2020 No https://doi.org/10.1016/j.jclepro.2019.118420 Becerra, Jose A. Europe Exposure Study Students Elementary (K-5) Middle/Jr High (6-8) High School (9-12) Carbon Dioxide (CO2) Particulate Matter (PM) Volatile Organic Compounds (VOCs) Dust Other Indoor air quality Air pollution Indoor air guideline values Mediterranean climate Measured CO₂, PM, dust, TVOC, and aldehydes in 18 classrooms across 9 Mediterranean schools. Indoor and outdoor sources shaped pollutant levels. Recommends targeted monitoring to reduce IAQ-related health risks.