Contribution of Condensed-Phase Hydrolysis to Atmospheric Production of GenX

Emma D'Ambro, BENJAMIN MURPHY, Ivan Piletic, Havala Pye, U.S. Environmental Protection Agency

     Abstract Number: 421
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
Per- and polyfluoroalkyl substances (PFAS) are a class of human-made compounds that can be emitted to the atmosphere, transported downwind, and deposited where they may contaminate surface water, ground water, and private well water, especially in the vicinity of large point sources. During transport, chemical transformations may occur which modify the solubility and reactivity of the emitted PFAS. One such transformation involves the hydrolysis of acyl fluoride compounds to form products with carboxylic acid functionality, which exhibit considerably higher water solubility and therefore faster deposition. The hydrolysis process itself is known to proceed rapidly in condensed water, which we extrapolate here to atmospheric water media (e.g., cloud drops and aqueous aerosols). The rate limiting step for this conversion is likely to be absorption of the sparingly soluble acyl fluoride precursor into the condensed phase. We apply the Community Multiscale Air Quality model (CMAQ) version 5.4 to a case study in Eastern North Carolina to model the PFAS emissions and transport at fine scale (1 km) from the Chemours Inc. Fayetteville-Works. The CMAQ-PFAS results inform our understanding of the extent to which condensed-phase hydrolysis can substantially convert hexafluoropropylene dimer acyl fluoride (HFPO-DAF) to hexafluoropropylene dimer acid (HFPO-DA), or GenX, in the atmosphere before it deposits. We evaluate the model’s predictions with deposition measurements of GenX in North Carolina.