Where does emission collide?

In physics, emission is the release of energy as light when an atom or molecule drops from a higher energy level to a lower one and gives off the extra energy as a photon, whose colour records the size of the drop; the collection of colours a substance gives off is its emission spectrum. Emission can happen on its own, called spontaneous, or be triggered by a passing photon of the same energy, called stimulated, and Schawlow and Townes's 1958 Infrared and Optical Masers showed how stimulated emission could be harnessed to produce the coherent light of a laser. The referent is a quantum of light leaving matter, described by its wavelength and its rate, and it is not a pollutant poured into the air or a new security placed into a market.[1]

Unit

A single emitted photon, set by the energy gap and seen as a spectral line

Recovery means

The emitting atom falls to a lower level and must be excited again before it can emit once more

Measured by

Recorded with a spectrometer as the wavelengths and intensities of the light given off

In environmental science, an emission is the release of a substance, such as a gas or a particle, from a source into the atmosphere; carbon dioxide emissions, for example, are the mass of that gas discharged when fuel is burned, and the totals are added up across many sources into emission inventories. Marland and Rotty's 1984 Carbon dioxide emissions from fossil fuels set out a procedure for estimating national totals from fuel-use figures, work that later inventories build on. The referent is a quantity of matter entering the air from a source, counted in mass over time, and it is not a photon leaving an atom or a new security placed into a market.[2]

Unit

A quantity of a substance released to the air from a source, in mass per unit time

Recovery means

Not applicable

Measured by

Estimated from activity data and emission factors, or measured directly at the source by monitoring