NO catalysing ozone depletion

Hey guys, this might end up being super obvious but I've always struggled to understand exactly what's happening in the depletion of the ozone layer by NO radicals and wondered if anyone could help clarify for me - I'm aware there's two versions of ozone depletion when looking at CFCs and Cl* radicals so maybe it's the same for NO.

Here's the reaction mechanism I've been given:

NO + O3 --> NO2 + O2
NO2 + O* --> O2 + NO
overall: O3 + O* --> 2O2

I don't understand where the O* radical is coming from in the second equation. For CFCs I usually prefer the version of the mechanism that says the overall equation is:

3O2 --> 2O3

So I was wondering if there's a form the NO equation could take to fit into this.

Sorry for the confusing question, it's kinda hard to explain what I mean!

Reply 1

jjeeeeeea

The O radical comes from O2 and O3 absorbing UV light and splitting into O radicals. You can use either because it is possible that the NO2 will bump into either O or O3, but I agree with you and much prefer the other form - I think it is actually more likely irl to happen with O3. You can display the reactions for NO radicals like this:

Screenshot 2023-06-08 141041.png

I think also you meant to say 2O3 -> 3O2 ?

Reply 2

eeaste

Original post by jjeeeeeea

I think also you meant to say 2O3 -> 3O2 ?

Omg tysm for the reply you're a lifesaver, my textbook didn't mention anything about UV light hitting the ozone radicals and splitting them up but that makes a lot of sense.

Also yeah, I did mean to put 2O3 --> 3O2, exam brain's got me making stupid mistakes!