The physical properties of greenhouse gases (GHG) contribute to the greenhouse effect. Their increased concentration in the earth’s atmosphere is causing global warming. The main non-manmade greenhouse gases are steam (H₂O), carbon dioxide (CO₂), methane (CH₄), dinitrogen oxide (N₂O) and ozone (O₃). Industrial greenhouse gases include fluorinated gases such as chloridofluoridocarbons (CFC) and chlorodifluoromethanes (HCFC-22) such as Freon, tetrafluoromethane (CF₄) and sulfur hexafluoride (SF₆).