Diurnal photodegradation of fluorinated diketones (FDKs) by OH radicals using different atmospheric simulation chambers: Role of keto-enol tautomerization on reactivity

Abstract

Rate coefficients for the gas-phase reactions of OH radicals with a series of fluorinated diketones have been determined for the first time at (298 ± 3) K and atmospheric pressure using the relative method and FTIR spectroscopy and GC-FID to monitor both reactants and references. The following values, in 10^-11 cm³ molecule^-1 s^-1, were obtained for 1,1,1-trifluoro-2,4-pentanedione (TFP), 1,1,1-trifluoro-2,4-hexanedione (TFH) and 1,1,1-trifluoro-5-methyl-2,4-hexanedione (TFMH), respectively: k₁(TFP + OH) = (1.3 ± 0.4), k₂(TFH + OH) = (2.2 ± 0.8), k₃(TFMH + OH) = (3.3 ± 1.0). The results are discussed with respect to the keto-enolic tautomerization specific for β-diketones. Based on the present results, the tropospheric lifetimes of TFP, TFH and TFMH upon degradation by OH radicals were calculated as 21, 13 and 8 h, respectively indicating that transport might play a role in the atmospheric fate of the studied compounds. Photochemical ozone creation potentials were estimated for TFP, TFH and TFMH to be: 23, 29 and 34, respectively.

Keywords: Diketones; Fluorinated carbonyls; In situ FTIR; Keto-enolic tautomerization; Reactivity; SPME-GC-FID.