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Ground-level ozone

Ground-level O3 is a common, pervasive and harmful air pollutant (see box). Fossil fuel combustion is the major source of NOx, with the transportation sector alone responsible for 60 per cent of NOx emissions in Canada (Hancey 1999) and 53 per cent in the United States (US EPA 2000b).

Ground-level ozone in North America

Research over the past decade has demonstrated that O3 is responsible for far greater impacts on health than was previously thought. Even average concentrations of O3 can exacerbate asthma and other respiratory diseases, and inhibit or interfere with the immune system, especially in young children, the elderly and outdoor sports enthusiasts (OMA 2000). Research in both Canada and the United States repeatedly documents a strong correlation between hospitalization and worker absenteeism, and episodic high O3 levels (CEC 1997).

Between 1984 and 1991, Canada's ozone guideline of 0.082 ppm over a one-hour period was exceeded at least once in all major cities (EC 2000a). In the United States, tens of millions of people lived in areas where the one-hour ozone standard of 0.120 ppm was regularly exceeded (US EPA 2000b). Control measures in the 1970s focused primarily on reducing VOCs and, in some cases, NOx emissions from factories and vehicles in the regions that were most affected. In many cases, however, controls failed to reduce ozone concentrations sufficiently to meet national health standards (US EPA 1997a).

Ozone molecules have been found to travel large distances from emission sources - the typical transport range of tropospheric O3 is 240-800 kilometres (CEC 1997). Between 30 and 90 per cent of eastern Canada's O3 comes from the United States, while the province of Ontario, the region in Canada that suffers from the worst O3 problem, is a source of NOx downwind into northeastern United States (EC 2000a).

Impact of air pollution on health in North America

Air pollution is emerging as a key contributor to some respiratory and cardiovascular diseases. Around 80 million US citizens are exposed to levels of air pollution that can impair health and more than 2 per cent of all deaths annually can be attributed to air pollution (UNDP, UNEP, World Bank and WRI 1998). Air pollution is also linked to an alarming rise over the past two decades in the prevalence of asthma among children and young adults. More than 5.5 million children in North America are affected by asthma. The impact of environmental pollution on children's health is a priority issue in North America.

Fossil fuel power plants are the largest point sources of NOx - significant amounts of O3 are formed and transported within the plumes of power plants. In addition, while VOCs have decreased in the United States over the past 30 years, NOx emissions increased between 1970 and 1999 by 17 per cent (US EPA 2000b). These findings led to a new approach in which North America recognized the need for aggressive strategies to reduce regional NOx emissions and for cooperation between the two countries.

Under the Canada/US Air Quality Agreement (1991), both countries set targets to reduce NOx emissions and in October 2000 they signed an annex to the agreement to reduce border emissions of NOx from fossil fuel power (EC 2000b). They have also engaged in the 1995 North American Research Strategy for Tropospheric Ozone and signed the 1999 CLRTAP Protocol to Abate Acidification, Eutrophication and Ground-Level Ozone.

Recognition that exposure to ozone at concentrations below 0.08 ppm results in severe health effects has prompted revisions in both Canadian and US ozone health standards (EC 2000a, US EPA 1997b). Although levels of SPM have decreased by 40 per cent since 1980, recent research has revealed serious health concerns at concentrations well within allowed levels attributable to the finer airborne particles released mainly from vehicles and power plants. Consequently, North American standards for particulate matter have been adjusted (EC 1999, EC 2000a, OMA 2000).