Estimates of HFC-134a Emissions over Europe informed by observations show a recent increase

Hydrofluorocarbons (HFCs) are a class of greenhouse gases (GHGs) primarily used as substitutes for ozone-depleting substances like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), phased out under the Montreal Protocol. However, HFCs significantly impact global warming due to their high global warming potential. In light of the pressing need to tackle climate change and mitigate the effects of GHG emissions, the United Nations Framework Convention on Climate Change (UNFCCC) has established rigorous commitments on emission reduction. As a commitment to the UNFCCC, Annex-I countries need to report their national emission estimates for regulated GHGs, including HFCs, based on the methodologies reported in the IPCC guidelines (Intergovernmental Panel on Climate Change). According to the guidelines, the comparison of estimates with top-down (models based on atmospheric measurements) is indicated as an effective tool for verifying the accuracy of inventories and there is a growing need for independent verification of these estimates. This study reports the most recent update on emissions of 1,1,1,2-Tetrafluoroethane (CH2FCF3) from 2008 to 2023, employing inverse modelling within the European domain, with a specific focus on Italy. CH2FCF3, commercially known as HFC-134a, stands as the most prevalent HFC on a global scale. Its thermodynamic properties, akin to those of dichlorodifluoromethane (CFC-12), render it an effective refrigerant for the RAC (refrigeration and air conditioning) sector. This study reveals a notable decline in HFC-134a emissions over the past decade, followed by a recent resurgence. Specifically, Italian emissions in 2020 show a 48% reduction compared to the levels of 2011 and a subsequent increase, with emissions rebounding by 25% in 2022. The availability of near real-time validated observations combined with the most recent inversion frameworks -such as Flexpart/flexinvert+ used here, could be a valuable tool to support the Inventories used to track progress and the effectiveness of the mitigation policies adopted by each country for this class of compounds (that could be extended to others major GHGs) to maximise the effectiveness of their investments.