Outgassing of organic materials can be approached as a surface evaporation combined with diffusion for bulk contaminant species. These species can be either initially present components, or decomposition products.
Initially present outgassing species can be: water, solvents, additives, uncured monomeric material, lubricants, ground contamination species, due to e.g. processes, test, storage, handling, prelaunch and launch.
The decomposition products are due to exposure of molecular materials to other environments, such as: thermal, solar radiation, electromagnetic and charged particles, atomic oxygen, impacts by micrometeoroids or debris, electrical discharges and arcing
These products consist of lower molecular weight (higher volatility) species than the original species.
Plume species can result from combustion, unburned propellant vapours, incomplete combustion products, sputtered material and other degradation products from a propulsion or attitude control system and its surroundings swept along with the jet.
Plumes can also be produced by dumps of gaseous and liquid waste materials of the environment control and life support systems in manned spacecraft or by leaks in systems or internal payloads. Return flux or back flow is possible due to ambient scattering, self scattering or diffusion processes.
During operation of pyrotechnics or other release mechanisms gases can evolve.
A surface can act as a secondary source if an incoming contaminant molecule reflects (i.e. does not accommodate, stick or condense on the surface) or if it has a limited residence time on that surface. Secondary sources can for example be solar panels having a higher temperature than the surrounding surfaces.