Sensemakers have been very active with projects on air quality, like the Air Quality Egg. Some hardware is still around for you to experiment with.
Several people in our community are very experienced in measuring (indoor) air quality. You can approach them for advice, or maybe pick-up an idea that we have the stuff for, but not the time to work it out:
- Hack the Rabbit: see when the CO2 in your room becomes unhealthy by watching a rabbit (nightlight) turn purple