Personal exposure of children to nitrogen dioxide

We read with interest a recently published study on personal exposure of asthmatic children to nitrogen dioxide (NO2), relative to concentrations in outdoor air.1 In their results, the authors did not find: “ . . .significant correlation . . . between each child's weekly mean personal exposures and mean outdoor concentrations for the corresponding periods”; “ . . .marked evidence of seasonality” on personal exposure . They concluded: “ . . .at low concentrations, changes in NO2 in outdoor air . . .contribute little to variations …