A volatile compound with a high mixing rate in the atmosphere. Methyl bromide escapes easily into the atmosphere where it contributes to the depletion of ozone. It works similarly to CFCs in its reaction with ozone molecules (O3). In the stratosphere, with the Sun's UV light as a catalyst, methyl bromide breaks down and exchanges a bromide ion for oxygen from ozone. By breaking down the ozone molecules in the stratosphere, methyl bromide thins the ozone layer and lets more UV light pass through.
Source: Atmospheric Chemistry Glossary