PFOS dominates PFAS composition in ambient fine particulate matter (PM2.5) collected across North Carolina nearly 20 years after the end of its US production

Contamination of drinking water by per- and polyfluoroalkyl substances (PFASs) emitted from manufacturing plants, fire-fighting foams, and urban waste streams has received considerable attention due to concerns over toxicity and environmental persistence; however, PFASs in ambient air remain poorly understood, especially in the United States (US). We measured PFAS concentrations in ambient fine particulate matter (PM_2.5) at 5 locations across North Carolina over a 1 year period in 2019. Thirty-four PFASs, including perfluoroalkyl carboxylic, perfluoroalkane sulfonic, perfluoroalkyl ether carboxylic and sulfonic acids were analyzed by UHPLC/ESI-MS/MS. Quarterly averaged concentrations ranged from <0.004-14.1 pg m^-3. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) ranged from <0.18 to 14.1 pg m^-3, comparable to previous PM_2.5 measurements from Canada and Europe (<0.02-3.5 pg m^-3). Concentrations above 1 pg m^-3 were observed in July-September at Charlotte (14.1 pg m^-3, PFOA), Wilmington (4.75 pg m^-3, PFOS), and Research Triangle Park (1.37 pg m^-3, PFOS). Notably, PM_2.5 has a short atmospheric lifetime (<2 weeks), and thus, the presence of PFOS in these samples raises questions about their sources, since PFOS production was phased out in the US ∼20 years ago. This is the first US study to provide insights into ambient PFAS concentrations in PM_2.5.