Greenhouse Gas (GHG)

Gas with physical properties that cause the Earth's atmosphere to warm up. There are a number of naturally occurring greenhouse gases, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and, the most common, water vapor. There are also synthetic greenhouse gases: halogenated hydrocarbons — chlorofluorocarbons (CFCs), used as aerosol propellants; hydrochlorofluorocarbons (HCFCs) such as HCFC-22 Freon, used in refrigerators; and perfluorocarbons (PFCs), used in air-conditioning units — and sulfur hexafluoride (SF6), which is used in electrical engineering and metallurgy.