ in the oil sands region and the industrial heartland northeast of Edmonton. The one-hour AAAQO of 172 ppb for SO₂ is based on the protection of human health. The 24-hour AAAQO of 48 ppb for SO₂ is based on the protection of human health.

Air quality reporting and resources

• Alberta reports annually on the status of air quality for existing regional air quality management frameworks (AQMFs) as well as the Canadian Ambient Air Quality Standards (CAAQS).
  • SO₂ is one of the pollutants reported on through the Lower Athabasca Region (LAR) AQMF as well as the CAAQS.
  • The most recent assessment results are available in Alberta’s Air Zone Reports. 
• Published reports and scientific papers on air quality in Alberta are available via the Air Indicators landing page under ‘Related Publications’.
• Alberta also provides air quality data and information to the public through the near real-time AQHI website and provides access to quality assured data via Alberta’s Air Data Warehouse.

Focused study

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

• SO₂ concentrations at several stations in the Lower Athabasca Region (Lower Camp, Mannix, Mildred Lake, and Christina Lake) exceeded the Level 3 and Level 4 triggers for the upper range of hourly data (calculated as the 99th percentile) over the period from 2016 to 2021 (Figure 4) (see the Status of Air Quality in Alberta: Air Zones report 2019-2021).
• The relationships between SO₂ and weather conditions, such as wind-speed and wind direction, and hydrogen sulphide (H₂S) were explored.
• The characteristics of the elevated SO₂ episodes suggest nearby industrial operations as the major contributing sources at each station.
• This work is part of a broader investigation in the Lower Athabasca Regional Plan Management Response.