Atmospheric Chemistry of Perfluoroalkanesulfonamides: Kinetic and Product Studies of the OH Radical and Cl Atom Initiated Oxidation of N-Ethyl Perfluorobutanesulfonamide

Abstract

Perfluorooctanesulfonamides [C₈F₁₇SO₂N(R¹)(R²)] are present in the atmosphere and may, via atmospheric transport and oxidation, contribute to perfluorocarboxylates (PFCA) and perfluorooctanesulfonate (PFOS) pollution in remote locations. Smog chamber experiments with the perfluorobutanesulfonyl analogue N-ethyl perfluorobutanesulfonamide [NEtFBSA; C₄F₉SO₂N(H)CH₂CH₃] were performed to assess this possibility. By use of relative rate methods, rate constants for reactions of NEtFBSA with chlorine atoms (296 K) and OH radicals (301 K) were determined to be k_Cl = (8.37 ± 1.44) × 10^-12 and k_OH = (3.74 ± 0.77) × 10^-13 cm³ molecule^-1 s^-1, indicating OH reactions will be dominant in the troposphere. Simple modeling exercises suggest that reaction with OH radicals will dominate removal of perfluoroalkanesulfonamides from the gas phase (wet and dry deposition will not be important) and that the atmospheric lifetime of NEtFBSA in the gas phase will be 20−50 days, thus allowing substantial long-range atmospheric transport. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis showed that the primary products of chlorine atom initiated oxidation were the ketone C₄F₉SO₂N(H)COCH₃; aldehyde 1, C₄F₉SO₂N(H)CH₂CHO; and a product identified as C₄F₉SO₂N(C₂H₅O)^- by high-resolution MS but whose structure remains tentative. Another reaction product, aldehyde 2, C₄F₉SO₂N(H)CHO, was also observed and was presumed to be a secondary oxidation product of aldehyde 1. Perfluorobutanesulfonate was not detected above the level of the blank in any sample; however, three perfluoroalkanecarboxylates (C₃F₇CO₂^-, C₂F₅CO₂^-, and CF₃CO₂^-) were detected in all samples. Taken together, results suggest a plausible route by which perfluorooctanesulfonamides may serve as atmospheric sources of PFCAs, including perfluorooctanoic acid.