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

BACKGROUND

Exposure to fine particulate matter (PM) is associated with adverse health outcomes but communities are not randomly exposed to PM. Previous cross-sectional environmental injustice analyses in Canada found disproportionately higher exposure to PM in low-income populations, visible minorities and immigrants. Beyond static surveillance, it is also important to evaluate how changes in PM 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 from 2001 to 2016 in Canada.

METHODS

We derived census tract level estimates of average annual PM using validated satellite-based estimations of annual average PM concentration surfaces. We investigated how the spatial distribution of PM has evolved over 15 years (2001-2016) by comparing absolute values and rank percentiles of census tract level annual average PM 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, accounting for geographic boundary changes between census periods.

RESULTS

Overall, ambient PM concentrations decreased from 2001 (median of 9.1 μg/m) to 2016 (median of 6.4 μg/m), with varying provincial patterns. Across communities, ranked census tract specific PM 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, 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 from 2001 to 2016.

CONCLUSIONS

Identifying sociodemographic groups that benefit least from decreasing exposure to PM highlights the need to consider environmental injustice when designing or revising air pollution policies.