Key Points

• Deadly smog events in the 20th century led to important insights and research into
   the toxicity of outdoor air pollutants.

• One-third of Canadians live in Toronto, Montreal, and Vancouver—urban centres
   where they are regularly exposed to air pollutants from traffic-related emissions
   that can cause adverse health effects.

• Traffic-related air pollutants vary in kind and quantity over time and from one
   neighbourhood to another, but usually include nitrogen dioxide (NO2), sulfur dioxide
   (SO2), and particulate matter (PM).

• Particulate matter less than 2.5 microns in diameter (PM2.5) is small enough to reach
   the lungs and is strongly associated with adverse health effects.

• Exposure to all traffic-related pollutants is most commonly, although not exclusively,
   associated with respiratory disease and cardiovascular disease.

Research in Canada’s “big three” urban centres suggests that we are underestimating the health impacts of exposures with large-area model studies of outdoor air quality.