氯氟烃Chlorofluorocarbon

C–F 键能高（约 485 kJ/mol），分子在对流层中几乎不分解，大气寿命 CFC-11 约 50 年、CFC-12 约 100 年。到达平流层后，C–Cl 键被短波紫外线打断，释放出催化分解臭氧的氯原子。CFC 的全球变暖潜能值为 CO₂ 的数千至一万倍以上。编号规则：CFC-abc 中 a+1 为碳数减 1、b−1 为氢数、c 为氟数（CFC-12 即 CCl₂F₂）。

The C–F bond is very strong (about 485 kJ/mol), so CFCs barely decompose in the troposphere; atmospheric lifetimes are about 50 years for CFC-11 and 100 years for CFC-12. In the stratosphere short-wave UV breaks the C–Cl bond, releasing chlorine atoms that catalytically destroy ozone. Their global warming potentials are thousands to over ten thousand times that of CO₂. In the numbering CFC-xyz, x is carbons minus one, y is hydrogens plus one and z is fluorines, so CFC-12 is CCl₂F₂.

1928 年通用汽车的米奇利和亨内合成 CCl₂F₂，作为氨和二氧化硫的安全替代制冷剂，杜邦以“氟利昂”为商标生产。米奇利还曾发明四乙基铅汽油添加剂，两项发明都在后来造成严重环境问题。1974 年莫利纳和罗兰预言 CFC 破坏臭氧层，1987 年《蒙特利尔议定书》开始淘汰，发达国家 1996 年、发展中国家 2010 年停止生产。

In 1928 Thomas Midgley and Albert Henne at General Motors made CCl₂F₂ as a safe replacement for ammonia and sulfur dioxide refrigerants, and DuPont sold it under the Freon trademark. Midgley had also invented tetraethyl lead for petrol, and both inventions later caused serious environmental harm. Molina and Rowland predicted ozone damage in 1974, and the 1987 Montreal Protocol phased CFCs out: production stopped in developed countries in 1996 and in developing countries in 2010.

第一代替代品是含氢的 HCFC（如 HCFC-22，CHClF₂），在对流层可被 OH 自由基降解，但仍有少量臭氧消耗；第二代是不含氯的 HFC（如 HFC-134a，CH₂FCF₃），不破坏臭氧但温室效应强，2016 年《基加利修正案》规定逐步削减；第三代是氢氟烯烃（HFO-1234yf）以及 CO₂、氨、碳氢化合物等天然制冷剂。

The first replacements were hydrogen-containing HCFCs such as HCFC-22 (CHClF₂), broken down by OH radicals in the troposphere but still slightly ozone-depleting; the second were chlorine-free HFCs such as HFC-134a (CH₂FCF₃), harmless to ozone but potent greenhouse gases, now being phased down under the 2016 Kigali Amendment; the third are hydrofluoroolefins such as HFO-1234yf and natural refrigerants like CO₂, ammonia and hydrocarbons.