2024 Yes Indoor air quality in inner-city schools and its associations withbuilding characteristics and environmental factors https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6360122/ Majd, Ehsan North America Observational Epidemiological Elementary (K-5) Middle/Jr High (6-8) Ventilation rates Filtration Temperature Humidity Carbon Dioxide (CO2) Carbon Monoxide (CO) Nitrogen Dioxide (NO2) Indoor air quality School Exposure Building characteristics Environmental factors PM2.5, NO₂, and CO were measured in 16 urban schools across seasons. Indoor NO₂ often exceeded WHO limits, with outdoor sources and poor building conditions driving exposures. Results support upgrades to school infrastructure and surroundings. 2019