2019 No https://www.sciencedirect.com/science/article/abs/pii/S0013935119303317 Branco, M.C.M Europe Review Elementary (K-5) Temperature Humidity Carbon Dioxide (CO2) Carbon Monoxide (CO) Particulate Matter (PM) Volatile Organic Compounds (VOCs) Ozone (O3) Nitrogen Dioxide (NO2) Children Nursery and Primary schools Exposure Indoor air quality Children faced thermal discomfort and inadequate humidity, respectively in 60.1% and 44.1% of the studied classrooms. They were also exposed to high levels of IAP, namely PM 2.5 and CO2 respectively in 69.0% and 41.3% of the studied classrooms, mostly in urban sites, depending on season and on occupancy and activity patterns (different amongst age groups). As PM2.5 and CO2 were the major concerning IAP, multivariate linear regression models were built to quantify (explained variability and relative importance) their main determinants, in both occupancy and non-occupancy (background) periods. Models for occupancy periods showed higher explained variability than for non-occupancy. In the cases of PM2.5 and PM10 occupancy concentrations, besides background concentrations type of school management (8.8% and 15.2%) and flooring material (13.9% and 13.9%), adjusted for season of sampling (6.1% and 3.8%), were the main predictors.