Abstract
Perfluorooctanoic acid, PFOA, is one of the many concerning pollutants in our atmosphere; it is highly resistant to environmental degradation processes, which enables it to accumulate biologically. With direct routes of this chemical to the environment decreasing, as a consequence of the industrial phase out of PFOA, it has become more important to accurately model the effects of indirect production routes, such as environmental degradation of precursors; e.g., fluorotelomer alcohols (FTOHs). The study reported here investigates the chemistry, physical loss and transport of PFOA and its precursors, FTOHs, throughout the troposphere using a 3D global chemical transport model, STOCHEM-CRI. Moreover, this investigation includes an important loss process of PFOA in the atmosphere via the addition of the stabilised Criegee intermediates, hereby referred to as the “Criegee Field.” Whilst reaction with Criegee intermediates is a significant atmospheric loss process of PFOA, it does not result in its permanent removal from the atmosphere. The atmospheric fate of the resultant hydroperoxide product from the reaction of PFOA and Criegee intermediates resulted in a ≈0.04 Gg year−1 increase in the production flux of PFOA. Furthermore, the physical loss of the hydroperoxide product from the atmosphere (i.e., deposition), whilst decreasing the atmospheric concentration, is also likely to result in the reformation of PFOA in environmental aqueous phases, such as clouds, precipitation, oceans and lakes. As such, removal facilitated by the “Criegee Field” is likely to simply result in the acceleration of PFOA transfer to the surface (with an expected decrease in PFOA atmospheric lifetime of ≈10 h, on average from ca. 80 h without Criegee loss to 70 h with Criegee loss).
Highlights
Perfluorinated carboxylic acids (PFCAs) constitute a class of organic acids with a general formula of Cn F(2n + 1) COOH, which, despite being exclusively anthropogenically generated, are found to be ubiquitous in the environment [1]
Despite these efforts to reduce direct emissions of perfluorooctanoic acid (PFOA), an alternative pathway of environmental contamination remains operational via the degradation of fluorotelomer alcohols (FTOHs); 8:2 FTOH which oxidatively degrades in the atmosphere to yield PFOA [16,17,18]
This is in line with what we would expect given the rapid rate of reaction of PFOA with SCI and the abundances of OH radicals in the troposphere
Summary
Perfluorinated carboxylic acids (PFCAs) constitute a class of organic acids with a general formula of Cn F(2n + 1) COOH, which, despite being exclusively anthropogenically generated, are found to be ubiquitous in the environment [1]. As a result of this, industrial production of PFOA was voluntarily phased out by most relevant companies in 2015 [14] and PFOA and its salts have recently been added to Annexe A of the Stockholm Convention for persistent organic pollutants (POPs) [15] Despite these efforts to reduce direct emissions of PFOA, an alternative pathway of environmental contamination remains operational via the degradation of fluorotelomer alcohols (FTOHs); 8:2 FTOH which oxidatively degrades in the atmosphere to yield PFOA [16,17,18]. A recent report suggests that reaction with Criegee intermediates (CIs) is likely to be significant in determining the atmospheric fate of PFOA, though it is important to note that this study did not explicitly investigate the impact of this loss process on a global scale [23].
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