M.P. Sulbaek Andersena,∗, E.J.K. Nilssonb, O.J. Nielsenb, M.S. Johnsonb,

M.D. Hurleyc, T.J. Wallingtonc

a Department of Chemistry, 572 Rowland Hall, University of California, Irvine, CA 92697-2025, USA

b Copenhagen Center for Atmospheric Research, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denm

c Systems Analytics and Environmental Sciences Department, Ford Motor Company, Mail Drop RIC-2122, Dearborn, MI 48121-2053, USA

article info

Article history:

Keywords:

CFC replacement

Atmospheric lifetime

abstract

Long path length Fourier transform infrared (FTIR)–smog chamber techniques 

kinetics of the gas-phase reactions of Cl atoms, OH radicals and O3 with

, in 700 Torr total pressure at 295 ± 2K. Values of 

(5.22 ± 0.72) 10−11 cm3 molecule−1 s−1, k(OH + = (4.40 ± 0.38) × 

and k(O3 + = (1.46 ± 0.12) × 10−21 cm3 molecule−1 s−1, were esta

tainties are 2; see Experimental section). The IR spectrum of is rep

lifetime of is determined by reaction with OH radicals and is app

global warming potential of is approximately 7 for a 100-year tim

1. Introduction

Recognition of the adverse environmental consequences of the

release of chlorofluorocarbons (CFCs) into the atmosphere [1,2] has

led to an international effort to replace these compounds with environmentally acceptable alternatives. While safeguarding the ozone

layer has been at the center of these efforts, concerns related to

global climate change are becoming an increasingly important consideration in the choice of alternative compounds because of their

significant atmospheric lifetime and radiative properties.

Saturated hydrofluorocarbons (HFCs), such as CH2FCF3 (HFC134a), have become widely used CFC replacements. HFCs do not

contain chlorine and therefore do not contribute to chlorinebased catalytic destruction of stratospheric ozone [3]. Unsaturated

hydrochlorofluorocarbons are a class of compounds which has been

developed as potential replacements for CFCs and saturated HFCs

in air conditioning units. Prior to any large-scale industrial use an

assessment of the atmospheric chemistry, and hence, environmental impact, of these compounds is needed. To address this need,

the atmospheric chemistry of was investigated. The

kinetics of the gas-phase reaction of Cl atoms and ozone with

were determined at Ford Motor Company (Ford)

and at University of Copenhagen (Copenhagen) using smog cham-

∗ Corresponding author. Tel.: +1 562 556 9880; fax: +1 949 824 2905.

E-mail address: mads@sulbaek.dk (M.P.S. Andersen).

ber/Fourier transform infrared (FTIR) techniq

of the title compound and the kinetics of its ga

OH radicals were measured at Ford. Results a

2. Experimental

Detailed descriptions of the experimenta

found elsewhere [4]. Therefore, only brief des

the subsections below. Chlorine atoms were p

of molecular chlorine:

Cl2 + hv→ Cl + Cl 

OH radicals were produced by photolysis o

ence of NO in air:

CH3ONO + hv→ CH3O + NO 

CH3O + O2 → HO2 + HCHO 

HO2 + NO → OH + NO2 

In relative rate experiments the following 

Cl + Reactant → products 

Cl + Reference → products 

OH + Reactant → products 

OH + Reference → products 
O3 + Reactant → products (9)

In smog chamber experiments it is important to check for

unwanted loss of reactants and products via photolysis, dark

chemistry and heterogeneous reactions. Control experiments were

performed at Ford and Copenhagen, in which mixtures of reactants

(except Cl2 or CH3ONO) in air were subjected to UV irradiation for

15 min and reactant/product mixtures obtained after the UV irradiation were allowed to stand in the dark in the chamber for 30 min.

There was no observable loss of reactants or reference compounds

suggesting that photolysis, dark chemistry and heterogeneous reactions are not a significant complication in the present work.

Unless otherwise stated, quoted uncertainties are two standard

deviations from the least squares regressions (forced through zero),

together with our estimated uncertainties (±1% of the initial concentration) associated with the IR spectral analysis of the relative

reactant and reference concentrations.

2.1. FTIR–smog chamber system at Ford

Experiments were performed in a 140-l Pyrex reactor interfaced

to a Mattson Sirus 100 FTIR spectrometer. The reactor was surrounded by 22 fluorescent blacklamps (GE F15T8-BL) which were

used to photochemically initiate the experiments. CH3ONO was

synthesized by the drop wise addition of concentrated sulfuric

acid to a saturated solution of NaNO2 in methanol. O3 was produced from O2 via silent electrical discharge using a commercial

O3 ozonizer. Samples of were supplied by

at purities >99.9%. All other reagents were

obtained from commercial sources at purities >99%.

Relative rate and absolute rate experimental methods were used

as described above. Experiments were conducted in 700 Torr total

pressure of air/N2 diluent at 295 ± 2 K. The loss of

and reference compounds was monitored by FTIR spectroscopy

using a calibrated analytical path length of 27.1 m and a spectral

resolution of 0.25 cm−1. A liquid nitrogen cooled midband MCT

detector was used in this study. Infrared spectra were derived from

32 coadded interferograms. Reactant and reference compounds

were monitored using absorption features over the following

wavenumber ranges (cm−1): C2H2, 650–800; C2H4, 900–1000; O3,

980–1070 669, 847, 935, 1311, and 1648.

2.2. FTIR–smog chamber system at University of Copenhagen

The Copenhagen experiments were performed in a 100-l quartz

reactor equipped with a Bruker IFS 66V FTIR spectrometer. The

experimental setup was equipped with a temperature control

system that kept the temperature steady at 293 ± 0.5 K. An InSb

detector was chosen for this study. Chlorine atoms were produced by photolysis of Cl2 according to reaction (1), using UVA

derived from 64 coadded interferograms. 

compounds were monitored using absorp

wavenumber ranges (cm−1): C2H2, 3175–3

O3, 2950–3065; 3060–3130

lyzed using a linear least squares fitting p

Griffith [5]. Reference spectra of O3 and H

HITRAN database [6], and used to improv

the larger molecules. For the other comp

tra were recorded using the same condition

employed in the kinetics experiments.

3. Results and discussion

3.1. Relative rate study of k(Cl + 

Copenhagen

The kinetics of reaction (10) were meas

reactions (11) and (12):

Cl + → products 

Cl + C2H4 → products 

Cl + C2H2 → products 

Initial reaction mixtures employed 

2.80–3.82 mTorr of 100–10

10.0–19.8 mTorr C2H4, or 7.20–10.6 mTor

air diluent. Reaction mixtures employe

sisted of 5.6–47.8 mTorr of 

and either 4.1–7.1 mTorr of C2H4 or 3.1

700 Torr of N2 diluent. The observed los

sus those of the reference compounds is 

least squares analysis of the data in F

shown in Table 1. The measured rate cons

on an absolute scale using k11 = 9.29 × 10

[7] and k12 = 5.07 × 10−11 cm3 molecule−1 

k10 obtained using different experimenta

Company and University of Copenhagen w

imental uncertainties, indistinguishable. 

for k10, which is the average of the det

limits which encompass the extremes of 

k10 = (5.22 ± 0.72) × 10−11 cm3 molecule−1 

While there have been no previous stu

pare our result with data for the reactions 

propene and other halogen substituted 

Table 2 [8–13]. The reaction of chlorine at

ceeds primarily via electrophilic addition to 

Substitution of the electron donating CH3 

withdrawing CF3 group would be expecte

ity of chlorine atoms towards the substitu

reactivities of t-CF3CH CH

CF3CF CHF, are all comparable and/or with
Fig. 1. Kinetic data for reactions of Cl atoms with measured at

295 ± 2K in 700 Torr of air (Ford, A) and in 700 Torr of N2 (Copenhagen, B). The error

bars reflect uncertainty (±1% of the initial concentration) in the determination of

the reactant concentrations.

individual determinations, inspection of Table 2 reveals a general

trend of decreased reactivity with increasing number and electron

withdrawing strength of the halogen substituents.

3.2. Relative rate study of k(OH + ) at Ford

The kinetics of reaction (13) were measured relative to reactions

(14) and (15):

OH + → products (13)

OH + C2H4 → products (14)

Fig. 2. Decay of vs. C2H2 (circles) and C2H

of OH radicals in 700 Torr of air at 295 ± 2 K. The error ba

of the initial concentration) in the determination of the 

OH + C2H2 → products 

Initial reaction mixtures consisted of 

100–330 mTorr CH3ONO, 

C2H4 or 1.47–2.74 mTorr C2H2, and 0–25

shows the loss of plotted 

reference compounds. Linear least squ

k13/k14 = 0.053 ± 0.003 and k13/k15 = 0.

k14 = 8.52 × 10−12 [14] (atmospheric pre

k15 = 8.45 × 10−13 [15] gives k13 = (4.52 

(4.28 ± 0.26) × 10−13 cm3 molecule−1 s−1. Ind

of k13 were obtained using the two differen

that consistent values of k13 were derived fro

different reference compounds suggests the 

systematic errors in the present work. We 

value which is the average of the individual 

error limits which encompass the extremes o

yielding k13 = (4.40 ± 0.38) × 10−13 cm3 mole

has been reported for k13 previously.

Kinetic data for the reactions of hydroxyl r

and fluorinated propenes are presented in T

Based on the structural similarity, one migh

ity of towards OH radicals 

that of t-CF3CH CHF. Interestingly, the reacti

is substantially lower (roughly a factor of 

atoms, the reaction with hydroxyl radicals 

electrophilic addition to the C C double b

reactivity towards OH radicals is expected 

introduction of electron withdrawing subst

groups, chlorine and fluorine. Inspection of Ta

reactivity of OH radicals towards propene is 

orinated propenes and that there is a genera

Table 1

Results of the Cl atom relative rate experiments

Setup Reference k /kReference kReference (×10−11 cm3 molecule−1 s−1) kCl+ (×

Ford (air) C2H4 0.55 ± 0.04 9.29 [7] (5.11 ± 0.37)

Ford (air) C2H2 1.03 ± 0.06 5.07 [7] (5.22 ± 0.30)

Copenhagen (N2) C2H4 0.59 ± 0.05 9.29 [7] (5.48 ± 0.46)

Copenhagen (N2) C2H2 1.00 ± 0.09 5.07 [7] (5.07 ± 0.46)
reactivity with increasing fluorination. However, in contrast to this

general trend, perfluoropropene is significantly more reactive than

the less fluorinated propenes. Furthermore, in contrast to a simple

trend of decreasing reactivity with increasingly electron withdrawing substituents, as noted above, CF3CH CHF is more reactive than

It has recently been suggested that hydrogen bonding

between OH and fluorine could lead to the observed enhancement of the reactivity of OH radicals towards the highly fluorinated

propenes [13]. Computational work would be useful to investigate

this suggestion.

3.3. Absolute rate study of k(O3 + at Ford and

Copenhagen

The kinetics of reaction (16) were studied by observing the decay

of l when exposed to O3 in excess in the reaction

chambers at Ford and Copenhagen:

O3 + → products (16)

An OH radical scavenger (cyclohexane) was added to the reaction mixtures to avoid potential problems associated with the loss

of via reaction with OH radicals formed in reaction (16) [14]. Initial concentrations of reactants at Copenhagen

were 6.9–14.2 mTorr 15.6–20.3 mTorr cyclohexane,

and 3.42–4.36 Torr O3 in 700 Torr of air diluent. Initial concentrations of reactants at Ford were 5.9–6.3 mTorr

14.0–30.6 mTorr cyclohexane, and 414–2070 mTorr O3 in 700 Torr

of air diluent. Variation of the [cyclohexane]/ ] ratio

over the range 2.2–5.2 had no discernable effect on the observed

decay of suggesting that loss via reaction with OH

radicals is not a significant complication. The loss of

followed pseudo first-order kinetics in all experiments (see insert

in Fig. 3).

A plot of the pseudo first-order decay of versus O3 concentration is shown in Fig. 3. A linear least squares

fit to the data gives k16 = (1.46 ± 0.10) × 10−21 cm3 molecule−1 s−1.

We choose to cite a final value for k16, with error limits which

include two standard deviations from the least squares regression and a propagated 5% uncertainty in the O3 calibration, of

k16 = (1.46 ± 0.12) × 10−21 cm3 molecule−1 s−1.

The result is compared to the reactivity of O3 towards

propene and analogous fluorine substituted propenes in Table 2

[8–10,12,13,21]. In its reaction with O3, t-CF3CH CHF is less reactive than its non-substituted counterpart by a factor of 6850. The

reaction occurs by electrophilic addition to the C C double bond.

When compared with Cl atoms and OH radicals, O3 has the lowest

reactivity and hence, is most sensitive to the presence of electron

withdrawing constituents. The existing literature shows a broad

trend of decreasing reactivity towards O3 with increasing number and electron withdrawing strength of the halogen constituents.

However, there are exceptions to this broa

inspection of the data in Table 2. The pre

has a remarkably low react

than the corresponding fluorinated compou

than E-CF3CF CHF, and comparable to Z-CF

decreasing reactivity with increasingly ele

stituents is not entirely sufficient to explain 

trend. Computational work would be of in

factors involved in determining the trend 

propenes towards ozone.

3.4. Infrared spectrum of

The IR spectrum of 

present work in 700 Torr of air di

shown in Fig. 4. has IR 

935, 1152, 1311 and 1648 cm−1. The 

integrated IR absorption cross-section 

(1.74 ± 0.20) × 10−16 cm molecule−1. Indivi

cross-sections are 6.22 × 10−18 (600–690 c

1030 cm−1), 1.27 × 10−16 (1030–1350 cm

(1600–1790) cm molecule−1. There are n

to compare with our result

Fig. 3. Pseudo-first order loss o vs. O3 

at Ford Motor Company and at University of Copenhag

bols and gray symbols, respectively. The insert show

when exposed to 414 mTorr (open circles), 911 mT

1.47 Torr (open downward triangles), 2.07 Torr (open s

and 4.36 Torr (gray triangles) of O3 in 700 Torr of air a
Fig. 4. IR spectrum of in 700 Torr of air, 295 ± 2 K (base e).

4. Implications for atmospheric chemistry

The present work improves our understanding of the

atmospheric chemistry of Cl atoms and OH

radicals react with with rate coefficients of

(5.22 ± 0.72) × 10−11 and (4.40 0.38) 10−13 cm3 molecule−1 s−1,

respectively. O3 reacts with with a rate constant

of (1.46 ± 0.12) × 10−21 cm3 molecule−1 s−1. is not

expected to undergo wet or dry deposition or photolysis [17] to an

appreciable extend. Cl atoms are not present in the atmosphere in

sufficient quantities to have a significant influence on the lifetime

of

The value of k(OH + derived in the present work

can be used to provide an estimate of the atmospheric lifetime of

Using a global weighted-average OH concentration

of 1.0 106 molecules cm−3 [22] leads to an estimated lifetime of

with respect to reaction with OH radicals of 26 days. In

a similar fashion our value for k(O3 + derived above

can be combined with the global background concentration of O3

of approximately 35 ppb [23] to provide an estimate of the atmospheric lifetime of with respect to reaction with O3

of 25 years. Hence we conclude that the atmospheric lifetime of

is determined by reaction with OH radicals and is

approximately 26 days. The approximate nature of this lifetime

estimate should be stressed; the average daily concentration of OH

radicals in the atmosphere varies significantly with both location

and season [24]. The values above are estimates of global average lifetimes; local lifetimes could be different from those quoted

above.

Using the method outlined by Pinnock et al. [25], the IR spectra

of shown in Fig. 4 and the IR spectrum of CFC-11 [26]

we calculate instantaneous forcings for and CFC-11

of 0.214 and 0.26W m−2 ppb−1, respectively. Values of the halocarbon global warming potential, HGWP [27], for

(relative to CFC-11) can then be estimated using the expression

(II):

HGWP =

IF

IFCFC-11   MCFC-11CFC-11M



×

1 − exp(−t/ )

1 − exp(−t/CFC-11)



(II)

where IF , IFCFC-11, M , MCFC-11, 

and CFC-11 are the instantaneous forcings, molecular weights

and atmospheric lifetimes of and CFC-11, and t

is the time horizon over which the forcing is integrated. Using

 = 26 days and CFC-11 = 45 years [28] we estimate that

the HGWP of relative to CFC-11 is 3.8 × 10−3 for a

Acknowledgements

We thank ( 

ing the high-purity samples of 

OJN, MSJ and EJKN acknowledge financial sup

Natural Science Research Council and the Vil

Foundation for the Copenhagen Center for A

(CCAR). MPSA acknowledges financial supp

Foundation and thanks F.S. Rowland and D.R

California, Irvine) for helpful discussions.

Appendix A. Supplementary data

Supplementary data associated with this 

in the online version, at

References

[1] M.J. Molina, F.S. Rowland, Nature 249 (1974) 810.

[2] J.D. Farman, B.G. Gardiner, J.D. Shanklin, Nature 315 

[3] T.J. Wallington, W.F. Schneider, J. Sehested, O.J. Nie

Discuss. 100 (1995) 55.

[4] T.J. Wallington, S.M. Japar, J. Atmos. Chem. 9 (1989) 

[5] D.W.T. Griffith, Appl. Spectrosc. 50 (1996) 59.

[6] L.S. Rothman, D. Jacquemarta, A. Barbeb, D. Chris B

M.R. Carleer, C. Chackerian Jr., K. Chance, L.H. Coude

Flaud, R.R. Gamache, A. Goldman, J.-M. Hartmann, 

Mandin, S.T. Massie, J. Orphal, A. Perrin, C.P. Rinsland

R.N. Tolchenov, R.A. Toth, J. Vander Auwera, P. Var

Spectrosc. Radiat. Transf. 96 (2005) 139.

[7] T.J.Wallington, J.M. Andino, I.M. Lorkovic, E.W. Kaise

94 (1990) 3644.

[8] M.P. Sulbaek Andersen, O.J. Nielsen, A. Toft, T. Nakaya

land, R.C. Buck, M.D. Hurley, T.J. Wallington, J. Photo

176 (2005) 124.

[9] R. Atkinson, D.L. Baulch, R.A. Cox, J.N. Crowley, R.F. 

Jenkin, M.J. Rossi, J. Troe, IUPAC Subcommittee, At

3625.

[10] O.J. Nielsen, M.S. Javadi, M.P. Sulbaek Andersen, M.D

Singh, Chem. Phys. Lett. 439 (2007) 18.

[11] M. Mashino, Y. Ninomiya, M. Kawasaki, T.J. Wallin

Chem. A 104 (2000) 7255.

[12] M.D. Hurley, J.C. Ball, T.J. Wallington, J. Phys. Chem. 

[13] R. Søndergaard, O.J. Nielsen, M.D. Hurley, T.J. Wallin

Lett. 443 (2007) 199.

[14] J.G. Calvert, R. Atkinson, J.A. Kerr, S. Madronich, G.K

G. Yarwood, The Mechanisms of Atmospheric Oxida

University Press, Oxford, 2000.

[15] M. Sørensen, E.W. Kaiser, M.D. Hurley, T.J. Wallingto

Kinet. 35 (2003) 191.

[16] M.K. Dubey, T.F. Hanisco, P.O. Wennberg, J.G. Ander

(1996) 321.

[17] V.L. Orkin, R.E. Huie, M.J. Kurylo, J. Phys. Chem. A 10

[18] K. Tokuhashi, A. Takahashi, M. Kaise, S. Kondo, A. 

Phys. Lett. 325 (2000) 189.

[19] A. McIlroy, F.P. Tully, J. Phys. Chem. 97 (1993) 610.

[20] V.C. Papadimitriou, R.K. Talukdar, R.W. Portman

Burkholder, Phys. Chem. Chem. Phys. 10 (2008) 821

[21] G. Acerboni, J.A. Buekes, N.R. Jensen, J. Hjorth, G. Myh

Atmos. Environ. 35 (2001) 4113.