Abstract

Objectives: Evidence on the health risks associated with exposure to ambient ultrafine particles is limited, although toxicological data indicate importance of this fraction of particulate matter. The objective was to study the association between short-term exposure to ultrafine particles and morbidity in Copenhagen, Denmark. Methods: We studied the association between urban background levels of the total number concentration of particles (NCtot, 6-700 nm in diameter) measured at a single site (15.05.2001 – 31.12.2004) and hospital admissions due to cardiovascular (CVD) and respiratory disease (RD) in the elderly (age ≥ 65 years), and asthma in children (age 5-18 years). We examined these associations in the presence of PM10, PM2.5 (particulate matter < 10 and 2.5 µm in diameter, respectively) and ambient gasses. We utilized data on the size distribution to assign NCtot to four modes with median diameters 12, 23, 57 and 212 nm, and calculated the NC100 (number concentration of particles < 100 nm in diameter), for examination of their associations with the health outcomes. We used a time-series Poisson generalized additive model adjusted for overdispersion, season, day of the week, public holidays, school holidays, influenza, pollen, and meteorology, with up to 5 days lagged exposure. Results and Conclusions: We found that adverse health effects of particulate matter on CVD and RD hospital admissions in the elderly were mainly mediated by PM10 and accumulation mode particles with lack of effects of NC100. For paediatric asthma, the results indicated relevance of accumulation mode particles as well as NC100 and nitrogen oxides, mainly from traffic related sources, whereas PM10 appeared to have little effect. Our results suggest the relevance of particle volume/mass from long-range transported air pollution for CVD and RD admissions in the elderly, and possibly of particles numbers from traffic sources for paediatric asthma.