Several people in our community are very experienced in measuring (indoor) airquality. You can approach them and try to build your own, e.g. Let us know beforehand if you want to try work on this!
- Hack the Rabbit: see when the CO2 in your room becomes unhealthy by watching a rabbit (nightlight) turn purple
- Measure air quality https://www.instructables.com/id/Sensly-Hat-for-the-Raspberry-Pi-Air-Quality-Gas-De/ (board available, but calibration needed)