Atmospheric Fate of 4:2 Fluorotelomer Alcohol using an Oxidation Flow Reactor and Proton Transfer Reaction Time-of-Flight Mass Spectrometry

Abstract

Commonly used methodologies applied to studying the atmospheric degradation of per- and polyfluoroalkyl substances (PFAS) require analyses to be conducted offline and under dry conditions, potentially limiting the atmospheric relevance of the resulting mechanism and kinetics. We coupled an oxidation flow reactor (OFR) to a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS), focusing on the NOx-free oxidation of a perfluorocarboxylic acid precursor – the 4:2 fluorotelomer alcohol (FTOH) – in the first application of this system to PFAS. The PTR-ToF-MS was calibrated under dry conditions (0 to 1% RH) and at relative humidities (RHs) of 22%, 44%, and 60%. The oxidation of 4:2 FTOH by OH radicals was observed in real-time, as a function of RH, with PTR-ToF-MS detecting both primary and secondary 4:2 FTOH degradation products: the 4:2 fluorotelomer aldehyde and 4:2 fluorotelomer carboxylic acid, respectively. The resulting pseudo-first-order kinetics (k_obs) were determined and compared to previously reported FTOH values. The determined k_obs values were (1.0 ± 0.1) × 10^-12 (22% RH), (7.4 ± 0.8) × 10^-13 (44% RH), and (7.2 ± 0.8) × 10^-13 cm³ molecules^-1 s^-1 (60% RH), comparable to prior reports at 22% RH and lower as RH increased. This type of experiment demonstrates that the OFR + PTR-ToF-MS technique can be transferred to study other suspected, but uncharacterized, atmospheric PFAS transformations