# MEMORANDUM

To: Debbie Ottinger, EPA From: Mollie Averyt, Becky Ferenchiak, Mark Flugge, and Kasey Knoell , ICF Date: July 14 , 2014 Re: Revised Analysis o f Atmospheric Lifetimes, Radiative Efficiencies, and Global Warming

Potentials of Saturated Hydrofluoroethers by Number of Carbon

- Hydrogen and Carbon

Fluorine 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 memo randum presents a revised summary of an ICF analysis to determine the correl ation between the number of carbon

- hydrogen (C

- H) bonds and carbon

- fluorine (C

- F) bonds in saturated hydrofluoroether s (HFE s ) and saturated hydrochlorofluoroethers (HCFEs) and their atmospheric lifetime s (τ) , radiative efficiencies (REs), and global warmin g potential s (GWP s ). 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 a nd other parameters are not affected by differences among GWPs that are attributable only to different levels of understanding of GWPs in AR4 and AR5, th e s e analys e s (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 HFE s 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 p er unit of concentration of each compound (W m − 2 ppm − 1 ) in the atmosphere

. For this ICF analysis, t he saturated HFEs and HCFEs that are found in the Revised A nalysis of Default GWPs for Fluorinated GHGs Reported Under the GHGRP were further disaggregated u sing 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 a tmospheric behavior and GWPs of the saturated HFE s and HCFEs , I CF 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 A nalysis 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 correspo nding atmospheric lifetimes , R E s, an d 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 demonstrate s a moderately strong relationship between the atmospheric lifetime and the number of C

- H bonds

. The pr evious 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 Page 2 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

− 0.50 2 and an R 2 value of 0.61 4 , which demonstrates a moderately strong relationship between the GWP and the number of C

- H bonds

. The previous analysis resulted in a slightly lower R 2 value 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 BondsRevised 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 3 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 R 2 value 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 R 2 value 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 a n 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 R 2 value 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/m 2 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 BondsRevised 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 4 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 Life time, Radiative Efficiency, and G WP X Variable Y Variable Slope Current R 2 Previous R 2 (a) Relationship Results l og τ Number of C

- H Bonds

− 0.399 0.644 0.601 Moderately strong Figure 1 l og GWP Number of C

- H Bonds

− 0.50 2 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 lifet ime 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 number s of C

- H and C

- F bonds . These analyses are included in A ppendix A . There did not a ppear to be a simple combination of number s 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 plot s serve to demonstrate the trend s of the proposed classification of saturated HFEs an d HCFEs in light of this analysis

. For example, a s 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-segregatedRevised 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 non
segregated saturated HFEs .

Figure 7 . Plot of the log of GWP versus number of C
- F bonds of partially segregated and non
s egregated 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-segregatedRevised 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 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 H CFE 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 predic t able GWP ranges

.

Figure 8 . His togram comparing GWPs of saturated HFEs and HCFEs based on the number of C
- H bonds . Table 2 summarize s the average GWPs , standard deviation s , and relative standard deviation s 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 count s , average GWP s , standard deviation s , relative standard deviation s , and possible default GWP s of the saturated HFEs /HCFEs ba sed 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 BondRevised 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 B onds 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 B onds 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 saturat ed HFEs and HCFEs based on the number of C - H bonds : Three aggregated grouping levels . Number of C - H B onds 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 saturat ed HFEs

and HCFEs based on the number of C - H bonds : Four aggregated grouping levels . Number of C - H B onds 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% 180Revised 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 saturat ed 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 impl ies 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 grea test 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 ea ch 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 th e 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 o r four C

- H bonds. This set, unlike the sets containing fewer than three or more than four C

- H bon ds, includes both non

segregated 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 subs ets 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 Res ults 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

− 0.5 296 , and their statistical analysis show s that approximately 83 percent of the atmospheric lifetime s 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; h owever, 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 Page 10 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 show s 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 an d the number of C

- F bonds with the atmospheric lifetimes, GWPs, and REs from AR5 only generally did not differ significant ly 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 fou nd 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 1 1 through 1 4 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 vers us 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) R adiative forcing versus the number of C

- F bonds in the HFCRevised 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 11 The R 2 values of the first three regression analyses demonstrate moderate relationships that are some what 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 dem onstrates 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 BondsRevised 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 12 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 h istogram below (see F igure 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/m 2 ppb)

Number of C

- F BondsRevised 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 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.

F igure 15 . Histogram of HFC GWPs and Number of C
- H Bonds
Table 9 . Summary of average GWP s , standard deviation s , and possible default GWP s of saturated

HFCs based on the number of C
- H bonds: Six discrete grouping levels. Number of C - H B onds 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 GWP s , standard deviation s , and possible default GWP s of saturated

HFCs based on the number of C
- H bonds: Two discrete grouping levels. Number of C - H B onds 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 BondRevised 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 14 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, Figure s 12 and 15 and Table s 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 increas es 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 o f 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 accur ately 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 Page 15 

## Appendix A: Evaluation of Correlation between GWPs and Combinations of the Number s 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 b e attributed to the fact that the analysis does not account for th e 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 R 2 value 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 b onds [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)/MWRevised 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)