Canada-United States Air Quality Agreement: overview

The Canada-United States Air Quality Agreement was signed by Canada and the United States in 1991, to address transboundary air pollution leading to acid rain. Both countries agreed to reduce emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx), 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 Canada-United States Air Quality Agreement (December 2000) to address the transboundary air pollution leading to high air quality levels of ground-level ozone, a major component of smog. The long-term goal of the Ozone Annex is the attainment of the ozone air quality standards in both countries. Where there are transboundary flows of the pollution that creates ozone, the Ozone Annex commits both countries to reduce their emissions of nitrogen oxides and volatile organic compounds, the precursor pollutants to ground-level ozone.

Canada-United States Air Quality Agreement Progress Reports

Introduction

In 1991, Canada and the United States established the air quality agreement to address transboundary air pollution. The Agreement initially focused on reducing levels of acid deposition, or acid rain, in each country. In 2000, the Agreement was updated to include ground-level ozone. A bilateral Air Quality Committee issues a progress report every two years, highlighting the progress on the commitments included in the Agreement and describing the continued efforts by both countries to address transboundary air pollution. The 2018 Progress Report is the 14th biennial report completed under the Agreement.

Report Highlights

Both Canada and the United States have made significant progress in reducing emissions of pollutants that cause acid rain and ground-level ozone since 1991.

  • As of 2017, emissions of sulphur dioxide in Canada and the U.S. decreased by 69% and 88%, respectively, from 1990 emission levels; and,
  • Between 2000 and 2017, emissions of nitrogen dioxide in Canada and the U.S. decreased by 59% and 61%, respectively, in the transboundary ozone area (central and southern Ontario, southern Quebec, 18 U.S. states and the U.S. District of Columbia) covered by the Agreement.
  • Both countries continue to monitor acid deposition and ambient levels of ground-level ozone.
  • Between 1990 and 2017, significant reductions have occurred in the deposition of wet sulphate and wet nitrate (the primary indicators of acid deposition) in eastern Canada and the eastern United States; and
  • Annual ozone levels in the Canada- United States border region decreased between 1995 and 2017. Regulations and non-regulatory programs designed to meet emission reduction commitments in the Ozone Annex, as well as programs designed to meet program goals for Canada and the United States individually, have contributed to the reduction in ozone concentrations.

Conclusion

Canada and the United States continue to meet their commitments set forth in the 1991 Agreement

Despite the results achieved under the Agreement, the covered pollutants (sulphur dioxide, nitrogen oxides, and volatile organic compounds) remain a concern and continue to have significant impacts on human health and the environment in both countries. Continued bilateral efforts are needed to reduce the transboundary impact of these pollutants and to ensure that transboundary air pollution does not affect each country’s ability to attain and maintain its national ambient air quality standards for pollutants such as ozone and fine particulate matter (PM2.5), and protect the health and environment of its citizens.

The Agreement provides a proven and successful way for addressing transboundary air pollution that affects tens-of-millions of people. Canada and the United States continue to cooperate to address ongoing, emerging and future air quality issues

Canada-United States Air Quality Agreement and Ozone Annex

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