2020 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7246548/ Pallarés, Susana Europe Observational Elementary (K-5) Emissions produced outdoors (i.e., traffic, construction or industry emissions) penetrate the interior of buildings, and these represent the primary contribution to indoor air quality [19,22,23]. The use of natural ventilation favors, in general, indoor particle reduction. However, there are cases in which the orientation of the school encourages the penetration of particles aided by the wind. Schools located in urban locations have higher concentrations of particulate matter from combustion processes than the ones found in industrial or rural environments.