Abstract

Objectives: 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 (NC_tot, 6–700 nm in diameter) measured at a single site (15 May 2001 to 31 December 2004) and hospital admissions due to cardiovascular (CVD) and respiratory disease (RD) in the elderly (age ⩾65 years), and due to asthma in children (age 5–18 years). We examined these associations in the presence of PM₁₀, PM_2.5 (particulate matter <10 and 2.5 µm in diameter, respectively) and ambient gasses. We utilised data on size distribution to calculate NC_tot for four modes with median diameters 12, 23, 57 and 212 nm, and NC₁₀₀ (number concentration of particles <100 nm in diameter) and examined their associations with health outcomes. We used a time series Poisson generalised 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: The 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 for NC₁₀₀. For paediatric asthma, accumulation mode particles, NC₁₀₀ and nitrogen oxides (mainly from traffic related sources) were relevant, whereas PM₁₀ appeared to have little effect. Our results suggest that particle volume/mass from long-range transported air pollution is relevant for CVD and RD admissions in the elderly, and possibly particle numbers from traffic sources for paediatric asthma.