Ionized-air glow

Ionized-air glow is the luminescent emission of characteristic blue–purple–violet light, often of a color called electric blue, by air subjected to an energy flux either directly or indirectly from solar radiation.

Water vapor, when present, may also play a role; its presence is characterized by the hydrogen emission lines.

While deexcitation can occur by emission of photons, the more probable mechanism at atmospheric pressure is a chemical reaction with other oxygen molecules, forming ozone:[2] This reaction is responsible for the production of ozone in the vicinity of strongly radioactive materials and electrical discharges.

This may happen when the air contains high amount of water, e.g. with lightnings in low altitudes passing through rain thunderstorms.

Despite the production of similarity-colored light and an association with high-energy particles, Cherenkov radiation is generated by a fundamentally different mechanism.