It’s actually quite easy.
The air is still, cool and only has limited nasty contaminants to deal with. You can make one yourself with a couple of sensors and a raspberry Pi. Accuracy is good enough (plus/minus 10/15% on amount of contaminant at a guess). Only limitations is that some sensors are quite expensive, so you might not get a full sweep of all potential domestic pollutors.
Exhaust emissions systems are testing nasty, hot, aggressive, corrosive gasses travelling at speed and need to remain accurate over a long period of time and with heavy commercial use.
I’m still waiting for someone to integrate the newest IKEA sensor into smartthings or Matter properly (it doesn’t report out all the comtaminants yet).