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.