I carried a CO2 meter on a flight recently, to use CO2 as a proxy for COVID risk. The levels were quite high for the whole flight--over 1000 pretty much the whole time iirc and worse on the tarmac.
It's true for every other mode of transport but objectively false for planes in flight. However, I'd be curious to see the average when including time sitting on the ground, taxiing, etc., and how that much lower speed affects circulation.
The refreshed air in the cabin is driven by engine bleed air (or a dedicated pressure pump) so even at idle power there is nothing preventing a high rate of cabin air exchange. There might still be less air flowing on the ground due to 0 cabin air pressure differential, but speed of the plane isn't a relevant factor.
