2024 Yes Organic Air Quality Markers of Indoor and Outdoor PM2.5 Aerosols in Primary Schools from Barcelona https://www.mdpi.com/1660-4601/17/10/3685 van Drooge, Barend Europe Observational Elementary (K-5) Particulate Matter (PM) Primary schools Polycyclic aromatic hydrocarbons (PAHS) Trap Indoor air quality Playgrounds Organic aerosol PM2.5 in six Barcelona schools showed traffic emissions as main PAH sources, with higher levels downtown. Indoor PAHs mirrored outdoor traffic pollutants, while indoor air also contained food-related markers, plastic additives, clothing residues, and fragrances. 2020