2021 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8624555/ Zaeh, Sandra E North America Exposure Study Students Temperature Carbon Dioxide (CO2) Carbon Monoxide (CO) School Indoor air quality Renovation Prior to renovation, indoor CO measurements were within World Health Organization (WHO) guidelines, and indoor PM2.5 measurements rarely exceeded them. Within the seven schools with pre- and post-renovation data, over 30% of indoor CO2 measurements and over 50% of indoor temperatures exceeded recommended guidelines from the American Society of Heating, Refrigerating, and Air Conditioning Engineers. Following renovation, 10% of indoor CO2 measurements and 28% of indoor temperatures fell outside of the recommended ranges. Linear mixed models showed significant improvement in CO2, indoor PM2.5, and CO following school renovation. Even among schools that generally met recommendations on key guidelines, school renovation improved the indoor air quality.