Oxides of nitrogen
Oxides of nitrogen means nitric oxide and nitrogen dioxide. Oxides of nitrogen are expressed quantitatively as if the nitric oxide were in the form of nitrogen dioxide (oxides of nitrogen are assumed to have a molecular weight equivalent to nitrogen dioxide).
Source
40 CFR § 94.2
Scoping language
The definitions of this section apply to this subpart. They also apply to all subparts of this part, except where noted otherwise.