LAUSR

RATIONALE Exposure to ambient air pollution has been associated with adverse effects on morbidity and mortality. However, the evidence for ultrafine particles (UFP; 10-100nm) based on epidemiological studies remains scarce and inconsistent. OBJECTIVES We examined associations between short-term exposures to UFP and total particle number concentrations (PNC; 10-800nm) and cause-specific mortality in the three German cities Dresden, Leipzig, and Augsburg. METHODS We obtained daily counts of natural, cardiovascular, and respiratory mortality between 2010 and 2017. UFP and PNC were measured at six sites and fine particulate matter (PM2.5) and nitrogen dioxide (NO2) were collected from routine monitoring. We applied station-specific confounder-adjusted Poisson regression models. We investigated air pollutant effects at aggregated lags (0-1, 2-4, 5-7, and 0-7) and used a novel multilevel meta-analytical method to pool the results. Additionally, we assessed interdependencies between pollutants using two-pollutant models. MEASUREMENTS AND MAIN RESULTS For respiratory mortality, we found a delayed increase in relative risk of 4.46% [95% confidence interval: 1.52%, 7.48%] per 3,223 particles/cm3 increment 5 to 7 days after UFP exposure. Effects for PNC showed smaller but comparable estimates consistent with the observation that the smallest UFP fractions showed the largest effects. No clear associations were found for cardiovascular or natural mortality. UFP effects were independent of PM2.5 in two-pollutant models. CONCLUSIONS We found delayed effects for respiratory mortality within a week after exposure to UFP and PNC but no associations for natural or cardiovascular mortality. This finding adds to the evidence on independent health effects of UFP.