2018 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6309359/ Fsadni, Peter Europe Review Students Elementary (K-5) Ventilation rates Temperature Humidity Carbon Dioxide (CO2) Carbon Monoxide (CO) Particulate Matter (PM) Volatile Organic Compounds (VOCs) Ozone (O3) Radon Respiratory symptoms Asthma Atopy Ozone (O3) School The mean indoor PM 2.5 level of 17.78 μg/m3 and CO (9.11 ppm) exceeded World Health Organization thresholds. Indoor ozone levels exceeded the mean European school's indoor ozone concentration of 8 μg/m3. High exposure to formaldehyde, NO2, and ozone was associated with atopy in children. Heavy vehicles passing near the schools were associated with current wheezing (P < 0.001) but not nocturnal cough (P = 0.34).