1
Online Supplemental Material
Integrated IR absorption intensities and calibration.
From Beer-Lambert’s law, the absorption cross-section of a compound J at a specific
wavenumber ~ is given by  ~   Ae / n J l , where Ae   ln  ~  is the napierian absorbance, 
is the transmittance, nJ is the number density of J and l is the path length over which the
absorption takes place. The integrated absorption intensity, Sint, is given by:
S int    ~ d~
Band
The integrated cross-sections of the absorption bands of the compounds under study were
determined by plotting the integrated absorbance intensities against the product of the number
density and pathlength. Conservative estimates of systematic errors are: pressure measurements
(0.5%), path length (1%), temperature (1%), and definition of the baseline in the integration
procedure (1%). Supplemental Tables 1 and 2 summarize the calibration results while
Supplemental Figure 1 (see Supplemental Digital Content 1, http://links.lww.com/AA/A145; see
Figure 1 legend at end of supplement) displays the linear relationship between number density
times pathlength and the measured integrated absorbance.
The integrated absorption cross-section (often referred to as the integrated band intensity,
or IBI) of the 2000-450 cm-1 region of isoflurane has previously been reported by Sihra et al.(1)
who gave a value of 27.44×1017 cm2 molecules-1 cm-1. The two results for IBI2000-450 are within
the estimated systematic errors in the two studies. Brown et al.(2) have reported a value of (15.9
± 0.8) ×1017 cm2 molecules-1 cm-1 for the 1200-800 cm-1 region of isoflurane. For the same region
the present result is IBI1200-800 = (16.2 ± 0.2) ×1017 cm2 molecules-1 cm-1.
2
For sevoflurane Brown et al.(2) reported a value of IBI1200-800 = (10.4 ± 0.6) ×1017 cm2
molecules-1 cm-1 for sevoflurane. The present result is somewhat larger, (11.6 ± 0.3) ×1017 cm2
molecules-1 cm-1. However, it should be noted that that one of the integration limits used in the
study of Brown et al.(2) fall in a cluster of bands and we therefore consider the two results
consistent. For desflurane, Imasu et al. (3) reported a value of IBI2000-500 = (29.9 ± 0.7) ×1017 cm2
molecules-1 cm-1 in perfect agreement with the present result.
IR absorption cross-sections and radiative forcing.
The infrared absorption cross-sections were derived from the absorbance spectra assuming that
the gases were ideal. The absorption cross-sections (base e) of isoflurane and sevoflurane in the
1600 – 400 cm-1 region are shown in Supplemental Figures 2 (see Supplemental Digital Content
2, http://links.lww.com/AA/A146; see Figure 2 legend at end of supplement) and 3 (see
Supplemental Digital Content 3, http://links.lww.com/AA/A147; see Figure 3 legend at end of
supplement). We routinely use the absorption cross-section of HCFC-22, which has been
critically evaluated by Ballard et al. (4) as a benchmark (5-12). Our measurements of HCFC-22
(CHClF2) are constantly within 5% of the absorption intensities reported by Ballard and coworkers. As can be seen in Supplemental Table 3, the statistical variance in the integrated
absorption cross-section of the compounds is at most 2%. Adding to this the above-mentioned
systematic errors allows us to suggest that our spectroscopic results are accurate to within 5%.
Pinnock et al.(13) have provided a simple method for estimating the instantaneous cloudysky radiative forcing (IF) directly from a molecule’s absorption cross-sections. The
instantaneous cloudy-sky radiative forcings are summarised in Supplemental Table 3 in which
the previously reported results for desflurane (14) have been included for comparison.
3
It is interesting that sevoflurane, which has the largest integrated absorption cross section
of the three anaesthetics, has the smallest instantaneous radiative forcing. This is due to the fact
that several of the strongest absorption bands in sevoflurane fall in wavenumber regions where
the CO2, O3 and water vapour dominates the radiative transfer properties of the atmosphere.
Supplemental Figures 2 (http://links.lww.com/AA/A146; see Figure 2 legend at end of
supplement), 3 (http://links.lww.com/AA/A147; see Figure 3 legend at end of supplement), and 4
(see Supplemental Digital Content 4, http://links.lww.com/AA/A148; see Figure 4 legend at end
of supplement) illustrate this point.
Atmospheric Lifetimes and Global Warming Potentials.
The main atmospheric removal process for the compounds under investigation is the reaction
with OH radicals. For isoflurane there are several reports of the rate coefficient for this reaction.
In 1990 Brown et al. (2) reported a value of kOH+Isoflurane = (2.1 ± 0.7) × 10-14 cm3 molecule–1 s–1
in a study employing the discharge-flow resonance-fluorescence technique. In 1999 appeared
three kinetic studies of the OH reaction with isoflurane. Tokuhashi et al.(15) studied the
temperature dependency of the reaction rate constant using the flash photolysis, laser photolysis,
and discharge-flow methods combined with the laser induced fluorescence technique to monitor
the OH radical concentration and reported kOH+Isoflurane(T) = (1.12 ± 0.18) × 10-12 × exp(-1280 ±
50 K/T) cm3 molecule–1 s–1. Langbein et al.(16) reported kOH+Isoflurane = (2.3 ± 0.19) × 10-14 cm3
molecule–1 s–1 from the pseudo first-order decay of OH using the laser long-path absorption
technique. Nolan et al.(17) reported kOH+Isoflurane = (2.3 ± 0.19) × 10-14 cm3 molecule–1 s–1 from
relative rate experiments employing GC separation and flame ionisation detection. Finally,
Beach et al.(18) determined the temperature dependency of the reaction rate constant using the
4
discharge-flow resonance-fluorescence technique and reported kOH+Isoflurane(T) = (4.5 ± 1.3) × 1013
×exp(-940 ± 100 K/T) cm3 molecule–1 s–1. The available kinetic data are summarised in
Supplemental Figure 5 (see Supplemental Digital Content 5, http://links.lww.com/AA/A149; see
Figure 5 legend at end of supplement). The data are generally in good agreement although it can
be seen that the k(298 K) data of Beach et al. (18), Brown et al. (2) and Nolan et al. (17)
apparently are 25-40% higher than the other data. A fit of the Arrhenius expression to the other
data give kOH+Isoflurane(T) = (1.11 ± 0.12) × 10-12 × exp(-1275 K/T) cm3 molecule–1 s–1.
There are only two sets of kinetic data for the OH reaction with sevoflurane. Brown et
al.(2) reported results for two temperatures from a study employing the discharge-flow
resonance-fluorescence technique and gave kOH+Sevoflurane = 1.53 × 10-12 × exp(-900 ± 500 K/T)
cm3 molecule–1 s–1. The other study is by Langbein et al.(16) who reported kOH+Sevoflurane = (2.7 ±
0.5) × 10-14 cm3 molecule–1 s–1 at 298 K from the pseudo first-order decay of OH using the laser
long-path absorption technique. The scatter in the available data, Supplemental Figure 5
(http://links.lww.com/AA/A149; see Figure 5 legend at end of supplement), only allows a rough
estimate of the reaction rate constant. Assuming Ea/R to be the same in sevoflurane as in
isoflurane results in kOH+Sevoflurane(T) = 3.3 × 10-12 × exp(-1275 K/T) cm3 molecule–1 s–1 as a first
approximation.
For comparison we include literature data for desflurane, CF3CHF-O-CHF2.(14) There are
only two kinetic studies of the OH radical reaction with this compound, both carried out at room
temperature. Langbein et al.(16) reported kOH+Desflurane = (4.4 ± 0.8) × 10-15 cm3 molecule–1 s–1
from the pseudo first-order decay of OH using the laser long-path absorption technique. Oyaro et
al.(14) reported kOH+Desflurane = (6.5 ± 0.8) × 10-15 cm3 molecule–1 s–1 from relative rate
measurements employing GS-MS detection. Taking the average of these and assuming Ea/R to
5
be the same as in sevoflurane and isoflurane results in kOH+Desflurane(T) = 3.9 × 10-13 × exp(-1275
K/T) cm3 molecule–1 s–1 as a first approximation.
The atmospheric lifetime of a long-lived compound due to removal by reaction by OH
radicals may be estimated once its rate coefficient for reaction with OH is known. Assuming that
the compounds studied here (fluorinated ethers, FE) will have the same atmospheric distribution
OH
as CH3CCl3 their atmospheric lifetimes,  FE
, may be calculated relative to that of CH3CCl3
from:(19)
OH
 FE

kOH CH 3CCl 3 272 K  OH
  CH 3CCl 3
kOH  FE (272 K)
OH
where  CH
3CCl 3  5.9 years (20) is the atmospheric lifetime of CH3CCl3 with respect to reaction
with OH, and the scaling temperature of 272 K is chosen to compensate for the tropospheric OH
distribution.(21) Using kOH+CH3CCl3(272 K) = 6.14  10-15 cm3 molecule–1 s–1 from the latest JPL
OH
evaluation,(22) the following lifetimes in the gas-phase are found:  Isoflurane
~3.6 years,
OH
OH
 Sevofluran
e ~1.2 years,  Desflurane ~ 10 years.
Global warming potentials for the FEs relative to CFC-11 (CCl3F), HGWP(t), can then be
calculated from the following expression:(23)
HGWP (t ) 
IFFE
 FE
M FE  1  exp  t /  FE  


IFCFC 11  CFC 11 M CFC 11  1  exp  t /  CFC 11  
where M is the molecular mass and t is the time horizon over which the instantaneous forcing is
integrated. Global warming potentials for a 20-year, 100-year and 500-year time horizon for the
FEs are summarized in Supplemental Table 4. The data on CFC-11 were taken from the IPCC
2007 report. (24) For compounds with atmospheric lifetimes in excess of 1 year, the Global
6
warming potentials relative to CO2, GWP(t), were estimated from that of CFC-11 referenced to
CO2:(25)
GWPFE(t) = HGWPFE(t) × GWPCFC-11(t)
Pinnock et al.(13) has reported that their model for estimating the instantaneous radiative
forcing generally overestimates the real forcing when calculating the instantaneous radiative
forcing directly from the absorption cross-sections. It is therefore likely that the present results
provide upper estimates for the global warming potentials of the three FEs studied here. For
comparison the values listed in the latest IPPC report for the GWP of isoflurane are included in
Supplemental Table 4. The present estimates of the GWP for isoflurane compares quite well
with the results of the more elaborate calculations behind the IPPC recommendation (24)
suggesting that the more simplified estimation method gives reliable values. The slightly lower
values in GWP for desflurane in the present work than in the previous study by Oyaro et al. (14)
is due to a lowering of the estimated atmospheric lifetime from 10.288 to 10.08 years.
7
Supplemental Table 1. Integrated absorption intensity and absorption cross-section (base e) of
the 2000-450 cm-1 region of isoflurane.
Pressure
Number density
Integrated absorption
Pathlength
intensity (base e)
cross-section (base e)
/mbar
/1017molecules cm-2 /cm-1
/1017 cm2 molecules-1cm-1
1.08 ± 0.01
2.62 ± 0.04
74.08 ± 1.17
28.24 ± 0.4
1.52 ± 0.02
3.69 ± 0.05
104.66 ± 0.36
28.35 ± 0.4
1.89 ± 0.02
4.59 ± 0.06
129.58 ± 0.61
28.23 ± 0.4
2.55 ± 0.03
6.19 ± 0.09
174.93 ± 0.67
28.25 ± 0.4
2.66 ± 0.03
6.46 ± 0.09
186.53 ± 2.53
28.88 ± 0.4
2.67 ± 0.03
6.48 ± 0.09
184.61 ± 0.46
28.47 ± 0.4
3.01 ± 0.03
7.31 ± 0.10
206.38 ± 1.26
28.23 ± 0.4
4.67 ± 0.05
11.3 ± 0.2
325.12 ± 2.77
28.67 ± 0.4
9.93 ± 0.10
24.1 ± 0.3
694.74 ± 1.94
28.81 ± 0.4
Integrated absorption
28.5 ± 0.3 (average)

8
Supplemental Table 2. Integrated absorption intensity and absorption cross-section (base e) of
the 2000-475 cm-1 region of sevoflurane.
Pressure
Number density
Integrated absorption
Pathlength
intensity (base e)
cross-section (base e)
/mbar
/1017molecules cm-2 /cm-1
/1017 cm2 molecules-1cm
1.05 ± 0.01
2.55 ± 0.04
78.29 ± 0.82
30.70 ± 0.4
1.41 ± 0.02
3.42 ± 0.05
106.73 ± 0.63
31.17 ± 0.4
1.49 ± 0.02
3.62 ± 0.06
112.93 ± 0.41
31.21 ± 0.4
1.90 ± 0.03
4.61 ± 0.09
139.15 ± 0.56
30.16 ± 0.4
2.50 ± 0.03
6.07 ± 0.09
187.18 ± 0.24
30.83 ± 0.4
2.69 ± 0.03
6.53 ± 0.09
202.04 ± 0.30
30.93 ± 0.4
3.34 ± 0.03
8.11 ± 0.10
241.50 ± 0.98
29.77 ± 0.4
4.16 ± 0.05
10.1 ± 0.2
299.03 ± 0.49
29.60 ± 0.4
4.62 ± 0.10
11.2 ± 0.3
343.06 ± 0.49
30.58 ± 0.4
Integrated absorption
30.6 ± 0.6 (average)

9
Supplemental Table 3. Instantaneous radiative forcing (IF) of isoflurane, sevoflurane and
desflurane.
a
Compound
Data from Oyaro et al.((26))
M
Int. absorption cross section
IF
/g mol-1
/10-17 cm2 molecule-1 cm-1
/W m-2
Isoflurane
184.5
28.5 ± 0.3
0.453
Sevoflurane
200.0
30.6 ± 0.6
0.365
Desflurane a
168.0
30.3 ± 0.7
0.447
10
Supplemental Table 4. Estimated Global Warming Potentials HGWP(t) and GWP(t) for 20year, 100-year and 500-year Time Horizons relative to CFC-11 and CO2, respectively.
a
From IPPC 2007, (24). b From Brown et al. (2). c From Oyaro et al., (14) d From Imasu et al. (3)
Compound
Lifetime HGWP20 HGWP100 HGWP500 GWP20 GWP100 GWP500
/year
CFC-11 a
45
1
1
1
6300
4600
1600
Sevoflurane
1.19
0.070
0.027
0.023
349
106
32
Isoflurane
3.57
0.280
0.107
0.093
1401
429
130
2.6 b
Desflurane
10.08
0.743
10.288 c 0.753 c
5.8 d
0.328
0.335 c
0.284
1100 a 340 a
110 a
3714
398
1314
3766 c 1341 c
3100 a 960 a
300 a
11
12
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17
Figure Legends
Supplemental Figure 1. Integrated absorption intensities (base e) of the 2000-450 cm-1 region
in isoflurane and the 2000-475 cm-1 region in sevoflurane. The sevoflurane data have been
shifted by 100 for the sake of clarity.
Supplemental Figure 2. Absorption cross section of isoflurane and radiative forcing per unit
cross section for a 0 to 1 ppbv increase in mixing ratio.
Supplemental Figure 3. Absorption cross section of sevoflurane and radiative forcing per unit
cross section for a 0 to 1 ppbv increase in mixing ratio.
Supplemental Figure 4. Absorption cross section of desflurane and radiative forcing per unit
cross section for a 0 to 1 ppbv increase in mixing ratio. Infrared data from Ref. (26).
Supplemental Figure 5. Arrhenius plots of rate constants for the reactions of OH radicals with
isoflurane and sevoflurane. (×)Tokuhashi et al.(15); (●) Brown et al.(2); (o) Langbein et al.(16);
(▲) Nolan et al.(17); (♦)Beach et al.(18) The dotted line corresponds to kOH+isoflurane(T) = 1.11 ×
10-12 × exp(-1275 K/T) cm3 molecule–1 s–1, the full line corresponds to kOH+sevoflurane(T) = 3.3 ×
10-12 × exp(-1275 K/T) cm3 molecule–1s–1. The data and curve for sevoflurane have been shifted
by ln(10) for the sake of clarity.