Wet deposition transfers per- and polyfluoroalkyl substances (PFAS) from the atmosphere to the Earth's surface. This introductory pathway is particularly important in remote areas and for lakes with water budgets dominated by over-lake precipitation, such as Lake Superior. Despite this, the sources, atmospheric controls, and seasonal and compositional variability of PFAS in wet deposition remain poorly constrained. To investigate this variability in the Great Lakes region, 33 PFAS compounds were measured continuously via weekly integrated sampling at five National Atmospheric Deposition Program National Trends Network (NADP-NTN) sites in Minnesota and Michigan from summer 2023 to summer 2025.

These observations found ubiquitous PFAS contamination of precipitation, with at least one PFAS species detected in 100% of the samples and the sum of PFAS concentrations ranging from 0.05 to 10.4 ng/L. Perfluorocarboxylic acids (PFCAs) dominated the PFAS mass in wet deposition, representing 80% of the measured PFAS mass flux. Perfluoroheptanoic acid (PFHpA) was the most commonly detected species, detected in 99% of samples. Although PFCAs dominated the observed PFAS mass, other families, including GenX, perfluoroalkane sulfonic acids (PFSAs), and perfluoroalkane sulfonamides (FASAs), were detected regularly but more sporadically, indicating event- or source-driven changes in atmospheric composition for these species. These observations underscore the importance of atmospheric deposition as a significant source of PFAS in the Great Lakes region, highlighting the need to constrain its magnitude and controls.