Integrated Evidence of Winter Childhood Exposure to CO2 in Housing and Classrooms in Santiago de Chile

During the winter, school-age children spend much of their time in two indoor environments, homes and classrooms, where ventilation is often restricted to conserve heat, favoring the accumulation of carbon dioxide (CO2). This study evaluated CO2 exposure in both environments in Santiago de Chile to characterize real conditions and their daily combinations. Continuous CO2 monitoring was conducted using sensors in four dwellings with school-age children and four classrooms from different schools during August 2024. Hourly profiles, time over the operating threshold of 1250 ppm, and equivalent hours of exposure, standardized to a daily reference time, were analyzed. In classrooms, levels above the threshold were observed episodically. They were more concentrated during school hours, with marked differences between establishments, ranging from recurrent exposure to high levels to no exposure above the established level. In the bedrooms, the increases were concentrated during the night and early morning hours, consistent with reduced effective ventilation during prolonged stays. Overall, the bedroom-classroom combined exposure showed high variability across cases; together, it allows identifying priority scenarios and the orientation of winter ventilation strategies without neglecting thermal comfort. These results support the incorporation of winter ventilation operational criteria into schools and homes as input for implementing indoor environmental quality policies and standards in urban contexts.