Increasing and Widespread Deposition of Trifluoroacetic Acid from Global Emissions of HFO-1234yf in Mobile-Air Conditioning

Abstract. HFO-1234yf is an emerging low global warming potential refrigerant with increasing emissions, especially from mobile air-conditioning (MACs), that are poorly constrained. It is oxidised in the atmosphere to form trifluoroacetic acid (TFA), a persistent, mobile, and widespread pollutant. Despite growing concerns around TFA accumulation in the environment, the contribution of HFO-1234yf to its global deposition is not known. Here, we present the first global bottom-up emissions inventory for HFO-1234yf from passenger vehicles. We use a chemical transport model to calculate the global TFA budget from these emissions and quantify source–receptor relationships from idealised emission scenarios. The magnitude and trend in HFO-1234yf emissions from North-West Europe are in close agreement with top-down assessments. Using our derived emissions, the model reproduces surface HFO-1234yf observations from the AGAGE network reasonably well. A sensitivity study using estimates of fugitive emissions from HFO-1234yf production improves agreement, particularly at Gosan, South Korea, where the model underestimates observations. We find that global TFA deposition from HFO-1234yf in MACs has increased from 0.10 (0.05–0.17) Gg yr^-1 in 2014 to 3.7 (1.6–6.4) Gg yr^-1 in 2024, with 75 % of cumulative HFO-1234yf emissions coming from Europe. A large proportion of TFA from HFO-1234yf (57 %) is deposited in oceans. Source–receptor analysis shows that most (86–97 %) TFA deposition occurs outside of the original HFO-1234yf emission region. All regions except Europe are net atmospheric importers of TFA, underscoring the importance of international efforts to reduce future TFA pollution.