The third phase of the International Study of Asthma and Allergies in Childhood (ISAAC) was carried out in 13- to 14-year-old and 6- to 7-year-old children across the world. A question about frequency of truck traffic on the street of residence was included in an additional questionnaire.

The great smog disasters of the past have made clear that air pollution can kill people in a matter of days: extremely high concentrations of air pollution building up under conditions of low wind speed and stable atmospheric conditions have been associated with excess deaths in the Meuse Valley, Belgium (1930); Donora, PA, United States (1948); and London, United Kingdom (1952).