The Montreal Protocol on Substances That Deplete the Ozone Layer was signed on September 16, 1987 and has been ratified by 197 parties (all member states of the United Nations, as well as Niue, the Cook Islands, the Holy See, and the European Union), making it the most universally adopted UN treaty or protocol in history. The Protocol called for the phase-out of ozone-depleting substances (ODS) by certain deadlines in order to facilitate stratospheric ozone protection and recovery.
Chemical manufacturing, chemical production, and chemical import are all affected by this phase-out. But how has the phase-out been managed in the United States?
Ozone-depleting Substances: Class Determinations
The United States Environmental Protection Agency (EPA) adopted essentially a “worst first” approach to phasing out ODS, accomplished by establishing two classes of ODS: Class I and Class II.
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Class I Ozone-depleting Substances
Class I ozone-depleting substances are mostly chlorofluorocarbons (CFCs) that were either listed in Title VI of the Clean Air Act (CAA) when Congress amended the law to empower EPA to enact regulations in support of the Montreal Protocol (such as tricholorethane and trichlorofluoromethane) or were added later by the EPA (such as methyl bromide and chlorobromomethane). These are the substances considered to have the greatest potential to permanently damage the stratospheric ozone layer.
Class II Ozone-depleting Substances
Class II ODS are largely hydrochlorofluorocarbons (HCFCs), chemicals originally intended to replace the Class I ODS but almost as bad for the stratospheric ozone layer. This group includes substances such as pentachlorofluoropropane and dichlorofluoromethane.
Class I ODS were scheduled to be phased out of production by January 1, 2000 (with the exception of methyl chloroform, which was scheduled to be phased out by January 1, 2002). [57 FR 33754
] Methyl Bromide’s phase-out was completed in 2005.
Class II ODS follow a different schedule, with full HCFC phase-out of production and consumption to be accomplished by 2030. While HCFC reduction is incremental each year, they are still in use in the United States for the time being.
Refrigerant blends that include Class II ODS are also due to be phased out by 2030. This includes, for instance, blends that contain HCFC-22 (monochlorodifluoromethane), such as R-401A, R-402A, R-408A, R-409A, R-414B, and R-502A.
Further reading: Managing Ozone-depleting Substances in Refrigerating Appliances
Significant New Alternative Policy (SNAP)
As part of implementing the Montreal Protocol, Clean Air Act (CAA) Section 612 authorizes the EPA to use the Significant New Alternative Policy (SNAP) to find new substances to replace the phased-out ODS as adhesives, coatings, inks, aerosols, cleaning solvents, fire suppression and explosion protection, foam-blowing agents, refrigerants, sterilants, and tobacco expansion agents. Manufacturers, formulators, and end users can submit proposed substitutes for ODS to the Agency. The EPA then classifies proposed alternative substances as either:
- Acceptable (reduce overall risk to human health and the environment compared to other substitutes for a particular end-use);
- Acceptable subject to use conditions (okay only if used in a certain way);
- Acceptable subject to narrowed use limits (certain specialized applications); or
- Unacceptable (prohibited, pose significantly higher health/environmental risks).
The EPA’s newest expansion of the list of acceptable substitutes, Notice #34, was issued on October 4, 2018. That notice, as well as all previous Notices and Rules (covering substitutes deemed unacceptable or subject to use conditions/limits) can be found at https://www.epa.gov/snap/snap-regulations#notice34
Progress Made on the Ozone Layer
Since the ratification of the Montreal Protocol, the ozone layer is recovering. So far, phasing out ozone-depleting substances has reduced greenhouse gas emissions significantly. The UN predicts that, if the gains made since 1987 hold, the upper ozone layer above the Northern Hemisphere will be fully recovered by the 2030s. The Antarctic ozone hole is expected to be completely gone sometime around mid-century.
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