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Size distribution and total number concentration of ultrafine and accumulation mode particles and hospital admissions in children and the elderly in Copenhagen, Denmark

¹ Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark
² Department of Environmental and Occupational Health, University of Copenhagen, Copenhagen, Denmark
³ Department of Atmospheric Environment, National Environmental Research Institute, Aarhus University, Århus, Denmark
⁴ Institute of Cancer Epidemiology, The Danish Cancer Society, Copenhagen, Denmark

Correspondence to:
Zorana J Andersen, Department of Biostatistics, Institute of Public Health, Copenhagen University, Øster Farimagsgade, 5 Entr. B, PO Box 2099, 1014 Copenhagen K, Denmark; zorana{at}cancer.dk

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.