Nitric oxide from supersonic aircraft depletes stratospheric ozone through the steps $\mathrm{NO}+\mathrm{O}{}_3\to \mathrm{NO}{}_2+\mathrm{O}{}_2$ and $\mathrm{NO}{}_2+\mathrm{O}\to \mathrm{NO}+\mathrm{O}{}_2$. The net reaction and the role of $\mathrm{NO}$ are

1. A$\mathrm{NO}+\mathrm{O}\to \mathrm{NO}{}_2$, with $\mathrm{O}{}_3$ acting as a catalyst
2. B$\mathrm{O}{}_3+\mathrm{O}\to 2\mathrm{O}{}_2$, with $\mathrm{NO}$ acting as a catalyst
3. C$2\mathrm{O}{}_3\to 3\mathrm{O}{}_2$, with $\mathrm{NO}$ acting as a reactant that is consumed
4. D$\mathrm{O}{}_3+\mathrm{O}\to 2\mathrm{O}{}_2$, with $\mathrm{NO}{}_2$ acting as a catalyst