Ambient Levels of Sulphur Dioxide

Sulphur dioxide (SO2) is a gas emitted when a fuel or raw material containing sulphur is burned or used in industrial processes, such as metal ore smelting. The major sources of SO2 emissions in Canada are the combustion of fuel for electricity generation and heating, and processes in both the non-ferrous smelting and refining industry and the oil and gas industry. SO2 emissions contribute to acid deposition and are a major precursor to fine particulate matter (PM2.5). High concentrations of SO2 can adversely affect the respiratory systems of humans and animals, and can damage vegetation.

National ambient levels of sulphur dioxide

In 2011, the annual average concentration of sulphur dioxide (SO2) in outdoor air was 1.8 parts per billion (ppb) in Canada, 4% higher than in 2010. A declining trend was detected from 1997 to 2011, representing a concentration decrease of 66% over that period. The decrease observed for this indicator is mainly due to the reduction in SO2 emissions in Canada, resulting from efforts to curb acid rain and ambient particulate matter, and federal regulations on sulphur content in fuels.

Sulphur dioxide concentrations, Canada, 1997 to 2011

Sulphur dioxide concentrations, Canada, 1997 to 2011

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How this indicator was calculated

Note: The national SO2 indicator is based on the annual average of the daily concentrations recorded at 48 monitoring stations across Canada. Monitoring stations located close to major sources may have a great impact on the measured SO2 levels. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

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Regional ambient levels of sulphur dioxide

Atlantic Canada

In Atlantic Canada, the annual average concentration of sulphur dioxide (SO2) in the air in 2011 was 0.8 parts per billion (ppb), similar to the value in 2010. A declining trend was detected from 1997 to 2011, representing a decrease of 97% over that period. Emission reduction measures implemented at power plants in Atlantic Canada contributed substantially to this reduction of SO2 in the air.

Sulphur dioxide concentrations, Atlantic Canada, 1997 to 2011

Sulphur dioxide concentrations, Atlantic Canada, 1997 to 2011

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How this indicator was calculated

Note: For Atlantic Canada, the SO2 indicator is based on the annual average of the daily concentrations recorded at 3 monitoring stations. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

Southern Quebec

In southern Quebec, the annual average concentration of sulphur dioxide (SO2) in outdoor air for 2011 was 1.7 parts per billion (ppb), 14% lower than in 2010.Footnote[1] A declining trend was detected from 1997 to 2011, representing a decrease of 67% over that period. Emission reduction measures, implemented in southern Quebec at non-ferrous smelters and pulp and paper plants, contributed substantially to this reduction of SO2 in the air.

Sulphur dioxide concentrations, southern Quebec, 1997 to 2011

Sulphur dioxide concentrations, Southern Quebec, 1997 to 2011

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How this indicator was calculated

Note: For southern Quebec, the SO2 indicator is based on the annual average of the daily concentrations recorded at 13 monitoring stations. Major sources located close to monitoring stations may have a great impact on the measured SO2 levels. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level. Two monitoring stations in 1997 and 3 in 2010 and 2011 located close to industrial sources did not report concentrations for these years in the National Air Pollution Surveillance (NAPS) program, partially explaining the results in the chart.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

Southern Ontario

In southern Ontario, the annual average concentration of sulphur dioxide (SO2) in outdoor air for 2011 was 2.9 parts per billion (ppb), or 44% higher than in 2010. A declining trend was detected from 1997 to 2011, representing a decrease of 67% over that period. Emission reduction measures implemented for power plants and for the non-ferrous refining and smelting industry contributed substantially to this reduction of SO2 in the air.

Sulphur dioxide concentrations, southern Ontario, 1997 to 2011

Sulphur dioxide concentrations, Southern Ontario, 1997 to 2011

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How this indicator was calculated

Note:  For southern Ontario, the SO2 indicator is based on the annual average of the daily concentrations recorded at 11 monitoring stations. Major sources located close to monitoring stations may have a great impact on the measured SO2 levels. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

Prairies and northern Ontario

In the Prairies and northern Ontario, the annual average concentration of sulphur dioxide (SO2) in outdoor air for 2011 was 0.9 parts per billion (ppb), or 18% higher than in 2010. A declining trend was detected from 1997 to 2011, representing a decrease of 62% over that period. Emission reduction measures implemented at power plants and oil and gas facilities contributed substantially to this reduction of SO2 in the air.

Sulphur dioxide concentrations, Prairies and northern Ontario, 1997 to 2011

Sulphur dioxide concentrations, Prairies, 1997 to 2011

View data for these charts
How this indicator was calculated

Note: For the Prairies and northern Ontario, the SO2 indicator is based on the annual average of the daily concentrations recorded at 7 monitoring stations. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

British Columbia

In British Columbia, the annual average concentration of sulphur dioxide (SO2) in outdoor air for 2011 was 1.7 parts per billion (ppb), or 18% lower than in 2010. A declining trend was detected from 1997 to 2011, representing a decrease of 31% over that period.

Sulphur dioxide concentrations, British Columbia, 1997 to 2011

Sulphur dioxide concentrations, British Columbia, 1997 to 2011

View data for these charts
How this indicator was calculated

Note: For British Columbia, the SO2 indicator is based on the annual average of the daily concentrations recorded at 13 monitoring stations. A trend line is reported only when a statistically significant trend is detected at the 95% confidence level.
Source: Environment Canada (2013) National Air Pollution Surveillance (NAPS) program.

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Ambient levels of sulphur dioxide at monitoring stations

The National Air Pollution Surveillance (NAPS) program measures air pollutant concentrations at monitoring stations across Canada. The Canadian Environmental Sustainability Indicators (CESI) provide this information through an interactive indicator map. With the CESI interactive map, you can drill down to sulphur dioxide (SO2) concentrations at specific monitoring stations.

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Other information

Footnotes

Footnote 1

Part of this large drop is attributable to the absence of monitoring data in 2010 and 2011 from three stations that were located close to industrial areas.

Return to footnote 1 referrer