National Recreation Areas - areas of federal land that have been set aside by Congress for recreational use by members of the public.

nitrogen oxides - harmful gases (which contribute to acid rain and global warming) emitted as a byproduct of fossil fuel combustion.

noise pollution - environmental pollution made up of harmful or annoying noise.

nuclear energy - energy or power produced by nuclear reactions (fusion or fission).

nuclear power - see nuclear energy.

nuclear reactor - an apparatus in which nuclear fission may be initiated, maintained, and controlled to produce energy, conduct research, or produce fissile material for nuclear explosives.

nuclear tests - government tests carried out to supply information required for the design and improvement of nuclear weapons, and to study the phenomena and effects associated with nuclear explosions.