They are the gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of radiation emitted by the Earth’s surface, the atmosphere itself and clouds. This property causes the greenhouse effect. Water vapor (H₂O), carbon dioxide (CO₂), nitrous oxide (N₂2O), methane (CH₄) and ozone (O₃) are the main GHGs present in the Earth’s atmosphere. In addition, there are a series of GHGs entirely produced by man in the atmosphere, such as halocarbons and other substances that contain chlorine and bromine, treated under the Montreal Protocol. In addition to CO₂, N₂O and CH₄, sulfur hexafluoride (SF6), hydrofluorocarbons (HFC) and perfluorocarbons (PFC) are also GHGs.
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