Outgassing (sometimes called
offgassing, particularly when in reference to
indoor air quality) is the release of a
gas that was dissolved, trapped,
frozen or
absorbed in some material. Outgassing can include
sublimation and
evaporation which are
phase transitions of a substance into a gas, as well as
desorption, seepage from cracks or internal volumes and gaseous products of slow
chemical reactions.
Boiling is generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into a vapor made of the same substance.
