Kinetic study of the OH and Cl-initiated oxidation, lifetimes and atmospheric acceptability indices of three halogenated ethenes

Abstract

26 27 The gas-phase kinetics for the reactions of OH radicals and Cl atoms with (E/Z)-28CHCl=CHF, (E/Z)-CFCl=CFCl, and CCl 2 =CF 2 were investigated at room-temperature 29 and atmospheric pressure. A conventional relative-rate technique was used to determine 30 the rate coefficients k(OH + (E/Z)-CHCl=CHF) = (6.3 ± 1.2) x 10 -12 , k(OH + (E/Z)-31 CFCl=CFCl) = (1.6 ± 0.2) x 10 -12 , k(OH + CCl 2 =CF 2 ) = (5.0 ± 0.7) x 10 -12 , k(Cl + 32 (E/Z)-CHCl=CHF) =(11 ± 2) x 10 -11 , k(Cl + (E/Z)-CFCl=CFCl) = (5.4 ± 1.3) x 10 -11 , 33 and k(Cl + CCl 2 =CF 2 ) = (6.3 ± 1.5) x 10 -11 cm 3 molecule -1 s -1 . These rate coefficients 34 were compared with previous literature data to analyze the effect of halogen substitution 35 in ethenes on the reactivity towards OH and Cl, and used to estimate the global 36 atmospheric lifetimes for the studied haloethenes. The calculated lifetimes, using 37 average global concentrations of OH radicals and Cl atoms, indicate that the 38 atmospheric loss of these compounds is determined by the OH-initiated oxidation. Also, 39 the atmospheric implications of the halogenated ethenes studied were evaluated by 40 estimating acceptability indices such as the global warming potential (GWP) and the 41 ozone depletion potential (ODP). From these potentials, the contribution of (E/Z)-42CHCl=CHF, (E/Z)-CFCl=CFCl, and CCl 2 =CF 2 to radiative forcing of climate change 43 and to ozone layer depletion is expected to be negligible. 44 45 46 47 48 49 50

Relative Rate and Product Studies of the Reactions of Atomic Chlorine with Tetrafluoroethylene, 1,2-Dichloro-1,2-difluoroethylene, 1,1-Dichloro-2,2-difluoroethylene, and Hexafluoro-1,3-butadiene in the Presence of Oxygen

“…While this work was in progress, a new spectrum was published by Davis et al 33 Our spectrum is in Our measured rate constant is k 3 = (7.1 ± 1.1) × 10 −11 cm 3 molecule −1 s −1 , and therefore, reaction 3 is another example of a rate constant that is close to the hard-sphere collision value. This value agrees with the determination of (6.3 ± 1.5) × 10 −11 cm 3 molecule −1 s −1 by Barrera et al 28 Infrared spectra of mixtures with Cl 2 and O 2 before and after UV photolysis are shown in Figure 5. The major product peaks are assigned to chlorodifluoroacetyl chloride, CClF 2 CClO.…”

“…We dissolved some of our CFClCFCl in CDCl 3 (l) and used 19 F NMR 27 to determine an initial composition of 51 ± 2% cis isomer. The effective overall rate constant for reaction of this mixture with Cl is k 2 = (6.5 ± 1.0) × 10 −11 cm 3 molecule −1 s −1 , very similar to that for C 2 F 4 and in accord with the value of (5.4 ± 1.3) × 10 −11 cm 3 molecule −1 s −1 obtained recently by Barrera et al 28 Similar remarks therefore apply to the atmospheric lifetime with respect to reaction 2. This lifetime will be even shorter in the presence of hydroxyl, but it is already clear that the GWP is minor.…”

“…, very similar to that for C 2 F 4 and in accord with the value of (5.4 ± 1.3) × 10 −11 cm 3 molecule −1 s −1 obtained recently by Barrera et al 28 Similar remarks therefore apply to the atmospheric lifetime with respect to reaction 2. This lifetime will be even shorter in the presence of hydroxyl, but it is already clear that the GWP is minor.…”

The Spectroscopic Characterization of Halogenated Pollutants through the Interplay between Theory and Experiment: Application to R1122

“…Containing at least one C=C double bond, they possess a reactive site that makes their scavenging from the atmosphere much more efficient. Thus, many studies have focused on the kinetics and mechanisms that may be involved in the atmospheric removal processes of these compounds, and so their reactions with OH radicals, as well as the ones with O( P), have been investigated (see, for example [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ] and references therein). However, it should be noted that some halogenated ethenes are considered to be potential threats to human health (see, for example [ 8 , 9 , 10 ] and references therein), so the assessing of their presence in real-time is clearly desirable, both for experimentally studying their atmospheric chemistry as well as for quantifying their concentrations.…”

Kinetic Analysis of Unimolecular Reactions Following the Addition of the Hydroxyl Radical to 1,1,2-Trifluoroethene

“…There are several studies on the kinetic reactions of fluorinated ethylenes with OH radicals in the literature. These include the following • The gas-phase kinetic studies of OH radicals with halogenated ethenes by Barrera et al 6 • A study of CHFCH 2 and CH 2 CF 2 with OH radicals by Baasandorj et al 7 • Reactions of bromofluoroalkenes with OH radicals by Orkin et al 8 reported the kinetic parameters of tetrafluoroethylene with OH radicals by Acerboni et al 9 and McIlroy et al 10 • Reported rate constants for the reaction of OH radicals with CH 2 CHF by Perry et al 11 • The study of ethylene and halogenated ethylene compounds with OH radicals by Howard. 12 Several studies on the initial kinetic reaction of OH radical addition (initiation) to trifluoroethene have been carried out experimentally.…”