Definition of chemical fog in English:

chemical fog

noun

  • 1Photography a diffuse background darkening in a photographic film or paper caused by a chemical reaction with substances in the developing solution, the atmosphere, etc.

  • 2A cloud of suspended particles or droplets in the air resembling fog or smoke and produced by the release of chemicals.

Origin

Mid 19th century; earliest use found in Charles Smyth (1819–1900), astronomer.