2017 No https://doi.org/10.1080/15287394.2017.1286932 Oliveira, Marta Europe Observational Exposure Study Students Temperature Humidity Carbon Dioxide (CO2) Carbon Monoxide (CO) Particulate Matter (PM) Volatile Organic Compounds (VOCs) Ozone (O3) Other This study measured PM2.5, VOCs, formaldehyde, CO, O₃, CO₂, temperature, and humidity in two Portuguese preschools, finding TVOC levels exceeded recommendations; suggests ventilation improvements for safer preschool air quality.