[gblargg]

> One can measure CO₂ as a proxy to rebreathed air fraction.

On this topic, I got a CO₂ meter fairly recently and was shocked how quickly it spikes with a couple of people in a car with the windows up and on recirculate. Easily over 2000 after a few minutes. I have to remind myself regularly when it's really hot or cold outside to keep the vent setting on fresh air.

[xattt]

I’d love for cars to get some sort of sniffer that will switch to recirc if it detects a spike in exhaust fumes.

[FireBeyond]

I had a Jaguar that had an air quality sensor that would switch to recirc based on particulates and then back to fresh air when the threshold indicated.