Environmental impacts and sources
NOx (Nitrogen oxides)

Nitrogen oxides are air pollutants insofar as they affect human health and contribute to acid rain and deposition, photochemical smog, the greenhouse effect and stratospheric ozone depletion.

Thus, acid pollution (by acid deposition or fallout) is partly linked to acid pollutants of the NO_x type, but also to SO₂, NH₃, HCl or HF compounds. This pollution is deposited partly close to emitting sources, but also hundreds or even thousands of kilometers away (transboundary pollution).

These pollutants precipitate in dry form (aerosol) or wet form (as HNO₃) when the atmosphere is humid, with effects on materials (corrosion), forest ecosystems (causing damage to plants and trees directly or via soils) and freshwater ecosystems.