Why Does O₂ & O₃ Stay in the Stratosphere?

[Suraj M]

we all know that the stratosphere has ozone O₃ molecules and also O₂.:.but
O₂ and O₃ are heavy molecules (comparitively) why are they all the way up there(>10km) shouldn't they come down?
My guess ... because of that altitude maybe the centrifugal force acting on the molecules is enough to keep them up there..but then again Earth's rotation and there mass is a bit too small for a large enough centrifugal force
is there some other reason??

 

[SteamKing]

Perhaps you would see such stratification if the atmosphere remained completely static. However, since the Earth rotates and is exposed to the sun, the atmosphere is heated unevenly, which causes a certain amount of mixing to occur by the winds which develop as a result.

Also, ozone is created at altitude by the effect which solar radiation has on the oxygen molecules present in the upper atmosphere; the ozone layer which protects the surface against UV radiation largely is created and destroyed by processes which occur at high altitudes, so the ozone molecules there are not rising from the surface. What ozone is present at low altitudes is regarded as a pollutant, and is created as a result of sunlight causing reactions of atmospheric oxygen with hydrocarbons and oxides of nitrogen emitted by combustion or other industrial processes.

http://en.wikipedia.org/wiki/Ozone

 

[DaveC426913]

My guess ... because of that altitude maybe the centrifugal force acting on the molecules is enough to keep them up there..

Definitely not.

As SK points out,
1] there is plenty of mixing.
2] O₃ is formed in the upper atmo.

That and the fact that O₂'s molar mass (31) is very similar to N₂'s (28). It's just not that heavy, comparatively.