The Montreal Protocol categorizes which two substances based on their ozone-depletion potential?

The Montreal Protocol specifically targets substances known to have significant ozone-depletion potential, primarily focusing on chlorofluorocarbons (CFCs) and halons. CFCs are widely recognized for their role in ozone layer depletion, as they release chlorine atoms in the stratosphere, which can destroy ozone molecules. Halons, used in fire extinguishers, also release bromine upon degradation, which is even more effective at depleting ozone than chlorine.

Both CFCs and halons are considered controlled substances under the Montreal Protocol due to their adverse environmental impacts, specifically their ability to contribute to the thinning of the ozone layer, leading to increased UV radiation reaching the Earth's surface. This is critical for both environmental health and public health, as greater UV exposure can lead to skin cancer and other health issues as well as ecological damages.

In contrast, although other options include methane and hydrochlorofluorocarbons, these substances are not categorized alongside CFCs and halons in the same context under the Montreal Protocol. Methane, for instance, is a greenhouse gas but does not deplete the ozone layer, while hydrochlorofluorocarbons are subject to different regulatory aspects and do not represent the same level of risk