Assessment of exposure to traffic related air pollution of children attending schools near motorways

To assess exposure to air pollution from traffic of children attending schools near motorways, traffic related air pollution (PM2.5, NO2 and benzene) was measured in and outside 24 schools located within 400 m of motorways in the Netherlands. Reflectance of PM2.5 filters was measured as a proxy for elemental carbon (EC). The relationship between this proxy and measurements of EC was studied in a sub-sample and a high correlation was established. In both indoor and outdoor air, concentrations of PM2.5 and "soot" significantly increased with increasing truck traffic density and significantly decreased with increasing distance. Indoor NO2 concentrations significantly increased with increasing car traffic. The percentage of time that the school was downwind of the motorway during the measurements was significantly associated with "soot" and NO2, but not with PM2.5 and benzene. Estimated yearly averaged concentrations, calculated after standardising for differences in the background concentrations during the measurements, showed an about 2.5 fold range in "soot", benzene (indoors and outdoors) and NO2 (indoors) concentrations. For PM2.5 (indoors and outdoors) and NO2 outdoors the range was smaller (1.4-1.7). Standardised concentrations were highly correlated with the results of two other approaches that were used to order the exposures at the schools. This study has shown that concentrations of air pollutants in and outside schools near motorways are significantly associated with distance, traffic density and composition, and percentage of time downwind. These variables can therefore be used to assess exposure to traffic related air pollution of subjects living near motorways. Furthermore, the yearly averaged concentrations of PM2.5, "soot", NO2 and benzene can be used as a more direct measure of long-term exposure in epidemiological studies of the children attending the 24 schools. (C) 2001 Elsevier Science Ltd. All rights reserved.