The combustion of fossil fuels generates a complex mixture of gases, particles and chemicals, many of which have the potential to impair human health.¹ In older adults, epidemiological studies have consistently shown increased cardiovascular mortality associated with increased levels of air pollution.² There is also concern, acknowledged by regulatory authorities, that very young children represent another vulnerable population. Many of the factors that could increase the vulnerability of young children to air pollution remain speculative. One known variable is that infants have a higher minute ventilation relative to lung surface area.³ Thus for the same pollutant concentration, infants’ airways will receive a higher exposure than adults. However, paediatric mortality associated with air pollution has not, until recently, been regarded as a major issue. The paper by Klonoff-Cohen and colleagues⁴ in this issue is therefore of particular interest. In …