• air pollution
• asthma exacerbations
• emergency department visits
• intervention

Outdoor air pollution is a major risk factor for both acute and chronic respiratory illness and mortality. Short-term exposure (from a few hours to several days) to elevated levels of air pollution has been associated with a range of adverse health effects on lung function. There is increasing epidemiological evidence of the association between air pollution and asthma exacerbations in children,1 with some studies also suggesting a contribution to new onset of asthma. Air pollution, however, is a complex mixture of particles and gases emitted from a wide range of sources or generated in the atmosphere through reactions of chemical species. It is difficult to disentangle the effect of specific pollutants on health using common epidemiological methods, particularly in cases where these pollutants, for example, combustion-related particles and nitrogen dioxide, correlate strongly.

From a mechanistic point of view, fine particles <2.5 µm in diameter (PM_2.5) can penetrate deep into the airways and induce alveolar inflammation. In addition to PM_2.5, gaseous air pollutants such as nitrogen dioxide (NO₂) and ozone (O₃) can cause oxidative injury to the airways, leading to inflammation and remodelling.2 Young children with asthma are particularly susceptible to air pollution because of their developing lungs, immature metabolic pathways, high breathing rates per bodyweight and amount of time spent exercising outdoors.1

In a large longitudinal study presented in this journal, Bouazza et al 3 examined paediatric visits for asthma exacerbation to emergency departments (EDs) in …