Ozone Depleting Substances (ODS) are manufactured chemical compounds that threaten the stratospheric ozone layer. Once released, these stable chemicals migrate upward into the upper atmosphere, where they remain for decades. In the stratosphere, intense ultraviolet (UV) radiation breaks them down, releasing halogen atoms that catalytically destroy ozone molecules. This thinning allows higher levels of harmful UV-B radiation to reach the planet’s surface, increasing the risks of skin cancer, cataracts, and damage to plant and marine life.
Primary Categories of Ozone Depleting Substances
ODS generally fall into distinct families, all characterized by high stability and the presence of chlorine or bromine atoms. Chlorofluorocarbons (CFCs) were the earliest and most widespread group, valued for being non-toxic, non-flammable, and highly effective. Their long atmospheric lifetimes mean a single chlorine atom can destroy thousands of ozone molecules.
Hydrochlorofluorocarbons (HCFCs) were introduced as temporary substitutes for CFCs. They contain hydrogen, making them less stable and less damaging to the ozone layer than CFCs. Halons are potent, bromine-containing compounds with a much higher ozone-depleting potential than chlorine-based substances. Methyl bromide, a gas primarily used as a fumigant to control pests, is also a significant ODS due to its bromine content.
Refrigeration and Air Conditioning Equipment
The single largest historical application for ODS was in the temperature control industry, primarily using CFCs and HCFCs as refrigerants. Refrigerators and freezers manufactured before the mid-1990s often contain CFC-12 (R-12) within their cooling circuits. Improper disposal of these appliances can release the entire refrigerant charge into the atmosphere.
In air conditioning, the most common legacy ODS is HCFC-22 (R-22), which was standard for residential and commercial units installed until the early 2010s. Although R-22 production has ceased, the chemical remains in millions of existing systems, requiring careful handling during servicing to prevent leaks. Vehicle air conditioning systems in cars made before 1994 relied heavily on CFC-12, necessitating strict rules for its recovery and recycling during repair or scrapping.
ODS were also incorporated into foam insulation used in these appliances and in building materials. CFCs and HCFCs acted as “blowing agents” to create rigid foam structures found in refrigerator doors, freezer walls, and polyurethane panels. Even after the refrigerant is removed, these foams can slowly release their ODS content over time or during demolition. This trapped ODS must be addressed through specialized recycling processes that capture the foam-blowing agent.
Consumer and Industrial Aerosols and Solvents
The second major category of ODS-containing products includes aerosols and solvents. Historically, consumer aerosol spray cans, such as those for hairspray and household cleaners, utilized CFCs as propellants. This application was phased out decades ago, with modern aerosols now using alternatives like propane or butane.
ODS use in industrial and specialized applications persisted longer due to the chemicals’ unique properties. Halons were adopted in sophisticated fire suppression systems for protecting valuable equipment in data centers, military vehicles, and aircraft. They extinguish fires quickly without damaging electronics. These systems are now tightly regulated, and Halon supplies are limited to recycled material for existing safety-critical uses.
CFCs and HCFCs also functioned as highly effective cleaning solvents and degreasers in industrial settings, particularly for the precision cleaning of electronic circuit boards and metal components. This practice has since been replaced by aqueous cleaning solutions and other modern solvent alternatives. The use of carbon tetrachloride as a solvent was also common in chemical manufacturing and dry-cleaning until its ozone-depleting properties were regulated.
Global Phase-Outs and Current Regulatory Status
The control of ODS is governed by the Montreal Protocol, a landmark international treaty established in 1987 that set mandatory timetables for their phase-out. The agreement defined two classes: Class I substances (CFCs and Halons), which are almost completely phased out globally, and Class II substances (HCFCs), which were scheduled for a later phase-out due to their lower short-term threat. In the United States, the Environmental Protection Agency (EPA) implements these controls under the Clean Air Act.
While the production and import of most ODS have ceased, the chemicals remain in the existing “bank” of legacy equipment. The complete phase-out of HCFCs, such as R-22, for use in new equipment has largely occurred. However, regulatory frameworks mandate that refrigerants removed from older units must be reclaimed or destroyed, ensuring ODS are not vented into the atmosphere during servicing or disposal.
Consumers play a direct role by ensuring older appliances are disposed of correctly. When a refrigerator or air conditioner reaches the end of its life, it should be sent to a dedicated recycling program to safely recover the refrigerant and the ODS trapped within the foam insulation. The transition away from ODS has led to the adoption of new refrigerants like Hydrofluorocarbons (HFCs) and Hydrofluoroolefins (HFOs), which shift the focus to managing their global warming potential.