Again: if you’re on an airplane, you should be wearing a high-filtration mask. It’s sound practice for the entire flight, but especially before takeoff and after landing.
Here are the CO2 measurements from a flight I took yesterday - the two peaks are from embarking and disembarking, showing the plane’s ventilation systems being shut off. This is unfortunately a frequent practice.
Planes do not have CO2 scrubbers on board and CO2 is not removed by normal filtration.
Whatever you're measuring, it's not what you think it is.
Air is replenished with outside air, but because you're flying at altitude it's only a fraction. The fraction is controllable. The primary reason to replenish is CO2 buildup, but because part of the cabin air is recycled CO2 levels in the air will naturally go up.
https://aircraft.airbus.com/en/newsroom/news/2021-01-cabin-air-quality-key-to-a-comfortable-flight
CO2 is what drives the breathing cycle. High CO2 in your blood turns it slightly acidic and your body responds to that by raising your breathing rate to get rid of CO2. This is why you breath hard when you work. Burn more O2, generate CO2, breath hard to get rid of it.
If you're breathing a gas with too high a level of CO2 you cannot reduce your CO2 level in your blood and you hyper ventilate. This is the only way that it's dangerous. Our bodies know how to deal with CO2 and respond quite violently to high levels of it. It sounds flippant, but you know the CO2 level is safe because nobody is breathing heavily.
You don't have a CO2 scrubber on a plane because you'd need about 1.5 tonnes of scrubber material for each 8hr flight and there's perfectly good air outside, just not as much as normal.
@weebull why is it "only a fraction"?
Because the air is cold and unpressured?
@windrunner Yes exactly.
@weebull why isn't it removed by an air change (which should be normal)?
Further, maybe they *should* have scrubbers. These levels of CO2 are not good for anyone.