2. Environmental impacts and sources

2.1 Environmental impact

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 SO ₂ , NH ₃ , 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 HNO _...