2020 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7559628/ Settimo, Gaetano Europe Modeling Indoor air quality School Students Carbon dioxide (CO2) Volatile organic compounds (VOCs) Fine particulate matter (PM 2.5) Denuder PCA Risk PM2.5 and CO2 rapidly increase their levels as soon as the activities begin, e.g., administrative staff from 7:00 and students from 8:00. In this period, a strict correlation between PM2.5 and CO2 is detected in all schools where no other activities are present. At the end of school activities, i.e., the end of both lessons and work by administrative staff (14:00), a clear decrease of indoor PM2.5 and CO2 is detected. A CO2 peak can be revealed around 16:00 along with a low PM2.5 increase.