nox

noun3

1. •
   The period of darkness in each twenty-four hours; a night.
2. •
   Abbreviation of nitrous oxide (“N₂O”).
3. •
   (rare) millilux (unit of illuminance)

noun1

1. •
   Any of the various nitrogen oxides produced during combustion.

   • "The NOx and particulate reductions provide clean air in the cities and communities we serve. [...]" — 2020