At present, the most used refrigerants are CFCs and HCFCs, followed by HFCs. The production and use of CFCs in developed countries have been banned on January 1, 1996, but some developing countries are still using them. CFCs are banned because CFCs split in the atmosphere and release chlorine atoms that destroy the ozone layer. According to information provided by UNEP (United Nations Environment Programme), if the total amount of ozone in the stratosphere is reduced by 1%, it is estimated that harmful ultraviolet rays reaching the ground will increase by 2%. The increase of harmful ultraviolet rays will produce some harms: reduce human immunity, increase the number of skin cancer and cataract patients, and increase the incidence of infectious diseases; destroy the ecosystem, inhibit plant growth and photosynthesis, and reduce crop production. It may cause mutations in certain biological species and cause new environmental problems. Therefore, the protection of ozone has attracted great attention from all countries and has become a global urgent task.
HCFCs and HFCs can also destroy ozone. The two are just different in the amount of chlorine atoms they contain. At the same time, CFCs, HCFCs and HFCs refrigerants are all considered greenhouse gases. Their impact on global warming depends on their ability to absorb infrared energy and their impact on global warming. Their size is relative to CO2. For the greenhouse effect, the GWP value of CO2 is specified as 1. The ability of a substance to destroy the ozone layer is also measured by the ODP (Atmospheric Ozone Depletion Potential). Taking CFC11 as the benchmark, the ODP value of CFC11 is specified as 1.