Question

How does electromagnetic radiation change atoms and molecules in the upper atmosphere?

Answer 1

Basically, it is an energy source that gives atoms and molecules the additional energy that they need to form other compounds.

Explanation:

The impact of pollutants such as chlorofluorocarbons is in part due to their transformation in the upper atmosphere from relatively inert compounds into more reactive ones.

Ozone destruction (and hence, the need to replenish it naturally) is also a result of electromagnetic radiation in the upper atmosphere.
https://science.madison.k12.wi.us/files/science/Material_on_Ozone%20.pdf