An invisible chemical rain is falling across the planet

Researchers in atmospheric science, led by a team at Lancaster University, have calculated for the first time how much of this pollution has accumulated worldwide. Their analysis estimates that chemicals used to replace CFCs, along with certain anesthetic gases, led to roughly a third of a million tonnes (335,500 tonnes) of trifluoroacetic acid (TFA) being deposited from the atmosphere onto Earth’s surface between 2000 and 2022.

Pollution That Continues to Rise

The study also warns that the problem is far from peaking. Many CFC replacement chemicals remain in the atmosphere for decades, allowing TFA to continue entering the environment long after the original emissions. Researchers estimate that annual TFA production from these sources could reach its highest levels sometime between 2025 and 2100.

The findings were published in the journal Geophysical Research Letters. To reach their conclusions, the scientists relied on chemical transport modeling, a method that recreates how chemicals circulate, transform, and eventually settle out of the atmosphere.

How Refrigerants and Anesthetics Produce TFA

Using this approach, the researchers measured how TFA forms when specific gases break down in the air. These include hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), which are widely used in refrigeration systems, as well as compounds used as inhalation anesthetics.

Although these substances, known as F-gases, are being phased out (following the Montreal Protocol and the later Kigali Amendment), their overall concentration in the atmosphere continues to increase.

TFA belongs to the broader family of per- and polyfluorinated alkyl substances (PFAS). These man-made chemicals are often referred to as forever chemicals because they resist natural breakdown and can persist in the environment for extremely long periods.

Environmental and Health Questions Remain

Scientists are still refining their understanding of TFA’s potential effects. The European Chemicals Agency considers TFA harmful to aquatic life. The chemical has also been detected in human blood and urine, and the German Federal Office for Chemicals has recently proposed classifying TFA as potentially toxic to human reproduction.

While some regulatory bodies say current environmental levels of TFA are below thresholds expected to harm people, concern is growing about its steady and potentially irreversible buildup. This has prompted calls for TFA to be treated as a planetary boundary threat.

“Our study shows that CFC replacements are likely to be the dominant atmospheric source of TFA,” said Lucy Hart, PhD researcher at Lancaster University and lead author of the study. “This really highlights the broader risks that need to be considered by regulation when substituting harmful chemicals such as ozone-depleting CFCs.”

Matching Models With Real-World Evidence

To validate their results, the researchers compared their modeled estimates of TFA formation and deposition with real measurements. These included data from Arctic ice-cores and rainwater samples collected around the world.

The model was fed information on the amount and location of source gases using data from a global monitoring network. As these gases interact with other components of the atmosphere, they chemically break down and generate TFA.

Weather patterns were also incorporated into the simulations to show how TFA moves and settles. The chemical can be removed from clouds by rainfall or deposited directly from the air onto land and water surfaces.

Arctic Ice Reveals Global Reach

The results show that nearly all TFA detected in the Arctic comes from CFC replacement chemicals, even though the region is far from major emission sources. This finding underscores how widely TFA pollution is distributed across the globe.

“CFC replacements have long lifetimes and are able to be transported in the atmosphere from their point of emission to remote regions such as the Arctic where they can breakdown to form TFA,” said Lucy Hart. “Studies have found increasing TFA levels in remote Arctic ice-cores and our results provide the first conclusive evidence that virtually all of these deposits can be explained by these gases.”

New Refrigerants Add to Future Uncertainty

Outside polar regions, the study points to additional sources of concern. At midlatitude locations, the modeling supports growing evidence that HFO-1234yf, commonly used in car air conditioning systems, is becoming an important and likely expanding source of atmospheric TFA.

“HFOs are the latest class of synthetic refrigerants marketed as climate friendly alternatives to HFCs,” said Professor Ryan Hossaini of Lancaster University and co-author of the study. “A number of HFOs are known to be TFA-forming and the growing use of these chemicals for car air conditioning in Europe and elsewhere adds uncertainty to future levels of TFA in our environment.”

“There is a need to address environmental TFA pollution because it is widespread, highly persistent, and levels are increasing,” Professor Hossaini said.

Calls for Global Monitoring and Action

“The rising levels of TFA from F-gases is striking. Although HFC use is gradually being phased down, this TFA source will remain with us for decades. There’s an urgent need to understand other TFA sources and to assess TFA’s environmental impacts. This requires a concerted international effort, including more extensive TFA monitoring in the UK and elsewhere,” he said.

Professor Cris Halsall, Director of the Lancaster Environment Centre and co-author, noted that TFA’s origins are broader than once believed.

“We’ve generally viewed TFA as a breakdown product from the use of a few fluorinated pesticides, but it’s clear that TFA (a very persistent chemical in the environment) arises from the use and breakdown of a very wide group of organofluorine chemicals including refrigerants, solvents, pharmaceuticals and the PFAS group in general.”

Co-author Dr Stefan Reimann, whose research group in Switzerland closely tracks TFA-forming F-gases in the atmosphere, said the trend is consistent worldwide.

“In all regions where TFA measurements are available, a consistent picture of increasing atmospheric concentrations and deposition to Earth’s surface is emerging,” he said.

“This study is outstanding, as it combines for the first time all the important sources of atmospheric TFA and has a global focus. With increasing use of HFOs, accumulation of TFA in water bodies will potentially grow and this makes long-term monitoring a necessity.”

Their findings are detailed in the paper ‘Growth in production and environmental deposition of trifluoroacetic acid due to long-lived CFC replacements and anesthetics’.

The study involved researchers from: Lancaster University; the University of Leeds; the University of Urbino; the Commonwealth Scientific and Industrial Research Organisation, Australia; the Norwegian Institute for Air Research; the University of California San Diego; the University of Bristol; the Kyungpook National University, Korea; the Swiss Federal Laboratories for Materials Science and Technology; and the Goethe University Frankfurt.