Just a point about the frequency of changing the cabin air, from my experience of modelling fluid dynamics.
To say that the air is changed every 8 minutes or whatever may be true in terms of volume, but is not true of actual air molecules. It would be more correct to say that half the air is changed twice every 8 minutes, or even that a quarter of the air is changed 4 times every 8 minutes.
You can guarantee that at least some of the air inside the cabin at the end of a long haul flight is still the original.