Earlier quoted context omitted.
How does air recirculation with increasing co2 compare to having to breath/smell car exhaust, cigarette smoke, etc through vents? I started doing recirculation as my default years ago due to that.
Generally, use recirc only briefly when driving through heavy exhaust, smoke, dust, chemicals, smells. Return to fresh air once you've cleared that. Some sources suggest recirc for heavy traffic -- I'd prefer a good filtration system. And for rapidly heating or cooling a car, recirc can help. My preference is to open windows & sunroof (where present) to flush out hot air first, in hot weather. In cold weather, the he…
I've questioned why fresh is even there (seems unlikely co2 would be the reason) - it's always going to be less efficient and you can open a window if you want fresh air.
Anecdotally I feel fine driving for 2 hours straight in recirculated air with closed windows.