2.3 Ozone-Depleting Substances and Their Regulation

Ozone-depleting substances (ODSs) are chemicals that harm the Earth's protective ozone layer. These include CFCs, halons, and HCFCs, which were widely used in refrigerants, aerosols, and fire suppressants. Their atmospheric lifetimes range from months to over a century.

International efforts to reduce ODSs have been largely successful. The Montreal Protocol and its amendments have led to a 98% reduction in ODS production since 1986. However, challenges remain due to long-lived ODSs and illegal trade. Ongoing monitoring and developing alternatives are crucial.

Ozone-Depleting Substances

Classes of ozone-depleting substances

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• Chlorofluorocarbons (CFCs) contain chlorine, fluorine, and carbon atoms damage ozone layer (CFC-11, CFC-12, CFC-113)
• Halons contain bromine, fluorine, and carbon atoms highly effective fire suppressants (Halon-1211, Halon-1301)
• Hydrochlorofluorocarbons (HCFCs) transitional replacements for CFCs contain hydrogen, chlorine, fluorine, and carbon atoms
• Carbon tetrachloride ($CCl_4$) industrial solvent and cleaning agent
• Methyl chloroform ($CH_3CCl_3$) degreasing agent and industrial solvent
• Methyl bromide ($CH_3Br$) agricultural fumigant and pest control substance

Sources and lifetimes of ODSs

• CFCs used as refrigerants, aerosol propellants, foam blowing agents persist in atmosphere 50-100 years
• Halons found in fire extinguishing systems remain in atmosphere 65-120 years
• HCFCs utilized as refrigerants and in foam production have shorter atmospheric lifetime 1-20 years
• Carbon tetrachloride industrial solvent and cleaning agent lasts 26 years in atmosphere
• Methyl chloroform industrial solvent and degreasing agent persists for 5 years
• Methyl bromide agricultural fumigant and pest control substance has shortest lifetime 0.7 years

International Agreements and Effectiveness

International agreements for ODS reduction

• Vienna Convention for the Protection of the Ozone Layer (1985) established framework for international cooperation
• Montreal Protocol on Substances that Deplete the Ozone Layer (1987) legally binding agreement phased out ODSs ratified by all UN member states
• London Amendment (1990) added carbon tetrachloride and methyl chloroform to controlled substances list
• Copenhagen Amendment (1992) accelerated phase-out schedules included HCFCs and methyl bromide
• Montreal Amendment (1997) established licensing system for import/export of ODSs
• Beijing Amendment (1999) added bromochloromethane to controlled substances
• Kigali Amendment (2016) focused on phasing down hydrofluorocarbons (HFCs)

Effectiveness of ODS regulations

• Successes include 98% reduction in ODS production and consumption since 1986 observed ozone layer recovery in upper stratosphere projected full recovery by mid-21st century
• Challenges persist due to long atmospheric lifetimes of ODSs illegal production and trade of banned substances difficulty finding suitable replacements for all ODS applications
• Ongoing efforts involve monitoring atmospheric concentrations of ODSs developing ozone-friendly alternatives addressing unexpected emissions of banned substances
• Future concerns include potential impact of climate change on ozone layer recovery balancing ozone protection with climate change mitigation ensuring compliance in developing countries