Halogenated hydrocarbons are extensively used as refrigerants and contain chlorine atoms, which are responsible for the depletion of the ozone layer in the stratosphere of the earth. When halogenated hydrocarbons containing chlorine are released into the atmosphere, they slowly move into the upper layers of the earth’s atmosphere where the cloud of ozone is located. Here the chlorine atoms from the halogenated carbons get liberated and they react with ozone converting it into oxygen. Ozone has the capacity to block sun’s ultraviolet radiations, but oxygen cannot block them.
Here are some of the halogenated hydrocarbon refrigerants that cause ozone layer depletion and greenhouse:
Chlorofluorocarbons (CFCs): The halogenated carbons that contain at least one atom of chlorine in their compound are called chlorofluorocarbons. The larger the number of chlorine atoms in the CFCs the more their tendency to destroy the ozone layer. The refrigerant R-11 (CCL3F) that contains three atoms of chlorine has maximum tendency to deplete the ozone layer. The “Relative Ozone Destruction Efficiency" of R-11 is considered to be 1, which is maximum amongst all the refrigerants. In fact R-11 is used as the reference to compare the relative ozone destruction capacity of all the refrigerants. Some of the other dangerous CFCs are R-12, R-113, and R-114.
CFCs are considered to be the most dangerous to the ozone layer and greatest cause of the global warming. Sometimes their life in atmosphere can be even more than a hundred years. As per the Montreal Protocol signed in 1987, all the CFCs are supposed to be out of production by January 1996 in developed countries and by 2000 in the developing countries.
Hydrochlorofluorocarbons (HCFCs): These are the halogenated hydrocarbons from which not all the atoms of hydrogen are removed. That means they contain at least one atom of hydrogen. The HCFCs used as the refrigerants usually contain lesser numbers of the chlorine atoms and have less overall life in the atmosphere. This makes them less dangerous to the depletion of the ozone layer and the cause of the global warming or greenhouse effect. The HCFC refrigerant most widely used is R-22 (CCL2F2), which has Relative Ozone Destruction Efficiency of 0.05.
Since they have less detrimental effects, HCFCs are being used as the transitional refrigerants till the new alternative refrigerants for various applications are found. Eventually, all the HCFCs have also to be phased out by the year 2030.
Most of the CFCs and HCFCs causing ozone layer depletion and greenhouse effect are already being phased out. A number of alternative refrigerants have been developed and still many more new are being developed. Some of these refrigerants are entirely new ones, while the others are the mixture of two or more refrigerants.
Read more about refrigerants here:
Ozone Layer Friendly Refrigerants: Alternatives to CFCs