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Fact sheets

Acid Rain

While considerable progress has been made in reducing acid rain, many lakes and forests in eastern Canada are still being damaged, and new research has shown that acidic air pollution is also affecting human health.

Over the last 15 years, major progress has been made in reducing sulphur dioxide, one of the key pollutants which forms acid rain. Since 1980, eastern Canada has cut its emissions of sulphur dioxide by more than half. Reductions are also underway in the United States. Yet despite this progress, the latest scientific studies show that the recovery of natural ecosystems has been much slower than anticipated, and that our actions will still not be enough to protect our most vulnerable lakes and forests.

What is Acid Rain?

Two common air pollutants, sulphur dioxide and nitrogen oxides (NO_x), are the major cause of acid rain. The main sources of these pollutants are coal-fired power plants, nickel and copper smelters, and motor vehicles. Sulphur dioxide is produced from burning sulphur-containing coal and smelting sulphur-containing ore. While airborne, it reacts with water vapour to form sulphuric acid. Similarly, nitrogen oxides, released mainly during high-temperature fuel combustion, form nitric acid. These pollutants can stay in the air for days, sometimes travelling thousands of kilometres. When precipitation washes these acids out of the atmosphere, virtually anything they contact

• soil, water, plants and building materials can be affected.
• Airborne sulphur dioxide and nitrogen oxides can also be converted to fine particles, which can remain suspended in the atmosphere, forming a key component of smog.

Most acid rain falls in the eastern half of Canada, since the largest sources of acidic air pollutants are found in eastern North America, and the winds that carry these pollutants blow generally towards the east.

For Further Information:

Minister of Public Works and Government Services Canada, 1999.

The Green Lane^TM,
Environment Canada's World Wide Web Site.