2017 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5486271/ Sá, Juliana P. Europe Review Elementary (K-5) Indoor air Mitigation measures evaluation Nursery schools Primary schools Exceedances to the values set by the national legislation and World Health Organization (WHO) were found for PM 2.5, PM10, CO2 and CH2O during both indoor air quality campaigns. Temperature and relative humidity values were also above the ranges recommended by American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). In general, pollutant concentrations measured after the implementation of low-cost mitigation measures were significantly lower, mainly for CO2. However, mitigation measures were not always sufficient to decrease the pollutants’ concentrations till values considered safe to protect human health