Question

What does this formula represent: `NO_x`?

Answer 1

It is used for nitrogen oxides.

Explanation:

`NO, NO_2, NO_3, N_2O, N_2O_3, N_2O_4`, and `N_2O_5`.

But only two of them are important:

`NO` (nitrogen monoxide or nitric oxide) and
`NO_2` (nitrogen dioxide) in air pollution.