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Researchers sound further warnings about HFOs

A new report from the German Environment Agency, and research from the University of New South Wales have raised more concerns about the environmental impacts of HFO refrigerants.

When hydrofluorocarbons (HFCs) were identified as greenhouse gases, and targeted for phase-down under the Kigali Amendment to the Montreal Protocol, hydrofluoroolefins (HFOs) were put forward as an ideal alternative. Because of their chemical composition, HFOs break down quickly in the atmosphere and therefore have very low global warming potential (GWP).

But increasingly, researchers are identifying issues with HFOs and the chemicals they produce when they break down.

HFOs “problematic”

A new report published by the German Environment Agency has taken a closer look at HFOs and their degradation products, in particular trifluoroacetic acid or TFA.

TFA finds its way into water bodies such as rivers and lakes through precipitation, and eventually into plants, fish, animals and humans. Although it has previously been classed as having very low toxicity, recent research has indicated it may impact health. It is extremely persistent in the environment, has high mobility, and cannot be removed by current water treatment technology.

The report models the demand, the emissions, and the amount of degradation products of HFOs up to 2050. Of particular note is R1234yf, used extensively in automotive air conditioning as a replacement for R134A.

The modelling indicates that HFOs, especially R1234yf, will add a large additional share to the amounts of TFA in the atmosphere.

To quantify how much TFA would enter the environment via precipitation, a two-year nationwide measurement program was carried out in Germany, from February 2018 to March 2020. This found significantly higher concentrations of TFA in rainwater. This research was also used to inform the modelling, which indicated that by 2050 the refrigerant R1234yf alone is expected to cause TFA inputs from precipitation of 2.5kg/km2 per year for Europe and up to 4kg/km2 per year for Germany – a tenfold increase over today’s TFA inputs.

The researchers concluded that the use of HFOs “must be regarded as problematic” and suggested they should be replaced by “more sustainable solutions with halogen-free substances”.

“If manufacturers and operators now change over to systems using natural substances with a low global warming potential, such as hydrocarbons, carbon dioxide or ammonia,” says German Environment Agency President Dirk Messner, “both the emissions of TFA can be significantly reduced and the climate can be protected.”

Could HFOs be adding to greenhouse effect?

Adding to the concerns over TFA, a new study from the University of New South Wales has found that R1234ze – an HFO used in chillers, commercial air conditioning, supermarkets and other medium-temperature applications – may decompose partially into R23. This is a particularly potent greenhouse gas, with a GWP of 12,690.

Although the paper is yet to be peer-reviewed and the findings must still be confirmed by further research, preliminary results show that R1234ze can produce significant amounts of R23. If this is factored in to the GWP value of R1234ze, its effective 100-year GWP could be somewhere between 600 and 2,100.

The finding could also tie in with large and unexpected increases in emissions of R23 – previously thought to be generated during the production of R22.

Although the paper stops short of recommending the withdrawal of R1234ze, it does call for “urgent experiments” to determine the yield of R23. It also notes that if R1234ze is found to have a significant “secondary GWP”, it may be ineligible as a refrigerant under HFC phase-down rules.

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