OK, here's an altitude question:

[mycrofft]

We know that there is less oxygen at altitude than at sea level. We know some gasses are heavier than others. So, are heavier gasses at altiture replaced by lighter gasses?
(Remember partial opressures and lower overall ambient pressure).....GO!

 

[ptemt]

The percentage of O2 in the air is the same at 10,000 ft as it is at sea level.......the air is less dense.

 

[mycrofft]

Very good! No red herrings for you. What about 35,000 ft?

Exclusing condensatation and pollutants .

 

[mycrofft]

Just to finish it off...it's still the same.

Had a discussion with a pilot one time and we wound up emailing NASA, who routed the question and had ther answer back in a week. Basically, it stays mixed enough that it is the same until outside influences, or additives, screw it up.
Thanks everyone (all two of you):blush: