Personal exposures of children to nitrogen dioxide relative to concentrations in outdoor air

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Abstract
OBJECTIVES To investigate the relation between fluctuations in personal exposure to nitrogen dioxide (NO2) in school children and changes in outdoor NO2 concentrations. METHODS 114 Asthmatic school children aged 7–12 years were recruited from the Southampton area. Weekly average personal exposures to NO2 were measured over a 13 month period with passive diffusion tubes. At the same time, outdoor NO2 concentrations were monitored at a fixed site in the centre of Southampton. Correlations between weekly personal exposures and mean outdoor concentrations during the same periods were examined. RESULTS Mean duration of follow up was 32 weeks. Measurements of weekly mean personal NO2 exposures were generally low and ranged from 0.7 to 496 μg/m3 with a geometric mean of 17 μg/m3. Substantial variation in personal exposures occurred between children and more especially within individual children from week to week. Daily outdoor concentrations of NO2 ranged from 4.3 to 29.8 μg/m3, with a geometric mean of 12.3 μg/m3. There was no evidence of seasonal variation in outdoor concentrations. No significant correlation was found between each child's weekly mean personal exposures to NO2 and mean outdoor concentrations for the corresponding periods. CONCLUSION At low outdoor NO2 concentrations, fluctuations in NO2in outdoor air as measured at a central monitoring station do not contribute importantly to variations in personal exposure when averaged over a week.