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How do halons differ from CFCs in ozone-depleting potential?

Halons have a higher ozone-depleting potential than CFCs due to their higher number of reactive bromine atoms.

Halons and CFCs (Chlorofluorocarbons) are both types of ozone-depleting substances (ODS). They are man-made chemicals that have been used in various applications, such as refrigeration, air conditioning, aerosols, and fire extinguishing systems. However, their impact on the ozone layer varies significantly due to their chemical composition.

Halons are bromine-based compounds, while CFCs are chlorine-based. The difference lies in the fact that bromine is much more efficient at destroying ozone than chlorine. A single bromine atom can destroy up to 100 times more ozone molecules than a chlorine atom. This makes halons much more destructive to the ozone layer on a molecule-for-molecule basis.

The ozone-depleting potential (ODP) of a substance is a measure of its ability to destroy ozone in the stratosphere relative to a reference substance, usually CFC-11. The ODP of CFC-11 is defined as 1. Halons, due to their bromine content, have ODPs that are much higher than 1. For example, Halon-1301, a common type of halon, has an ODP of 10, meaning it is 10 times more destructive to the ozone layer than CFC-11.

Furthermore, halons have longer atmospheric lifetimes than CFCs, meaning they remain in the atmosphere for a longer period of time, increasing their potential to deplete the ozone layer. This is because halons are less reactive in the lower atmosphere and are not easily removed by rainfall or other atmospheric processes. As a result, they can reach the stratosphere where they can deplete the ozone layer.

In conclusion, while both halons and CFCs contribute to ozone depletion, halons are significantly more potent due to their higher number of reactive bromine atoms and longer atmospheric lifetimes. This is why the phase-out of halons has been a key focus of international efforts to protect the ozone layer.

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