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Comment by w-m | Hacker News Reader

I don't think you can cleanly compare this: In the study, they added CO2 to the room, while keeping O2 at normoxic levels throughout the experiment. In your meeting room, O2 levels will be dropping in lock-step with the CO2-levels rising. It may be the lack of oxygen that leads to drowsiness, not the additional CO2. But it's the CO2 levels that you can measure as a good proxy of overall air quality.

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I don't think this is correct. The concentration of CO2 in air is about 0.04%, whereas the concentration of oxygen is 20%, so the partial pressure of oxygen is about 500x higher. This means that if, for example, 10% of the oxygen in a room spontaneously disappeared, it would be replaced about sqrt(500) = 22x faster through leaks in the room than a 10% spontaneous CO2 increase would dissipate. (This ignores a small effect due to the different density of the two gases).

So in practice the oxygen level can never drift meaningfully far from the atmospheric pressure, whereas carbon dioxide easily can because the pressures involved are so low.

Ok, fair points, including the sister comment, it's likely not a drop in O2 levels.

But then why can we see problems with concentration in studies of people in poorly ventilated rooms, but not replicate that when just adding CO2 to normal air? What is the CO2 that we can measure in meeting rooms actually a proxy for?

The Satish 2012 study that seems to have started this trend was a small cohort of 22 people split in 6 smaller groups where they also just injected pure CO2 in a small room. There have been several attempts to reproduce, which sometimes found no clear effect, or a significantly smaller effect.

This original study has been used to market these CO2 monitors for years, but the evidence is quite thin and doesn't support a strong effect. It seems likely that there is a small effect, and it has been wildly exaggerated thanks to a small study with N=22.

So is this all bullshit?

Lacking a large study, we can't know. Of course the CO2 meter companies benefit if people believe it is true.

This is kind of a bummer. I have a nice co2 meter. another reason to be skeptical of everything.

Can it not just be that what happens in stuffy meeting rooms is boring? Opening the windows changes the temperature, the noise levels, perhaps the light levels ≈ adds some novelty, which makes you feel a bit more awake.

I think this is (in turn) wrong. Yes: having 500x the amount of O2 as CO2 means that a 10% drop in O2 will trigger 500x as many molecules diffusing in per second as the same drop in CO2. But, each molecule of CO2 will change the relative percentage 500x as much as a molecule of O2, so isn't it a wash?

O2 is 200000ppm so if co2 goes up 400 to 2000ppm does o2 go down to 198400ppm?

Don't neglect the 80% nitrogen which dominates proportionally.

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