What is the issue?

Just over 45% of Canada's total surface area is highly sensitive to acid rain. Much of this area is in eastern Canada, where the Canadian Shield's thin, coarsely textured soil and granite-type bedrock have little ability to neutralize acidic pollutants. This region continues to receive acid rain at levels above the tolerance level for the environment. About half of the acid deposition in eastern Canada comes from sources in the United States.

The effects of acid rain are severalfold:

• High levels of acid rain can result in the acidification of lakes, rivers, and streams and can cause metals to leach from surrounding soils into the water system. Both acidification and metal leaching can seriously impair the ability of water bodies to support aquatic life.
• Prolonged exposure to acid deposition causes forest soils to lose valuable nutrients, contributing to declining growth rates in trees. Until recently, it was believed that the supply of nutrients would be replenished through natural processes. It is now evident that, at least in the short term, this does not happen.
• Acid rain has been linked to increased rates of deterioration of structures containing cement, limestone, or sandstone.
• Recent research indicates a relationship between decreased lung function or increased cardiorespiratory mortality and long-term exposure to acid rain-causing pollutants.

What do we know?

While considerable progress has been made in reducing acid rain, many areas in Canada are still being damaged. Since 1980, eastern Canada has reduced its emissions of sulphur dioxide by more than half, and emissions across the country declined by 42% over the same period. There has been minimal progress in reducing nitrogen oxide emissions in both Canada and the United States, however, and Canadian emissions of nitrogen oxides have remained relatively unchanged since 1980.

•  Download Sulphur dioxide (SO2) emissions in Canada, 1980-98 (MS-Excel)
• Sulphur dioxide (SO2) emissions in Canada, 1980-98 (HTML)

In areas where acid deposition has decreased in large amounts, such as the greater Sudbury region of Ontario, there have been striking ecological improvements. However, reductions in lake acidity in other regions of Ontario, Quebec, and Atlantic Canada have been modest, and some surface waters are continuing to acidify.

Even after commitments laid out in the Canada–U.S. Air Quality Agreement are fully met in 2010, large areas in eastern Canada, encompassing tens of thousands of lakes, will continue to receive acid deposition above critical load limits. To meet critical load limits in all of eastern Canada, sulphur dioxide emissions will need to be reduced by up to 75% in key emitting areas of both Canada and the United States.

Although sulphate deposition has been decreasing, more progress needs to be made in reducing nitrogen oxide emissions and nitrate deposition. Otherwise, the contribution of nitrate deposition to acidification will eventually erode the benefits gained from reductions in sulphur dioxide emissions and sulphate deposition.

What additional information do we need?

Continued monitoring will bring a better understanding of the effects of acid deposition on sensitive lakes, rivers, streams, and forests, and on the fish, wildlife, and other organisms that they support. At the same time, more information is needed on the effects of high acidity levels and the elevated levels of metals that result, particularly their effects on the ability of ecosystems to support life and be economically productive. Part of this knowledge is needed to establish critical load limits for nitrate deposition in sensitive ecosystems.

Further research and monitoring will help to clarify the links between human health and exposure to particulate matter, particularly sulphate and acidic aerosols.

•  Download Area in eastern Canada receiving wet sulphate deposition above critical load limits, 1980-96 (MS-Excel)  
• Area in eastern Canada receiving wet sulphate deposition above critical load limits, 1980-96( HTML)

What are we doing based on the information we have?

Progress on the acid rain issue has been largely due to several key agreements, including the Eastern Canada Acid Rain Program (1985) and the Canada–U.S. Air Quality Agreement (1991). Canada is committed to a permanent national limit on sulphur dioxide emissions of 3.2 million tonnes per year and a 10% reduction in projected nitrogen oxide emissions from stationary sources by 2000.

The Canada-wide Acid Rain Strategy for Post-2000 was signed by the Canadian Ministers of Energy and Environment in October 1998. It provides a framework for further actions, such as establishing new sulphur dioxide emission reduction targets in Ontario, Quebec, New Brunswick, and Nova Scotia; pursuing further emission reduction commitments from the United States; minimizing increases in emissions in areas where acid deposition is still below levels that cause harm; and ensuring the adequacy of acid rain monitoring.

Further information

For more information on the acid rain issue, check the following*:

• Annual Progress Report (2000) on the Canada-wide Acid Rain Strategy for Post-2000:
  www.ccme.ca/assets/pdf/acid_rain_e.pdf
• Canada-wide Acid Rain Strategy for Post-2000:
  www.ec.gc.ca/www.ec.gc.ca/acidrain/strat-e.pdf
• Environmental Indicator Bulletin on Acid Rain:
  www.ec.gc.ca/ind/English/AcidRain/default.cfm
• Environment Canada's acid rain web site:
  www.ec.gc.ca/acidrain/index.html

*Note: Information found on some sites is presented only in the language in which it was written. We apologize for any inconvenience.