Transboundary air overview

Air pollution can be released at one location and travel long distances through the atmosphere with prevailing winds. In this way, air pollution can affect air quality locally as well as many miles away.

In all regions of Canada, air pollution from other jurisdictions and international sources can be important factors in addressing air pollution concerns.

Between Canada and United States

While Canada is a source of some pollution crossing into the United States, prevailing wind direction and large U.S. emissions mean that the U.S.can be a significant source of smog and acid rain in certain regions of Canada .

The Canada-United States Air Quality Agreement was signed by Canada and the United States in Ottawa, Ontario, on March 13, 1991, to address transboundary air pollution leading to acid rain. Both countries agreed to reduce emissions of sulphur dioxide (SO₂) and nitrogen oxides (NO_x), the primary precursors to acid rain and to work together on acid rain related scientific and technical cooperation.

The Ozone Annex was added to the Agreement (December 2000) to address the transboundary air pollution leading to high air quality levels of ground-level ozone, a major component of smog.

Efforts to address particulate matter (PM) levels in the air are important in both the United States and Canada. Canada and the United States have completed a joint transboundary particulate matter science assessment report in support of the Canada-U.S. Air Quality Agreement.

In January 2003, the Government of Canada, led by Environment Canada, began working with the Environmental Protection Agency of the United States to develop a Border Air Quality Strategy (news release) to identify appropriate border air quality pilot projects to address transboundary air pollution of concern and to continue on the path to reduce transborder air pollution.

When governments are developing regulatory proposals that will have important air quality results for Canadians, Environment Canada, working with its partners, may submit comments and advice to support the completion of the governmental action. Learn more about Environment Canada's key positions taken with respect to air quality-related initiatives within Canada and the United States.

Between Canada and International Sources

Air pollution from international sources, both on a regional and hemispheric scale, has an impact on Canada's domestic air quality.  For this reason, Canada and the United States participate in the Commission for Environmental Cooperation (CEC) North American Air Working Group and theUnited Nations Economic Commission for Europe where acid rain, smog and other transboundary air issues are a focus of concern.