Atmospheric Environment 33 (1999) 4447}4458
Infrared absorption cross section, radiative forcing,
and GWP of four hydro#uoro(poly)ethers
G. Myhre *, C.J. Nielsen, D.L. Powell, F. Stordal
Department of Geophysics, University of Oslo, P.O.Box 1022 Blindern, N-0315 Oslo, Norway
Department of Chemistry, University of Oslo, P.O.Box 1033 Blindern, N-0315 Oslo, Norway
Received 26 February 1998; received in revised form 30 March 1999; accepted 19 April 1999
Abstract
Quantitative infrared cross-sections of the unbranched hydro#uoro(poly)ethers CHF OCHF , CHF OCF OCHF
and CHF OCF CF OCHF have been obtained at 298 K in the region 25}4000 cm\. Radiative forcing calculations
have been performed for these compounds and for CHF OCF OCF CF OCHF , and the values found per molecule are
high compared to those of other CFCs and CFC replacements. Atmospheric lifetimes, calculated on the basis of
experimental reaction rates with OH radicals, and global warming potentials are presented for all four compounds. 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Reduction of the ozone depleting chloro#uorocarbons
(CFCs) in accordance with the Montreal Protocol has led
to investigations of CFC replacements. Like most of the
CFCs, the CFC replacements also absorb thermal infrared radiation and may contribute to an enhanced
greenhouse e!ect. Several studies have investigated the
climate e!ect of CFC replacements in use or with the
potential for use in the future (Fisher et al., 1990; Shi and
Fan, 1992; Clerbaux et al., 1993; Pinnock et al., 1995;
Imasu et al., 1995; Christidis et al., 1997). The present
study focuses on the four simplest linear hydro#uoropolyethers (HFPEs) with the general structure CF HO
(CF O) (CF CF O) CF H, that is, CHF OCHF ,
CHF OCF OCHF , CHF OCF CF OCHF
and
CHF OCF OCF CF OCHF , later to be abbreviated
HG-00, HG-10, HG-01, and HG-11 according to the
values of (n, m) in the general structure formula. This
class of hydro#uoropolyethers maintain several of the
remarkable properties of per#uorinated compounds and
can therefore be used in a variety of applications includ-
* Corresponding author. Fax: #47-22855269.
On leave from the College of Wooster, Wooster, Ohi, USA.
E-mail address: gunnar.myhre@geofysikk.uio.no (G. Myhre)
ing CFC substitution in the areas of solvents, highperformance #uids, "re suppressants, heat exchange, etc.
Qualitative mid infrared spectra including ab initio
calculations have been published for HG-10, HG-01 and
HG-11 (Radice et al., 1998). Quantitative mid infrared
vapour-phase spectra have previously been presented for
HG-00 (Imasu et al., 1995; Heath"eld et al. 1998), HG-10
(Tuazon, 1997; Cavalli et al., 1998), HG-01 (Tuazon,
1997; Cavalli et al., 1998), and HG-11 (Tuazon, 1997;
Christidis et al., 1997; Cavalli et al., 1998). Quantitative
spectra have also been presented for an industrial mixture of HGs having n/m ratio of 1.03, an average molecular weight of 414 and a boiling point ranging from 40 to
1403C (BruK hl et al., 1993). No far infrared spectra of the
compounds have so far been published. Reaction rate
coe$cients for the OH reactions with the HG compounds have recently been reported (Zhang et al., 1992;
Garland et al., 1993; Hsu and DeMore, 1995; DeMore,
1996; Tuazon, 1997; Cavalli et al., 1998). An UV-Visible
vapour-phase spectrum at 298 K of an industrial mixture
of HGs has also been presented (BruK hl et al., 1993).
The radiative forcing concept is often used to compare
radiative e!ects of di!erent atmospheric radiatively active components (IPCC 90; 95). Recently, Hansen et al.
(1997) have shown that the relationship between radiative forcing and surface temperature changes is reasonably good for known radiatively active components. This
1352-2310/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved.
PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 2 0 8 - 3
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G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
is based on the assumption that radiative forcing is taken
at the tropopause level and that the stratospheric temperature adjustment is taken into account.
The experimental conditions and infrared cross-sections in the region 25}3250 cm\ for HG-00, HG-10, and
HG-01 are presented in Sections 2 and 3, respectively.
Calculations and results for lifetimes of HG-00, HG-10,
HG-01, and HG-11 are described in Section 4. In Sections 5 and 6 we describe radiative transfer models used
and radiative forcing due to the HGs. The potential
climate e!ect of the four HGs is estimated using global
warming potentials (GWP) which are presented in Section 7. Finally, a summary is given in Section 8.
2. Experimental
The samples of CHF OCHF , CHF OCF OCHF
and CHF OCF CF OCHF were obtained from Ausi
mont S.p.A. and had stated purities better than 98%.
They were used without further puri"cation after degassing and distillation in vacuo.
Infrared spectra of the pure gases at room temperature
were recorded in the region 25}4000 cm\ using
a Bruker IFS 113v employing a nominal resolution of
1 cm\ and a 4P apodization (breakpoint 0.9) of the
interferograms. KBr and Mylar威 beamsplitters of 3.5, 6,
12, 24, 50 and 75 lm thickness were used to cover the
spectral region. To ensure optical linearity, only DTGS
detectors were used. Cells of 10 and 19 cm length equipped with windows of CsI and high-density polyethylene
were employed, respectively. The partial pressures of the
gasses in the cells were from 0.5 to 90 mbar and were
measured using MKS Baratron pressure transducers.
The very strong absorption by the C}F stretching vibrations necessitated the use of low partial pressures and
calibration procedures involving higher pressures and
more reliable pressure measurements were based on the
absorption in the well isolated C}H stretching region. On
this basis the infrared cross sections are believed to be
accurate within $10%.
3. Spectral results
The IR spectra of HG-00, HG-10 and HG-01 are
shown in Fig. 1. For completeness, Fig. 1 also includes
the spectrum of HG-11 (courtesy of Cavalli et al., 1998).
The integrated absorption cross sections (base e) are
listed in Table 1 and compared to previous results (Imasu
et al., 1995; Christidis et al., 1997; Heath"eld et al., 1998;
Cavalli et al., 1998). Unfortunately, Tuazon (1997) only
presents the spectra (base 10) and not the integrated cross
sections, but a comparison between the peak heights of
the HG-10 and HG-01 spectra in Fig. 1 with those shown
by Tuazon reveals compatible spectral data with our
values being slightly lower. Cavalli et al. (1998) used
a long path system with a high sensitivity MCT detector.
We suggest that some of the di!erences between our
results and those of Cavalli et al. (1998) may be caused by
non-linearity in their detection system.
The bending and torsional modes situated in the far
infrared region give rise only to very weak absorptions,
Fig. 1. This agrees with results from ab initio calculations
(Radice et al., 1998; Marstokk et al., 1999). Current investigations in our laboratory show that nearly all strong
absorption bands of the di!erent conformers present in
HG compounds overlap, and that only minor di!erences
are observed in the region between 800 and 25 cm\ (e.g.
Marstokk et al., 1999). Further, the minuscule absorption
cross-sections of these modes imply that there will not be
any substantial change with temperature relative to the
room temperature mid infrared absorption cross section.
4. Lifetimes
The UV-Visible absorption cross section of HGs was
shown to have its maximum below 200 nm, where it is
less than 10\ cm molecule\ dropping to less than
10\ cm molecule\ at wavelengths above 230 nm
(BruK hl et al., 1993). Photolysis of the HGs will therefore
only be an important removal mechanism in the upper
stratosphere.
The lifetimes of the four HGs are calculated on the
basis of the reaction rates with OH only. Two methods
have been used: one assuming the reaction rates with OH
to be independent of temperature, the other assuming the
same temperature dependence of the OH reaction rates
for all four HGs. Table 2 collects the available kinetic
data for OH reactions with the HGs. For HG-00 two
investigations (Garland et al., 1993; Hsu and DeMore,
1995) report consistent reaction rate coe$cients and we
have used an average of their results in our calculations,
k (¹)"8.66;10\;exp(!1735/¹) and k "
-&
2.6;10\ cm molecule\ s\. With this temperature
dependence the reaction rate coe$cient is an order of
magnitude smaller at 200 K than at 300 K. For the other
three HGs we have used the experimental kinetic results
of Cavalli et al. (1998) obtained at 298 K. Laboratory
experiments have not been made to identify the temperature dependence of the reaction rates between the OH
radical and HG-10, HG-01, and HG-11. However, the
reactive parts of the four HG molecules considered are
structurally similar, and we have therefore assumed that
the OH reaction has the same temperature dependence
for all the four HGs. With OH reaction rate coe$cients
of these magnitudes, Table 2, the lifetimes are su$ciently
long to ensure a relatively homogeneous distribution in
the troposphere.
Assuming the reaction rate to be spatially invariable
(no temperature dependence) the lifetimes may then be
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
4449
Fig. 1. Quantitative vapour-phase infrared spectra 25}3250 cm\ of CHF OCHF (HG-00), CHF OCF OCHF (HG-10),
CHF OCF CF OCHF (HG-01) and CHF OCF OCF CF OCHF (HG-11), the latter courtesy of Cavalli et al. (1998). The
absorption cross sections are given in units of 10\ cm molecule\ (base e).
estimated using averaged OH concentrations in the
calculations. Monthly OH values are taken from a threedimensional (3D) chemistry transport model (CTM)
(Berntsen and Isaksen, 1997) with a horizontal resolution
of 103 in longitudinal and 83 in latitudinal direction and
with 9 vertical layers. An average OH concentration of
1.1;10 molecules cm\ is calculated in the model leading to the lifetimes shown in Table 3.
Data from the 3D chemistry transport model have also
been used in combination with temperature-dependent
reaction rates (see above) to calculate the lifetime of the
HGs (Table 3). The calculated lifetimes are a factor of 2.5
4450
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
Fig. 1. (continued)
higher than the ones using temperature-independent reaction rates demonstrating that the loss of HGs to a large
extent take place at temperatures which are signi"cantly
lower than 298 K. We emphasise that the temperaturedependent reaction rate coe$cients used for HG-10,
HG-10 and HG-11 are estimates and that the results
obtained for these compounds must be used with caution. However, the temperature dependence of the reac-
tion rates has to be greatly di!erent from the one used
here to change the calculated lifetimes substantially. To
investigate this further, we also performed a sensitivity
study in which the activation energy was increased and
decreased by 10 and 20%, respectively. In both cases the
pre-exponential factors were adjusted to give the same
values for the reaction rate coe$cients at 298 K as in the
reference cases. Table 3 includes the results from this
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
4451
Table 1
Integrated absorption cross sections of hydro#uoro(poly)ethers
Compound
Integrated cross-section
(10\ cm molecule\)
Integration limits (cm\)
Reference
CHF OCHF
(HG-00)
2.5$0.3
2.55
2.56$0.4
4.0$0.4
5.19$0.23
5.0$0.5
6.04$0.13
6.55$0.33
8.49$0.34
25}3250 cm\
Not stated
750}1480 cm\
25}3250 cm\
978}1584 cm\
25}3250 cm\
930}1501 cm\
450}2000 cm\
963}1587 cm\
This work
Imasu et al. (1995)
Heath"eld et al. (1998)
This work
Cavalli et al. (1998)
This work
Cavalli et al. (1998)
Christidis et al. (1997)
Cavalli et al. (1998)
CHF OCF OCHF
(HG-10)
CHF OCF OCHF
(HG-01)
CHF OCF OCF OCF OCHF
(HG-11)
Table 2
Arrhenius parameters and reaction rate coe$cients at 298 K for the reaction of hydro#uoro(poly)ethers with the OH radical
Compound
A
(10\ cm
molecule\ s\)
E/R
CHF OCHF
(HG-00)
5.4$3.5
19.0$1.9
1560$200
2006$200
CHF OCF OCHF
(HG-10)
CHF OCF CF OCHF
(HG-01)
CHF OCF OCF CF OCHF
(HG-11)
k
(10\ cm
molecule\ s\)
Reference
25!
5.06$0.37
2.9
2.3
1.34
2.4$0.7
4.7$1.6
Zhang et al. (1992)
Huie and Kurylu (1993)
Garland et al. (1993)
Hsu and DeMore (1995)
DeMore (1996)
Cavalli et al. (1998)
Cavalli et al. (1998)
4.6$1.6
Cavalli et al. (1998)
Table 3
Atmospheric lifetimes of hydro#uoro(poly)ethers
Compound
Lifetime (yr)
k (¹)"k (298)
-&
-&
CHF OCHF (HG-00)
11.3
CHF OCF OCHF (HG-10)
12.1
CHF OCF CF OCHF (HG-01)
6.2
CHF OCF OCF CF OCHF (HG-11)
6.3
k (¹)/A "exp(!1735/¹)
-&
-&
#2.0
28.4
!3.7
#2.1
30.4
!4.0
#1.1
15.5
!2.0
#1.1
15.5
!2.1
Estimated uncertainty in the atmospheric lifetimes arising from an increase and decrease in the activation energy by 10 and 20%,
respectively, see text.
analysis showing that the lifetimes in these experiments
increased and decreased by 7 and 13%, respectively.
Cavalli et al. (1998) estimated lifetimes for HG-10,
HG-01, and HG-11 using temperature-independent reac-
tion rates. Christidis et al. (1997) assumed a lifetime for
HG-11 of 48 y (based on unpublished data for HG-01).
The Cavalli et al. (1998) values are about 1 yr higher than
our lifetimes using temperature independent reaction
4452
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
rates. Therefore our best estimates of lifetimes are about
a factor of 2 higher than the Cavalli et al. (1998) values,
and for the lifetime of HG-11 the Christidis et al. (1997)
value is a factor of 3 higher than our value.
5. Radiative forcing: method
5.1. Radiative transfer models
We used two thermal infrared radiative transfer models; one line-by-line (LBL) model and one broad-band
model (BBM). The LBL model (Edwards, 1992) is used to
calculate optical depths, whereas the discrete ordinate
method of Stamnes et al. (1988) is used to calculate
radiative #uxes (see also Myhre and Stordal, 1997). Absorption data from the Hitran-92 database (Rothman et
al., 1992) are used for the greenhouse gases, except for the
CFC replacements studied in this work. The BBM (Stordal, 1988; Myhre and Stordal, 1997) is shown to compare
well with the LBL model, mostly within 5% (Myhre and
Stordal, 1997; Myhre et al., 1998), and is used for most of
the calculations in this work.
The HG gases are represented by 7 bands for each of
the components HG-00, HG-01, and HG-11, and
9 bands for HG-10 in the BBM. In both models the
calculations are performed with 0.1 ppbv of the gases to
ensure that the weak limit approximation is valid, which
follows the procedure from Pinnock et al. (1995) and
Myhre and Stordal (1997).
5.2. Radiative forcing
In the de"nition of radiative forcing used in IPCC
(1994) and WMO (1994) radiative forcing is calculated as
the net change in irradiance at the tropopause level after
allowing the temperature in the stratosphere to be adjusted to restore the radiative equilibrium in the stratosphere. The radiative forcing must represent global and
annual mean atmospheric conditions. The "xed dynamical heating approximation (Ramanathan and Dickinson, 1979) is used. An iterative process is performed to
restore the radiative equilibrium. We refer to radiative
forcing calculations including stratospheric temperature
adjustment as adjusted radiative forcing. The much less
computer expensive calculations without stratospheric
temperature adjustments are referred to as instantaneous
radiative forcing.
5.3. Atmospheric proxles
It has been shown by e.g. Myhre and Stordal (1997)
that one global mean vertical pro"le of temperature,
humidity, and ozone as used in radiative transfer calculations cannot represent globally averaged conditions
with satisfactory accuracy. Freckleton et al. (1998)
showed that using three carefully selected vertical pro"les
representing the global atmosphere gives satisfactory results. We have performed instantaneous clear sky calculations to compare the BBM with the LBL model. In
these calculations we use the three pro"les of Freckleton
et al. (1998).
In the adjusted radiative forcing calculations a resolution of 103 in latitudinal and longitudinal direction is
used (Myhre and Stordal, 1997). Atmospheric distributions of temperature and water vapour are taken from
European Centre for Medium-Range Weather Forecasts
(ECMWF) whereas the ozone distribution is taken from
Liang and Wang (1995). Cloud data have been taken
from International Satellite Cloud Climatology Project
(ISCCP) (Rossow and Schi!er, 1991).
Overlap for the absorption bands of the HG molecules
with bands of the well mixed greenhouse gases is taken
into account, and mixing ratios of CO , CH , N O,
CFC-11, and CFC-12 are taken from IPCC (1995) with
values of 356 ppmv, 1.714 ppmv, 311 ppbv, 0.268 ppbv,
and 0.503 ppbv, respectively.
6. Radiative forcing: results
6.1. Instantaneous radiative forcing
The LBL model is only used to calculate global instantaneous radiative forcing using the three vertical pro"les
described earlier. The spectral radiative forcings as calculated with the LBL model are shown in Fig. 2. In the
results presented in Fig. 2 we have considered overlap
with H O, CO , O , CH , N O, CFC-11, CFC-12. The
results are shown for the spectral region 500}1500 cm\
as the contribution outside this spectral range is negligible. The thermal infrared energy decreases with increasing wavenumber for the spectral range shown in Fig. 2.
Overlap with other greenhouse gases, especially water
vapour, reduces the radiative forcing signi"cantly of
bands outside the `atmospheric window regiona (800}
1200 cm\), but only weakly inside this spectral region.
For instance, absorption bands near 1400 cm\ have
very low forcing as a combination of low thermal infrared energy and high water vapour overlap.
Table 4 shows instantaneous clear sky radiative forcing for the four molecules. The results are given for
di!erent cases including overlap with various groups of
greenhouse gases as well as a case where overlap with
other gases has been omitted. Radiative forcing results
are presented for the LBL model as well as the BBM. The
results are for constant vertical pro"les for the three
gases.
In the LBL calculations, overlap with other gases
reduces the forcing by about 35%, where water vapour is
the dominating contributor to this reduction. Generally,
the two radiative transfer models agree within 5%. The
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
4453
Fig. 2. Instantaneous clear sky radiative forcing due to HG-00, HG-10, HG-01, and HG-11. Absorption cross sections for HG-00, HG10, and HG-01 are from this work, whereas absorption cross-section from Cavalli et al. (1998) for HG-11 is used. The LBL model is used
in the calculations and results are shown in the spectral region 500}1500 cm\ as the radiative forcing outside this spectral range is
negligible. Overlap with other greenhouse gases is taken into account.
4454
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
Fig. 2. (continued)
overlap with water vapour in the BBM is in general
agreement with the LBL model, whereas overlap with
gases other than water vapour seems to be slightly underestimated in the BBM.
HG-11 has the strongest forcing as the integrated band
strength is largest for this gas. We have chosen to use the
spectral data of Cavalli et al. (1998) for HG-11 although
our results indicate that their cross sections are generally
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
4455
Table 4
Radiative forcing calculated with the LBL model and the BBM for overlap with all greenhouse gases (H O, CO , O , CH , N O,
CFC-11, CFC-12), H O#CO #O , H O, and no overlap with other gases. Values are given in W m\ ppbv\
Compound
HG-00
HG-10
HG-01
HG-11
LBL
All gases
H O#CO #O
H O
No overlap
0.51
0.83
1.07
1.65
0.53
0.89
1.12
1.77
0.55
0.93
1.16
1.83
0.75
1.35
1.61
2.54
0.55
0.89
1.11
1.83
0.73
1.29
1.58
2.52
BBM
HG-00
HG-10
HG-01
HG-11
0.51
0.82
1.10
1.73
0.53
0.87
1.11
1.81
too large. This way we are likely to get an upper estimate
of the radiative forcing for HG-11. The ratio between
forcing including overlap with all gases and the integrated band strength di!ers by 10% among the four HG
molecules. HG-01 has the higher ratio as more of the
absorption is in the `atmospheric window regiona
800}1200 cm\ than for the three other HG gases, which
absorb more strongly in the 1200}1300 cm\ region.
6.2. Ewect of decay of the mixing ratio with altitude
The results shown in Table 4 are for a constant vertical
pro"le of the HG molecules. This assumption is not quite
realistic and the mixing ratio will most likely decrease
with altitude in the stratosphere due to photochemical
loss there. To study the sensitivity of the forcing to the
vertical distribution of the gases in the stratosphere, we
have assumed two further pro"les: one with a decay
similar to CH , and one with zero concentration in the
stratosphere. The forcings based on these two pro"les are
compared to the forcings assuming constant vertical pro"les; the results are shown in Table 5.
For instantaneous forcings the e!ect of including the
gases in the stratosphere is up to about 10%. The vertical
pro"le of the HG molecules can only be found through
chemistry transport model calculations taking into account the photochemical destruction and the transport of
the HGs.
6.3. Adjusted radiative forcing
We have used the BBM and the atmospheric input
data as described in Myhre and Stordal (1997) to perform
globally averaged radiative forcing for the four HG species. The results are shown in Table 6. Clouds and stratospheric temperature adjustment are included. The decay
Table 5
Relative di!erence in radiative forcing (%) compared to constant vertical pro"le
Compound
Decay as CH
No concentration in
the stratosphere
HG-00
HG-10
HG-01
HG-11
!1.3
!1.5
!1.3
!1.2
!8.3
!9.5
!8.5
!8.0
of the mixing ratios of the HG molecules in the stratosphere is assumed to be similar to the decay of CH , as
the main removal mechanism is the same.
The calculated radiative forcing of HG-11 is
1.37 W m\ ppbv\. This is an extremely high radiative
forcing per 1 ppbv and is obviously due to the many
-CF - groups. Relative to CFC-11 the forcing of HG-11
is 5.5 times stronger per molecule. For the other three
components the forcing is lower than for HG-11 but still
very high compared to other CFCs or CFC replacements.
The e!ects of clouds and stratospheric temperature
adjustment on the forcing for the four species have very
similar e!ects as most of the other halocarbons (Pinnock
et al., 1995; Christidis et al., 1997; Myhre and Stordal,
1997). Omitting clouds increases the forcing by about
40% and omitting stratospheric temperature adjustment
reduces the forcing by about 10%.
The e!ect of changing the vertical pro"le in the stratosphere is larger in the adjusted case than in the instantaneous case for the HG molecules. Changing from
a pro"le with decay like CH to no concentration in the
stratosphere reduces the forcing by 20% in the adjusted
4456
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
Table 6
Comparison of radiative forcing due to HGs. The value for HG-00 in Imasu et al. (1995) is given relative to CFC-11. We have used our
best estimate of CFC-11 from Myhre et al. (1998) to scale the value of HG-00 in Imasu et al. (1995)
Compound
Radiative forcing
(W m\ppv\)
Absorption
section
Radiative transfer
calculation
HG-00
0.40
0.43
0.66
0.87
0.87
1.01
1.37
1.11
This work
Imasu et al. (1995)
This work
Cavalli et al. (1998)
This work
Cavalli et al. (1998)
Cavalli et al. (1998)
Christidis et al. (1997)
This work
Imasu et al. (1995)
This work
This work
This work
This work
This work
Christidis et al. (1997)
HG-10
HG-01
HG-11
case, but only 10% in the instantaneous case (see Table
5). The absorption of the gases in the stratosphere leads
to a heating yielding a larger #ux from the stratosphere
to the troposphere with a corresponding increase in the
radiative forcing of about 10%, see above. Absorption by
a halocarbon only in the troposphere leads to a small
negative stratospheric temperature adjustment (Pinnock
et al., 1995).
Radiative forcing calculations due to HG-10 and HG01 using absorption cross sections from Cavalli et al.
(1998) have also been performed. Table 6 shows radiative
forcing due to HG-10 and HG-01 for absorption cross
sections from this work as well as from Cavalli et al.
(1998). The higher forcing using the Cavalli et al. (1998)
data re#ects the higher absorption cross sections in their
work than obtained in this work, as shown in Table 1.
Christidis et al. (1997) have performed radiative forcing
calculations of several CFC replacements including HG11, see also Table 6. They calculated 19% lower forcing
using an integrated band strength which was 23% lower
than in our work. They used a global and annual mean
atmospheric pro"le and no decay of the gases in the
stratosphere. They obtained a slightly lower e!ect from
clouds than in this work. Imasu et al. (1995) have performed radiative forcing calculations for HG-00 among
many others. However, their calculations are performed
for a single vertical pro"le and radiative forcing is given
relative to CFC-11. Clouds and stratospheric adjustment
are not taken into account in the calculations by Imasu et
al. (1995). Using our estimate from Myhre et al. (1998) for
CFC-11 the radiative forcing due to HG-00 is about 5%
lower in this work than in Imasu et al. (1995). For HG-10
and HG-01 no previous radiative forcing studies are
known to the authors.
7. Global warming potential
The GWP has been developed as a tool to rank the
e!ectiveness of climate gases in terms of the relative
contribution of their emissions to the greenhouse e!ect
(IPCC, 1990,1995). It is de"ned to give the global and
annually averaged radiative forcing, as a cumulative
measure over a speci"ed time horizon, taking into account the decay of the atmospheric concentration following the emission of 1 kg of the compound. The GWP is
given relative to another gas, usually CO or CFC-11.
Table 7 shows GWP values relative to CFC-11. In the
GWP calculations the radiative forcings presented in
Table 6 from this work are used, and for HG-10 and
HG-01 based on the cross sections from this work. The
lifetimes based on temperature dependent reaction rates
shown in Table 3 are used. The radiative forcing due to
CFC-11 is taken from Myhre et al. (1998) using the BBM,
with a forcing of 0.24 W m\. The lifetime of CFC-11 is
50 y (IPCC, 1995).
The GWP values decrease with increasing time horizon
as the HG lifetimes are shorter than for CFC-11. On
a short-time horizon all HGs have higher GWP values
than CFC-11, whereas for the longest time horizon when
the e!ect decreases relative to CFC-11 the two HG-00 and
HG-10 have higher GWP values than CFC-11, and HG01 and HG-11 have lower GWP values than CFC-11.
HG-00 and HG-10 have higher GWP values than HG01 and HG-11, except in one case; nevertheless the radiative forcing due to HG-00 and HG-10 are lower on
Table 7
GWP values of hydro#uoro(poly)ethers relative to CFC-11 for
three time horizons
Compound
HG-00
HG-10
HG-01
HG-11
Time horizon (yr)
20
100
500
1.69
1.80
1.45
1.80
1.23
1.37
0.76
0.96
1.10
1.23
0.66
0.83
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
Table 8
GWP values of hydro#uoro(poly)ethers relative to CO for
three time horizons
Compound
HG-00
HG-10
HG-01
HG-11
Time horizon (yr)
20
100
500
10700
11400
9200
11400
6300
7000
3900
4900
2000
2300
1200
1500
a molecular basis. There are two reasons for this. First,
GWP values are given relative to emitted mass and the
molecular weight is lower for HG-00 and HG-10. Second, the lifetimes of HG-00 and HG-10 are higher compared to those of HG-01 and HG-11.
GWP values relative to CO for the HGs are shown in
Table 8. Radiative forcing due to CO is taken from
Myhre et al. (1998) where 1990 is used as reference year
for the CO concentration. We have used the same decay
function for CO as IPCC (1995).
The lifetimes are much shorter for the HG molecules
compared to CO . The GWP values are therefore re
duced substantially for long-time horizons.
8. Summary
Absorption cross sections for HG-00, HG-10, and
HG-01 in the spectral region 25}3250 cm\ have been
measured. The contribution of bands in the thermal
far-infrared region to the total integrated cross section is
almost negligible. Our integrated cross sections are about
20% lower than those of Cavalli et al. (1998).
Radiative forcing calculations are performed for HG00, HG-10, and HG-01 using absorption cross sections in
this work and for HG-10, HG-01, and HG-11 using
absorption cross sections from Cavalli et al. (1998). The
radiative forcings per molecule are very high for the HGs
compared to other CFCs and CFC replacements.
The lifetime of the four HGs is found to be in the range
6}12 y assuming temperature-independent reaction rates
with OH and using OH distribution from a 3D chemistry
transport model. The lifetimes are found to increase by
a factor of 2.5 when an estimate of the temperaturedependent reaction rates is used instead of the rates at
298 K. The resulting GWP values are comparable to
those of CFC-11 on a 100 y time horizon, ranging from
0.76 to 1.37.
Acknowledgements
We thank Sigrun Karlsdottir for providing OH
data from the Oslo 3D chemistry transport model. This
4457
work has received support from the Research Council
of Norway (Programme for Supercomputing) through
a grant of computing time, and from the Environment
Programme of the University of Oslo. We thank
one of the reviewers for drawing our attention to an
error in the cross-section of HG-00 in the original
manuscript.
References
Berntsen, T., Isaksen, I.S.A., 1997. A global three-dimensional
chemical transport model for the troposphere;1. Model description and CO and ozone results. Journal of Geophysical
Research 102, 21239}21280.
BruK hl, C., Peter, T., Moortgat, G., Boglu, D., Meller, R., Brasseur, G., Isaksen, I., Crutzen, P., 1993. Modellstudie zu
ozonstoK rung und Treibhause!ekt von halogenirten kohlenwassersto!en mit schwerpunkt bei FCKW-Ersazatzsto!en.
Report 10402729, Umweltbundesamtes, Germany.
Cavalli, F., Glasius, M., Hjorth, J., Rindone, B., Jensen, N.R.,
1998. Atmospheric lifetimes, infrared spectra and degradation products of a series of hydro#uoropolyethers. Atmospheric Environment 32, 3767}3773.
Christidis, N., Hurley, M.D., Pinnock, S., Shine, K.P., Wallington, T.J., 1997. Radiative forcing of climate change by
CFC-11 and possible CFC replacements. Journal of Geophysical Research 102, 19597}19609.
Clerbaux, C., Colin, R., Simon, P.C., Granier, C., 1993. Infrared
cross sections and global warming potentials of 10 alternative hydrohalocarbons. Journal of Geophysical Research 98,
10491}10497.
DeMore, W.B., 1996. unpublished results.
Edwards, D.P., 1992. GENLN2: a general line-by-line atmospheric transmittance and radiance model. NCAR Technical
Note, NCAR/TN-367#STR. National Center for Atmospheric Research, Boulder, CO.
Fisher, D.A., Hales, C.H., Wang, W.-C., Ko, M.K.W., Sze, N.D.,
1990. Model calculations of the relative e!ects of CFCs and
their replacements on global warming. Nature 344, 513}516.
Freckleton, R.S., Highwood, E.J., Shine, K.P., Wild, O., Law,
K.S., Sanderson, M.G., 1998. Greenhouse gas radiative forcing: e!ects of averaging and inhomogeneities in trace gas
distribution. Quarterly Journal of the Royal Meteorological
Society 124, 2099}2127.
Garland, N.L., Medhurst, L.J., Nelson, H.H., 1993. Potential
chloro#uorocarbon replacements: OH reaction rate constants between 250 and 315 K and infrared absorption
spectra. Journal of Geophysical Research 98, 23107}23111.
Hansen, J., Sato, M., Ruedy, R., 1997. Radiative forcing and
climate response. Journal of Geophysical Research 102,
6831}6864.
Heath"eld, A.E., Anastasi, C., McCulloch, A., Nicolaisen, F.M.,
1998. Integrated infrared absorption coe$cients of several
partially #uorinated ether compounds: CF OCF H, CF
HOCF H, CH OCF CF H, CH OCF CFClH, CH CH
OCF CF H, CF CH OCF CF H and CH }CHCH OCF
CF H. Atmospheric Environment 32, 23227}23238.
Hsu, K.J., DeMore, W.B., 1995. Rate constants and temperature
dependence for the reactions of hydroxyl radical with several
4458
G. Myhre et al. / Atmospheric Environment 33 (1999) 4447}4458
halogenated methanes, ethanes, and propanes by relative
rate measurements. Journal of Physical Chemistry 99,
1235}1244.
Imasu, R., Suga, A., Matsuno, T., 1995. Radiative e!ects and
halocarbon global warming potentials of replacement compounds for chloro#uorocarbons. Journal of the Meterological Society Japan 73, 1123}1136.
Intergovernmental Panel on Climate Change (IPCC), 1990. In:
Houghton, J.T., Jenkins, G.J., Ephraums, J.J. (Eds.) Climate
Change: The IPCC Scienti"c Assessment. Cambridge University Press, Cambridge, UK.
Intergovernmental Panel on Climate Change (IPCC), 1994. In:
Houghton, J.T., Meira Filho, L.G., Bruce, J. Hoesung Lee,
Callander, B.A., Haites, E., Harris, N., Maskell, K. (Eds.),
Radiative Forcing of Climate Change and an Evaluation of
IPCC IS92 Emission Scenarios. Cambridge University
Press, Cambridge, UK.
Intergovernmental Panel on Climate Change (IPCC) 1995. In:
Houghton, J.T., MeiraFilho, L.G., Callander, B.A., Harris,
N., Kattenberg, A., Maskell, K. (Eds.), Climate Change 1995:
The Science of Climate Change. Cambridge University
Press, Cambridge. UK.
Liang, X.-Z., Wang, W.-C., 1995. A GCM study of the climatic
e!ect of 1979-1992 ozone trend. In: Wang, W.-C., and Isaksen, I.S.A.(Eds.), Atmospheric Ozone as a Climate Gas.
NATO ASI series, Springer, Berlin.
Marstokk, K.-M., M+llendal, H., Nielsen, C.J., Powell, D. L.,
1999. Conformational Properties of Bis(di#uoromethyl)
Ether as studied by Microwave, Infrared, Raman spectroscopy and by Ab Initio computations. Journal of Moleclar
Structure (in press).
Myhre, G., Stordal, F., 1997. Role of spatial and temporal
variations in the computation of radiative forcing and GWP.
Journal of Geophysical Research 102, 11181}11200.
Myhre, G., Highwood, E.J., Shine, K.P., Stordal, F., 1998. New
estimates of radiative forcing due to well mixed greenhouse
gases. Geophysical Research Letters 25, 2715}2718.
Pinnock, S., Hurley, M.D., Shine, K.P., Wallington, T.J., Smyth,
T.J., 1995. Radiative forcing of climate by hydrochlorofluorocarbons and hydro#uorocarbons. Journal of Geophysical Research 100, 23277}23288.
Radice, S., Causà, M., Marchionni, G., 1998. Vibrational spectra
and ab initio calculation of Hydro#uoropolyethers (HFPE).
Journal of Fluorine Chemistry (in press).
Ramanathan, V., Dickinson, R.E., 1979. The role of stratospheric ozone in the zonal and seasonal radiative energy
balance of the earth-troposphere system. Journal of Atmospheric Science 36, 1084}1104.
Rossow, W.B., Schi!er, R.A., 1991. ISCCP cloud data products.
Bulletin of American Meteorological Society 72, 2}20.
Rothman, L.S., et al., 1992. The HITRAN molecular database:
editions of 1991 and 1992. Journal of Quantitative Spectroscopy and Radiative Transfer 48, 469}507.
Shi, G., Fan, X., 1992. Past, present and future climate forcing
due to greenhouse gases. Advances in Atmospheric Science
9, 279}286.
Stamnes, K., Tsay, S.-C., Wiscombe, W., Jayaweera, K., 1988.
A numerically stable algorithm for discrete-ordinate-method
radiative transfer in multiple scattering and emitting layered
media. Applied Optics 27, 2502}2509.
Stordal, F., 1988. A wide band model for transfer of infrared
radiation: altitudinal, latitudinal and yearly variation of
cooling rates in the troposphere and the stratosphere, Report
68, Institute for Geophysics, University of Oslo.
Tuazon, E.C., 1997. Tropospheric degradation products of novel
hydro#uoropolyethers. Environmental Science Technology
31, 1817}1821.
World Meteorological Organization (WMO), 1994. Scienti"c
Assessment of ozone depletion: 1994. Global Ozone Research and Monitoring Project, WMO, Report 37, Geneva.
Zhang, Z., Saini, R.D., Kurylo, M.J., Huie, R.E., 1992. Rate
constants for the reactions of the hydroxyl radical with
several partially #uorinated ethers. Journal of Physical
Chemistry 96, 9301}9304.