From Oxidation To Deposition: Novel Tools For Measuring Atmospheric Per- And Polyfluoroalkyl Substances

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of persistent, bioaccumulative, and toxic compounds characterized by strong carbon-fluorine bonds and their resulting environmental stability. Volatile and semi-volatile neutral PFAS and their precursors can undergo gas-phase oxidation to form perfluoroalkyl acids (PFAAs), including perfluorocarboxylic acids (PFCAs), which are widely detected in environmental matrices. Although long-chain PFAS have been phased out over the past two decades, increased production and degradation of precursor compounds have led to growing concern over the persistence, mobility, and expanding global distribution of ultrashort- and short-chain PFAAs. Chapter 2 investigates the hydroxyl (OH)-initiated oxidation of 4:2 fluorotelomer alcohol, a PFCA precursor, under low-NOx conditions at atmospherically relevant relative humidities (22%, 44%, and 60%). Using an oxidation flow reactor coupled to proton transfer reaction time-of-flight mass spectrometry, we detected the 4:2 fluorotelomer aldehyde and carboxylic acid, confirming proposed mechanisms and providing initial constraints on humidity-dependent OH kinetics. This technique provides an alternative to traditional dry smog chamber experiments with improved representation of ambient atmospheric conditions. Chapter 3 presents an open-source, modular, and affordable automatic wet deposition sampler capable of off-grid operation. The system was deployed across the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect and operated continuously using solar-assisted battery power. Performance was evaluated under summer and winter conditions, and proof-of-concept validation included routine rainwater chemistry measurements. Chapter 4 describes the development and validation of an artifact-minimized denuder sampling method to measure gas-phase perfluoropropionic acid (PFPrA), achieving 99.83 ± 0.03% capture efficiency. Additionally, year-long deposition and denuder sampling in regions home to endangered Canadian whale populations, at Tadoussac, Québec and Saturna Island, British Columbia, showed trifluoroacetic acid (TFA) and PFPrA as dominant PFCAs and demonstrated site-specific differences in wet versus dry deposition. A concurrent intercomparison with passive air samplers showed consistent seasonal trends for TFA, supporting the consistency of the denuder sampling. These measurements establish baseline levels in the two whale habitats and show that atmospheric deposition is an important source of ultrashort-chain PFCAs there. Together, these results present novel tools and foundational data to better understand atmospheric PFAS oxidation, transport, and deposition, while developing monitoring capabilities in remote and sensitive environments.