Disparities in fine particulate matter (PM_2.5) monitoring capacity in eastern Canada

Standards for air pollution are becoming more stringent. Canada will update the annual average fine particulate matter (PM_2.5) standard to 8 µg m^-3 in 2030, which questions the adequacy of existing PM_2.5 monitoring capacity for evaluating potential exceedances and exposure risk at community level. Although PM_2.5 monitoring has expanded beyond regulatory monitors to include low-cost sensors, concerns remain regarding inequalities in its effective coverage and thus data representativeness for exposure estimations. Understanding the connections between PM_2.5 monitor density, surface exposure, and neighbourhood socio-economic deprivation and health vulnerability is important for addressing compounded inequities. In this study, we applied locally adaptive kernel density estimation to calculate total PM_2.5 monitor density from 2020 to 2024 in Ontario, Quebec, and Atlantic Canada. Local bandwidths were defined for each monitored location by considering the surrounding variability of surface PM_2.5 concentrations and its sensitivity to distinguish exceedances. Suburban communities of Montreal, Toronto, near-border regions of Windsor and Niagara, southeast Kitchener, and remote communities in northwest Ontario had observed multiple disparities, with more pronounced socio-economic marginalization, higher surface exposure, but inadequate monitoring. Based on mixed-effects logistic regression, residential instability and situationally vulnerable populations had 25% and 54% higher odds of being deprived in PM_2.5 monitoring capacity, respectively, after controlling for surface PM_2.5 and emission facility density. Assessments of random-effects also suggested the importance of locally adapted strategies to account for provincial and inter-municipality variations in monitoring disparities among socio-economically marginalized groups and populations with physical or psychological disabilities. Overall, our findings inform vulnerable communities in need of monitoring expansion for precise air quality control and health risk assessments in light of the new standard.