There isn't one single symbol for nitrogen oxides because it's a group of compounds. Here's how it's represented:

* NOx: This is the most common symbol used to represent nitrogen oxides as a group. The "x" represents the variable number of oxygen atoms in the different compounds.

* Individual formulas: You can also use the specific chemical formula for individual nitrogen oxides:

* NO: Nitric oxide

* NO2: Nitrogen dioxide

* N2O: Nitrous oxide (laughing gas)

* N2O4: Dinitrogen tetroxide

* N2O5: Dinitrogen pentoxide

So, depending on the context, you can use either NOx or the specific formula of the nitrogen oxide you're referring to.