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BACKGROUND: Whereas serious health effects associated with particles with an aerodynamic diameter ≤ 10 µm (PM10) and ≤ 2.5 µm (fine fraction; PM2.5) are documented in many studies, the effects of coarse particles with aerodynamic diameter between 2.5 and 10 µm (PM2.5-10) are still under debate. In this study we estimate the effects of short-term exposure of coarse particles on daily mortality in Stockholm.

METHOD: We collected data on daily mortality for the years 2000-2008. Concentrations of PM10, PM2.5, O3 and CO were measured simultaneously in central Stockholm. We used additive Poisson regression models to examine the association between daily mortality and the coarse fraction at day of death and day before. Effect estimates were adjusted for other pollutants (two-pollutant models) during different seasons.

RESULTS: We estimated a 1.68% increase [95% confidence interval (CI) 0.20, 3.15%] in daily mortality per 10 µg m-3 increase in PM2.5-10 (single-pollutant model). The association with PM2.5-10 was stronger for November - May when road dust is most important (1.69% increase, CI 0.21, 3.17%) compared to the rest of the year (1.31% increase, CI -2.08, 4.70%), although the difference was not statistically significant. When adjusted for other pollutants, particularly PM2.5, the effect estimates per 10 µg m-3 for coarse particles decreased slightly, but were still higher than corresponding effect estimates for PM2.5.

CONCLUSIONS: Our analysis shows an increase in daily mortality associated with elevated urban background levels of coarse particles. Regulation of the coarse particle fraction should be considered, along with actions to specifically reduce coarse particle emissions, especially road dust suspension, in cities.