Volatile and Semi-volatile Per- and Polyfluoroalkyl Substances (PFAS): Air–Water Partitioning, Atmospheric Emissions, and Environmental Fate and Transport

Abstract Volatile and semi-volatile per- and polyfluoroalkyl substances (V/SV-PFAS) represent a class of PFAS that can partition into the gas phase, enabling atmospheric transport and inhalation exposure pathways that remain poorly understood. Recognizing that air–water partitioning is a fundamental determinant of environmental volatility, this review critically evaluates the current understanding of air–water partitioning coefficients (Kaw), atmospheric emissions, and subsurface occurrence and associated vapor intrusion (VI) risks of V/SV-PFAS. Experimentally determined Kaw values are compiled, highlighting variability spanning multiple orders of magnitude and uncertainties that may arise from limitations of conventional measurement techniques or differences in experimental methodologies. Recent advances, such as thermodynamic cycle methods, are assessed for their potential to expand the range of measurable V/SV-PFAS. Field observations from major atmospheric emission sources, including landfills, wastewater treatment plants, PFAS manufacturing facilities, vadose-zone soil gas at contaminated sites, and indoor environments, are evaluated. Fluorotelomer alcohols dominate V/SV-PFAS profiles, with concentrations of up to 105–106 ng/m3 in landfill and soil gas, 103–104 ng/m3 in industrial indoor air, 103–104 pg/m3 in ambient air near source regions, and 103 to 106 pg/m3 in indoor environments. Addressing critical knowledge gaps in air–water partitioning, source characterization, and subsurface fate and transport is essential for improving V/SV-PFAS exposure assessment and developing effective management strategies.