We've given this a lot of attention in the age of Covid, as you might imagine. Many modern HVAC control systems include CO₂ sensors in the return air streams to make sure they're bringing in enough outdoor air to meet indoor air quality standards, and that's fairly easy to simulate. Particulate counts are trickier, and may be better estimated using out-of-simulation engineering calculations based on the type of filtration in place.

Interesting, mind if I shoot you an email? My family has a business in this space (residential side) and I'd love to chat more.

Sure! brian at bractlet dot com