FCKW, or fluorochlorocarbons, are chemical compounds that were commonly used in refrigeration, air conditioning, and aerosol propellants. They are known for their ability to cool and propel products but have been found to contribute significantly to the depletion of the ozone layer in the Earth's atmosphere. Due to their harmful environmental effects, the production and use of FCKW have been largely phased out under the Montreal Protocol, an international treaty aimed at protecting the ozone layer. Alternatives, such as hydrofluorocarbons (HFCs), have been developed, although they also pose environmental challenges.