2017 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5639812/ Matic, Branislava Europe Observational Modeling Students Elementary (K-5) Temperature Humidity Carbon Dioxide (CO2) Carbon Monoxide (CO) Particulate Matter (PM) Indoor air quality Classrooms Particulate matter (PM) Respirable particulate matter (PM 10) Primary schools Exposure Serbia PM10 concentrations were significantly most frequent in an interval of ≥80.1μg/m3, that is, in the interval above 50μg/m3. Mean PM10 value was 82.24±42.43 μg/m3, ranging from 32.00μg/m3 to of 197.00μg/m3