Relationships between nitrogen dioxide personal exposure and ambient air monitoring measurements among children in three French metropolitan areas: VESTA study

In epidemiological studies, investigators have routinely used ambient air c oncentrations, measured by air-quality monitoring networks, to assess expos ure of subjects. When there is great spatial variability of ambient air con centrations or when there are specific indoor exposures, this approach may yield substantial exposure misclassification and distort the associations b etween exposure and the health endpoints of interest. In 3 French metropoli tan areas, the cross-sectional relationships between 48 hr of nitrogen diox ide personal exposure of 73 children and the corresponding 48-hr background ambient air concentrations were analyzed. The crude correlation between am bient air concentrations and personal exposures was poor in all cities (r(2 ) -.009 for Grenoble, r(2) =.04 for Toulouse, and r(2) =.02 for Paris). The se correlations were improved when the authors took into account other ambi ent air or indoor air sources of nitrogen dioxide emissions (the correspond ing multiple linear regression, r(2), increased to .43 in Grenoble, .50 in Toulouse, and .37 in Paris). The main variables that explained personal exp osures were an index of traffic intensity and proximity and use of a gas co oker at home. The results of this study confirm that ambient air-monitoring site measurements are poor predictors of personal exposure. Investigators should carefully characterize the proximity of roads occupied by dense traf fic to the home/school as well as indoor sources of nitric oxide emissions; both of these careful characterizations will assist researchers in the pre diction of personal exposure in epidemiological studies.