# Why NOx will break the ozone sphere

I've found that a reason for people to oppose supersonic aeroplanes was the $\ce{NO_{$x$}}$ gases it released would do harm to the ozone layer. So what is the mechanism of this?

• The mechanism is rather complex, I discussed some of it already for chlorine. In short, it basically removes the oxygen radicals from the ozone cycle: $$\ce{O2 ->[h\nu] O + O} \\ \ce{O + O2 ->[<M>] O3}\\ \ce{O3 ->[h\nu] O + O2}$$ – Martin - マーチン Mar 3 '16 at 11:23
• Don't UV and cosmic radiation also produce NOx? – Karl Jun 1 '16 at 20:14

An important component of aircraft exhaust is nitric oxide ($$\ce{NO}$$) formed by oxidation of atmospheric $$\ce{N2}$$ at the high temperatures of the aircraft engine. In the stratosphere $$\ce{NO}$$ reacts rapidly with $$\ce{O3}$$ to produce $$\ce{NO2}$$, which then photolyzes:

$$\ce{NO + O3 -> NO2 + O2}$$ $$\ce{NO2 + h\nu -> NO + O}$$

Note that there is no net consumption of $$\ce{NO_x}$$, thus it is able to act as a catalyst such that a single $$\ce{NO_x}$$ molecule can destroy many molecules of ozone by these reactions.

Please don't hesitate to ask for any clarifications in the comments below, particularly if I've failed to address any aspect of your question.

$$\ce{O3 + NO->O2 + NO2}$$ $$\ce{O + NO2 -> NO + O2}$$

$\ce{NO_x}$ is a catalyst.

• I would explicitly add that being a only a catalyst it can convert a huge amount of ozone even if only small amounts are released. – caconyrn May 2 '16 at 15:48