Rising Trifluoroacetic Acid Levels: Evaluating Contributions from long-lived CFC replacements and anaesthetics

Trifluoroacetic acid (TFA), a short chain perfluorocarboxylic acid (scPFCA), is a contaminant of emerging concern because its emissions are projected to rapidly increase, it is highly persistent, and remediation is challenging. Recent studies based on ice core records report large increases (up to a factor of ~10) in Arctic TFA deposition since the 1970s. The ice core temporal trends suggest that CFC replacement gases introduced following the Montreal Protocol could be an important source. However, TFA is a “substance from multiple sources” and their relative importance remains poorly quantified; a challenge which needs to be addressed for the emission trend to be reversed through regulation. Here we use a chemical transport model (FRSGC/UCI-CTM) to examine the global TFA budget from the production of long-lived source gases, namely, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and inhalation anaesthetics. A detailed degradation scheme describing TFA production from each precursor was added to the model and simulations performed using time-varying loadings of its major emitted precursors. Model results showed that TFA production from CFC-replacements increased by a factor of four from 2000 (6.3 Gg/yr) to 2016 (25.4 Gg/yr), with cumulative deposition over this period reaching 226 Gg/yr. HCFC-123, HCFC-124, and HFC-134a account for the majority of this production. TFA deposition shows a latitudinal dependence with the majority occurring in extrapolar regions. Model results are compared to measurements from ice core data and precipitation concentrations. While demonstrating the increasing contribution of CFC replacements to TFA, we highlight the challenges in elucidating their significance against other sources from sparse TFA measurements records, particularly in regions where TFA deposition is highest.