The United States and Canada committed to addressing transboundary air pollution issues in the 1991 AQA, a bilateral executive agreement. The AQA established a framework for addressing shared concerns relating to transboundary air pollution, and, in the first annex to the agreement, set out objectives for each country to reduce emissions leading to acidic deposition. An additional annex to the Agreement addressed Scientific Cooperation and in 1997, the Parties signed a "Commitment to Develop a Joint Plan of Action for Addressing Transboundary Air Pollution" to jointly address the shared problems of ground-level ozone and PM. While science assessment activities were under way to better understand transboundary particulate matter issues, the Parties moved ahead in 2000 to establish an annex addressing ground-level ozone in the eastern border region.
Both Parties have made excellent progress in achieving reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx), the two major pollutants leading to acidic deposition. Since 2000, the Parties also have made good progress in reducing emissions of volatile organic compounds (VOCs) and further reducing emissions of NOx, to address ground-level ozone in the border region.
Joint scientific assessment work on the transboundary movement of particulate matter culminated in the December 2004 release of the Canada-United States Transboundary PM Science Assessment by the AQA subcommittee on Scientific Cooperation. The conclusions of the subcommittee were: (1) there is a significant relationship between the emissions of PM (and its precursors) and elevated levels of PM in both Canada and the United States; and (2) the transport of PM and PM precursors across the Canada-U.S. border can be significant. The U.S. has recently strengthened its national ambient air quality standards for fine particles and its regulations governing sources and emissions of PM and its precursors. Canada adopted standards for PM2.5 and ozone in 2000.
The Deputy Assistant Secretary for Environment heads the U.S. delegation, which also includes the Environmental Protection Agency, and serves as co-chair of the Air Quality Committee with the Assistant Deputy Minister of Environment Canada. The committee has been meeting annually since the AQA was signed over 15 years ago.