2021 No http://dx.doi.org/10.1016/j.scitotenv.2021.152271 Hu, Dawei Europe Observational Exposure Study Students Staff Elementary (K-5) High School (9-12) Ventilation rates Volatile Organic Compounds (VOCs) Indoor air quality High-resolution PTR-ToF-MS measured formaldehyde (HCHO) in French classrooms (10.96–17.95 μg/m³); ventilation reduced HCHO by up to 38%; VOC reactions and smoking were key sources. Findings support ventilation strategies to control school indoor air quality.