2019 No https://doi.org/10.1016/j.buildenv.2019.04.038 Deng, Shihan North America Observational Exposure Study Students Teachers Elementary (K-5) Middle/Jr High (6-8) High School (9-12) Ventilation rates Temperature Humidity Carbon Dioxide (CO2) Particulate Matter (PM) Other Ventilation rate Seasonal variation Formaldehyde Classrooms Midwestern United States 2-year repeated seasonal monitoring of IAQ and thermal conditions in 220 Midwestern US classrooms assessed CO₂, ventilation, particles, and formaldehyde; results highlight need for year-round monitoring to improve school environmental quality.