Atmospheric fate of hydrofluoroolefins, CxF2x+1CH[dbnd]CH2 (x = 1,2,3,4 and 6): Kinetics with Cl atoms and products

Abstract

Rate coefficients for the gas-phase reactions of CxF2x+1CHCH2 (x = 1, 2, 3, 4 and 6) with Cl atoms were determined at (298 ± 2) K and (710 ± 5) Torr of air using a relative rate technique. Two experimental setups with simulation chambers were employed with Fourier Transform Infrared (FTIR) spectroscopy and Gas Chromatography coupled to Mass Spectrometry (GC-MS) as detection techniques. The Cl-rate coefficients obtained were (in 10−10 cm3 molecule−1 s−1): (0.85 ± 0.11) for CF3CHCH2, (1.11 ± 0.08) for C2F5CHCH2, (1.12 ± 0.18) for C3F7CHCH2, (0.97 ± 0.09) for C4F9CHCH2, and (0.99 ± 0.08) for C6F13CHCH2. Additionally, the gas-phase products were identified and quantified, when possible, by FTIR spectroscopy or GC-MS. The main reaction product was reported to be CxF2x+1C(O)CH2Cl. The fluorinated species, CxF2x+1CHO and CxF2x+1C(O)CH2Cl, were identified. CF3C(O)CH2Cl and CF3CHO were found to be formed with molar yield of (69 ± 5)% and (9 ± 1)%, respectively. The global lifetime of the investigated CxF2x+1CHCH2 due to their Cl-reaction is more than 100 days so this route does not compete with the removal by OH radicals. This lifetime is long enough for CxF2x+1CHCH2 to be transported to remote areas where they can be degraded. However, at a local scale, in marine regions at dawn the removal of CxF2x+1CHCH2 is expected to occur in ca. 1 day. The atmospheric degradation of these hydrofluoroolefins by Cl atoms is not expected to be a source of bioaccumulative perfluorinated carboxylic acids, CxF2x+1C(O)OH. Additionally, the UV absorption cross sections of CF3C(O)CH2Cl were determined together with the rate coefficient of the OH reaction by an absolute kinetic method at room temperature.