Refrigerants that deplete the ozone layer all share one thing in common: they contain chlorine or bromine atoms. The two main classes are chlorofluorocarbons (CFCs) like R-11 and R-12, and hydrochlorofluorocarbons (HCFCs) like R-22. CFCs are the worst offenders, while HCFCs cause less damage but still contribute. Modern replacements like R-410A and R-32 contain no chlorine and have zero ozone depletion potential.
CFCs: The Most Destructive Refrigerants
Chlorofluorocarbons, made of chlorine, fluorine, and carbon, were the original synthetic refrigerants and the primary cause of the ozone hole. The most common ones used in cooling systems were CFC-11 (R-11) and CFC-12 (R-12). CFC-11 has an ozone depletion potential (ODP) of 1.0, which serves as the baseline all other substances are measured against. CFC-12 is close behind at 0.82. These chemicals are extraordinarily stable in the lower atmosphere, with CFC-11 lasting about 45 years and CFC-12 persisting for roughly 100 years before breaking down.
R-12 was once the standard refrigerant in car air conditioners and household refrigerators. R-11 was widely used in large commercial chillers. Other CFCs in the same family, including CFC-113, CFC-114, and CFC-115, were used in various industrial applications including solvents and foam-blowing agents. All CFCs were classified as Class I ozone-depleting substances under the U.S. Clean Air Act, the most harmful category. Production and import of CFCs in the United States ended in the mid-1990s.
HCFCs: Less Harmful but Still Damaging
Hydrochlorofluorocarbons were introduced as transitional replacements for CFCs. They still contain chlorine, so they still damage the ozone layer, but far less aggressively. The most widely used HCFC refrigerant was HCFC-22 (R-22), the standard in residential air conditioners for decades. R-22 has an ODP of 0.055, meaning it causes roughly one-twentieth the ozone damage of CFC-11 per unit of mass. It also breaks down much faster, with an atmospheric lifetime of about 12 years compared to 45 or 100 years for major CFCs.
Other HCFCs include HCFC-141b, used as a solvent and foam-blowing agent, and HCFC-142b, used in foam manufacturing. All HCFCs are classified as Class II ozone-depleting substances, with ODPs below 0.2. Despite being less potent than CFCs, the sheer volume of R-22 used worldwide still made it a significant contributor to ozone loss.
How These Refrigerants Destroy Ozone
CFCs and HCFCs are so stable that normal weather and chemistry in the lower atmosphere can’t break them apart. They drift upward over time into the stratosphere, where intense ultraviolet light splits them open and releases free chlorine atoms. Those chlorine atoms then attack ozone molecules in a repeating cycle: a single chlorine atom reacts with an ozone molecule, breaking it into ordinary oxygen and forming chlorine monoxide. The chlorine monoxide then reacts with a free oxygen atom, releasing the chlorine atom to go attack another ozone molecule.
This is what makes the damage so severe. Chlorine acts as a catalyst, meaning it isn’t used up in the reaction. A single chlorine atom can destroy thousands of ozone molecules before it eventually gets locked into a stable compound and removed from the stratosphere. Bromine atoms from other chemicals like halons and methyl bromide work the same way, and atom for atom, bromine is even more destructive.
The Phase-Out Timeline
The 1987 Montreal Protocol created a global schedule to eliminate ozone-depleting refrigerants. CFCs and halons were banned first, with U.S. production ending in the mid-1990s. HCFCs followed a slower, step-wise phase-out:
- 2010: Ban on production, import, and use of R-22 and HCFC-142b, except for servicing existing equipment
- 2015: Ban on production, import, and use of all HCFCs, except for servicing existing refrigeration equipment
- 2020: Ban on remaining production and import of R-22 and HCFC-142b. After this point, servicing old R-22 systems relies entirely on recycled or stockpiled supplies
- 2030: Complete ban on remaining production and import of all HCFCs
If you still have an older air conditioning system that runs on R-22, it can legally continue operating, but finding refrigerant to recharge it will become increasingly expensive and difficult as stockpiles shrink toward the 2030 deadline.
Modern Refrigerants and Why They Changed
Today’s refrigerants are hydrofluorocarbons (HFCs) and hydrofluoro-olefins (HFOs), neither of which contain chlorine. This gives them an ODP of zero. R-410A, a blend of R-32 and R-125, became the standard replacement for R-22 in home air conditioning systems. R-32 is increasingly used on its own in newer equipment because it performs well and has a lower environmental footprint than R-410A.
HFCs solved the ozone problem, but they introduced a different one. R-410A has a global warming potential of 2,088, meaning a kilogram of it traps 2,088 times more heat than a kilogram of carbon dioxide. That’s why the 2016 Kigali Amendment to the Montreal Protocol now requires a global phase-down of high-GWP HFCs as well. The next generation of refrigerants, HFOs like R-1234yf and R-1234ze, have both zero ozone depletion potential and very low global warming potential. R-1234yf is already standard in new car air conditioning systems.
Natural refrigerants, including ammonia, carbon dioxide, and propane, are also gaining ground in commercial and industrial applications. These substances have zero ODP and negligible global warming potential, though each comes with its own practical trade-offs around flammability, toxicity, or operating pressure.
Is the Ozone Layer Recovering?
The Montreal Protocol is widely considered the most successful international environmental agreement ever enacted. With CFC production essentially eliminated worldwide and HCFC use declining sharply, stratospheric chlorine levels have been dropping for years. The 2022 assessment by the World Meteorological Organization and the United Nations projects near-complete recovery of the ozone layer by the middle of this century.
That recovery matters for human health. Ozone depletion allows more UV-B radiation to reach Earth’s surface, which increases rates of skin cancer, cataracts, and weakened immune response. Without the Montreal Protocol, unrestricted CFC emissions could have quadrupled skin cancer incidence by 2100. Instead, projections show skin cancer rates peaking around 10% above current levels near 2060, then declining as the ozone layer heals. For every 1% sustained decrease in ozone, cataract incidence rises by about 0.5%, so the ongoing recovery has direct consequences for eye health as well.