The Role of UV Radiation in Ozone Formation and Depletion

[pivoxa15]

The majority of the ozone in the atomsphere occur because of UV breaking O2 into O and than O + O2 -> O3.

But for the half of the hemisphere where no sun is shining, this chemical reaction wouldn't occur because no UV rays are apparent. Hence there are virutally no ozone in the atompshere at night?

 

[Gokul43201]

No. The mechanism for most ozone decomposition is also primarily photochemical, and is driven by UV. So, most ozone production happens by day, as does most ozone loss. At night, there's much less activity (of either kind), keeping ozone levels virtually unchanged.

 

[pivoxa15]

No. The mechanism for most ozone decomposition is also primarily photochemical, and is driven by UV. So, most ozone production happens by day, as does most ozone loss. At night, there's much less activity (of either kind), keeping ozone levels virtually unchanged.

Would breaking ozone into O2 be exothermic or endothermic?

If exothermic than it means there is a certain amount of nontrivial activation energy that must be met in order for this reaction to happen doesn't it? That is why UV is needed for its backward reaction?