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\xa0±\xa03) 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\xa0cm3 molecule-1\xa0s-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\xa0+\xa0OH) = (1.3\xa0±\xa00.4), k2(TFH\xa0+\xa0OH) = (2.2\xa0±\xa00.8), k3(TFMH\xa0+\xa0OH) = (3.3\xa0±\xa01.0). 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\xa0h, 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.