Inequities in ambient fine particulate matter: A spatiotemporal analysis in Canadian communities.

Background: Exposure to fine particulate matter (PM _2.5 ) is associated with adverse health outcomes but communities are not randomly exposed to PM _2.5 . Previous cross-sectional environmental injustice analyses in Canada found disproportionately higher exposure to PM _2.5 in low-income populations, visible minorities and immigrants. Beyond static surveillance, it is also important to evaluate how changes in PM _2.5 exposure over time may differentially impact disadvantaged communities. We examine whether communities with different sociodemographic characteristics benefited equitably from the overall decreases in ambient concentrations of PM _2.5 from 2001 to 2016 in Canada.
Methods: We derived census tract level estimates of average annual PM _2.5 using validated satellite-based estimations of annual average PM _2.5 concentration surfaces. We investigated how the spatial distribution of PM _2.5 has evolved over 15 years (2001-2016) by comparing absolute values and rank percentiles of census tract level annual average PM _2.5 concentrations in 2001 and 2016. Using decennial census data and multivariable linear regression, we determined if sociodemographic characteristics are associated with changes in exposure to PM _2.5 , accounting for geographic boundary changes between census periods.
Results: Overall, ambient PM _2.5 concentrations decreased from 2001 (median of 9.1 μg/m ³ ) to 2016 (median of 6.4 μg/m ³ ), with varying provincial patterns. Across communities, ranked census tract specific PM _2.5 in 2001 and in 2016 are highly correlated (Spearman's rho = 0.75). We found that, on average and accounting for provincial differences and baseline PM _2.5 , communities with greater density of aboriginal population, lower education, higher shelter-cost-to-income ratio, unemployment or lower income experienced smaller absolute decreases in PM _2.5 from 2001 to 2016.
Conclusions: Identifying sociodemographic groups that benefit least from decreasing exposure to PM _2.5 highlights the need to consider environmental injustice when designing or revising air pollution policies.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Hong Chen reports financial support was provided by Government of Canada.
(Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)