2022 Yes https://www.sciencedirect.com/science/article/pii/S2405844022006429 Konstantinou, Corina Europe Opinion Elementary (K-5) Temperature Humidity Carbon Dioxide (CO2) Particulate Matter (PM) Volatile Organic Compounds (VOCs) Indoor air quality School Environmental pollutants Sensors Exposure COVID-19 measures Indoor PM, temperature, RH and VOCs increased with progressing school periods in the day, while indoor CO2 decreased. Indoor RH and CO2 were negatively associated with % open windows, while indoor PM2.5 was positively associated. Most of school time (85%), indoor air temperature exceeded the recommended upper limit (27 °C), while a third of indoor PM2.5 (24-h) measurements exceeded 15 μg/m3.