MEMORANDUM

To: Debbie Ottinger, EPA

From: Mollie Averyt, Becky Ferenchiak, Mark Flugge, and Kasey Knoell, ICF

Date: July 14, 2014

Re: Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming 

Potentials of Saturated Hydrofluoroethers by Number of Carbon-Hydrogen and CarbonFluorine Bonds

(EPA Task Order EP-B14H-00017, ICF Task Order 022: Support for Implementing and Refining 

Mandatory GHG Reporting Requirements for Various Emitters of Fluorinated GHGs, Task 3: 

Support for Evaluation of GWPs)

I. Introduction

This memorandum presents a revised summary of an ICF analysis to determine the correlation between 

the number of carbon-hydrogen (C-H) bonds and carbon-fluorine (C-F) bonds in saturated 

hydrofluoroethers (HFEs) and saturated hydrochlorofluoroethers (HCFEs) and their atmospheric 

lifetimes (τ), radiative efficiencies (REs), and global warming potentials (GWPs). Furthermore, a similar 

analysis was added for saturated hydrofluorocarbons (HFCs). The previous analysis used GWPs from 

both the IPCC Fourth (AR4) and Fifth (AR5) Assessment reports. To ensure that estimated correlations 

between GWPs and other parameters are not affected by differences among GWPs that are attributable 

only to different levels of understanding of GWPs in AR4 and AR5, these analyses (i.e., for saturated 

HFEs and saturated HFCs) uses only the GWPs from AR5.

The complete results of the analysis are contained in the spreadsheet “Saturated HFE Analysis_7-1-

14.xlsx” and in the spreadsheet “Saturated HFC Analysis_7-1-14.xlsx.”

Please contact Mollie Averyt at 202-862-1569 (mollie.averyt@icfi.com) with any questions or comments.
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 1

II. Overview

A study by Blowers et al. (2008): Global Warming Potentials of Hydrofluoroethers observed that HFEs 

with more hydrogen atoms have shorter atmospheric lifetimes than HFEs with fewer hydrogen atoms.

The C-H bonds lead to shorter atmospheric lifetimes through hydrogen abstraction by hydroxyl radicals. 

The atmospheric lifetime is reduced by approximately one-half order of magnitude for each additional 

hydrogen atom that is available on the HFE for attack by hydroxyl radicals, which initiates the 

degradation mechanism of HFEs (Blowers et al. 2008).

1

The study examined the GWPs for 48 HFEs based on observations about molecular structure including 

the number of C-H bonds in an HFE compared to its atmospheric lifetime, and the number of C-F bonds 

compared to its radiative forcing. The number of C-F bonds is of interest because it is the C-F bonds in 

HFEs that contribute the most to their radiative efficiency, the amount of radiative forcing per unit of 

concentration of each compound (W m−2 ppm−1) in the atmosphere.

For this ICF analysis, the saturated HFEs and HCFEs that are found in the Revised Analysis of Default 

GWPs for Fluorinated GHGs Reported Under the GHGRP were further disaggregated using the following 

classifications:

 Partially segregated compounds contain a fully hydrogenated alkyl group on one side of the 

oxygen with no fluorine substitutes and a partially or fully fluorinated alkyl group on the other 

side.

 Non-segregated compounds contain fluorine substitutes on all alkyl groups, but are not 

necessarily fully fluorinated.

III. Analysis of the Influence of C-H and C-F Bonds in Saturated HFEs and 

HCFEs

To further evaluate the atmospheric behavior and GWPs of the saturated HFEs and HCFEs, ICF 

performed an analysis similar to Blowers et al. (2008) to determine whether the results could be 

duplicated using the dataset of compounds being used to determine the default GWP for saturated 

HFEs. ICF disaggregated the 62 saturated HFEs that are found in the Revised Analysis of Default GWPs 

for Fluorinated GHGs Reported Under the GHGRP by the number of C-H bonds and number of C-F bonds 

found in each molecular structure and developed plots of this data versus corresponding atmospheric 

lifetimes, REs, and GWPs that are found in AR5.

a. Results of Saturated HFE and HCFE Analysis

Figure 1 shows the linear regression of the log of the atmospheric lifetime versus the number of C-H

bonds in the HFE/HCFE, and results in a slope of −0.399 and an R

2

value of 0.644, which demonstrates a 

moderately strong relationship between the atmospheric lifetime and the number of C-H bonds. The 

previous analysis (i.e., using GWPs from both AR4 and AR5) resulted in a slightly lower R

2

value of 0.601.

 

1 Blowers, P., D.M. Moline, K.F. Tetrault, R.R. Wheeler, and S.L. Tuchawena. 2008. Global Warming Potentials of 

Hydrofluoroethers. Environ. Sci. Technol. 42, 1301–1307.
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Figure 1. Plot of log of the atmospheric lifetime versus the number of C-H bonds in the HFE/HCFE.

Figure 2 shows the linear regression of the log of the GWP versus the number of C-H bonds in the 

HFE/HCFE, and results in a slope of −0.502 and an R

2

value of 0.614, which demonstrates a moderately 

strong relationship between the GWP and the number of C-H bonds. The previous analysis resulted in a 

slightly lower R2value of 0.607.

Figure 2. Plot of log of GWP versus the number of C-H bonds in the HFE/HCFE.

R2 = 0.6445

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4 5 6

Log τ (years)

Number of C-H Bonds

R2 = 0.6138

 1.0

 1.5

 2.0

 2.5

 3.0

 3.5

 4.0

 4.5

0 1 2 3 4 5 6

Log of GWP at 100-year TH

Number of C-H Bonds
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Figure 3 shows the linear regression of the radiative forcing versus the number of C-F bonds in the 

HFE/HCFE, and results in a slope of 0.086 and an R2value of 0.588 demonstrating a moderate 

relationship between the radiative forcing and, in this case, the number of C-F bonds. The previous 

analysis resulted in a slightly lower R2value of 0.546.

Figure 3. Plot of radiative forcing versus the number of C-F bonds.

Figure 4 shows the linear regression of the log of the GWP versus the number of C-F bonds in the 

HFE/HCFE, and results in a slope of 0.090 and an R

2

value of 0.128, which demonstrates a weak

relationship between the global warming potential and, in this case, the number of C-F bonds. The 

previous analysis resulted in a slightly higher R2value of 0.147.

Figure 4. Plot of log of GWP versus the number of C-F bonds.

R2 = 0.5881

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 5 10 15 20 25

Radiative Efficiency (W/m2 ppb)

Number of C-F Bonds

R2 = 0.1283

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 5 10 15 20 25

Log of GWP at 100-year TH

Number of C-F Bonds
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Table 1 shows a summary of the results of the linear regression analyses (shown in the Figures 1–4 

above) for the number of C-H bonds and C-F bonds in the HFEs with respect to atmospheric lifetime, RE, 

and GWP.

Table 1. Summary of the Linear Regression Results for the Number of C-H bonds and C-F Bonds in the 

HFEs/HCFEs with Respect to Atmospheric Lifetime, Radiative Efficiency, and GWP

X Variable Y Variable Slope Current R2 Previous R2(a) Relationship Results

log τ Number of C-H Bonds −0.399 0.644 0.601 Moderately strong Figure 1

log GWP Number of C-H Bonds −0.502 0.614 0.607 Moderately strong Figure 2

RE Number of C-F Bonds 0.086 0.588 0.546 Moderate Figure 3

log GWP Number of C-F Bonds 0.090 0.128 0.147 Weak Figure 4

(a) Including data from both AR4 and AR5

The weak relationship shown in Figure 4 is most likely attributable to the fact that the number of C-F 

bonds in each HFE or HCFE does not have a direct impact on that compound’s atmospheric lifetime, and 

it is the atmospheric lifetime of the HFE or HCFE that has the largest impact on the 100-year GWP of that 

compound.

ICF also investigated correlations between GWPs and simple combinations of the numbers of C-H and 

C-F bonds. These analyses are included in Appendix A. There did not appear to be a simple combination 

of numbers of C-H and C-F bonds that showed a closer correlation with GWPs than the number of C-H 

bonds alone showed with GWPs.

These plots serve to demonstrate the trends of the proposed classification of saturated HFEs and HCFEs 

in light of this analysis. For example, as seen in Figure 5, 100 percent of the non-segregated HFEs/HCFEs

have 4 or less C-H bonds whereas 80 percent of the partially segregated HFEs/HCFEs have 4 or more C-H 

bonds.

Figure 5. Plot of the log of atmospheric lifetime versus number of C-H bonds of partially segregated 

and non-segregated saturated HFEs.

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4 5 6

Log τ (years)

Number of C-H Bonds

Partially Segregated

Non-segregated
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 5

Figure 6. Plot of the log of GWP versus number of C-H bonds of partially segregated and nonsegregated saturated HFEs.

Figure 7. Plot of the log of GWP versus number of C-F bonds of partially segregated and nonsegregated saturated HFEs.

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6

Log of GWP at 100-year TH

Number of C-H Bonds

Partially Segregated

Non-segregated

 (0.5)

 -

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

0 5 10 15 20

Log of GWP at 100-year TH

Number of C-F Bonds

Partially Segregated

Non-segregated
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Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 6

IV. Setting Default GWPs based on the Number of C-H and C-F Bonds

ICF analyzed the feasibility of establishing default GWPs based on the number of C-H and/or C-F bonds 

in a saturated HFE or HCFE in comparison to the default GWPs that were based on the classifications of 

the HFE molecular structure (i.e., segregated, partially segregated, or non-segregated).

The histogram below (see Figure 8) shows the GWPs of the saturated HFEs and HCFEs based on the 

number of C-H bonds in each compound. This graph was developed to evaluate whether the number of 

C-H bonds in a saturated HFE or HCFE is an indicator of whether a compound is likely to have a low or 

high GWP, and whether the number of C-H bonds could be used to separate this class of compounds

into two or more sets with predictable GWP ranges.

Figure 8. Histogram comparing GWPs of saturated HFEs and HCFEs based on the number of C-H bonds.

Table 2 summarizes the average GWPs, standard deviations, and relative standard deviations of the 

partially segregated and non-segregated saturated HFEs.

Table 2. Summary of average GWP, standard deviation, and relative standard deviation of 

classifications of saturated HFEs based on position of fluorine atoms.

Saturated HFE Classification Count Average 

GWP

Standard 

Deviation

Relative 

Standard 

Deviation

Partially segregated 25 219 214 98%

Non-segregated 37 2,728 2,619 96%

The following tables (Table 3, Table 4, Table 5, Table 6, and Table 7) summarize the counts, average 

GWPs, standard deviations, relative standard deviations, and possible default GWPs of the saturated 

HFEs/HCFEs based on various groupings—i.e., the number of C-H bonds in multiple aggregated levels 

(Tables 3–6) and the number of C-F bonds (Table 7).

0

1

2

3

4

5

6

7

8

9

10

0 to 100 100 to

250

250 to

500

500 to

750

750 to

1,000

1,000 to

2,500

2,500 to

5,000

5,000 to

7,500

7,500 to

10,000

Over

10,000

Frequency

GWP Range

6 C-H Bonds

5 C-H Bonds

4 C-H Bonds

3 C-H Bonds

2 C-H Bonds

1 C-H Bond
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 7

Table 3. Summary of average GWP, standard deviation, and possible default GWP of saturated HFEs 

and HCFEs based on the number of C-H bonds: Six discrete grouping levels.

Number of C-H 

Bonds Count Average GWP

Standard 

Deviation

Relative 

Standard 

Deviation

Possible Default 

GWP

1 5 6,592 3,547 54% 6,600

2 23 2,725 1,905 70% 2,700

3 10 647 187 29% 650

4 10 269 225 83% 270

5 8 34 27 77% 30

6 6 222 225 101% 220

Table 4. Summary of average GWP, standard deviation, and possible default GWP of saturated HFEs 

and HCFEs based on the number of C-H bonds: Two aggregated grouping levels.

Number of C-H 

Bonds Count Average GWP

Standard 

Deviation

Relative 

Standard 

Deviation

Possible Default 

GWP

1–2 28 3,416 2,664 78% 3,400

3–6 34 317 293 92% 320

Table 5. Summary of average GWP, standard deviation, and possible default GWP of saturated HFEs 

and HCFEs based on the number of C-H bonds: Three aggregated grouping levels.

Number of C-H 

Bonds Count Average GWP

Standard 

Deviation

Relative 

Standard 

Deviation

Possible Default 

GWP

1 5 6,592 3,547 54% 6,600

2 23 2,725 1,905 70% 2,700

3–6 34 317 293 92% 320

Table 6. Summary of average GWP, standard deviation, and possible default GWP of saturated HFEs 

and HCFEs based on the number of C-H bonds: Four aggregated grouping levels.

Number of C-H 

Bonds Count Average GWP

Standard 

Deviation

Relative 

Standard 

Deviation

Possible Default 

GWP

1 5 6,592 3,547 54% 6,600

2 23 2,725 1,905 70% 2,700

3 10 647 187 29% 650

4–6 24 179 206 115% 180
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 8

Table 7. Summary of average GWP, standard deviation, and possible default GWP of saturated HFEs 

and HCFEs based on the number of C-F bonds.

Number of C-F Bonds Count Average GWP Standard Deviation

Relative 

Standard 

Deviation

Possible 

Default 

GWP

1–4 14 646 1,438 223% 650

5–8 33 1,626 2,567 158% 1,600

9–12 11 3,119 2,391 77% 3,100

13–16 2 2,850 N/A N/A 2,900

17–20 2 1,843 N/A N/A 1,800

As can be seen by comparing Table 4 with Table 2, grouping the saturated HFEs and HCFEs by the

number of C-H bonds in the molecule rather than by the positions of the fluorine atoms in the molecule 

slightly lowers the relative standard deviations of the GWPs within each group of saturated HFEs and 

HCFEs. This implies that the two default GWPs based on the number of C-H bonds may be more 

accurate and precise than the two default GWPs based on the positions of the fluorine atoms. When the 

number of HFE/HCFE groups is increased to three or more, as in Tables 3, 5, and 6, the relative standard 

deviations of the GWPs decline significantly. At the same time, a clear trend in the average GWPs for the 

groups is shown, with the average GWP declining markedly as the number of bonds increases from one 

to two and then from two to three, with less marked declines (and even one small increase) thereafter. 

This indicates that setting three or more default GWPs based on the number of C-H bonds may lead to 

significantly more accurate and precise GWPs than setting two default GWPs based on the positions of 

the fluorine atoms, with the greatest benefit gained by distinguishing among HFEs/HCFEs with one, two, 

and three C-H bonds. 

Table 7 confirms that the relationship between the number of C-F bonds and the GWPs of saturated 

HFEs is weak. The relative standard deviations of the GWPs in each grouping are generally over 100 

percent, and the average GWPs do not show a clear trend. This indicates that the number of C-F bonds 

is not a useful parameter for establishing saturated HFE groups and associated default GWPs.

Additional insight into the relative importance of the number of C-H bonds and the position of the 

fluorine atoms may be gained by examining the set of HFEs that include either three or four C-H bonds. 

This set, unlike the sets containing fewer than three or more than four C-H bonds, includes both nonsegregated and partially segregated HFEs and HCFEs. Table 8 summarizes the average GWPs of this set, 

disaggregated both by number of C-H bonds and by position of the fluorine atoms. (The number of data 

points in each of the four subsets or groups ranges from four to six; these data points are shown in 

Figure 6.)
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 9

Table 8. Average GWPs for HFEs and HCFEs by Number of C-H Bonds and Position of the Fluorine 

Atoms

Number of C-H Bonds Ratio of GWPs for 

Groups with 3 vs. 

4 C-H Bonds 3 4

Position of Fluorine 

Atoms

Non-Segregated 796 328 2.4

Partially Segregated 498 230 2.2

Ratio of GWPs for Non-Segregated vs. 

Partially Segregated Groups 1.6 1.4

As shown in Table 8, the GWPs for this set of HFEs vary both by the number of C-H bonds and by the 

position of the fluorine atoms; however, the influence of the number of C-H bonds is stronger than that 

of the position of the fluorine atoms.

V. Comparison to the Results from the Blowers et al. (2008) Study

In the Blowers et al. (2008) study, a linear regression of the log of the atmospheric lifetime (log τ) of the 

48 HFEs in their data set versus number of C-H bonds (reproduced using the data in this analysis in

Figure 5) results in a slope of −0.5296, and their statistical analysis shows that approximately 83 percent

of the atmospheric lifetimes is correlated with the number of C-H bonds.

Figure 10, reproduced from Blowers et al. (2008), demonstrates that adding a C-F bond does not 

necessarily increase GWP significantly on a log scale; however, the number of C-H bonds more strongly 

affects the GWP by about a half-order of magnitude per C-H bond.

Figure 9. Plot of log of the atmospheric lifetime versus the number of C-H bonds in the HFE 

(reproduced from Blowers et al. 2008).
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Figure 10. Affects of molecular structure on GWP estimates on a log surface plot of GWP at the 100 

year time horizon (TH) versus the number of C-H and C-F bonds (reproduced from Blowers et al. 2008).

In comparison to the results of the study by Blowers et al. (2008), ICF’s analysis on the saturated HFEs

shows a similar relationship between the number of C-H bonds and the atmospheric lifetime. 

Furthermore, the correlation between the number of C-H bonds and the GWP of the HFE again shows a 

similar relationship, with the ICF analysis indicating that approximately 60 percent of the atmospheric 

lifetime and GWP are correlated with the number of C-H bonds.

The relationships between the number of C-H bonds and the number of C-F bonds with the atmospheric 

lifetimes, GWPs, and REs from AR5 only generally did not differ significantly from the results of the 

previous analysis that used GWPs from both AR4 and AR5. However, the relative standard deviations 

among the GWPs in some sets of HFEs declined.

VI. Analysis of the Influence of C-H and C-F Bonds in Saturated HFCs

To further evaluate the atmospheric behavior and GWPs of the saturated HFC—as opposed to HFE—

compounds, ICF performed an analysis similar the one above to determine whether the results observed 

were justified in the dataset of compounds being used to determine the default GWP for saturated 

HFCs. ICF disaggregated the 26 saturated HFCs that are found in the Revised Analysis of Default GWPs 

for Fluorinated GHGs Reported Under the GHGRP by the number of C-H bonds and number of C-F bonds 

found in each molecular structure and developed plots of this data versus corresponding atmospheric 

lifetimes, REs, and GWPs that are found in AR5.

a. Results of Saturated HFC Analysis

Figures 11 through 14 below show the linear regression of the following variables, respectively:

(1) log of the atmospheric lifetime versus the number of C-H bonds in the HFC

(2) log of the GWP versus the number of C-H bonds in the HFC

(3) log of the GWP versus the number of C-F bonds in the HFC

(4) Radiative forcing versus the number of C-F bonds in the HFC
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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The R2values of the first three regression analyses demonstrate moderate relationships that are 

somewhat weaker than the relationships seen for the saturated HFEs and HCFEs. However, as shown in 

Figure 14, the regression analysis of the radiative forcing versus the number of C-F bonds in the HFC 

demonstrates a strong relationship, which is expected.

Figure 11. Plot of log of the atmospheric lifetime versus the number of C-H bonds in the HFC.

Figure 12. Plot of log of GWP versus the number of C-H bonds in the HFC.

R2 = 0.4888

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6

Log τ (years)

Number of C-H Bonds

R2 = 0.5215

 1.0

 1.5

 2.0

 2.5

 3.0

 3.5

 4.0

 4.5

0 1 2 3 4 5 6

Log of GWP at 100-year TH

Number of C-H Bonds
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Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Figure 13. Plot of log of GWP versus the number of C-F bonds.

Figure 14. Plot of radiative forcing versus the number of C-F bonds.

The histogram below (see Figure 15) shows the GWPs of the saturated HFCs based on the number of C-H 

bonds in each compound. This graph was developed to evaluate whether the number of C-H bonds in a 

saturated HFC is an indicator of whether a compound is likely to have a low or high GWP, and whether 

R2 = 0.3374

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 2 4 6 8 10 12

Log of GWP at 100-year TH

Number of C-F Bonds

R2 = 0.8964

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 2 4 6 8 10 12

Radiative Efficiency (W/m2 ppb)

Number of C-F Bonds
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Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 13

the number of C-H bonds could be used to separate this class of compounds into two or more sets with 

predictable GWP ranges.

Figure 15. Histogram of HFC GWPs and Number of C-H Bonds

Table 9. Summary of average GWPs, standard deviations, and possible default GWPs of saturated 

HFCs based on the number of C-H bonds: Six discrete grouping levels.

Number 

of C-H 

Bonds

Count Average GWP Standard Deviation Relative Standard 

Deviation

Possible Default 

GWP

1 5 4,784 4,276 89% 4,800

2 7 2,192 2,604 119% 2,200

3 8 1,495 2,000 134% 1,500

4 2 77 86 112% 80

5 3 295 443 150% 300

6 1 144 NA N/A 140

Table 10. Summary of average GWPs, standard deviations, and possible default GWPs of saturated 

HFCs based on the number of C-H bonds: Two discrete grouping levels.

Number 

of C-H 

Bonds

Count Average GWP Standard Deviation Relative Standard 

Deviation

Possible Default 

GWP

1-2 12 3,272 3,482 106% 3,300

3-6 14 939 1,623 173% 940

 -

 1

 1

 2

 2

 3

 3

 4

 4

 5

 5

0 to 100 100 to

250

250 to

500

500 to

750

750 to

1,000

1,000 to

2,500

2,500 to

5,000

5,000 to

7,500

7,500 to

10,000

Over

10,000

Frequency

GWP Range

6 C-H Bonds

5 C-H Bonds

4 C-H Bonds

3 C-H Bonds

2 C-H Bonds

1 C-H Bond
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Although the relationship between the number of C-H bonds in each saturated HFC and the GWP of that 

HFC is not as strong as this relationship in saturated HFEs, Figures 12 and 15 and Tables 9 and 10 

indicate that there is a relationship that may be useful in setting multiple default GWPs for HFCs. Similar 

to the average GWPs for saturated HFEs, the average GWPs for saturated HFCs show marked declines as 

the number of C-H bonds increases from 1 to 2, from 2 to 3, and from 3 to 4, with less marked declines 

(and even one small increase) thereafter. The relative standard deviations of the first four groups range 

from 89 percent to 134 percent. In contrast, the relative standard deviation of the GWPs of all HFCs is 

153 percent, and the average GWP for that set is 2,187. This indicates that two or more default GWPs 

for saturated HFCs that are based on the number of C-H bonds in each molecule may model unknown 

GWPs of saturated HFCs more accurately and precisely than a single default GWP for all saturated HFCs.
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

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Appendix A: Evaluation of Correlation between GWPs and Combinations 

of the Numbers of C-H and C-F Bonds

ICF also investigated correlations between GWPs and simple combinations of the numbers of C-H and 

C-F bonds. There did not appear to be a simple combination of C-H and C-F bonds that showed a closer 

correlation with GWPs than the number of C-H bonds alone. This could be attributed to the fact that the 

analysis does not account for the molecular weight (MW) parameter in the calculation of GWP. To 

investigate this possibility, ICF analyzed the relationship between the GWP and the ratio of number of 

C-F bonds to MW [i.e., (Number of C-F bonds)/MW)] in Figure 16. However, there is a weak relationship 

between these two variables which is demonstrated by the R2value of 0.239.

Figure 16. Plot of log of GWP versus the ratio of number of C-F bonds to MW.

To further investigate the relationship between number of C-H bonds and C-F bonds and the GWP and 

to analyze these variables together, ICF plotted the log of GWP versus the ratio of the number of C-H 

bonds to the number of C-F bonds [i.e., (Number of C-H bonds)/(Number of C-F bonds)] and the log of 

GWP versus the number of C-H bonds minus the number of C-F bonds [i.e., (Number of C-H Bonds) –

(Number of C-F Bonds)]. These plots are shown in Figure 17 and Figure 18, respectively.

R2 = 0.2389

 -

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

 3.5

 4.0

 4.5

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045

Log of GWP at 100-year TH

(Number of C-F bonds)/MW 
Revised Analysis of Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming Potentials of Saturated 

Hydrofluoroethers by Number of Carbon-Hydrogen and Carbon-Fluorine Bonds Using only AR5 GWPs

Page 16

Figure 17. Plot of log of GWP versus the ratio of the number of C-H bonds to the number of C-F bonds.

Figure 18. Plot of log of GWP versus the number of C-H bonds minus the number of C-F bonds.

R2 = 0.3384

 -

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

 3.5

 4.0

 4.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Log of GWP at 100-year TH

(Number of C-H bonds)/(Number of C-F bonds)

R2 = 0.322

 -

 0.5

 1.0

 1.5

 2.0

 2.5

 3.0

 3.5

 4.0

 4.5

 5.0

-20 -15 -10 -5 0 5

Log of GWP at 100-year TH

(Number of C-H bonds) - (Number of C-F bonds)