Submitted by oxo42 t3_zd3sq9 in askscience
I recall from high school that air is roughly 21% oxygen. At altitude, the air is thinner so each breath contains less oxygen but is it still the same proportional make up?
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Chemomechanics t1_iz2i5t3 wrote
The composition remains approximately the same, as thermal diffusion is enough to ensure even mixing over the accessible atmosphere. There is some varying sedimentation that becomes a factor at vertical scales of many kilometers (although over that scale, one also needs to consider, e.g., gas reactions from cosmic rays). I go into the math here. The characteristic sedimentation height scales with kT/gM, with Boltzmann's constant k, temperature T, gravitational acceleration g, and molecular mass M.
[deleted] t1_iz1uo05 wrote
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