"z" wrote in message
ups.com...
On Feb 10, 8:42 am, (Doug Miller) wrote:

Oxygen is 14% heavier than nitrogen (16 vs 14). And when you consider
that the
molecular weight of CO is virtually the same as that of N2 -- but
significantly *less* than that of O2 -- it makes quite a difference.

But the oxygen and nitrogen don't separate out of the air, so why
would the CO?

The "mix" of gasses in the air is driven by diffusion and by the density.

In the "steady state" diffusion trumps density although one would expect
that "lighter" gasses would tend to make it to the higher levels of the
atmosphere more easily than heavy stuff. But when you have a process that
is producing a LOT of a particular gas, in the short term the density of
the gas can be important. The grade school "science" shows CO2 going
"downhill" to snuff out a candle.