Understanding the Spatial and Temporal Distribution of Per- and Polyfluorinated Compounds in Atmospheric Deposition

Abstract

Per-and polyfluoroalkyl substances (PFAS) are persistent anthropogenic compounds that are distributed globally. However, uncertainties remain regarding dominant sources, long-range transport pathways, and atmospheric deposition mechanisms. This thesis advances the understanding of the spatial and temporal distribution of PFAS by analyzing atmospheric deposition across Arctic, boreal, urban, and tropical environments. To elucidate temporal trends, a 16 meter ice core from the Mt. Oxford icefield, Ellesmere Island provided a continuous 50-year deposition record (1967–2016). Analysis revealed an increase in PFCA deposition after the 1990s. Homologue correlations, molar concentration ratios, and model comparisons suggest that PFCAs are primarily formed through oxidation of volatile precursors. In contrast, PFSAs showed no discernible trend, with episodic deposition observed before 1990, which may be linked to historical Arctic military activities. Spatial patterns in PFAS deposition were examined across the Newfoundland and Labrador Boreal Ecosystem Latitudinal Transect using integrated atmospheric deposition samples collected between 2013–2016. We also quantitively separate wet and dry deposition fluxes for perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA). We found that the dry deposition contribution was equal to or greater than the wet deposition flux. This research also specifically focused on trifluoroacetic acid (TFA), a highly persistent and mobile ultrashort chain PFAS. We quantified TFA in total, wet and dry deposition samples in Toronto, Canada between 2018–2024. Seasonal variations showed fluxes peaking in summer months and a decrease in 2020, coinciding with COVID-19 lockdown measures. This work provided the first field-based quantification of TFA in dry deposition, demonstrating that it is a significant and previously underrepresented removal pathway. Finally, a novel hemispheric comparison found substantial TFA deposition at both a tropical site in Georgetown, Guyana (1014–6641 µg m-2 a-1) and a temperate residential site in Lambton County, Canada (1969–5863 µg m-2 a-1), confirming the global reach of TFA. Collectively, this thesis demonstrates that PFAS distribution by the atmosphere is governed by complex interactions between direct emissions, atmospheric transformation of precursors, and seasonally variable deposition processes.