Thanks for the comment and a very good point! Nice blog posts too! I wrote a little about CO2 in https://www.babyfriendlyair.com/en/guides/air-pollution-primer

Thanks for the comment and a very good point! Nice blog posts too! I wrote a little about CO2 in https://www.babyfriendlyair.com/en/guides/air-pollution-primer/ https://www.babyfriendlyair.com/en/guides/air-pollution-prim... . I often see very high CO2 levels in bedrooms, which was also observed in the mini study https://www.mdpi.com/2076-3417/9/17/3533 https://www.mdpi.com/2076-3417/9/17/3533 , and the simple act of leaving the bedroom door open might presumably therefore improve sleep quality (https://onlinelibrary.wiley.com/doi/abs/10.1111/ina.12435 https://onlinelibrary.wiley.com/doi/abs/10.1111/ina.12435) according to these small studies. But of course, adequate ventilation could make sure this isn't a problem regardless if the door is open or not. Just to add to your point about the importance of ventilation, there are also VOCs (eg. from furniture off gassing and cleaning products) that HEPA filters can't do much about, and at least in my experience (which is a bit skewed due to only measuring with "cheap" sensors), active carbon filters only help for a short while. Other technologies, like photocatalytic air purification, seem to also have limited effect, and do in turn produce CO2 as they break down pollutants (I'm not sure how much though), which again means adequate ventilation is important. So having "control" over where air gets in to the building is very helpful indeed, as you can't get around needing an adequate air exchange. You seem to know quite a bit about this already, but in case you or anyone else is curious, a few more articles: Effects of Classroom Ventilation Rate and Temperature on Students’ Test Scores https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136165 https://journals.plos.org/plosone/article?id=10.1371/journal... Stuffy classrooms may lower test scores (easier read that discusses the above but also some other studies) https://www.sciencenewsforstudents.org/article/stuffy-classrooms-may-lower-test-scores https://www.sciencenewsforstudents.org/article/stuffy-classr... Poor air quality on the day of a test can have big impacts on how well a student performs (doesn't discuss CO2 specifically though) https://www.aeaweb.org/research/pollution-effects-highstakes-tests https://www.aeaweb.org/research/pollution-effects-highstakes... Possible future impacts of elevated levels of atmospheric CO2 on human cognitive performance and on the design and operation of ventilation systems in buildings https://journals.sagepub.com/doi/full/10.1177/0143624418790129 https://journals.sagepub.com/doi/full/10.1177/01436244187901...