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
Natural gas in the United States the oil and the gas are treated separately. Gas flows through a gathering system into a pipeline to a gas processing plant. As of 2014, there were 189,000 miles of interstate natural gas pipelines in the United States Natural gas has a variety of chemical constituents that must be removed or diluted with other gas to achieve consistent pipeline quality. Pipeline gas specifications vary from line to line, but generally the gas must contain no appreciable hydrogen sulfide (which is toxic), less than a few percent carbon dioxide (carbon dioxide reacts with water to form carbonic acid, which is corrosive