Air

Sulphur dioxide

Sulphur dioxide is produced by the combustion of fuels containing sulphur (coal, natural gas and gasoline).

The main environmental concern is acid rain when sulphur dioxide reacts with water vapor in the atmosphere to form sulphuric acid. A colorless gas emitted from smoke stacks, chimneys and exhaust pipes, sulphur dioxide can travel hundreds of kilometres before falling to the earth as rain, drizzle, snow or dry particles (this fallout is also known as “acid precipitation” or “acid deposition”).

Acid rain can:

• acidify soils, lakes, rivers and streams, damaging aquatic life
• harm trees and crops
• cause building structures to deteriorate

Nearly half of Canada’s surface area is sensitive to acid rain. In Eastern Canada, where acid rain is more common, researchers estimate that about 150,000 of 700,000 lakes have been damaged by acid rain. In Western Canada, there is less acidic fallout and the alkaline soils are better able to neutralize acid deposition.

Within its own borders, Canada has made significant progress in reducing sulphur dioxide emissions. Since 1980, national emissions decreased by about 45 per cent. But scientists and government experts say that large areas of Eastern Canada still receive high levels of acid deposition and that reductions of up to 75 per cent in key emitting areas are needed to address this problem.

About half of the acid rain and smog-producing emissions affecting Eastern Canada come from sources in the United Sates. Further action against sulphur dioxide emissions will depend on the cooperation of the United States.