Question:
Ozone is a gas heavier than air. Why does the ozone layer not settle down near the earth?
Solution:
The ozone layer is heavier than oxygen and is thermodynamically unstable and there is a dynamic equilibrium in the reaction between formation and dissociation of the ozone. So they do not settle down near the earth.
O2 (g) → O (g) + O (g)
O (g) + O2 (g) → O3 (g)