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There's been a lot of previous interest in indoor CO2 in the rationality community, including an (unsuccessful) CO2 stripper project, some researchsummaries and self experiments. The results are confusing, I suspect some of the older research might be fake. But I noticed something that has greatly changed how I think about CO2 in relation to cognition.
Exhaled air is about 50kPPM CO2. Outdoor air is about 400ppm; indoor air ranges from 500 to 1500ppm depending on ventilation. Since exhaled air has CO2 about two orders of magnitude larger than the variance in room CO2, if even a small percentage of inhaled air is reinhalation of exhaled air, this will have a significantly larger effect than changes in ventilation. I'm having trouble finding a straight answer about what percentage of inhaled air is rebreathed (other than in the context of mask-wearing), but given the diffusivity of CO2, I would be surprised if it wasn't at least 1%.
This predicts that a slight breeze, which replaces their in front of your face and prevents reinhalation, would have a considerably larger effect than ventilating an indoor space where the air is mostly still. This matches my subjective experience of indoor vs outdoor spaces, which, while extremely confounded, feels like an air-quality difference larger than CO2 sensors would predict.
This also predicts that a small fan, positioned so it replaces the air in front of my face, would have a large effect on the same axis as improved ventilation would. I just set one up. I don't know whether it's making a difference but I plan to leave it there for at least a few days.
(Note: CO2 is sometimes used as a proxy for ventilation in contexts where the thing you actually care about is respiratory aerosol, because it affects transmissibility of respiratory diseases like COVID and influenza. This doesn't help with that at all and if anything would make it worse.)
I had previously guessed air movement made me feel better because my body expected air movement (i.e. some kind of biophilic effect). But this explanation seems more likely in retrospect! I'm not quite sure how to run the calculation using the diffusivity coefficient to spot check this, though.
2Gunnar_Zarncke
As the respirator still has to breathe regularly, there will be still a significantly higher CO2 in the air for respiration. I'd guess maybe half - 20k PPM. Interesting to see somebody measure that.
This post is a container for my short-form writing. See this post for meta-level discussion about shortform.