Hydrofluorocarbons (HFCs) are potent greenhouse gases (GHGs). The most potent of these compounds is trifluoromethane, also known as HFC-23. One kilogram of HFC-23 in the atmosphere contributes as much to the greenhouse effect as 12,000 kilograms of CO₂. It takes around 200 years for the gas to break down in the atmosphere. For this reason, more than 150 countries have committed to significantly reducing their emissions of HFC-23 as part of the Kigali Amendment to the Montreal Protocol.

The main source of HFC-23 is the industrial production of certain coolants and of polytetrafluoroethylene (PTFE), better known as Teflon. HFC-23 is a by-product of the synthesis of a precursor to Teflon. Since 2020, all Teflon manufacturers are obligated to destroy the climate-damaging gas. According to the reports of the individual countries, this is happening: On paper, global emissions of HFC-23 for the year 2020 were only 2,000 tons. The actual global emissions, which have been determined in numerous studies, show a different picture: In 2020 alone, around 16,000 tons of the GHG were released into the atmosphere.

Accurate measurements thanks to tracer gas

Why this discrepancy? To answer this question, researchers from Empa, the University of Bristol and the Netherlands Organization for Applied Scientific Research (TNO) took a close look at HFC-23 emissions from a Teflon factory in the Netherlands. They have just published their latest findings in the journal Nature.

In order to record the factory's emissions as comprehensively and accurately as possible, the researchers used a novel method. They released a tracer gas right next to the factory: a non-toxic gas that does not occur in the atmosphere and decomposes within just a few weeks. At a distance of around 25 kilometers, they measured the concentrations of HFC-23 and other by-products of Teflon manufacture – and also the concentration of the tracer. "Since we knew exactly how much tracer we had released and how much of it arrived at the measuring point, we were able to calculate the emissions of HFC-23 and other gases," says first author Dominique Rust, who worked on the project as part of her doctorate at Empa.

The factory utilizes abatement measures to curb its HFC-23 emissions; the gas is burned off before it can escape. But the new study shows: "The emissions we measured were higher than the ones the factory reported", explains Empa researcher Martin Vollmer. "However, the amount emitted is still low, showing that the abatement measures work well." Co-author Kieran Stanley from the University of Bristol agrees: "These results are really encouraging. They show that abatement measures for plants producing fluoropolymers like Teflon can significantly reduce emissions of this highly potent GHG." And Empa researcher Stefan Reimann adds: "If all factories had emissions similar to the one we measured, we could prevent global HFC-23 emissions corresponding to almost 20% of CO₂ emissions from global air traffic."

Verification and compliance

So if the abatement measures are effective, how can the high readings in the atmosphere be explained? "We must assume that the measures reported by the countries do not correspond to reality everywhere," says Martin Vollmer. The authors of the study call on countries to have their Teflon factories independently audited. "Such independent verification of GHG emissions from the production of fluoropolymers and coolants are needed to help close the gaps in our understanding of emission sources and check that countries are fully compliant under different international climate and environment agreements," adds Stanley. "The collaboration with the Teflon manufacturer and the Dutch authorities was key to the success of our study," says Rust, who is now a research associate at the University of Bristol.

The tracer method developed by the researchers would be suitable for independent audits of factories and industrial areas – also for other gases, the scientists are convinced. Empa researchers are already planning another study in South Korea in October, in which they want to use the tracer method to determine the emissions of halogenated substances in the South Korean capital Seoul. "At the Cabauw measuring station, TNO will extend the monitoring of the GHG’s in the context of the European ICOS infrastructure with continuous monitoring of halogenated substances. This allows us to track the location and determine the emission of the sources of halogenated substances that were found to pass by the station during this experiment," adds TNO researcher Arnoud Frumau.

Novel measuring method for gas emissions - Greenhouse gas HFC-23: Abatement of emissions is achievable