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 the plant or surrounding surfaces, for example through acid deposition, commonly known as acid rain.
This indicator reports on the concentration of SO2 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 management of SO2 concentrations in Alberta under the Canadian Ambient Air Quality Standards (CAAQS).
Sulphur dioxide facts
- The major sources of SO2 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.
- 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.
Methodology
Summary of key results
Last updated: April 2023
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. 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 the industrial heartland to the east of Edmonton (Figures 1a and 1b).
Figure 1a. Annual average SO2 concentrations across Alberta for 2021
Select a circle on the map to view the 2021 concentration and the 10-year trend for a specific monitoring station.
Source: Government of Alberta
Figure 1b. Peak SO2 concentrations across Alberta for 2021
Select a circle on the map to view the 2021 concentration and the 10-year trend for a specific monitoring station.
Source: Government of Alberta
Changes over time
- Between 2000 and 2021, Alberta saw an overall decrease of annual average and peak concentrations of SO2 when averaged across all monitoring stations (Figures 2a and 2b, respectively). 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 concentrations. Grande Prairie, Lethbridge, Medicine Hat and Red Deer saw no significant trends.
- Peak SO2 concentrations also decreased in Calgary and Fort McMurray. No trend in peak SO2 was detected for the other major population centres.
Figure 2a. Trends in annual average SO2 concentrations over time
Chart data table
| Year | Provincial Average | 10th Percentile | 90th Percentile | Calgary | Edmonton | Fort McMurray | Grande Prairie | Lethbridge | Medicine Hat | Red Deer | CAAQS |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2000 | 1.3 | 0.6 | 2.3 | 2.9 | 2.4 | 0.9 | 0.7 | 5 | |||
| 2001 | 1.2 | 0.3 | 2.5 | 3 | 2.3 | 1 | 0.5 | 5 | |||
| 2002 | 1.3 | 0.4 | 2.2 | 2.2 | 1.8 | 1.3 | 0.5 | 5 | |||
| 2003 | 1.4 | 0.5 | 2.4 | 2.1 | 1.3 | 1.1 | 0.5 | 5 | |||
| 2004 | 1.4 | 0.5 | 2.5 | 1.6 | 1.3 | 1.3 | 0.4 | 0.6 | 5 | ||
| 2005 | 1.3 | 0.4 | 2.2 | 1.7 | 1.6 | 1.1 | 0.5 | 0.5 | 0.4 | 5 | |
| 2006 | 1.2 | 0.4 | 2.6 | 1.4 | 1.3 | 0.8 | 0.4 | 0.6 | 0.2 | 5 | |
| 2007 | 1 | 0.4 | 2.1 | 1.1 | 1.4 | 1 | 0.5 | 0.4 | 0.1 | 5 | |
| 2008 | 1 | 0.3 | 1.9 | 1.2 | 1.1 | 0.9 | 0.4 | 0.3 | 0.2 | 5 | |
| 2009 | 0.9 | 0.3 | 1.8 | 1.2 | 1.2 | 1 | 0.4 | 0.4 | 0.2 | 5 | |
| 2010 | 0.8 | 0.2 | 1.4 | 1 | 1 | 0.8 | 0.5 | 0.4 | 0.1 | 5 | |
| 2011 | 0.8 | 0.2 | 1.6 | 1 | 0.8 | 0.4 | 0.3 | 0.1 | 5 | ||
| 2012 | 0.7 | 0.2 | 1.3 | 0.9 | 0.5 | 0.2 | 0.3 | 0.2 | 0.1 | 5 | |
| 2013 | 0.8 | 0.2 | 1.3 | 1.1 | 0.8 | 0 | 0.2 | 0.3 | 0.1 | 5 | |
| 2014 | 0.8 | 0.2 | 1.4 | 1.1 | 0.9 | 0 | 0.2 | 0.4 | 0.1 | 5 | |
| 2015 | 0.7 | 0.1 | 1.1 | 0.3 | 0.9 | 0.9 | 0.2 | 0.1 | 0.4 | 0.1 | 5 |
| 2016 | 0.7 | 0.1 | 1.3 | 0.3 | 0.8 | 0.9 | 0.2 | 0.1 | 0 | 0.1 | 5 |
| 2017 | 0.6 | 0.1 | 1.1 | 0.3 | 1 | 0.6 | 0.3 | 0.2 | 0 | 0.1 | 5 |
| 2018 | 0.5 | 0.1 | 1 | 0.4 | 0.9 | 0.6 | 0.3 | 0.4 | 0 | 0.1 | 5 |
| 2019 | 0.6 | 0.1 | 1.2 | 0.3 | 0.8 | 0.7 | 0.3 | 0.4 | 0.1 | 0.1 | 5 |
| 2020 | 0.7 | 0.1 | 1.2 | 0.3 | 0.8 | 1 | 0.3 | 0.3 | 0 | 0.1 | 5 |
| 2021 | 0.6 | 0.1 | 1 | 0.2 | 0.9 | 0.8 | 0.3 | 0.4 | 0 | 0.1 | 5 |
The horizontal dashed lines represent the 2020 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standards are provided for illustrative purposes only and not for assessing the achievement status of the standards. For information on achievement status see the Alberta Air Zones report.
Accessible chart description
Line chart showing the change over time in annual average SO2 concentrations for large urban centres in Alberta, the provincial average, and the 10th and 90th percentile of all SO2 monitoring stations in the province.
The chart also displays the 2020 Canadian Ambient Air Quality Standard for SO2 annual average (5 ppb) for comparison. Provincial average SO2 annual average concentrations and several large urban centres' concentrations (Calgary, Edmonton, and Fort McMurray) have decreased since 2000. The Provincial Average of annual average SO2 concentrations was 1.3 ppb in 2000 and 0.6 ppb in 2021.
Figure 2b. Trends in peak SO2 concentrations over time
Chart data table
| Year | Provincial Average | 10th Percentile | 90th Percentile | Calgary | Edmonton | Fort McMurray | Grande Prairie | Lethbridge | Medicine Hat | Red Deer | CAAQS |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2000 | 33.2 | 12.5 | 73.8 | 20 | 33 | 28 | 11 | 70 | |||
| 2001 | 37.8 | 8.6 | 90.8 | 30 | 32 | 40.5 | 9 | 70 | |||
| 2002 | 38.6 | 7 | 94 | 16 | 31 | 43.5 | 7 | 70 | |||
| 2003 | 50.3 | 11.8 | 119 | 14 | 28 | 33.5 | 5 | 70 | |||
| 2004 | 56.3 | 10.2 | 112.6 | 13 | 26 | 52 | 4 | 6 | 70 | ||
| 2005 | 50.8 | 8 | 100 | 14 | 24 | 49 | 5 | 7.7 | 4 | 70 | |
| 2006 | 43.7 | 11.4 | 103 | 12 | 33 | 26.5 | 6 | 11.2 | 5 | 70 | |
| 2007 | 36.7 | 8.7 | 81.3 | 9 | 24 | 42 | 4 | 7.9 | 3 | 70 | |
| 2008 | 38.7 | 8.8 | 82.2 | 10.7 | 24 | 39 | 9 | 9.2 | 4 | 70 | |
| 2009 | 30.6 | 5.6 | 68.7 | 12 | 25 | 34 | 7.2 | 4.9 | 5 | 70 | |
| 2010 | 35.3 | 5.4 | 68.6 | 8.3 | 20 | 38.5 | 7.1 | 6.7 | 6 | 70 | |
| 2011 | 32.4 | 5.2 | 61.6 | 23 | 26.5 | 5 | 5.6 | 5 | 70 | ||
| 2012 | 29.2 | 4.4 | 66.6 | 25 | 27 | 2.1 | 5 | 3 | 4 | 70 | |
| 2013 | 29 | 4.5 | 59 | 20.5 | 36.5 | 3 | 5 | 4 | 4 | 70 | |
| 2014 | 27.9 | 5.5 | 49 | 26 | 26 | 2 | 5 | 7 | 4 | 70 | |
| 2015 | 26.4 | 4 | 42.8 | 7 | 19.5 | 23 | 3.5 | 5 | 4 | 4 | 70 |
| 2016 | 30 | 4.3 | 51.4 | 5 | 23 | 32 | 4.5 | 14 | 2 | 4 | 70 |
| 2017 | 27.5 | 4 | 59.5 | 6 | 29 | 25.5 | 5.5 | 7 | 2 | 3 | 70 |
| 2018 | 19.7 | 3.9 | 36.2 | 8 | 26 | 25 | 5.5 | 6.7 | 2 | 2 | 70 |
| 2019 | 19 | 4 | 38.4 | 5 | 23.8 | 20.5 | 4.3 | 24 | 2 | 4 | 70 |
| 2020 | 22.1 | 4 | 62.1 | 3.8 | 21.4 | 39.1 | 4.7 | 11.5 | 2 | 4.5 | 70 |
| 2021 | 21.1 | 3.2 | 39.6 | 4.7 | 24.2 | 21.5 | 5.3 | 26.4 | 2 | 2.7 | 70 |
The horizontal dashed lines represent the 2020 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standards are provided for illustrative purposes only and not for assessing the achievement status of the standards. For information on achievement status see the Alberta Air Zones report.
Table description
Line chart showing the change over time in peak SO2 concentrations for large urban centres in Alberta, the provincial average, and the 10th and 90th percentile of all SO2 monitoring stations in the province.
The chart also displays the 2020 Canadian Ambient Air Quality Standard for SO2 1-hour (70 ppb) for comparison. Provincial average SO2 peak concentrations and some large urban centres' concentrations (Calgary and Fort McMurray) have decreased since 2000. The Provincial Average of peak SO2 concentrations was 33.2 ppb in 2000 and 21.1 ppb in 2021.
- At stations located near industrial facilities, there has also been a decreasing trend in annual average and peak SO2 since 2000 (Figures 3a and 3b, respectively).
Figure 3a. Trends in annual average SO2 concentration over time by station classification
Chart data table
| Year | Provincial Average | 10th Percentile | 90th Percentile | Community | Near Industrial Facility | Regional | CAAQS |
|---|---|---|---|---|---|---|---|
| 2000 | 1.3 | 0.6 | 2.3 | 1.2 | 1.8 | 1.1 | 5 |
| 2001 | 1.2 | 0.3 | 2.5 | 1.2 | 2 | 0.8 | 5 |
| 2002 | 1.3 | 0.4 | 2.2 | 1.1 | 2 | 0.7 | 5 |
| 2003 | 1.4 | 0.5 | 2.4 | 1 | 2.4 | 0.9 | 5 |
| 2004 | 1.4 | 0.5 | 2.5 | 0.9 | 2.6 | 0.9 | 5 |
| 2005 | 1.3 | 0.4 | 2.2 | 0.9 | 2.2 | 1 | 5 |
| 2006 | 1.2 | 0.4 | 2.6 | 0.7 | 2.1 | 1 | 5 |
| 2007 | 1 | 0.4 | 2.1 | 0.7 | 2 | 0.9 | 5 |
| 2008 | 1 | 0.3 | 1.9 | 0.7 | 1.9 | 0.8 | 5 |
| 2009 | 0.9 | 0.3 | 1.8 | 0.7 | 1.5 | 0.7 | 5 |
| 2010 | 0.8 | 0.2 | 1.4 | 0.6 | 1.7 | 0.5 | 5 |
| 2011 | 0.8 | 0.2 | 1.6 | 0.7 | 1.6 | 0.5 | 5 |
| 2012 | 0.7 | 0.2 | 1.3 | 0.5 | 1.3 | 0.5 | 5 |
| 2013 | 0.8 | 0.2 | 1.3 | 0.6 | 1.3 | 0.6 | 5 |
| 2014 | 0.8 | 0.2 | 1.4 | 0.6 | 1.4 | 0.5 | 5 |
| 2015 | 0.7 | 0.1 | 1.1 | 0.5 | 1.5 | 0.5 | 5 |
| 2016 | 0.7 | 0.1 | 1.3 | 0.5 | 1.6 | 0.4 | 5 |
| 2017 | 0.6 | 0.1 | 1.1 | 0.5 | 1.1 | 0.5 | 5 |
| 2018 | 0.5 | 0.1 | 1 | 0.5 | 0.9 | 0.5 | 5 |
| 2019 | 0.6 | 0.1 | 1.2 | 0.5 | 0.9 | 0.4 | 5 |
| 2020 | 0.7 | 0.1 | 1.2 | 0.6 | 1.4 | 0.5 | 5 |
| 2021 | 0.6 | 0.1 | 1 | 0.5 | 1.1 | 0.5 | 5 |
The horizontal dashed lines represent the 2020 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standards are provided for illustrative purposes only and not for assessing the achievement status of the standards. For information on achievement status see the Alberta Air Zones report. Station classifications used in the figure: Community stations are located within a community; Near Industrial Facility stations are near an industrial facility and typically outside of population centres; Regional stations are typically located away from known sources.
Accessible chart description
Line chart showing the change over time in annual average SO2 concentrations in Alberta by station classification, as well as the provincial average and the 10th and 90th percentile of all SO2 monitoring stations in the province. Three station classifications are shown: Community, Near Industrial Facility, and Regional. All three station classification annual average concentrations have remained below 3 ppb since 2000. The chart also displays the 2020 Canadian Ambient Air Quality Standard for SO2 annual average (5 ppb) for comparison.
Figure 3b. Trends in peak SO2 concentrations over time by station classification
Chart data table
| Year | Provincial Average | 10th Percentile | 90th Percentile | Community | Near Industrial Facility | Regional | CAAQS |
|---|---|---|---|---|---|---|---|
| 2000 | 33.2 | 12.5 | 73.8 | 22.5 | 78.3 | 20.3 | 70 |
| 2001 | 37.8 | 8.6 | 90.8 | 29 | 85.8 | 11 | 70 |
| 2002 | 38.6 | 7 | 94 | 23.9 | 83.7 | 15.8 | 70 |
| 2003 | 50.3 | 11.8 | 119 | 27.3 | 109.6 | 27.3 | 70 |
| 2004 | 56.3 | 10.2 | 112.6 | 26.7 | 122.6 | 31.3 | 70 |
| 2005 | 50.8 | 8 | 100 | 25.2 | 114 | 33.4 | 70 |
| 2006 | 43.7 | 11.4 | 103 | 22 | 98.1 | 30.1 | 70 |
| 2007 | 36.7 | 8.7 | 81.3 | 20.4 | 82.4 | 24.7 | 70 |
| 2008 | 38.7 | 8.8 | 82.2 | 20.4 | 88.6 | 24.1 | 70 |
| 2009 | 30.6 | 5.6 | 68.7 | 18.3 | 66 | 21 | 70 |
| 2010 | 35.3 | 5.4 | 68.6 | 18 | 88 | 18.6 | 70 |
| 2011 | 32.4 | 5.2 | 61.6 | 18.5 | 77 | 17.4 | 70 |
| 2012 | 29.2 | 4.4 | 66.6 | 18.7 | 62.6 | 18 | 70 |
| 2013 | 29 | 4.5 | 59 | 18 | 60.6 | 17.8 | 70 |
| 2014 | 27.9 | 5.5 | 49 | 15.5 | 63.4 | 18.2 | 70 |
| 2015 | 26.4 | 4 | 42.8 | 13 | 61.5 | 21.4 | 70 |
| 2016 | 30 | 4.3 | 51.4 | 17 | 77.2 | 15.8 | 70 |
| 2017 | 27.5 | 4 | 59.5 | 16.6 | 67.4 | 18.4 | 70 |
| 2018 | 19.7 | 3.9 | 36.2 | 16.1 | 38.2 | 15.8 | 70 |
| 2019 | 19 | 4 | 38.4 | 16.1 | 34.6 | 13.5 | 70 |
| 2020 | 22.1 | 4 | 62.1 | 17.5 | 45.7 | 14.3 | 70 |
| 2021 | 21.1 | 3.2 | 39.6 | 16.2 | 42.8 | 13.6 | 70 |
The horizontal dashed lines represent the 2020 Canadian Ambient Air Quality Standards. The Canadian Ambient Air Quality Standards are provided for illustrative purposes only and not for assessing the achievement status of the standards. For information on achievement status see the Alberta Air Zones report. Station classifications used in the figure: Community stations are located within a community; Near Industrial Facility stations are near an industrial facility and typically outside of population centres; Regional stations are typically located away from known sources.
Accessible chart description
Line chart showing the change over time in peak SO2 concentrations in Alberta by station classification, as well as the provincial average and the 10th and 90th percentile of all SO2 monitoring stations in the province. Three station classifications are shown: Community, Near Industrial Facility, and Regional. The chart also displays the 2020 Canadian Ambient Air Quality Standard for SO2 1-hour (70 ppb) for comparison. The Community and Regional station averages have remained below 40 ppb since 2000. Near Industrial Facility stations have decreased from 78.3 ppb in 2000 to 42.8 ppb in 2021, with a peak in 2004 (with a peak value of 122.6 ppb).
- More recently, between 2012 and 2021, 7 out of 39 stations in the province saw increasing trends in SO2. Two of these 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. Three of these stations are located near Grande Prairie in the Upper Peace Region. The other 2 stations are regional monitoring stations in the North Saskatchewan Region and Upper Athabasca Region.
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.
- Figure 2a shows that between 2000 and 2021, annual average concentrations of SO2 were well below the annual AAAQO throughout the entire province. The annual AAAQO of 8.0 parts per billion (ppb) for SO2 is based on the protection of ecosystems.
- In 2021, there were 2 exceedances of the one-hour AAAQO at the Lower Camp station, which is located near an industrial facility in the Lower Athabasca Region. The one-hour AAAQO of 172 ppb for SO2 is based on the protection of human health.
- Historically, exceedances of the one-hour AAAQO 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
- 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, new since 2020).
- Annual reporting of Alberta’s air quality against the CAAQS is available in Alberta’s
Air Zone Reports.- In the first assessment of SO2 standards (2018-2020), 2 regions of the province (the North Saskatchewan Region and the Lower Athabasca Region) were at the Yellow Level – Actions for Preventing Air Quality Deterioration. The remaining regions of the province were at the Green Level – Actions for Keeping Clean Areas Clean. For details, see the Canadian Ambient Air Quality Standards under ‘Management plans’.
Figure 4. Upper range of hourly data for SO2 at select stations in the Lower Athabasca Region from 2016 to 2021.
Chart data table
| Year | Christina Lake | Lower Camp | Mannix | Mildred Lake | Level 2 | Level 3 | Level 4 |
|---|---|---|---|---|---|---|---|
| 2016 | 43 | 36 | 29 | 12 | 24 | 36 | |
| 2017 | 42 | 35 | 27 | 12 | 24 | 36 | |
| 2018 | 30 | 24 | 22 | 12 | 24 | 36 | |
| 2019 | 24 | 26 | 23 | 15 | 12 | 24 | 36 |
| 2020 | 35 | 32 | 39 | 33 | 12 | 24 | 36 |
| 2021 | 24 | 28 | 25 | 27 | 12 | 24 | 36 |
Results for 2021 are draft results. Official results will be those presented in the 2021 Status of Air Quality report.
Table description
Bar chart showing the upper range SO2 concentrations for Christina Lake, Lower Camp, Mannix, and Mildred Lake stations from 2016 to 2021. The Lower Athabasca Region Air Quality Management Framework triggers for Level 2, Level 3, and Level 4 are shown as horizontal lines.The Lower Camp station had the highest SO2 upper range concentrations in 2016 and 2017 (values of 43 ppb and 42 ppb, respectively) and exceeded the Level 4 trigger (36 ppb) in these years. SO2 levels at the Lower Camp station in subsequent years (2018 to 2021) were less than the Lever 4 trigger (with values ranging from 26 ppb to 32 ppb). The Mannix station exceeded the Level 4 trigger in 2020 (with an upper range concentration of 39 ppb) and was above the Level 3 trigger in 2016, 2017, and 2021. The Mildred Lake station had concentrations ranging from 15 ppb in 2019 to 33 ppb in 2020. The Christina Lake station had concentrations ranging from 24 ppb in 2019 and 2021 to 35 ppb in 2020.
Focused study
The Alberta government 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 2018-2020).
- 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.