2020 Yes https://www.sciencedirect.com/science/article/abs/pii/S0048969719362680?via%3Dihub Leppänen, Maija Europe Experimental Exposure Study Elementary (K-5) Indoor air quality Aerosol Respirable particulate matter (PM 10) Elemental analysis According to results, PM10 and PM15 concentrations in corridors were significantly higher in shoe schools compared to sock schools (p < 0.05). The shoeless course did not affect on the particle number concentrations, but the increases in the number concentrations originated from diners. The elemental concentrations (Li, Al, Si, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ba, Pb) in settled dust were also higher in shoe schools compared to sock schools, and the Zn concentrations differed significantly (p < 0.05).