Atmospheric and watershed modelling of trifluoroacetic acid from oxidation of HFO-1234ze(E) released by prospective pressurised metered-dose inhaler use in three major river basins

Abstract. Trans-1,3,3,3-tetrafluoroprop-1-ene (HFO-1234ze(E); E-CF3CH=CHF) is a hydrofluoroolefin (HFO) with near-zero global warming potential, developed as a propellant for use in pressurised metered-dose inhalers (pMDIs). HFO-1234ze(E) contains a “–CF3” moiety, which makes formation of trifluoroacetic acid (TFA) possible in the atmosphere. To quantify the contribution of TFA formed from prospective HFO-1234ze(E)-based pMDIs, we applied a global atmospheric model coupled with detailed watershed modelling. Our atmospheric model incorporates the master chemical mechanism for HFO-1234ze(E) and assumes pMDIs as its sole emission source. Based on global pMDI volume-sales data, we estimate HFO-1234ze(E) emissions at 4.736 Gg yr−1. Although emissions are higher in northern-temperate regions, our model predicts that the highest TFA deposition rates occur in the tropics, likely due to more intensive photolysis of trifluoroacetic aldehyde in temperate zones (favouring non-TFA products) and/or transport of TFA into the tropical zone from nearby regions. Using predicted TFA deposition rates around the Hudson, Cauvery, and Rhine river basins, we applied a fate-and-transport model to estimate TFA concentrations in surface water, soil, and sediments over 30 years. Modelled surface-water TFA levels ranged from 0.8 to 19.3 ng L−1 across the three watersheds, indicating substantial variability between regions. Comparison of Rhine results with the conservative Netherlands drinking-water thresholds (2200 ng L−1) yields a margin of exposure of approximately 700-to-2500-fold. These findings suggest that modelled TFA levels from continuous pMDI-related HFO-1234ze(E) emissions over the study period in the Rhine region are unlikely to pose a risk to human health or the environment.