I have yet to make such an investment as good air monitors are fairly expensive, but I’m hoping to get a few indoor monitors from Purple Air (~$200 USD).
You can build your own air quality sensor with our instructions. Our sensor uses the same PM sensor like in the purple air. You can build it for <USD 20.
BTW: Our main product is an air quality monitoring service specifically designed for schools. Since we are just starting, I would love to talk to parents, teachers etc. from schools that want to monitor their air quality better. Please contact me if you are interested to talk!
What do you folks use?