A new study led by researchers at the University of Bristol has found that a widely used car refrigerant introduced to reduce climate impacts may already be a major contributor to persistent “forever chemical” pollution across Europe.
The research suggests that HFO-1234yf, now used in almost every new vehicle manufactured since 2017, is generating substantial amounts of trifluoroacetic acid (TFA), a highly persistent per- and polyfluoroalkyl substance (PFAS) compound increasingly detected in water, crops, food and human samples.
The findings were published in Environmental Science & Technology Letters.
Using advanced atmospheric modelling and real-world emissions data, the researchers concluded that the replacement car refrigerant could already be responsible for greater TFA deposition across parts of Europe than the older refrigerant it replaced, despite being emitted in far smaller quantities.
Climate-friendly replacement under new scrutiny
HFO-1234yf was introduced to replace HFC-134a, a refrigerant with a high global warming potential that has been phased down under increasingly strict environmental regulations.
While the newer alternative significantly reduces direct greenhouse gas emissions, scientists say its atmospheric breakdown products deserve closer attention.
Both HFC-134a and HFO-1234yf eventually degrade in the atmosphere to form TFA. However, because HFO-1234yf reacts much more rapidly in the atmosphere, it can generate larger quantities of the persistent chemical over a shorter period.
TFA belongs to the broader family of PFAS, commonly referred to as “forever chemicals” because they resist natural degradation and can remain in the environment for extended periods.
Atmospheric model reveals growing impact
To assess the environmental consequences of refrigerant emissions, the research team used a global tropospheric chemistry transport model that simulates atmospheric movement, chemical reactions and the removal of pollutants through natural processes such as rainfall.
The model combined updated emissions estimates with atmospheric observations collected through the Advanced Global Atmospheric Gases Experiment (AGAGE) monitoring network to recreate present-day conditions.
Although emissions of HFC-134a remain approximately 22 times higher worldwide than HFO-1234yf, the researchers found that the newer car refrigerant may already be producing up to 75% as much TFA globally.
Across Europe, the impact appears even more pronounced. The model indicates that TFA deposited from HFO-1234yf degradation can be as much as 3.6 times higher than deposition associated with HFC-134a under conservative assumptions.
European hotspots identified
The modelling highlighted several areas where TFA deposition linked to HFO-1234yf is particularly elevated.
The greatest increases were predicted across Italy and parts of Austria, Germany, Switzerland, and France, where concentrations are closely linked to major vehicle emission regions.
Researchers say the findings demonstrate that local and regional emissions of the car refrigerant are already having measurable environmental effects despite the relatively early stage of its global adoption.
The study also examined uncertainty surrounding how much TFA is produced when HFC-134a breaks down. Under scenarios where the older refrigerant generates less TFA than current estimates suggest, the relative contribution from HFO-1234yf becomes substantially greater.
Growing concern over TFA
Interest in TFA has increased significantly as monitoring programmes continue to detect the compound across environmental and biological samples.
The study comes shortly after the European Chemicals Agency’s Risk Assessment Committee concluded that TFA should be classified as Reproductive Toxicity Category 1B, indicating it may impair fertility and harm unborn children.
The committee also supported classifying the substance as persistent, mobile and toxic (PMT), as well as very persistent and very mobile (vPvM).
These classifications have intensified efforts to understand where TFA originates and how much individual industrial sectors contribute to environmental contamination.
Calls for improved monitoring
The researchers emphasise that the worldwide transition away from HFC-134a remains ongoing, meaning emissions of HFO-1234yf are expected to continue increasing as more vehicles enter service.
As adoption expands, its contribution to TFA formation and environmental deposition is also expected to rise unless better understanding and monitoring are established.
The study highlights a major knowledge gap surrounding global HFO-1234yf emissions, noting that there is currently no international framework dedicated to monitoring or regulating worldwide production and releases of HFO refrigerants.
The researchers conclude that improved measurements of where the refrigerant is emitted, and in what quantities, will be essential for refining future estimates of TFA pollution and helping policymakers and industry better understand the environmental trade-offs associated with next-generation car refrigerant technologies.
