Atmosphere of Earth the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around . Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around
Inerting (gas) of liquid is drawn from a tank, a similar volume of air will enter the tank's headspace, potentially creating an ignitable atmosphere. The inerting systems use an inert gas generator to supply inert make-up gas instead of air. This procedure is often referred to as "inerting". Technically, the procedure ensures that the atmosphere in the tank's headspace remains unignitable. The gas mixture in the headspace is not "inert" per se, it's just unignitable. Because of its content of flammable vapors, it will burn if mixed with air. Only if enough inert gas is supplied as part of a "purge-out-of-service" procedure,