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I use something like this handheld air quality monitor. It's been close enough and useful enough to figure out how well my filter is working:

https://www.aliexpress.com/item/4000312301074.html?spm=a2g0o...

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.

https://www.airgradient.com/diy/

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!

also a cheap box fan and 20x20x1 merv 11+ rating filter should work wonders.

PMS5003