Halons are a group of brominated organic compounds used as fire retardants. The transport of these compounds to the stratosphere, followed by their photolysis to release Br (Bromine) atoms, gives this group a very high ozone depletion potential. The production of these compounds is now banned according to the Montreal Protocol.
Halogens are made up of the elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The first four members are present in trace amounts in the atmosphere as a result of both natural and anthropogenic activity.
Definition source: National Oceanic and Atmospheric Administration