Comment by Youden

Nothing against the rest of what you say but I wouldn't recommend a "cheap" air quality monitor for CO2.

"Cheap" usually means eCO2, which isn't actually a CO2 measurement but rather an estimation based on VOC measurements. This has basically zero correlation to actual CO2 levels [0].

For CO2, you need to look at air quality monitors that cost at least $100, or which do nothing but monitor CO2. These will have real sensors in them that actually measure CO2 levels (NDIR). You should check to confirm they advertise NDIR somewhere to be sure.

You also need to be very careful with calibration. If your area has consistent low levels that don't match ambient, the calibration will be thrown off and all your readings will be garbage.

TVOC and particles don't have the same problems, there are fairly cheap sensors for them that work pretty well, it's just CO2 you have to be picky about [0].

[0]: https://jsss.copernicus.org/articles/7/373/2018/