Abstract
The aim of this study was to summarize the extent of occupants' exposure to nitrogen dioxide (NO2) in European school and kindergarten buildings. Google Scholar and PubMed were used to search the literature. The calculated median, as well as the mean, concentrations of NO2 in school (median 20.8 µg/m3; mean 26.1 µg/m3) and kindergarten (median 17.2 µg/m3; mean 35.5 µg/m3) buildings were found to be below the World Health Organization (WHO)'s guideline of 40 µg/m3 for the annual mean NO2 concentration. However, mean O2 concentrations in many studies were over 40 µg/m3, indicating situations where the WHO guideline is exceeded. Outdoor levels of NO2 are a reliable predictor of indoor NO2 levels across seasons, with median Indoor/Outdoor (I/O) ratios of 0.7 and 0.8 in school and kindergarten environments, respectively. These findings support the importance of mitigation measures to reduce ambient NO2 levels, and to prevent high levels of NO2 exposure in school and ki ndergarten buildings.