Emission

Emission may refer to:

Chemical products

 * Emission of air pollutants, notably:
 * Flue gas, gas exiting to the atmosphere via a flue
 * Exhaust gas, flue gas generated by fuel combustion
 * Emission of greenhouse gases, which absorb and emit radiant energy within the thermal infrared range
 * Emission standards, limits on pollutants that can be released into the environment
 * Emissions trading, a market-based approach to pollution control

Electromagnetic radiation

 * Emission spectrum, the spectrum of frequencies of electromagnetic radiation generated by molecular electrons making transitions to lower energy states
 * Thermal emission, electromagnetic radiation generated by the thermal motion of particles in matter
 * List of light sources, including both natural and artificial processes that emit light
 * Emission (radiocommunications), a radio signal (usually modulated) emitted from a radio transmitter
 * Emission coefficient, a coefficient in the power output per unit time of an electromagnetic source
 * Emission line, or "spectral line", a dark or bright line in an otherwise uniform and continuous spectrum
 * Emission nebula, a cloud of ionized gas emitting light of various colors
 * Emission theory (relativity), a competing theory for the special theory of relativity, explaining the results of the Michelson-Morley experiment
 * Emission theory (vision), the proposal that visual perception is accomplished by rays of light emitted by the eyes

Other uses

 * Thermionic emission, the flow of charged particles called thermions from a charged metal or a charged metal oxide surface, archaically known as the Edison effect
 * Ejaculation, the ejection of semen from the penis; also, specifically:
 * Nocturnal emission, ejaculation experienced during sleep
 * Noise, emission
 * Exhalation of air, especially in the context of musical instruments