Industrial chemicals delay recovery of the ozone layer

Ozone protection under pressure

Peer-Reviewed Publication

Swiss Federal Laboratories for Materials Science and Technology (Empa)

News Release 16-Apr-2026

Although ozone-depleting chemicals such as carbon tetrachloride (CCl₄) or certain chlorofluorocarbons (CFCs) are no longer used in refrigerators and foams, they continue to serve as feedstocks in industrial processes for the production of modern refrigerants and plastics. Until now, these so-called feedstock chemicals have flown under the radar of international agreements because the quantities produced and leakage rates were significantly underestimated.

Working with international research groups, Empa researchers have now used global measurements to show that during the production and processing of these substances, approximately three to four percent escapes into the atmosphere through leaks. Furthermore, their use has increased significantly in recent decades. In a study published in Nature Communications, they have now calculated that, as a result, the ozone layer is likely to recover about seven years later than previously assumed – unless emissions are reduced. “These substances are not only ozone-depleting but also highly harmful to the climate. Lower emissions would thus benefit both the ozone layer and the climate,” says Stefan Reimann, an atmospheric scientist at Empa and lead author of the study.

Measurements show higher emissions

When the Montreal Protocol was negotiated in the 1980s and later strengthened, it led to a global ban on ozone-depleting substances in everyday products. Feedstock chemicals, however, were exempt from this ban. At the time, industry assumed that only about 0.5 percent of the quantities produced would escape into the atmosphere and that the use of these substances would decline in the long term. “But this assessment has not been accurate anymore for quite some time,” says Reimann. “Feedstock chemicals are now being released in increased quantities during production, transport, and further processing, and the volumes currently being produced are significantly larger than was assumed 30 years ago.”

These new findings are based on global atmospheric measurements from international networks such as the Advanced Global Atmospheric Gases Experiment (AGAGE), which includes the Empa research station on the Jungfraujoch. Since many ozone-depleting substances remain in the atmosphere for decades, their concentrations allow conclusions to be drawn about global emissions. “We measure the concentrations of these substances in the atmosphere. Based on their lifetimes, we can calculate how much they should actually be decreasing. If they aren’t, emissions must still be occurring,” explains Martin Vollmer, an Empa researcher and co-author of the study.

A comparison of these measurements with the production figures officially reported by individual countries shows that today, an average of three to four percent of the feedstock produced enters the atmosphere – several times the originally assumed values. For carbon tetrachloride, which is particularly harmful to the ozone layer, emission rates are even above four percent.

Why usage is increasing

However, emissions are rising not only because of higher production losses, but also because the overall use of feedstock chemicals is increasing – by about 160 percent since the year 2000. Some of these feedstocks were initially used to produce hydrofluorocarbons (HFCs), which were introduced as refrigerant substitutes following the ban on CFCs. Since these substitutes later proved to be potent greenhouse gases, they are now being phased out under the so-called Kigali Amendment. They are increasingly being replaced by hydrofluoroolefins (HFOs), which have little impact on the climate but whose production again relies heavily on ozone-depleting feedstock chemicals.

Added to this is a rapidly growing use in the polymer industry – for example, in the production of fluoropolymers such as Teflon (PTFE) or polyvinylidene fluoride (PVDF), an important material in lithium-ion batteries for electric cars. “The quantities of feedstock are not decreasing but will continue to grow, at least in the coming years,” says Reimann.

Both the ozone layer and the climate are affected

Based on these developments, the international research team calculated various future scenarios. They compared, for example, the originally assumed, very low emission rates with the values measured today from the use of feedstock chemicals. The established benchmark from 1980, when global ozone depletion was first observed, serves as a reference. Until now, it was assumed that this original state of the ozone layer would be reached again around the year 2066. However, the new calculations show that if feedstock emissions remain at current levels, this timeline will shift by about seven years. The stratospheric ozone layer would therefore not fully recover until around 2073. The margin of uncertainty for this estimate ranges from six to eleven years.

However, the feedstock chemicals released not only damage the ozone layer but also act as powerful greenhouse gases. If nothing changes, these additional climate-damaging emissions will reach around 300 million metric tons of CO₂ equivalents per year by mid-century – comparable to the current annual CO₂ emissions of a country like England or France. Reducing these emissions would therefore have a dual benefit.

Whether these emissions will be reduced in the future through binding emission limits or a targeted restriction of particularly problematic substances is, according to Stefan Reimann, ultimately a political decision. Even though the Montreal Protocol continues to be regarded as one of the greatest successes of international environmental policy, it should be regularly reviewed and, if necessary, adapted in light of new scientific findings. “The Montreal Protocol was successful because science, politics, and industry worked closely together. Such cooperation is crucial again today to address new challenges,” says Reimann.

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A regulatory loophole could delay ozone recovery by years

Scientists say an exception in the Montreal Protocol for the use of ozone-depleting feedstocks could set the ozone recovery back seven years.

Peer-Reviewed Publication

Massachusetts Institute of Technology

News Release 16-Apr-2026

Often hailed as the most successful international environmental agreement of all time, the 1987 Montreal Protocol continues to successfully phase out the global production of chemicals that were creating a growing hole in the ozone layer, causing skin cancer and other adverse health effects.

MIT-led studies have since shown the subsequent reduction in ozone-depleting substances is helping stratospheric ozone to recover. (It could return to 1980 levels by as early as 2040, according to some estimates.) But the Montreal Protocol made an exception in its rules for the use of ozone-depleting substances as feedstocks in the production of other materials. That’s because it was thought that only a small amount — just 0.5 percent — of the ozone-depleting substances used for this purpose would leak into the atmosphere.

In recent years, however, scientists have observed more ozone-depleting substances in the atmosphere than expected, and have increased their estimates of leakage from feedstocks.

Now an international group of scientists, including researchers from MIT, has calculated the impact of different feedstock leakage rates on the ozone’s fragile recovery. They find the higher leakage rates, if not addressed by the Montreal Protocol, could delay ozone recovery by about seven years.

“We’ve realized in the last few years that these feedstock chemicals are a bug in the system,” says author Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry, who was part of the original research team that linked the chemicals to the ozone hole. “Production of ozone-depleting substances has pretty much ceased around the world except for this one use, which is when you have a chemical you convert into something else.”

The paper, which will be published in Nature Communications, is the first to comprehensively quantify the impact of leaked feedstocks, which are currently used to make plastics and nonstick chemicals. They are also used to make substitute chemicals for the ones regulated under the Montreal Protocol. The researchers say it shows the importance of curbing use and preventing leakage of such feedstocks, especially as the production of their end products, like plastic, is projected to grow.

“We’ve gotten to the point where, if we want the protocol to be as successful in the future as it has been in the past, the parties really need to think about how to tighten up the emissions of these industrial processes,” says first author Stefan Reimann of the Swiss Federal Laboratories for Materials Science and Technology.

“To me, it’s only fair, because so many other things have already been completely discontinued. So why should this exemption exist if it’s going to be damaging?” says Solomon.

Joining Reimann on the paper are his colleagues Martin K. Vollmer and Lukas Emmenegger; Luke Western and Susan Solomon of the MIT Center for Sustainability Science and Strategy and the Department of Earth, Atmospheric and Planetary Sciences; David Sherry of Nolan-Sherry and Associates Ltd; Megan Lickley of Georgetown University; Lambert Kuijpers of the A/gent Consultancy b.v.; Stephen A. Montzka and John Daniel of the National Oceanic and Atmospheric Administration; Matthew Rigby of the University of Bristol; Guus J.M. Velders of Utrecht University; Qing Liang of the NASA Goddard Space Flight Center; and Sunyoung Park of Kyungpook National University.

Repairing the ozone

In 1985, scientists discovered a growing hole in the ozone layer over Antarctica that was allowing more of the sun’s harmful ultraviolet radiation to reach Earth’s surface. The following year, researchers including Solomon traveled to Antarctica and discovered the cause of the ozone deterioration: a class of chemicals called chlorofluorocarbons, or CFCs, which were then used in refrigeration, air conditioning, and aerosols.

The revelations led to the Montreal Protocol, an international treaty involving 197 countries and the European Union restricting the use of CFCs. The subsequent decision to exempt the use of ozone-depleting substances for use as feedstocks was based partially on industry estimates of how much of their feedstocks leaked.

“It was thought that the emissions of these substances as a feedstock were minor compared to things like refrigerants and foams,” Western says. “It was also believed that leakage from these sources was minor — around half a percent of what went in — because people would essentially be leaking their profits if their feedstocks were released into the atmosphere.”

Unfortunately, some of those assumptions are no longer true. Western and Reimann are part of the Advanced Global Atmospheric Gases Experiment (AGAGE), a global monitoring network co-founded by Ronald Prinn, MIT’s TEPCO Professor of Atmospheric Science. AGAGE monitors emissions of ozone-depleting substances around the world, and in recent years researchers have revised their estimates of feedstock leakage upwards, to about 3.6 percent. For some chemicals, the number was even higher.

In the new paper, the researchers estimated a 3.6 percent feedstock leakage as the baseline for most chemicals. They compared that with a scenario where 0.5 percent of feedstocks are leaked from 2025 onward and a scenario with zero feedstock-related emissions. The researchers also looked at production trends between 2014 and 2024 to project how much of each specific ozone-depleting chemical would be used as feedstock between 2025 and 2100.

The analysis shows that until 2050, total ozone-depleting chemical emissions decrease in all scenarios as rising feedstock emissions are offset by declining uses enforced by the Montreal Protocol. In the scenario with continued 3.6 percent leakage, however, emissions level off around 2045, and total emissions only decrease by 50 percent overall by 2100.

The researchers then evaluated the impact of feedstock-related emissions on stratospheric ozone depletion. In the scenario where feedstock leakage is 0.5 percent, the ozone returns to its 1980 status by 2066. In the scenario with zero feedstock leakage, the ozone reclaims its 1980 health in 2065. But in the baseline scenario, the recovery is delayed about seven years, to 2073.

“This paper sends an important message that these emissions are too high and we have to find a way to reduce them,” Reimann says. “Either that means no longer using these substances as feedstocks, swapping out chemicals, or reducing the leakage emissions when they are used.”

A global response

Solomon is confident industries will be able to adjust to the latest findings.

“There are a lot of innovators in the chemical industry,” Solomon says. “They make new chemicals and improve chemicals for a living. It’s true they can perhaps get too entrenched with certain chemicals, but it doesn’t happen that often. Actually, they’re usually quite willing to consider alternatives. There are thousands of other chemicals that could be used instead, so why not switch? That’s been the attitude.”

Solomon says the fact that AGAGE can detect the impact of feedstock emissions is a testament to the progress the world has made in reducing emissions from other sources up to this point. She believes raising awareness of the feedstock problem is the first step. 

“This isn't the first time that the AGAGE Network has made measurements that have allowed the world to see we need to do a little better here or there,” Western says. “Often, it’s just a mistake. Sometimes all it takes is making people more aware of these things to tighten up some processes.”

Members of the Montreal Protocol meet every year. In those meetings, they split into working groups around different topics. Feedstock emissions are already one of those topics, so participants will review the evidence together. Typically, they release a statement about mitigation strategies if needed.

“We wanted to raise the warning flag that something is wrong here,” Reimann says. “We could reduce the period of ozone depletion by years. It might not sound like a long time, but if you could count the skin cancer cases you’d avoid in that time, it would seem quite significant.”

The work was supported in part by the National Science Foundation, NASA, the Swiss Federal Office for the Environment, the VoLo Foundation, the United Kingdom Natural Environment Research Council, and the Korea Meteorological Administration Research and Development Program.