Question

Why does the reaction O + O3 -> 2 O2 not proceed on its own in the stratosphere to any appreciable extent?

Answer 1

Ozone is destroyed naturally in the stratosphere, being dissociated by ultraviolet radiation:

O₃ (hv) ----> O + O₂

This reaction is responsible for O₃'s absorption of ultraviolet radiation that would otherwise reach earth.

The O atom then typically joins with an O₂ molecule to reform O₃.

O + O₂ + M ---> O₃ + M

The O₃ goes on to dissociate and reform many times, usually until it collides with a free O atom, forming two relatively stable O₂ molecules.

O₃ + O --------> 20₂

That is, O₃ formation and destruction are normally in a steady state in the stratosphere, such that the rate of its formation is equal to the rate of its removal. So the reaction O + O₃ -> 2 O₂ not proceed on its own in the stratosphere to any appreciable extent.