ARTICLE IN PRESS
Atmospheric Environment 38 (2004) 6725–6735
www.elsevier.com/locate/atmosenv
Atmospheric gas-phase degradation and global warming
potentials of 2-fluoroethanol, 2,2-difluoroethanol,
and 2,2,2-trifluoroethanol
Stig Rune Sellevåga, Claus J. Nielsena,b,, Ole Amund Søvdeb, Gunnar Myhreb,
Jostein K. Sundetb, Frode Stordalb, Ivar S.A. Isaksenb
a
Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway
Department of Geosciences, University of Oslo, P.O. Box 1022, Blindern, N-0315 Oslo, Norway
b
Received 16 January 2004; accepted 2 September 2004
Abstract
The vapour phase reactions of 2-fluoroethanol, 2,2-difluoroethanol, and 2,2,2-trifluoroethanol with OH radicals and
Cl atoms were studied at 298 K and 1013 mbar using long-path FTIR detection. The following reaction rate coefficients
were determined by the relative rate method: k298(OH+CH2FCH2OH)=(1.4270.11) 1012, k298(OH+
CHF2CH2OH)=(4.5170.06) 1013, k298(OH+CF3CH2OH)=(1.2370.06) 1013, k298(Cl+CH2FCH2OH)=
(2.6770.3) 1011, k298(Cl+CHF2CH2OH)=(3.1270.06) 1012, and k298(Cl+CF3CH2OH)=(7.4270.12) 1013 cm3 molecule1 s1; the reported uncertainties represent 3s from the statistical analyses and do not include
any systematic errors or uncertainties in the reference rate coefficients. Quantitative infrared cross-sections of the title
compounds at 298 K are reported in the 4000–50 cm1 region.
A 3D chemistry transport model was applied to calculate the atmospheric distributions and lifetimes of the title
compounds; the global and yearly averaged lifetimes were calculated as 20 days for CH2FCH2OH, 40 days for
CHF2CH2OH, and 117 days for CF3CH2OH. Radiative forcing calculations were carried out assuming either constant
vertical profiles or the distribution derived from the chemistry transport model. The Global Warming Potentials for the
title compounds are insignificant compared to, e.g. CFC-11 (CCl3F).
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Infrared absorption cross-sections; Radiative forcings; OH radical; Cl atoms; Atmospheric lifetimes
1. Introduction
The Montreal Protocol and amendments (1987) led to
the phase out of a series of chlorofluoro carbons, CFCs,
Corresponding author. Department of Geosciences, Uni-
versity of Oslo, P.O. Box 1022, Blindern, N-0315 Oslo, Norway.
Tel.: +47 22855680; fax: +47 22855441.
E-mail address: c.j.nielsen@kjemi.uio.no (C.J. Nielsen).
in industrialised countries, mainly not only because of
their ozone depletion in the stratosphere, but also
because of their high global warming potentials, GWPs
(Zurer, 1993; IPCC, 1994). An intensive investigation of
potential CFC replacements, mainly organic compounds
containing hydrogen, fluorine or chlorine atoms was
therefore initiated about 10 years ago, in order to
estimate their ozone depletion potentials and their
GWPs (Fisher et al., 1990; Clerbaux et al., 1993;
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.atmosenv.2004.09.023
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S.R. Sellevåg et al. / Atmospheric Environment 38 (2004) 6725–6735
Ravishankara et al., 1993, 1994; Pinnock et al., 1995;
Christidis et al., 1997; Myhre et al., 1999; Highwood and
Shine, 2000).
Partially fluorinated alcohols, FAs, are potential
alternatives for CFCs and HCFCs in certain industrial
applications. To determine the environmental impact of
FAs released into the troposphere, the atmospheric
lifetimes and the nature and fate of the resulting
oxidation products are needed. This, in turn, requires
kinetic data for the atmospheric oxidation processes and
information on the degradation mechanisms; the first
step of their atmospheric degradation is the reactions
with OH radicals.
The aim of this investigation is to calculate the GWPs
for CH2FCH2OH, CHF2CH2OH, and CF3CH2OH, and
to this purpose infrared absorption cross-sections and
reaction rate constants have been determined. Further,
degradation products of these fluorinated alcohols have
been measured in order to contribute to the understanding of possible environmental impact of these
compounds. The compounds studied here react relatively fast in the atmosphere, indicating that these
components will not be homogeneously distributed in
the troposphere. In previous radiative forcing and GWP
studies of CFCs and CFC replacements it has been
assumed that the gases have a homogeneous mixing
ratio in the troposphere as the lifetime of such gases are
typically many years. For gases with a short lifetime the
abundance will decrease strongly with altitude. Greenhouse gases are most efficient in long wave radiation
trapping around the tropopause level, and therefore the
calculated radiative forcing and GWP will be reduced
substantially for short-lived components, compared to
results assuming a homogeneous mixing ratio in the
atmosphere.
Only limited information of direct relevance to the
environment is available on the title compounds besides
a few preliminary results (Kelly et al., 2001), only rate
coefficients for the OH reaction with 2,2,2-trifluoroethanol (Wallington et al., 1988; Tokuhashi et al., 1999), and
for the Cl atom reactions with the three ethanols are
available (Papadimitriou et al., 2003).
2. Experimental details and model description
2.1. Relative rate and product studies
Relative rate experiments and product studies of the
alcohol–radical reactions were carried out at 29872 K
and 101373 mbar in synthetic air in a 250 L stainlesssteel reactor equipped with a multiple reflection Whitetype mirror system having an optical base path of 2 m
and adjusted to give a total optical path of 120 m. The
optical system is connected to a Bruker IFS 88 FT-IR
spectrometer, allowing in situ analysis of intermediates
and final products. Spectra were generally recorded from
the time of mixing and to a maximum of 3 h by coadding 100 scan (collection time ca. 60 s) at 0.5 cm1
instrumental resolution.
In the relative rate method, RR, the reaction rate
coefficient for the compound of interest is measured
relatively to a reference compound with a known rate
coefficient. If the reactants react solely with the same
radical and none of the reactants is created in any side
reactions, the relative rate coefficient, krel, is given
according to the following expression:
½ A 0
½R0
kA
¼ krel ln
; krel ¼
ln
;
(1)
½ A t
½Rt
kR
where A is the compound of interest and R is the
reference compound. [A]0, [R]0, [A]t and [R]t are
concentrations of A and R at the start and at the time
t, respectively, and kA and kR are reaction rate
coefficients.
OH radicals were produced by photolysis of O3 in the
presence of H2O employing two Philips TL 20W/12
fluorescence lamps ðlmax 310 nmÞ in a quartz tube
inserted into the reaction chamber. Cl atoms were
generated by photolysis of Cl2 using two Philips TLD
18W/08 fluorescence lamps ðlmax 375 nmÞ: Typical
initial volume fractions were: alcohols, 2–5 ppm V;
reference compounds (acetone, ethane or 1,2-dichloroethane),
2–5 ppm V;
Cl2,
5–10 ppm V;
H2O,
500–1000 ppm V; O3, 50–100 ppm V. Purified air containing 80% N2 and 20% O2 (CO+NOxo100 ppb and
CnHmo1 ppm) and oxygen gas (99.95%) were delivered
from AGA. All organic compounds were purified/
degassed by doing three freeze–pump–thaw cycles.
Spectral subtraction was used to find the relative
concentrations of the reactants at different time intervals
during the reactions. The relative rate coefficients were
determined according to Eq. (1) by using a weighted
least-squares method that includes uncertainties in the
concentration of both reactants (York, 1966).
Each relative rate coefficient was determined from
three independent measurements. The reported uncertainties in this work represent 3s from the statistical
analyses and do not include any systematic errors or
uncertainties in the reference rate coefficients. Based on
the residuals in the spectral subtraction, the uncertainty
in the relative concentrations of the reactants is
estimated to be 0.01.
2.2. Infrared absorption cross-sections
The absorption cross-section of a compound J at a
specific wavenumber n~ is according to Beer–Lambert’s
law given by sð~nÞ ¼ Ae ð~nÞ=nJ l; where Ae ð~nÞ ¼ ln tð~nÞ is
the naperian absorbance, t is the transmittance, nJ is the
number density of J and l is the path length where the
absorption takes place. The integrated absorption
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intensity, Sint, is given by
Z
Sint ¼
sð~nÞ d~n:
(2)
band
Infrared spectra of the pure gases at room temperature were recorded in the region 50–4000 cm1 using a
Bruker IFS 113v FTIR employing a nominal resolution
of 1 cm1 (boxcar apodisation). KBr and Mylars
beamsplitters of various thicknesses were used to cover
the spectral region. To ensure optical linearity, only
deuterated triglycine sulphate (DTGS) detectors were
used. Cells of 2.34, 9.89 and 19 cm length equipped with
windows of KBr, CsI and high-density polyethylene,
respectively, were employed. The partial pressures of the
gases in the cells were from 4 to 70 mbar and were
measured using MKS Baratron pressure transducers.
The cross-sections were obtained from the absorbance
spectra assuming that the gas was ideal and applying a
baseline correction. The latter was performed by
subtracting a polynomial function, obtained by fitting
the regions of the spectrum where no absorptions were
expected.
2.3. Chemical transport model
The distribution of the three hydrofluoroalcohols is
simulated with a Chemical Tracer Model, the Oslo
CTM2. The model is run with spin up to make certain
that the tracer distribution is representative of the model
chemical steady state. The model is run in 5.6 5.61
horizontal resolution and with 19 levels from the surface
up to 10 hPa (approximately 32 km). Since the hydrofluoroalcohols are degraded by the hydroxyl radical,
which is produced when ozone is photo-dissociated, a
comprehensive chemical scheme is included in the
calculations. Further, emissions of a range of natural
and anthropogenic emissions need to be included, of e.g.
a range of ozone precursors. The anthropogenic surface
emissions are taken from the EDGAR data base (Olivier
et al., 1996) and the natural emissions from GEIA
(Yienger and Levy, 1995) and Müller (Muller, 1992). In
Acerboni et al. (2001) a similar set up was used to
estimate the 3D distribution of short-lived tracers, but
there the surface concentrations were set to 1 pptv as the
surface boundary for the whole globe. This is unrealistic
and has been refined here to make a more realistic
pattern of the surface concentrations. We have used
emissions for the three hydrofluoroalcohols with a
geographical distribution as for CFC-11 emissions, at
levels that yield globally averaged surface concentrations
of 1 ppbv. This will affect also the vertical distribution of
short-lived components under investigation. It is a
difficult task to model the vertical transport of such
components, since the transport (foremost the convection) and emission patterns must have a high degree of
coherence to be able to represent accurately the
6727
transport of the tracers to the upper troposphere. The
results in Acerboni et al. (2001) were likely an upper
limit on the effect of short-lived gases. The result here is
probably more realistic in establishing a realistic vertical
distribution of short-lived components with surface
emissions. Only chemical reaction with OH is included
in the CTM calculations, since reaction with Cl will be
of much smaller impact for the lifetime and atmospheric
distribution of the fluorinated alcohols.
2.4. Radiative transfer model
An emissivity/absorptivity thermal infrared broad
band model is used in the radiative forcing calculations.
It has been used in several studies of radiative forcing of
CFCs and CFC replacements (Myhre and Stordal, 1997;
Myhre et al., 1999; Acerboni et al., 2001). A spatial
resolution of 10 101 is used in the calculations with
climatological values of water vapour, temperature, and
clouds (Myhre and Stordal, 1997).
CH2FCH2OH, CHF2CH2OH, and CF3CH2OH are
included in the model with 6, 5, and 8 bands,
respectively. The annual mean latitudinal and height
distribution as calculated with the CTM is used for the
species. To comply with the weak line limit we have
scaled down the concentrations from the CTM linearly.
The radiative transfer calculations are performed for a
global and annual mean surface abundance of 0.1 ppbV.
In the radiative forcing calculations we follow the
concept described in IPCC (2001) to calculate cloudy
sky forcing with stratospheric temperature adjustment
included. Our estimates only include the thermal
infrared part. However, some of the gases studied here
may have a minor contribution at solar wavelengths.
3. Results and discussion
3.1. Kinetic study and degradation products
To determine the atmospheric chemical lifetimes, we
have investigated the rate coefficients of the OH and Cl
reactions
CH2 FCH2 OH þ OH=Cl!products;
(I)
CHF2 CH2 OH þ OH=Cl!products;
(II)
CF3 CH2 OH þ OH=Cl!products:
(III)
The rate coefficients for the OH reactions were
measured using ethane, CH3CH3, as the reference
compound. The wavenumber region 2920–2850 cm1,
i.e., part of the C–H stretching region, was analysed in
order to determine the relative concentrations of
CH3CH3 while the 960–900 cm1 region was used to
quantify CF3CH2OH, Fig. 1. FTIR reference spectra of
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6728
0.30
0.25
Absorbance
0.20
(c)
0.15
(d)
0.10
(a)
0.05
(e)
0.00
-0.05
960
950
940
930
920
910
900
Wavenumber / cm -1
0.35
0.30
Absorbance
0.25
0.20
(b)
0.15
0.10
(c)
(d)
0.05
(e)
0.00
2920
2910
2900
2890
2880
2870
2860
2850
Wavenumber / cm -1
Fig. 1. FTIR spectra of a 2,2,2-trifluorethanol and ethane
mixture during reaction with OH radicals. (Top) The
960–900 cm1 region used to quantify 2,2,2-trifluorethanol. (a)
Reference spectrum of 2,2,2-trifluorethanol, (c) spectrum of the
reaction mixture before reaction with OH radicals, (d) the last
spectrum in the series after reaction with OH, (e) the residual
spectrum after spectral subtraction, see text. (Bottom) The
2920–2850 cm1 region used to quantify ethane, (b) reference
spectrum of ethane.
HCHO, CF3CH2OH, C2H6, CH3CHO, HCOOH, H2O,
O3, H2O and a sloping baseline were included in the
spectral subtractions. An example of the residuals after
the spectral subtractions is also included in Fig. 1.
Details of the spectral subtractions employed to retrieve
the concentrations of the individual reactants are
summarized in Table 1.
Fig. 2 shows the decay of CF3CH2OH vs. CH3CH3 in
the presence of OH radicals, plotted according to Eq.
(1). As can be seen, there is a clear curvature in the data
series suggesting that secondary radical reactions are
taking place, and that these are faster for CH3CH3 than
for CF3CH2OH. As will be discussed later CF3O
radicals will eventually be produced in the degradation
of CF3CH2OH and it is this radical that causes the
interfering reactions. It is known that CF3O radicals
react with the reference compound ethane with a rate
coefficient of 1.2 10–12 cm3 molecule–1 s–1 (Saathoff
and Zellner, 1993), which is faster than the corresponding OH reaction. As illustrated in Figs. 3 and 4, the
kinetic data for the OH reactions with CHF2CH2OH
and CH2FCH2OH vs. CH3CH3 fall on straight
lines, indicating that interfering radicals are not
produced from these two reactions. Leaving out the
data points in the CF3CH2OH reaction for a degree of
reaction of more than 25% of CH3CH3 from the
analysis gives a relative rate coefficient of 0.54770.019
(3s statistical error) for CF3CH2OH vs. CH3CH3,
and 1.90370.016 and 5.8170.19 for the CHF2CH2OH
and CH2FCH2OH, respectively. Using k298(OH+
CH3CH3)=2.4 10–13 cm3
molecule–1 s–1
(Sander
et al., 2003) places the OH reaction rate coefficients
for CF3CH2OH, CHF2CH2OH, CH2FCH2OH on an
absolute scale at respectively (1.3170.05) 10–13,
(4.5770.04) 10–13, and (1.3970.05) 10–12 cm3 molecule–1 s–1, Table 2.
The rate coefficients for the Cl reactions were
measured using different reference compounds;
CH3C(O)CH3 (acetone) and CH2ClCH2Cl were used
in the case of CF3CH2OH, CHF2CH2OH was measured
relatively to CH3C(O)CH3, while CHF2CH2OH was
measured relatively to CH3CH3. The wavenumber
region 3050–3000 cm1, i.e., part of the C–H stretching region, was analysed in order to determine the
relative concentrations of CH3C(O)CH3. Again the
960–900 cm1 region was used to quantify CF3CH2OH.
FTIR reference spectra of CH3COCH3, CF3CH2OH
CH3COCl, CF2O, HCl, HCOOH, H2O and a sloping
baseline were included in the spectral subtractions.
Fig. 5 shows the decay of CF3CH2OH vs.
CH3COCH3 and vs. CH2ClCH2Cl in the presence of
Cl atoms, and was plotted according to Eq. (1). In both
cases the data fall on straight lines suggesting that the
secondary radical reactions interfering in the OH study
are of minor importance here. Also the data points from
the kinetic studies of CHF2CH2OH vs. CH3COCH3 and
CH2FCH2OH vs. CH3CH3 fall on straight lines as
shown in Figs. 6 and 7, respectively.
The kinetic results are collected in Table 2 and
compared with data from the literature. As can be seen,
there is good agreement between the different OH
reaction rate coefficients reported for CF3CH2OH, but
the rate coefficients measured by absolute techniques
(Wallington et al., 1988; Tokuhashi et al., 1999) are ca.
25% lower than the one from this work measured by the
relative rate technique. Some of the apparent discrepancy may be due to error in the value of the reaction
rate coefficient of the reference compound, some may be
due to secondary radical reactions. Our results for the
rate coefficients of the Cl reaction with the three
fluorinated alcohols agree with the recent results of
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Table 1
Spectral regions and compounds included in the spectral subtraction procedures
Reaction
Compound
Wavenumber region (cm1)
Other compounds included in the spectral subtraction procedure
OH
CH2FCH2OH
CH3CH3
920–840
2920–2850
CH3CH3, CH3CHO, O3, H2O
CH3CHO, HCHO, HCOOH, CH2FCH2OH, O3, H2O
OH
CHF2CH2OH
CH3CH3
920–860
2920–2850
CH3CH3, CH3CHO, CH3COOH, O3, H2O
CH3CHO, HCHO, HCOOH, CHF2CH2OH, O3, H2O
OH
CF3CH2OH
CH3CH3
960–900
2920–2850
CF2O, CH3CHO, O3, H2O
CH3CHO, HCHO, HCOOH, CF3CH2OH, O3, H2O
Cl
CH2FCH2OH
CH3CH3
920–840
2920–2850
CH3CH3, CH3CHO, CH3COOH
CH3CHO, HCHO, CH2FCH2OH, HCl
Cl
CHF2CH2OH
CH3C(O)CH3
950–910
3050–3000
CF2O, CH3COCl
HCOOH, CF3CH2OH, H2O, HCl
Cl
CF3CH2OH
CH3C(O)CH3
950–910
3050–3000
CH3COCl, CF2O
CF3CH2OH, HCOOH, H2O, HCl
Cl
CF3CH2OH
CH2ClCH2Cl
970–910
735–722
CH2ClCOCl, CF2O, HClCO, H2O
CH2ClCOCl, HClCO, H2O
A sloping baseline was added in all procedures.
1.2
0.5
ln {[CHF2CH2OH]0/[CHF2CH2OH]t}
ln {[CF3CH2OH]0 /[CF3CH2OH] t }
0.6
OH radical reaction with
CF3CH2OH and CH3CH3
0.4
0.3
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
ln {[CH3CH3]0 /[CH3CH3] t }
Fig. 2. Plot of lnf½CF3 CH2 OH0 =½CF3 CH2 OHt g vs.
lnf½CH3 CH3 0 =½CH3 CH3 t g during the reaction with OH
radicals. 13 data points from 3 independent experiments were
used to derive the relative reaction rate coefficient,
krel=0.54770.019 (3s). The points without error bars were
not included in the least-squares fit, see text.
Papadimitriou et al. (2003) taking the uncertainties in
the reaction rate coefficients of the reference compounds
into account.
The gas-phase degradations of CH2FCH2OH,
CHF2CH2OH and CF3CH2OH were studied using
chlorine atoms as the oxidizing agent. The corresponding fluoroacetaldehydes CH2FCHO, CHF2CHO and
CF3CHO were observed as intermediates in agreement
with the results of Papadimitriou et al. (2003). In the
1.0
OH radical reaction with
CHF2 CH2OH and CH3CH3
0.8
0.6
0.4
0.2
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
ln {[CH3CH3]0 /[CH3CH3]t}
Fig. 3. Plot of lnf½CH2 FCH2 OH0 =½CH2 FCH2 OHt g vs.
lnf½CH3 CH3 0 =½CH3 CH3 t g during the reaction with OH
radicals. 24 data points from 3 independent experiments were
used to derive the relative reaction rate coefficient,
krel=1.90370.016 (3s).
case of 2,2,2-trifluoroethanol, both CO and CO2, CF2O,
and additional traces of CF3COOH and HF were
observed. Papadimitriou et al. (2003) estimated the
reaction enthalpies and the C–H and O–H bond
enthalpies from B3P86/6-311++G(2df,p) DFT calculations and reported DbondH(CH2)DbondH(CHxF3x)
25 kJ mol1DbondH(OH)60 kJ mol1. Although the
OH reaction is ca. 55 kJ mol1 more exothermic than
the Cl reaction (DreacH(HCl+OH-Cl+H2O)=
57.5 kJ mol1, calculated at the same level of theory)
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6730
it is not unreasonable to assume that the OH and
Cl-initiated oxidations will have similar mechanisms. We
therefore propose that the first steps in the gas-phase
degradation of CH2FCH2OH (x=2), CHF2CH2OH
(x=1) and CF3CH2OH (x=0) are
O2
CHx F3x CH2 OH ! CHx F3x CHOH
O2
! CHx F3x CHO:
(IV)
The atmospheric chemistry of CF3CHO has recently
been studied by Sellevåg et al. (2004). It was found
that the atmospheric lifetime of CF3CHO is mainly
1.6
ln {[CH2FCH2OH]0 /[CH2FCH2OH]t }
1.4
1.2
3.2. Infrared absorption cross-section
OH radical reaction with
CH2FCH2OH and CH3CH3
1.0
0.8
0.6
0.4
0.2
0.0
0.00
0.05
0.10
0.15
determined by its OH reaction rate coefficient: only an
upper limit to the photolysis was reported suggesting
that photolysis might be of some importance. As far as
we are aware of, no experimental data is available on the
atmospheric fate of CH2FCHO and CHF2CHO. Based
on the results from the present work and analogies with
the reactions of CH3CHO, the gas-phase degradation of
the three fluoroacetaldehydes will mainly result in the
formation of the corresponding fluoromethyl radicals.
The atmospheric chemistry of the CF3 radical has been
described in detail by Ko et al. (1994) and by Sehested
and Wallington (1993). The CH2F and CHF2 radicals
will likely react with oxygen to form HFCO and CF2O,
respectively.
0.20
0.25
0.30
ln {[CH3CH3 ]0 /[CH3CH3 ]t }
Fig. 4. Plot of lnf½CH2 FCH2 OH0 =½CH2 FCH2 OHt g vs.
lnf½CH3 CH3 0 =½CH3 CH3 t g during the reaction with OH
radicals. 22 points from 3 independent experiments were used
to derive the relative reaction rate coefficient, krel=5.817
0.19 (3s).
The infrared spectra of CH2FCH2OH, CHF2CH2OH,
and CF3CH2OH are shown in Fig. 8. The integrated
absorption cross-sections (base e) for all three compounds are included in the legends. The quality of our
cross-section data has been investigated by comparing
with the earlier well-studied CHClF2, HCFC-22 (Ballard
et al., 2000). The integrated cross-sections obtained with
our Bruker 113v is within 3% of the average value
reported in this intercomparison. This in turn suggests
that the absolute error limits in our measurements be in
the order of 75%.
3.3. CTM2 model results
The spatial distribution of the hydrofluoroalcohols is
calculated with the CTM. Figs. 9 and 10 show the
Table 2
Rate coefficients for the reaction of OH radicals and Cl atoms with fluorinated ethanols at 298 K
Molecule
kOH (cm3 molecule1 s1)
kCl (cm3 molecule1 s1)
Technique and reference
CH2FCH2OH
(1.3970.05) 1012a
CHF2CH2OH
(4.5770.04) 1013a
CF3CH2OH
(1.3170.05) 1013a
(0.9670.07) 1013
(1.0170.05) 1013
(2.070.4) 1011
(2.6770.03) 1011b
(3.070.6) 1012
(3.1270.06) 1012d
(6.371.3) 1013
(7.3270.19) 1013b
(7.5170.17) 1013e
VLPRc
RR-FTIR (this work)
VLPRc
RR-FTIR (this work)
VLPRc
RR-FTIR (this work)
RR-FTIR (this work)
FP-RFf
DF-LIF, LP-LIF, FP-LIFg
Errors quoted correspond to 3s.
a
Relative to k298(OH+CH3CH3)=2.4 10–13 cm3 molecule–1 s–1 (Sander et al., 2003).
b
Relative to k298(Cl+CH3COCH3)=2.0 10–12 cm3 molecule–1 s–1 (Sellevåg and Nielsen, 2003).
c
VLPR, very low pressure reactor technique (Papadimitriou et al., 2003).
d
Relative to k298(Cl+CH3CH3)=5.7 10–11 cm3 molecule–1 s–1 (Sander et al., 2003).
e
Relative to k298(Cl+CH2ClCH2Cl)=1.3 10–12 cm3 molecule–1 s–1 (Wallington et al., 1996).
f
FP-RF, flash photolysis resonance fluorescence (Wallington et al., 1988).
g
DF, discharge flash; LP, laser photolysis; LIF, laser-induced fluorescence (Tokuhashi et al., 1999).
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0.8
ln {[CHF2CH2OH]0 /[CHF2CH2OH]t}
ln {[CF3CH2OH]0 / [CF3CH2OH]t }
0.5
Cl atom reaction with
CF3CH2OH and CH3COCH3
0.4
0.3
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.7
Cl atom reaction with
CHF2 CH2OH and CH3COCH3
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.4
0.0
0.1
ln {[CH3COCH3]0 / [CH3COCH3]t }
0.3
0.4
0.5
Fig. 6. Plot of lnf½CHF2 CH2 OH0 =½CHF2 CH2 OHt g vs.
lnf½CH3 COCH3 0 =½CH3 COCH3 t g during the reaction with Cl
atoms. 26 data points from 3 independent experiments were
used to derive the relative reaction rate coefficient,
krel=1.56570.015 (3s).
Cl atom reaction with
CF3CH2OH and CH2ClCH2Cl
0.5
0.4
0.3
0.8
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
ln {[CH2ClCH2Cl]0 /[CH2ClCH2Cl]t }
Fig. 5. (Top) Plot of lnf½CF3 CH2 OH0 =½CF3 CH2 OHt g vs.
lnf½CH3 COCH3 0 =½CH3 COCH3 t g during the reaction with Cl
atoms. 24 data points from 3 independent experiments were
used to derive the relative reaction rate coefficient, krel=
0.36670.009 (3s). (Bottom) Plot of lnf½CF3 CH2 OH0 =
½CF3 CH2 OHt g vs. lnf½CH2 ClCH2 Cl0 = ½CH2 ClCH2 Clt g
during the reaction with Cl atoms. 20 data points from 3
independent experiments were used to derive the relative
reaction rate coefficient, krel=0.57870.013 (3s).
surface abundance and the zonal mean vertical profile of
CF3CH2OH, which has the longest lifetime of the three
species. The surface pattern shows three distinct maxima
over industrialized regions reflecting the surface emissions. Fig. 10 shows a very strong hemispheric difference
and that the abundance of CF3CH2OH decreases
strongly with altitude. The patterns of the atmospheric
distribution of the two other hydrofluoroalcohols are
similar to the one for CF3CH2OH, but with a stronger
decrease in abundance with altitude. This is a result of
the difference in reaction rates with OH.
The chemical lifetimes calculated with the CTM are
19.8, 39.6, 117.4 days for CH2FCH2OH, CHF2CH2OH,
and CF3CH2OH, respectively. This is very short
compared to the CFCs and many CFC replacements,
ln {[CH2FCH2OH]0 /[CH2FCH2OH]t }
ln {[CF3CH2OH]0 /[CF3CH2OH]t}
0.7
0.6
0.2
ln {[CH3COCH3 ]0/[CH3COCH3 ]t }
0.7
Cl atom reaction with
CHF2CH2OH and CH3CH3
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
ln {[CH3CH3 ]0 /[CH3CH3]t}
Fig. 7. Plot of lnf½CH2 FCH2 OH0 =½CH2 FCH2 OHt g vs.
lnf½CH3 CH3 0 =½CH3 CH3 t g during the reaction with Cl atoms.
36 data points from 3 independent experiments were used
to derive the relative reaction rate coefficient, krel=0.45497
0.0025 (3s).
but longer than the species investigated in Acerboni
et al. (2001).
3.4. Radiative transfer calculations
The radiative forcing calculations for the three
hydrofluoroalcohols are shown in Table 3 for atmospheric distribution calculated with the CTM as well as
for a distribution which assumes a constant vertical
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Absorption cross section
-18
2
-1
/10 cm molecule
6732
0.4
0.3
CH2FCH2OH
0.2
0.1
0.0
4000
3500
3000
2500
2000
1500
1000
500
1000
500
1000
500
Absorption cross section
-18
2
-1
/10 cm molecule
Wavenumber/cm-1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
4000
CHF2 CH2OH
3500
3000
2500
2000
1500
Absorption cross section
-18
2
-1
/10 cm molecule
Wavenumber/cm-1
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4000
CF3CH2OH
3500
3000
2500
2000
1500
Wavenumber/cm-1
Fig. 8. Infrared absorption cross sections (4000–50 cm1, base
e) of 2-fluoroethanol, 2,2-difluoroethanol, and 2,2,2-trifluoroethanol. Absolute integrated absorption intensities in units of
1017 cm molecule1: CH2FCH2OH, Sint(1600–460 cm1)=
4.5370.14; CHF2CH2OH, Sint(1550–700 cm1)=6.2070.17;
CF3CH2OH, Sint(1600–610 cm1)=13.7370.18.
abundance in the atmosphere. The radiative forcing due
to the hydrofluoroalcohols is very low compared to
CFCs and many CFC replacements when applying the
atmospheric distribution from the CTM. This is owing
to the strong decrease of the species with altitude since
the greenhouse gases are most efficient in trapping
thermal infrared radiation around the tropopause
altitude. The radiative forcings, obtained by applying a
distribution with a constant vertical profile, are similar
to those of most CFCs and their replacements
0.1–0.35 Wm2 ppbv1 (IPCC, 2001). The short lifetimes of the fluorinated alcohols result in a decrease in
their concentrations with increasing altitude and in a
factor of 2.5–7 lower radiative forcing than calculated
using a constant vertical distribution.
Acerboni et al. (2001) introduced a normalized
radiative forcing, defined as the radiative forcing divided
by the integrated band strength (in 1017 W
molecule1 m3). We have calculated this quantity here
for the three components under investigation. In the
case with constant vertical distribution the normalized
radiative forcing is between 1.3 and 1.9 with
CHF2CH2OH and CF3CH2OH having the highest and
lowest value, respectively. CF3CH2OH has low values
owing to some strong absorption bands at high
wavenumbers in a spectral region with strong water
vapour overlap and with low thermal infrared energy.
Most of the CFCs have their absorption bands mainly in
the atmospheric window region (about 1200–800 cm1)
with weak overlap with other gases and thus a higher
normalized radiative forcing than these hydrofluoroalcohols, e.g. CFC-11 has a value around 2.5. However,
the normalized radiative forcings for the hydrofluoroalcohols in this study are higher than the values for the
Fig. 9. Atmospheric surface abundance of CF3CH2OH in ppbV as modelled with the Oslo CTM.
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6733
Fig. 10. Atmospheric zonal mean abundance (vertical–latitudinal cross-section) of CF3CH2OH in ppbV as modelled with the Oslo
CTM.
Table 3
Radiative forcing due to the three hydrofluoroalcohols with
atmospheric CTM distribution and with constant vertical
profile
Compound
CH2FCH2OH
CHF2CH2OH
CF3CH2OH
CTM distribution
Wm2 (ppbv)
Constant vertical
distribution
Wm2 (ppbv)
0.016
0.020
0.085
0.11
0.15
0.21
three perfluoroalkenes studied in Acerboni et al. (2001).
In the case with CTM calculated atmospheric distribution CF3CH2OH has normalized radiative forcing 0.55
and the two other compounds 0.26.
3.5. Global warming potentials
IPCC (2001) uses global warming potential (GWP) as
a simple measure to compare the effectiveness of equal
mass emissions of various climate gases. The report
discusses its limitations, and gives a background of its
concept. The GWP is given relative to another gas,
either CO2 or CFC-11.
GWP calculations are performed here using both
CFC-11 and CO2 as reference gases. For calculations
using CO2 as a reference gas the expression given in
IPCC (2001) (same expression as IPCC (1994) with
modified constant) is used to establish the radiative
forcing with an abundance of CO2 of 364 ppmv and an
increase of 1 ppmv. The lifetime expression for CO2 is
the same as the one adopted in IPCC (2001). With CFC11 as a reference gas, we use the radiative forcing of
0.25 W m2 ppb1 and lifetime of 45 years from IPCC
(2001).
Table 4 shows the GWP for the three hydrofluoroalcohol investigated for 3 time horizons for CO2 and
CFC-11 as reference gases. The three species have very
low GWP values compared to various halocarbons (see
IPCC, 2001). This is a result of two factors which are
both due to the short lifetime of the compounds. First,
the radiative forcing is low, since the concentration of
the species in the upper troposphere is low as discussed
above, and second the lifetime is an important factor for
the integrated radiative forcing over a time horizon.
However, the GWP values are higher than for the
perfluoroalkenes studied in Acerboni et al. (2001).
CF3CH2OH has more than a factor of ten higher
GWP values than the two other compounds owing to its
longer lifetime.
4. Atmospheric implications
The results show that the three fluorinated ethanols
have chemical lifetimes in the troposphere ranging from
20 to 120 days and that their primary oxidation products
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Table 4
GWP values of the three hydrofluoroalcohols relative to CFC-11 and CO2, applying CTM calculated atmospheric distribution
Compound
CH2FCH2OH
CHF2CH2OH
CF3CH2OH
Time horizon (yr)
20
100
500
3.00 (0.00046)
6.03 (0.00091)
61.4 (0.0093)
0.89 (0.00018)
1.79 (0.00037)
18.3 (0.0038)
0.28 (0.00016)
0.56 (0.00033)
5.67 (0.0033)
GWP values relative to CFC-11 are in parenthesis.
are fluorinated aldehydes, which in principle are benign
to the environment. The secondary gas-phase products
are CHFO and CF2O, which within days will be
incorporated into droplets/aerosols and hydrolysed to
give CO, CO2 and HF (Debruyn et al., 1995). The
additional fluorine ions in the liquid phase will be
negligible compared to the global F– budget (Sehested
and Wallington, 1993).
The fluorinated ethanols may, however, also be
removed from the troposphere by uptake in cloud
droplets and subsequent rainout. Recently, the Henry’s
law constant for 2,2,2-trifluoroethanol has been measured by Chen et al. (2003). The Henry’s law constant
varies between 44.6 and 255 M atm–1 in the temperature
range from 275 to 299 K, that is 2,2,2-trifluoroethanol is
less soluble than ethanol. Chen et al. (2003) also
estimated the wet-deposition lifetime to be 343 days,
suggesting that 30% of 2,2,2-trifluoroethanol is likely to
be oxidised in water droplets in the environment.
CF3CH2OH may therefore lead to trifluoroacetic acid
(TFA, CF3COOH) in water droplets.
The studied HFA’s are CFC replacements with very
low GWP values, as a result of their short lifetimes. The
GWP values are lower than most of earlier studies for
CFCs and CFC replacements.
Acknowledgements
This work is part of the project ‘‘Impact of
Fluorinated Alcohols and Ethers on the Environment’’,
and has received support from the Commission of the
European Communities under the Energy, Environment
and Sustainable Development Programme through
contract EVK2-CT-1999-00009.
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