Characterizing the Air Emissions, Transport, and Deposition of Per- and Polyfluoroalkyl Substances from a Fluoropolymer Manufacturing Facility

Abstract

Per- and polyfluoroalkyl substances (PFASs) have been released into the environment for decades, yet contributions of air emissions to total human exposure, from inhalation and drinking water contamination via deposition, are poorly constrained. The atmospheric transport and fate of a PFAS mixture from a fluoropolymer manufacturing facility in North Carolina were investigated with the Community Multiscale Air Quality (CMAQ) model applied at high resolution (1 km) and extending ∼150 km from the facility. Twenty-six explicit PFAS compounds, including GenX, were added to CMAQ using current best estimates of air emissions and relevant physicochemical properties. The new model, CMAQ-PFAS, predicts that 5% by mass of total emitted PFAS and 2.5% of total GenX are deposited within ∼150 km of the facility, with the remainder transported out. Modeled air concentrations of total GenX and total PFAS around the facility can reach 24.6 and 8500 ng m^-3 but decrease to ∼0.1 and ∼10 ng m^-3 at 35 km downwind, respectively. We find that compounds with acid functionality have higher deposition due to enhanced water solubility and pH-driven partitioning to aqueous media. To our knowledge, this is the first modeling study of the fate of a comprehensive, chemically resolved suite of PFAS air emissions from a major manufacturing source.

Figure 1.

(A) Pie chart of facility emissions, with the lowest 50 by mass grouped into “other”. (B) Facility emissions for the “other” category by carbon number, categorized by number of functional groups. Compounds with unknown structure are grouped in the “NA” bin. The * indicates the location of total GenX (HFPO-DA + HFPO-DAF, gas + particle).

Figure 2.

Daily averaged observed GenX deposition at 5 NC DEQ sampling sites paired with daily averaged deposition predictions for the base CMAQ-PFAS model configuration. The CarbAcid CMAQ model configuration is also shown and represents a bounding scenario for the hydrolysis rate of the acyl fluoride. Model predictions include the deposition of total GenX (HFPO-DA + HFPO-DAF, gas + particle). Also shown for comparison are CMAQ-PFAS predictions at the Chemours Fayetteville Works and in Fayetteville, NC, the nearest urban area. Error bars represent the standard deviation of data at each site.

Figure 3.

(A) The annual accumulated deposition of total GenX (HFPO-DA + HFPO-DAF). (B) The annually averaged air concentration of total GenX binned as a function of distance from the facility. (C) The cumulative time in 2018 that the simulated total GenX concentration was predicted above 1 ng m⁻³. Note the non-linear color scales on panels A and C.

Figure 4.

(A) The annually averaged fraction of HFPO-DA in the particle phase (F_p), and (B) the particle-phase fraction (F_p) for 8 acyl fluoride containing compounds explicitly implemented into the model for the Base simulation (yellow) and that of their analogous carboxylic acid forms (blue). Compounds with the lowest effective Henry’s Law constants at a pH of 3 are on the left, with the highest on the right.

Figure 5.

Annual-averaged deposition as a percent of emissions of all explicitly modeled compounds and the “PFASOTHER” compound (classified as NA) within the model domain, as a function of carbon number and grouped via wet and dry deposition.