If you go to places at high altitude, they literally sell compressed O2 in cans, at oxygen bars, etc. It is not a requirement per se for you to survive in thos

If you go to places at high altitude, they literally sell compressed O2 in cans, at oxygen bars, etc. It is not a requirement per se for you to survive in those environments, but boy does it feel good to get some O2 if you don't have enough red blood cells in your veins to get the oxygen your body needs to feel comfortable. The same is true, IIRC, in Beijing, where clean air can be hard to come by.