2024 Yes Indoor carbon dioxide concentrations in Croatian elementary school classrooms during the heating season https://doi.org/10.2478/aiht-2019-70-3343 Brdarić, Dario Europe Exposure Observational Students Elementary (K-5) Carbon Dioxide (CO2) Ventilation rates CO2 Indoor air quality Ventilation Measured CO2 levels in 60 Croatian elementary school classrooms during the heating season; all exceeded WHO limits, showing poor ventilation. Results call for multidisciplinary solutions to improve indoor air quality. 2019