Aerosol particles generated by diesel-powered school buses at urban schools as a source of children's exposure

► In this study, the indoor and outdoor aerosol at four urban elementary schools serviced by diesel-powered school buses was characterized with respect to the particle number concentrations and size distributions as well as the PM2.5 mass concentrations and elemental compositions. ► The presence of school buses significantly affected the outdoor particle size distribution, specifically in the ultrafine fraction. ► Significant associations were observed between indoor and outdoor aerosols for EC, EC/OC, and the total particle number concentration.