The process by which neutral atmospheric molecules or atoms are rendered electrically charged chiefly by collisions with high-energy particles: Atmospheric ionization is the charging of neutral particles in the atmosphere through violent contact with charged particles.

Atmospheric ionization is the production of ions in the atmosphere by the loss of an electron from a molecule, typically, for example, by cosmic rays or cosmic radiation.

Cosmic rays and radioactive decay are the main sources of atmospheric ionization.

Radioactivity at the surface can also produce ions in the lowest layer of the atmosphere.