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Characterizing volatile emissions and combustion by-products from aqueous film-forming foams using online chemical ionization mass spectrometry
Citation:
Mattila, J., J. Krug, W. Roberson, Rucker Burnette, S. McDonald, Pertti Virtaranta, J. Offenberg, AND W. Linak. Characterizing volatile emissions and combustion by-products from aqueous film-forming foams using online chemical ionization mass spectrometry. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, , 0, (2024). https://doi.org/10.1021/acs.est.3c09255
Impact/Purpose:
This paper reflects work performed on the pilot-scale natural gas-fired Rainbow Furnace in EPA’s RTP facilities, where four unique PFAS containing Aqueous Film Forming Foams (AFFFs) were introduced into the furnace at two post-flame locations at peak injection temperatures (~820 and 760 °C) designed to investigate the formation of fluorinated products of incomplete combustion (PICs) using real-time continuous chemical ionization mass spectrometry (CIMS) and compare these to headspace measurements above the same four AFFFs. These injection temperatures represent conditions conducive to elevated PIC formation and allowed comparison of PICs from four different AFFFs including legacy and contemporary formulations. CIMS measurements performed during AFFF solution incineration experiments showed that production of short-chain (C2 – C4) perfluorocarboxylic acids (PFCAs) increased considerably with decreasing AFFF incineration temperature, demonstrating the presence of PFCAs as PICs and highlighting the importance of furnace operating conditions for AFFF disposal and minimizing PFAS air emissions. Trifluoroacetic acid (TFA) was a ubiquitous product of AFFF incineration, often yielding mass concentrations an order of magnitude or higher than C3 – C8 PFCAs. However, TFA has not been previously directly measured as a gaseous PIC from AFFFs. Production of TFA from AFFF combustion could help explain previous reports of elevated TFA in surface and groundwater near sites impacted from AFFF usage. We also used CIMS to tentatively identify several PFAS and other novel compounds of interest from AFFF solution headspace and combustion emissions. This provided new practical insights into these respective volatile chemical spaces and help inform the development of kinetic mechanisms that describe PFAS thermal destruction.
Description:
Aqueous film-forming foams (AFFFs) are used in firefighting applications, and often contain per- and polyfluoroalkyl substances (PFAS), which can detrimentally impact environmental and biological health. Incineration is a potential disposal method for AFFFs, which may produce secondary PFAS and other air pollutants. We use online chemical ionization mass spectrometry (CIMS) to measure volatile PFAS emissions from incinerating AFFF concentrate solutions. We quantified perfluorinated carboxylic acids (PFCAs) during the incineration of legacy and contemporary AFFFs. Among these included trifluoroacetic acid, which reached mg m-3 quantities in the incinerator exhaust. These PFCAs likely arose as products of incomplete combustion of AFFF fluorosurfactants, with lower peak furnace temperatures yielding higher PFCA concentrations. We also detected other short-chain PFAS, and other novel chemical products in AFFF combustion emissions. The volatile headspace above AFFF solutions contained larger (C ≥ 8), less oxidized PFAS detected by CIMS. We identified neutral PFAS resembling fluorotelomer surfactants (e.g., fluorotelomer sulfonamide alkylbetaines and fluorotelomer thioether amido sulfonates), and fluorotelomer alcohols in contemporary AFFF headspaces. Directly comparing the distinct chemical spaces of AFFF volatile headspace and combustion by-products as measured by CIMS provides insight toward the chemistry of PFAS during thermal treatment of AFFFs.
URLs/Downloads:
DOI: Characterizing volatile emissions and combustion by-products from aqueous film-forming foams using online chemical ionization mass spectrometry