The Montreal Protocol of 1987 is often cited as the most successful environmental treaty ever created. This is steadily phasing out chemicals worldwide that once damaged the ozone layer and increased the risk of diseases such as skin cancer.
An MIT-led study showed that by cutting out these ozone-depleting substances, the ozone layer slowly recovers. (Some estimates suggest a return to 1980 levels as early as 2040.) But the agreement included exceptions. Certain ozone-depleting chemicals are still used as raw materials to make other materials, with the idea that only a small portion, about 0.5 percent, escapes into the atmosphere.
That assumption is now being questioned.
Increase in chemical leaks raises new concerns
In recent years, scientists have detected higher-than-expected levels of ozone-depleting substances in the atmosphere. This led to updated estimates showing that leakage from raw material use was significantly greater than previously thought.
An international research team, including scientists from MIT, is now investigating how these high leakage rates will affect the recovery of the ozone layer. Their findings indicate that ozone recovery could be delayed by about seven years if this problem is not addressed.
“We’ve realized in the last few years that these feedstock chemicals are bugs in the system,” says author Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry, who helped identify the original cause of the ozone hole. “The production of ozone-depleting substances has all but stopped around the world, except for this one use, which turns chemicals into something else.”
Industrial applications that promote continuous emissions
The study, to be published in Nature Communications, is the first to fully measure the impact of emissions from raw materials. These chemicals are widely used in the production of plastics, non-stick coatings, and substitute chemicals for substances already restricted by the Montreal Protocol.
The researchers emphasize that reducing both the use of these raw materials and their leakage is becoming increasingly important, especially as global demand for products such as plastics continues to increase.
“If we want this protocol to be as successful in the future as it has been in the past, we have reached the point where the parties really need to think about how to regulate the emissions of these industrial processes,” says lead author Stefan Reimann of the Swiss Federal Institute for Materials Science.
“To me, this makes sense because so many other things have already been completely abolished. So why does this exemption need to exist if it’s going to cause harm?” Solomon says.
The research team includes scientists from institutions in the United States, Europe, and Asia, including MIT, NASA, NOAA, and several universities and research centers.
How was the ozone hole discovered?
Concern about ozone layer depletion dates back to 1985. At that time, scientists discovered a hole growing in the ozone layer above Antarctica. This thinning allows more harmful ultraviolet light from the sun to reach the Earth’s surface.
A year later, Solomon and other researchers traveled to Antarctica to confirm the cause. The damage was caused by chlorofluorocarbons (CFCs), which are widely used in refrigeration, air conditioning, and aerosol products.
These discoveries led to the creation of the Montreal Protocol, an international agreement involving 197 countries and the European Union to limit the use of these chemicals. The decision to allow the use of the feedstock was based in part on industry estimates that leakage remains very low.
“The emissions of these materials as raw materials were thought to be small compared to things like refrigerants and foam,” Western says. “Also, because people are essentially leaking profits if the raw materials are released into the atmosphere, leaks from these sources were believed to be small, about 0.5 percent of what came in.”
New data shows high leakage rates
Those assumptions no longer seem to hold true. Western and Reimann are part of the Advanced Global Atmospheric Gases Experiment (AGAGE), a worldwide monitoring network that tracks emissions of ozone-depleting substances.
Recent measurements suggest feedstock leakage rates are close to 3.6%, with even higher losses for some chemicals.
The researchers used 3.6 percent as a baseline scenario in their analysis and compared it to a lower leak rate of 0.5 percent and a scenario with no material emissions. They also analyzed production trends from 2014 to 2024 and estimated future use of these chemicals through 2100.
The results show that total emissions of ozone-depleting substances will continue to decline under all scenarios until around 2050, thanks to regulations already in place. However, if higher leakage rates persist, emissions will level off around 2045 and only decline by about 50% by 2100.
Possible delay in ozone recovery schedule
The team then assessed how these emissions affected the ozone layer itself. If leakage were reduced to 0.5%, the ozone layer would return to its 1980 state by 2066. Once emissions are completely eliminated, recovery will occur by 2065.
However, current estimates of leakage mean recovery will be delayed until 2073, approximately seven years later.
“This paper sends an important message that these emissions are too high and we must find ways to reduce them,” Lyman said. “That means either eliminating the use of these materials as raw materials, replacing the chemicals, or reducing fugitive emissions during use.”
Can industry and policy adapt?
Despite their concerns, researchers are optimistic that a solution is within reach. Solomon points out that the chemical industry has a long history of innovation and adaptation.
“There are a lot of innovators in the chemical industry,” Solomon says. “They make a living creating new chemicals and refining chemicals. Sure, they might get too hung up on a particular chemical, but that doesn’t happen often. In fact, they’re usually very active in considering alternatives. Why not switch when there are thousands of other chemicals that could be used instead? That was the attitude.”
She also points out that the ability of monitoring networks like AGAGE to detect these emissions highlights how much progress has already been made in reducing other sources of ozone damage.
“This is not the first time that the AGAGE network has made measurements that have made the world realize that we need to do a little bit better here and there,” Western says. “Oftentimes it’s just a mistake. Sometimes strengthening some processes just requires making people more aware of these things.”
A global effort to close the gap
Countries participating in the Montreal Protocol meet annually to consider new issues. Feedstock emissions have already been discussed, and future meetings are likely to focus on how to reduce or eliminate these leaks.
“We wanted to send a warning that something was wrong here,” Lyman said. “We can reduce the period of ozone depletion by many years. That may not sound like a long time, but if you can count the number of skin cancers avoided in that time, it would seem very significant.”
This research was supported in part by the National Science Foundation, NASA, the Swiss Federal Environment Agency, the VoLo Foundation, the UK Natural Environment Research Council, and the Korea Meteorological Agency Research and Development Program.
