Factors influencing the outdoor concentration of carbonaceous aerosols at urban schools in Brisbane, Australia: Implications for children's exposure

•We aimed to find the contributing sources to children's exposure at school.•Measured outdoor organic carbon and elemental carbon at 25 urban schools.•Schools varied in exposure to primary and secondary sources.•Secondary organic carbon the largest component of carbonaceous aerosols.•Vehicle emission levels at schools are primarily dependent on local traffic counts.