Reaction of Perfluorooctanoic Acid with Criegee Intermediates and Implications for the Atmospheric Fate of Perfluorocarboxylic Acids

Abstract

The reaction of perfluorooctanoic acid with the smallest carbonyl oxide Criegee intermediate, CH2OO, has been measured and is very rapid, with a rate coefficient of (4.9 ± 0.8) × 10-10 cm 3 s-1 , similar to that for reactions of Criegee intermediates with other organic acids. Evidence is shown for the formation of hydroperoxymethyl perfluorooctanoate as a product. With such a large rate coefficient, reaction with Criegee intermediates can be a substantial contributor to atmospheric removal of perfluorocarboxylic acids. However, the atmospheric fates of the ester product largely regenerate the initial acid reactant. Wet deposition regenerates the perfluorocarboxylic acid via condensed-phase hydrolysis. Gas-phase reaction with OH is expected principally to result in formation of the acid anhydride, which also hydrolyzes to regenerate the acid, although a minor channel could lead to destruction of the perfluorinated backbone.

Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

“…Reactions of CIs with organic acids have also been implicated in the formation of aerosols (18,19). Fast removal of CIs by reaction with a number of organic acids has been measured (18)(19)(20). Global chemistry and transport modeling reveals that these reactions could significantly reduce modeled organic acid concentrations (18), with the greatest impacts over the Amazon area where CI concentrations are the highest (18).…”

“…Global chemistry and transport modeling reveals that these reactions could significantly reduce modeled organic acid concentrations (18), with the greatest impacts over the Amazon area where CI concentrations are the highest (18). Through a combination of experimental and theoretical work for reactions of simple one-to three-carbon CIs, a mechanism has been identified whereby the CI undergoes a net insertion into the acid (18)(19)(20), leading to highly oxygenated, lower-volatility, functionalized organic hydroperoxides.…”

Investigating the Atmospheric Sources and Sinks of Perfluorooctanoic Acid Using a Global Chemistry Transport Model

“…As alluded to previously, wet and dry deposition processes are believed to dominate the atmospheric fate of PFOA, given its slow oxidation and inefficient photolysis processes [21,22]. However, a recent report suggests that reaction with Criegee intermediates (CIs) is also 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]. Previous investigations surrounding PFOA and its related compounds include, but are not limited to: modelling pathways of PFOA to the Arctic [12]; biological monitoring of PFOA [24]; a global survey of PFOA in oceans [2]; global fate and transport modelling of PFOA from direct sources [25]; and modelling 8:2 FTOH degradation as a potential source of PFOA [16].…”

“…In fact, the rate coefficients for organic and inorganic acids have been shown to approach or even exceed the gas kinetic limit [31][32][33][34]. Taatjes et al [23] have recently experimentally determined the rate coefficient of PFOA's reaction with the simplest SCI, CH 2 OO, to be (4.9 ± 0.8) × 10 −10 cm 3 s −1 . Operating under the assumption that reactions of PFOA with all common SCIs occur at similar rates, it is clear that this atmospheric loss process is likely to be significant in determining the overall fate of PFOA in the atmosphere.…”

“…It is also important to consider the atmospheric fate of the SCI-mediated products. Taatjes et al [23] and Chhantyal-Pun et al [34] have shown that the simplest SCI, CH 2 OO, reacts with halogenated carboxylic acids to produce a hydroperoxide ester (HPE). The HPE product likely undergoes reaction with OH in the atmosphere.…”