Short-term effects of ambient air pollution on asthma hospitalization in children: Case-crossover and time series analyses.

Case-crossover and time series analyses were used to assess associations between ambient air pollutants and asthma hospitalization among children 6--12 years of age living in Toronto between 1981 and 1993. Exposures averaged over periods varying from one to seven days were used. The results from bi-directional case-crossover and time series analyses were similar. Coarse particulate matter (PM10--2.5) was significantly associated with asthma hospitalization in both males and females. The data showed no significant effects of fine (PM2.5) and thoracic (PM10) particulate matter on asthma hospitalizations. Gaseous pollutants, including carbon dioxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2) were significantly related to asthma hospitalization in males or females or both sexes, but ozone (O3) was not. These studies provide strong evidence for asthma hospitalization in children in relation to relatively low levels of ambient air pollution, and suggest that reducing current ambient levels of air pollution will have important population health benefits