Acid rain history

Scientific evidence of the acidification of aquatic systems in Scandinavia and North America mounted throughout the 1960's and 1970's. Between 1972 and 1977, evidence linked acidification to the long-range transport of sulphur dioxide from sources in other countries - for Scandinavia, nations of continental Europe, and for Canada, the United States; within Canada there was also long-range transport between provinces. Parts of the Canadian Shield in Eastern Canada were identified as being particularly sensitive to acidification.

In the late 1970's, domestic negotiations among the provinces and the federal government were initiated, resulting in a series of domestic agreements over the years that followed, beginning with a declaration signed by the federal government and the seven eastern most provinces in 1985 establishing the Eastern Canada Acid Rain Program. The goal of this program was to limit the deposition of sulphates in precipitation to no more than 20 kg per hectare per year.  The provinces agreed to cap SO₂ emissions at 2.3 million tonnes to be achieved throughout eastern Canada by 1994 based upon calculations from a science assessment that determined how many tonnes of SO₂ could be emitted in Canada in order to achieve the 20 kg/ha/yr “target load”,  provided commensurate SO₂ reductions occurred in the U.S.

The federal government was responsible for reducing the flow of acid pollutants into Canada because half of the acid deposition in eastern Canada came from American sources.  To address this issue, Canada and the US began negotiations on establishing a bilateral agreement.  On March 31, 1991, the two countries signed the Canada-US Air Quality Agreement to deal with transboundary air pollution problems. The Acid Rain Annex committed both countries to scheduled reductions of SO₂ and NO_x emissions, particularly from the electric power generation sector.

In 1994, Canada and the provinces began working with stakeholders to develop a new national acid rain strategy since the 20 kg/ha/yr deposition target under the Eastern Canada Acid Rain Program was sufficient only to protect moderately sensitive lakes.  This resulted in The Canada-Wide Acid Rain Strategy for Post-2000,signed in 1998 by all 26 federal, provincial and territorial Ministers of Energy and Environment. The Strategy serves as a framework for addressing the country’s acid rain problem, thus protecting our lakes and forests and helping protect human health by reducing PM precursor emissions. The second phase of SO₂ reductions is intended to help bring wet sulphate deposition throughout eastern Canada to below “critical load” levels, which for some areas is as low as 8 kg/ha/yr.

During this period Canada also began entering into multi-lateral negotiations with member nations of the United Nations Economic Commission for Europe (UNECE) to address long-range transport of acid rain-causing pollutants. These negotiations resulted in a series of international agreements over the years that followed, beginning with the 1979 UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP).