Long-term exposure to particulate matter from road traffic and residential heating and mortality: a multi-cohort study in Sweden

Abstract Exposure to particulate air pollution increases total natural and cardiovascular mortality. However, it is less clear which types and sources of particles are the most harmful. We analyzed associations between long-term exposure to source-specific locally emitted particles and total natural and cardiovascular mortality in Swedish cohorts. Using high-resolution dispersion models of particles from different sources, and address registries, we assigned annual individual residential mean concentrations to population-based cohorts in Gothenburg, Stockholm and Umeå 1990–2011. Time and cause of death were assigned from registries. Associations between long-term mean lagged exposures and mortality were estimated using Cox regression models adjusted for possible confounders, and meta-analyzed. 7344 natural deaths, including 2755 cardiovascular deaths, occurred among the 68,679 participants. Exposure levels were moderate but generally above the WHO 2021 guidelines. We observed positive associations with natural mortality for the last five years of exposure to road traffic exhaust particles (HR 1.02, 95% CI 1.00-1.04, per IQR, and 1.10, 95% CI 1.00-1.22, per 1 µg/m 3 ), and road wear particles (HR 1.02, 95% CI 1.00-1.04, per IQR, and HR 1.02, 95% CI 1.00-1.03, per 1 µg/m 3 ), but not for particles from residential heating. Adjustment for road traffic noise, or particles from residential heating, did not substantially affect the results for traffic-related particles. For cardiovascular mortality, associations with particles from both sources were positive but not statistically significant. Natural mortality was associated with local emissions of traffic-related particles in a multi-cohort study at moderate exposure-levels, lending some support for further efforts to reduce traffic emissions.