Air Pollution

Importance of Population Characteristics

Recent studies of urban air pollution illustrate the range of approaches currently in use: some studies are population-based while others focus on at-risk groups; some use pollution monitoring data while others model exposures; some use a case-control design while others follow a cohort. Whatever the approach, researchers recognize that population characteristics—including socioeconomic status, gender, age, and disease status—are often important considerations in the impact of air pollution on health. For instance, Brook and colleagues (2008) found gender differences in response to NO2 exposures among respiratory health clinic patients with diabetes mellitus in Toronto and Hamilton.1

When Clark and colleagues (2010) studied Vancouver subjects exposed in utero and as infants to local pollutants, especially those generated by traffic, they found that these exposures led to the development of asthma in children up to 4 years of age.2 When Smargiassi and colleagues (2009) used a time-series approach to study children in Montreal living close to a source of industrial sulfur emissions, they found emission spikes were associated with increased emergency room visits for asthma.3 Finally, a study by Ebelt and colleagues (2005) showed that even though patients with cardiopulmonary disease were exposed to a smaller proportion of outdoor particles than indoor particles (such as those generated by cooking and smoking), adverse health effects were associated primarily with outdoor particles.4

Lessons from Research in Canada’s “Big Three”

Studies undertaken in Canada’s “big three”—Toronto, Montreal, and Vancouver— show that the health effects of ambient air quality vary over short distances and that we have likely been underestimating exposure and health impacts with large-area models. This research also provides lessons for all communities in Canada. In each of these cities, exposure to air pollution from motor vehicles is a risk factor for heart disease, asthma, and lung cancer. There are exceptions to these findings, of course, owing to measurement problems and the diversity of groups observed for different periods and using different approaches. Nevertheless, the impact of exposure to pollutants seen in Toronto, Montreal, and Vancouver is not unique to these urban centres and shows that all communities should be concerned about air quality.