Variability in ambient ozone and fine particle concentrations and population susceptibility among Canadian health regions.

Objectives: To estimate the proportion of the Canadian population that is more susceptible to adverse effects of ozone (O) and fine particle (PM) air pollution exposure and how this varies by health region alongside ambient concentrations of O and PM.

Methods: Using data from the census, the Canadian Community Health Survey, vital statistics and published literature, we generated cross-sectional estimates for 2014 of the proportions of the Canadian population considered more susceptible due to age, chronic disease, pregnancy, outdoor work, socio-economic status, and diet. We also estimated 2010-2012 average concentrations of O and PM. Analyses were conducted nationally and for 110 health regions.

Results: Restrictive criteria (age < 10 or ≥ 75; asthma, chronic obstructive pulmonary disease, heart disease, or diabetes; pregnancy) suggested that approximately one third of the Canadian population is more susceptible, while inclusive criteria (restrictive plus age 10-19 and 65-74, outdoor work, less than high school education, low vitamin C intake) increased this proportion to approximately two thirds. Across health regions, estimates ranged from 24.4% to 41.2% (restrictive) and 61.2% to 87.0% (inclusive). Ten health regions were in the highest quartile of both population susceptibility and O or PM concentrations, all of which were outside major urban centres.

Conclusions: A substantial proportion of the Canadian population exhibits at least one risk factor that increases their susceptibility to adverse effects of O and PM exposure. Both risk communication and management interventions need to be increasingly targeted to regions outside large urban centres in the highest quartiles of both susceptibility and exposure.