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 was published in Nature Communications today , 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 U.S. National Science Foundation, the U.S. National Aeronautics and Space Administration (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.
