Final answer:
The Montreal Protocol controls the production and emission of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons, all of which deplete the ozone layer. Due to global cooperation under this treaty, the use of these substances has significantly declined, allowing the ozone layer to gradually recover.
Step-by-step explanation:
The Montreal Protocol is an international agreement designed to phase out substances that deplete the ozone layer. This treaty controls the production and emission of various chemicals, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons. CFCs were once widely used in refrigerants and aerosol sprays but have been phased out due to their damaging effects on the ozone layer. HCFCs have been introduced as a temporary replacement for CFCs, but they are also on a phase-out schedule due to their less harmful yet still ozone-depleting effects. Halons, which are used in fire extinguishers, are also controlled by the Montreal Protocol because of their ozone-depleting potential.
The protocol has successfully reduced the use of these harmful substances globally, contributing to the ongoing recovery of the ozone layer. The most promising alternatives that have been proposed in place of CFCs and HCFCs include hydrofluorocarbons (HFCs) and other more environmentally friendly chemicals.