Non-methane organic gases

Non-Methane Organic Gases (NMOG)
The sum of all organic air pollutants. Excluding methane they account for aldehydes, ketenes, alcohols, and other pollutants that are not hydrocarbons but are precursors of ozone.
Non-potable ...

Reactive Organic Gas (ROG): A photochemically reactive chemical gas, composed of non-methane hydrocarbons, that may contribute to the formation of smog. Also sometimes referred to as Non-Methane Organic Gases (NMOGs).

Non-Methane Organic Gases (NMOG)
Non-Point Sources
Non-potable
Non-Road Emissions
Non-Transient Non-Community Water System
No-Observed-Effect-Level (NOEL)
Notice of Deficiency
Notice of Intent to Cancel
Notice of Intent to Deny ...

See also: Ambient air quality standards, Waste, Emission, Nitrogen, Radiation