It's rather dumb at the moment, but when number gets too high, it kicks on for 1 hour and if it's back below threshold it shuts off. There's also a human presence detector that will "pause" it for 5 minutes since it's in my kitchen window.
It's built out of cardboard (laminated, with wheat paste) as a proof of concept/tinker with design and placement of things and also serves as a platform for the cats to nap in the window.
This, mainly, helps from bringing in all the outside humidity during the summer and the bitter cold during the winter. Otherwise, prior, I'd just keep an exhaust fan running all the time (eating the losses on air conditioning/heat) but we'd end up closing the window when it was super hot/cold and then the iaq would get terrible.
Lots and lots of people are automating their various systems due to monitoring these values. An application I've seen lots of is to just kick on the hvac systems fans when the aq drops below a particular threshold in one room or another.
> Lastly, ensuring your house is positively pressurized by paying a testing and balancing contractor to come over and adjust your HVAC system will do more to keep out particulate matter than measuring it ever will.
Sadly, it took me a while to figure out that having this window fan in my kitchen on "exhaust" rather than "intake" was creating a negative pressure environment and that was.. not optimal.