The Ontario Medical Association has expressed concern about ground-level ozone levels, which have increased steadily in Ontario for the past 20 years and which frequently occur at levels that are of concern for public health, especially for seniors, asthmatic children, and people of all ages who have problems with their respiratory and cardiovascular systems.
Numerous health effects studies have been conducted on air pollutants and, in particular, on smog pollutants (e.g., ground-level ozone and fine particles). These studies are showing adverse health effects at much lower levels than were previously thought to be a problem. As a result, the Canadian Council of Ministers of the Environment has set new standards for ozone and fine particles, and the Ontario Ministry of the Environment has recently revised its air quality index to reflect new knowledge on the health effects of fine particulate matter. While people are still being significantly harmed by today's pollution levels, they are increasingly aware of this alarming fact due to frequent air quality advisories and extensive media coverage, especially during the late spring/early summer smog season.13
It should also be noted that smog and other air pollution levels in Ontario are often much higher than they might otherwise be since the Midwestern States are generators of coal-fired electricity. During periods of widespread ground-level ozone pollution, it is estimated that more than 50% of Ontario's smog can be attributed to transboundary air pollution. Nevertheless, Ontario generates significant amounts of air pollution both for itself and for downstream jurisdictions in Canada and the U.S. To address transboundary air pollution concerns, in December 2000, the federal government signed the Ozone Annex to the Canada-U.S. Air Quality Agreement, agreeing to smog reduction targets for the electricity sector, transportation and other sectors in southern Ontario.