When scientists discovered a hole in the ozone layer in the 1980s, they quickly attributed it to the action of chlorofluorocarbons (CFCs). The international community reacted swiftly. Countries phased out the use and production of CFCs after the passage of the Montreal Protocol and replaced them with apparently safer alternatives, which has allowed the ozone hole to heal over time.
But these chemical replacements have their own drawbacks: they’re greenhouse gases and break down into short-chain per- and polyfluoroalkyl substances (PFAS) in the atmosphere that spread to every corner of the world. A third of global atmospheric pollution of trifluoroacetic acid (TFA) comes from replacement CFCs, according to new research (Geophys. Res. Lett. 2026, DOI: 10.1029/2025GL119216). While scientists are still untangling the health effects of TFA, early research suggests that it may harm human reproduction.
“We’ve known for quite a long time that some of these CFC replacements can break down in the atmosphere to TFA, but this has never been quantified in a global model,” says Lucy Hart, a PhD student in atmospheric science at Lancaster University and lead author of the report.
Fluorinated gases that leak out of machinery such as air conditioners and refrigerators react with species such as hydroxyl radicals to break down into shorter, more-persistent molecules. In 2020, Cora Young, an analytical environmental chemist at York University, discovered a rise in TFA pollution deposited in Arctic ice cores since the 1990s; she hypothesized that the increase was connected to the refrigerants that replaced CFCs.
In the new study, Hart and a team of international researchers sought to quantify that increase in TFA using a chemical transport model. They modeled TFA production from CFC replacements like hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), and inhalation anesthetics. The model uses realistic weather patterns, atmospheric chemical processes, and degradation rates to predict where pollutants travel, what they break down to, and how fast they degrade. According to the model, 335,500 metric tons of TFA came from CFC replacements between 2000 and 2022.
The model suggests that virtually all TFA measured in Arctic ice cores came from HFCs and HCFCs. “The observational evidence from the Arctic is in excellent agreement with the model,” says Young, who wasn’t involved in this study. Young says that, since current methods for tracking TFA pollution rely heavily on ice core data, Hart’s work will be useful in capturing global pollution outside the Arctic.
Newer refrigerants like hydrofluoroolefins (HFOs), brought to the market because of their lower global warming potential, are much shorter-lived. When Hart added to the transport model a common air conditioner refrigerant for cars called 2,3,3,3-tetrafluoropropene (HFO-1234yf), she noticed that it contributes a greater share of TFA deposition at lower latitudes than HFCs and HCFCs, which contribute more TFA at higher latitudes. Since HFOs quickly break down into TFA, they may deposit TFA closer to emission sources.
Hans Peter H. Arp, an environmental chemist at Norwegian University of Science and Technology who wasn’t involved in the study, isn’t surprised by Hart’s findings. He wonders if she and her team could also use the model to create a map of TFA pollution sources, but he admits that “emission data can be very hard to get, since companies protect production volumes as confidential [intellectual property].”
Still, Hart hopes to expand the model to identify HFO emission and deposition hot spots—places where “targeted policy could have the most impact,” she says. That may be especially important, according to Arp. Production of HFOs will probably grow, he says, because a planned phaseout of most HFCs by the late 2040s and a subsequent “transition [to HFOs] will definitely increase the TFA output.” While Hart shifts her focus to HFOs, we shouldn’t wait for more research to make regulatory decisions, Arp says. “We can do that at the same time.”
