Assessment of schoolchildrenʹs exposure to traffic-related air pollution in the French Six Cities Study using a dispersion model

The purpose of this work was to estimate exposure to traffic-related air pollution (TAP), of the 6683 schoolchildren included in a cross-sectional epidemiological study conducted in six French cities to determine the effects of urban air pollution (AP) on respiratory and allergic health. Annual mean concentrations of benzene, CO, NO2, NOx, PM10 and SO2 were calculated, in front of the 108 schools attended by the children, by the validated STREET 5 software, which combines data on regional and local components of AP. STREET contains a database of emissions estimated by the IMPACT 2.0 software developed by ADEME-France and results of ambient concentrations modelled by the WinMISKAM 4.2 dispersion model. The input data required were background AP, traffic conditions (daily traffic density; average speed; percentage of gridlocks and proportion of each type of vehicle) and dispersion conditions (topography of the street segments modelled and meteorology). Emissions of air pollutants in front of the 108 schools were considerably scattered. Calculated concentrations (μg m−3) also varied considerably at: [1.0–5.1] for benzene, [303.8–988.1] for CO, [17.8–78.9] for NO2, [23.3–195.2] for NOx, [10.0–52.0] for PM10 and [2.4–16.4] for SO2. About 64% (29%, respectively) of the schools had annual mean concentrations of NO2 (PM10, respectively) exceeding the European quality objectives (40 and 30 μg m−3, respectively). These exposure indicators, capable of identifying small area variations in AP contrary to surrogate measures usually used in epidemiology, will enable better studies on the impact of urban AP on health.