OnlineOpen: This article is available free online at www.blackwell-synergy.com Clinical and Experimental Allergy

Objective To examine the association of air pollutants with hospital admission for childhood asthma in Hong Kong. Methods Data on hospital admissions for asthma, influenza and total hospital admissions in children aged418 years at all Hospital Authority hospitals during 1997–2002 were obtained. Data on daily mean concentrations of particles with aerodynamic diameter o 10mm (i. e. PM10) and o 2.5 mm (i. e. PM2.5), nitrogen dioxide (NO2), sulphur dioxide (SO2), and ozone (O3) and data on meteorological variables were associated with asthma hospital admissions using Poisson’s regression with generalized additive models for correction of yearly trend, temperature, humidity, day-of-week effect, holiday, influenza admissions and total hospital admission. The possibility of a lag effect of each pollutant and the interaction of different pollutants were also examined. Results The association between asthma admission with change of NO2, PM10, PM2.5 and O3 levels remained significant after adjustment for multi-pollutants effect and confounding variables, with increase in asthma admission rate of 5.64 % (3.21–8.14) at lag 3 for NO2, 3.67% (1.52–5.86) at lag 4 for PM10, 3.24 % (0.93–5.60) at lag 4 for PM2.5 and 2.63 % (0.64–4.67) at lag 2 for O3. Effect of SO2 was lost after adjustment. Conclusion Ambient levels of PM10, PM2.5, NO2 and O3 are associated with childhood asthma hospital admission in Hong Kong