Estimated Short-Term Effects of Coarse Particles on Daily Mortality in Stockholm, Sweden

Background: Although serious health effects associated with particulate matter (PM) with aerodynamic diameter ≤ 10 μm (PM(10)) and ≤ 2.5 μm (PM(2.5); fine fraction) are documented in many studies, the effects of coarse PM (PM(2.5–10)) are still under debate. Objective: In this study, we estimated the effects of short-term exposure of PM(2.5–10) on daily mortality in Stockholm, Sweden. Method: We collected data on daily mortality for the years 2000 through 2008. Concentrations of PM(10), PM(2.5), ozone, and carbon monoxide were measured simultaneously in central Stockholm. We used additive Poisson regression models to examine the association between daily mortality and PM(2.5–10) on the day of death and the 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 PM(2.5–10) (single-pollutant model). The association with PM(2.5–10) was stronger for November through May, when road dust is most important (1.69% increase; 95% CI: 0.21%, 3.17%), compared with the rest of the year (1.31% increase; 95% CI: –2.08%, 4.70%), although the difference was not statistically significant. When adjusted for other pollutants, particularly PM(2.5), the effect estimates per 10 μg/m(3) for PM(2.5–10) decreased slightly but were still higher than corresponding effect estimates for PM(2.5). Conclusions: Our analysis shows an increase in daily mortality associated with elevated urban background levels of PM(2.5–10). Regulation of PM(2.5–10) should be considered, along with actions to specifically reduce PM(2.5–10) emissions, especially road dust suspension, in cities.