Objectives for SO2

Last updated on January 20, 2026

Sulphur Dioxide (SO₂) is a reactive gas generated mainly from the combustion of sulphur-containing fuels, smelting of sulphur-containing metal ores, and other industrial facilities.

SO₂ is a main precursor to acid rain, an environmental problem with widespread effects such as:

acidifying lakes
destroying ecosystems
damaging infrastructure

Short term exposure to high concentrations of SO₂ can also aggravate respiratory conditions of sensitive individuals such as those with asthma and the elderly.

Refer to Health Canada’s publication on Human Health Risk Assessment for Sulphur Dioxide for more information.

In 2017, B.C. adopted interim air quality objectives for SO₂ to support the transition to the Canadian Ambient Air Quality Standards (CAAQS), which replaced the interim objectives at the end of 2019.

Canadian ambient air quality objectives for SO2
Metric or criteria	Level	Calculation method
1-hour	65 parts per billion	99th percentile of daily 1-hour maximum over three years
Annual	4 parts per billion	Average of 1-hour concentrations over one year

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Objectives for SO2