MEMORANDUM

To: Debbie Ottinger, EPA

From: Mollie Averyt, Rebecca Ferenchiak, Mark Flugge, and Alex Lataille, ICF

Don Wuebbles, University of Illinois

Date: March 26, 2013

Re: Analysis of GWPs Submitted by 3M for Inclusion in Table A‐1

(EPA Contract Number EP‐BPA‐12‐H‐0022, EP‐B13H‐00006/Task Order 007: Support for

Implementing and Refining Mandatory GHG Reporting Requirements for Various Emitters of

Fluorinated GHGs, Task 3: Support for Evaluation of GWPs)

Introduction

Per technical direction received on February 5, 2013, this memorandum presents an analysis by Dr. Donald

Wuebbles and ICF on Global Warming Potentials (GWPs) submitted by 3M for eight compounds that currently

do not appear in Table A‐1: The compendium of GWPs for the Greenhouse Gas Reporting Program (GHGRP).

The purpose of the analysis is to:

1. Review the submitted GWPs;

2. Consider the adequacy and persuasiveness of the information submitted to support the GWPs; and

3. Identify any possible errors in the GWPs and their magnitudes.

The remainder of this memorandum is organized into the following sections:

 Background

 Analysis of GWPs for Eight Compounds as Submitted by 3M to EPA

 General Findings: Atmospheric Lifetimes

 General Findings: Radiative Forcing and GWPs

 General Findings: Supporting Materials

 Conclusions

 References

Background

On January 28, 2013, the 3M Company submitted documentation of global warming potentials (GWPs) for

several compounds not currently included in Table A‐1 of the Greenhouse Gas Reporting Rule (GHGRP). On

February 8, 2013, the 3M Company participated in a conference call with EPA, Dr. Donald Wuebbles, and ICF to

discuss follow‐up questions on some of the GWP estimation information provided in the submissions. On

February 14, 2013, the 3M Company submitted revised documentation for PMM, PTPA, and PTAA to provide a

radiative forcing value for PTPA and  more information on the QSAR used to estimate the radiative forcing of

PTAA. On February 18, 2013, EPA submitted additional questions to 3M addressing radiative efficiency values

and impacts to GWPs. The 3M Company responded to these questions on March 8, 2013, providing updated
Analysis of Submitted GWPs for Table A‐1    Page 2 of 6

radiative efficiency and GWP values for PTAA, PMM, and HFE‐7300, as well as additional detail on cloud‐sky

adjustment factors. The 3M Company provided resubmissions for PIPM, PMM, PTAA, PTBA, PTPA, HFE‐7300,

and HFE‐7500 to clarify and revise GWP calculations on March 8, 2013.

EPA is considering including these GWPs in Table A‐1.

Analysis of GWPs for Eight Compounds as Submitted to EPA

The GWPs for eight compounds have been submitted by 3M, as shown in Table 1 below.

Table 1: Estimated GWPs submitted by 3M for eight compounds that currently do not appear in Table A‐1

Compound CAS # Submitted GWP*

Perfluorotripropyl amine (PTPA) 338‐83‐0 8,690

Perfluorotributyl amine (PTBA) 1064698‐37‐8 9,020

Perfluorotriamyl amine (PTAA) 338‐84‐1 8,900

Perfluoromethyl morpholine (PMM) 382‐28‐5 9,500

Perfluoroisopropyl morpholine (PIPM) 338‐84‐1 11,000

2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9‐

hexadecafluorooxonane (C8F16O) 1978‐24‐1 9,600

1,1,1,2,2,3,4,5,5,5‐decafluoro‐3‐methoxy‐4‐

trifluoromethyl‐pentane (HFE‐7300) 132182‐92‐4 310

3‐ethoxy‐1,1,1,2,3,4,4,5,5,6,6,6‐dodecafluoro‐2‐

trifluoromethyl‐hexane (HFE‐7500) 297730‐93‐9 100

* 3M submissions as of March 8, 2013.

For each of these compounds, 3M presents supporting evidence for the listed submitted 100‐year integration

GWPs. Dr. Donald Wuebbles analyzed those materials, and his evaluation is provided below.

General Findings: Atmospheric Lifetimes

The atmospheric lifetimes for the eight compounds were determined in several different ways.

The estimated atmospheric lifetimes for both PTPA and PTAA relied upon measurements of kinetic rate

constants for the vapor phase reaction of perfluorotriethyl amine with the hydroxyl radical (OH) and ozone

(O3). 3M cites Y. Tang’s unpublished M.S. thesis as the source for these measurements. The measurements

resulted in a minimum estimated atmospheric lifetime of 2,000 years for perfluorotriethyl amine. Because of

the physical and chemical similarity between perfluorotriethyl amine, PTPA, and PTAA with respect to the

mode of atmospheric degradation, the minimum atmospheric lifetimes for PTPA and PTAA were also
Analysis of Submitted GWPs for Table A‐1    Page 3 of 6

estimated to be 2,000 years. All three compounds are in the same class of compounds (i.e., perfluorinated

amines) and differ only in perfluorinated alkyl chain length.

This approach is reasonable, but the data are considered questionable until the quality of the work in the

thesis can be verified. In general, data from an unpublished, M.S. thesis is considered to be questionable given

that in science, research for an M.S. degree is not usually performed at the same level as research for a Ph.D.

Dr. Wuebbles contacted Dr. Mario Molina for further information, and was able to confirm that no peer‐

reviewed journal articles were published for Y. Tang’s work. Data published in peer‐reviewed journals are

considered an acceptable source.

For PTBA, Atmospheric and Environmental Research (AER) measured the kinetic rate constants for the vapor

phase reaction of PTBA with OH and O3, and have estimated the atmospheric lifetime as >390 years. Further

discussions with 3M indicated that photolysis is the primary removal mechanism for this gas. In control

experiments PTBA was noted to degrade, and it was hypothesized that direct photolysis may have occurred at

wavelengths near 222 nm. 3M estimates the atmospheric lifetime to be 400 years; however, this only

represents the lower limit on the lifetime, so the actual lifetime could be much longer. Dr. Wuebbles is very

familiar with the 1‐D atmospheric model that was used at AER, which is no longer used at all, and knows it to

be very out‐of‐date. Analyses of atmospheric lifetimes that are performed using 1‐D models are unreliable

because they do not adequately model transport (i.e. horizontal and vertical distributions) within the

atmosphere.

The minimum atmospheric lifetime for PMM was derived from data from the Y. Tang master’s thesis.  As noted

above, data in an unpublished master’s thesis is considered to be questionable. The minimum atmospheric

lifetime of PIPM was derived from data obtained by Ko and Chang (1992) for PMM, which is structurally similar

to PIPM. PIPM contains two more CF2‐groups than PMM, but retains the same morpholine functionality. Since

the lifetime based on reactivity with OH and O3 is long, photolysis could actually be the more important

removal mechanism, but we have no data on this. The estimated lifetime of >1,600 years may contain errors

since the analysis is likely outdated. However, as illustrated below, the 100‐year GWPs of very long lived gases

are relatively insensitive to errors in lifetimes.

For C8F16O, 3M used an estimation approach using a structurally similar perfluorohexane as the model of

atmospheric degradation. This approach is appropriate for long‐lived compounds, but could be more rigorous.

C8F16O is likely to be extremely long lived. There does not appear to be published data on the compound’s

removal rates to determine an atmospheric lifetime directly.

The atmospheric lifetime of 3.8 years for HFE‐7300 was determined using a relative rate technique based on

measured kinetic rate constants from Guschin et al. (1998) for the vapor phase reaction of HFE‐7300 and OH.

For HFE‐7500, measured kinetic rate constants from Goto et al. (2002) for the vapor phase reaction of HFE‐

7500 and OH using a relative rate technique resulted in an atmospheric lifetime calculated at 2.2 years. These

approaches for determining atmospheric lifetime using relative rates are considered reasonable by Dr.

Wuebbles. However, as discussed further below, the atmospheric lifetime used by Guschin et al. (1998) for the

reference gas, methane, was lower than the currently accepted lifetime for methane. Consequently, the

atmospheric lifetime for HFE‐7300 is likely underestimated.

General Findings: Radiative Forcing and GWPs

For PTPA, C8F16O, PIPM, HFE‐7300, and HFE‐7500 radiative forcing (RF) was determined from individual

absorption cross‐sections from the spectrum for each compound that were weighted using factors reported in

Pinnock et al. (1995). This approach is considered to be acceptable for compounds that are sufficiently long‐

lived. For HFE‐7300 and HFE‐7500, which are much shorter lived than the other compounds, 3M applied a

scaling factor suggested by Sihra et al. (2001) to account for the fact that these compounds will not be well‐

mixed, i.e., will have uneven vertical distributions in the atmosphere. Although it is an approximation, this
Analysis of Submitted GWPs for Table A‐1    Page 4 of 6

factor is considered to be reasonable for longer lived gases. However, Dr. Wuebbles noted it likely over

estimates anything with a lifetime shorter than roughly 5 years. An exact evaluation of how good this scaling

approach is for HFE‐7300 and HFE‐7500 would require additional research.

For PMM and PTBA, band by band absorption cross‐sections obtained from averaged IR spectra were

obtained. These cross‐sections were then used to calculate the temperature change per part per billion by

volume (ppbv) introduction of the compound using an internal model (AER 1‐D RC, Ko and Chang, 1992). Each

temperature change was expressed relative to the temperature change calculated by the model for CFC‐11. To

translate the temperature change into a radiative forcing, the temperature change relative to CFC‐11 was

multiplied by the radiative efficiency of CFC‐11 published in the Intergovernmental Panel on Climate Change

(IPCC) Fourth Assessment Report (AR4) (IPCC, 2007).

For PTAA, radiative forcing was estimated using a quantitative structure–activity relationship (QSAR) model

developed by 3M using measured data for perfluorinated amines and PFCs as QSAR model inputs. Specifically,

3M added the radiative forcing of 6 and 12 C‐F bonds to the radiative forcings measured for PTBA and PTPA

respectively. The radiative forcing per C‐F bond (0.03 Wm‐2

ppbV‐1) was estimated from data for 10 PFCs in the

IPCC Fourth Assessment Report (2007) and in Ivy et al. (2012). EPA was able to derive a similar per‐bond

estimate using a simple regression analysis based on data for the same compounds. There are a number of

QSAR regression approaches in the science literature that use the structure of the compound to estimate

infrared absorption features, and this technique has been shown to be reasonably accurate. However, 3M did

not submit the results of any efforts to validate the QSAR against measured radiative efficiencies. To test the

QSAR for at least one data point, EPA compared the radiative efficiency predicted by the QSAR for PTBA (based

on the radiative efficiencies of PTPA and 6 C‐F bonds) to the radiative efficiency measured for PTBA by 3M. The

QSAR‐based result was 15 percent lower than the measured result.

The authors used the atmospheric lifetime and radiative forcing in the equation referenced by IPCC (2007) to

determine the GWPs for all compounds relative to carbon dioxide (CO2) with a 100‐year integration time

horizon. EPA was able to reproduce all of the GWPs submitted based on the radiative efficiencies and

atmospheric lifetimes submitted. (GWPs were rounded to two or three significant figures depending on the

level of significant figures reported by 3M.) Because the atmospheric lifetimes provided for several of the

compounds were minimums or were uncertain, ICF performed an analysis to examine the sensitivity of the

calculated 100‐year GWPs to increases in atmospheric lifetimes. Table 2 below shows the impact to GWPs if a

longer lifetime for a particular compound is assumed. As expected, there are smaller differences in the GWPs

for long‐lived compounds, but larger differences for short‐lived compounds (where the change in GWP is

essentially proportional to the change in the lifetimes).

Table 2: Change in GWP over Time Horizons

Compound 3M Proposed GWP

and Reported Lifetime*

GWP Resulting from an

Assumed Increase in

Lifetime**

Perfluorotripropyl amine (PTPA) 8,690

2,000‐years

8,733

2,500‐years

Perfluorotributyl amine (PTBA) 9,020

400years

9,240

500‐years

Perfluorotriamyl amine (PTAA) 8,900

2,000‐years

8,944

2,500‐years
Analysis of Submitted GWPs for Table A‐1    Page 5 of 6

Perfluoromethyl morpholine (PMM) 9,500

1,600‐years

9,559

2,000‐years

Perfluoroisopropyl morpholine (PIPM) 11,000

1,600‐years

11,068

2,000‐years

C8F16O   9,600

2,300‐years

9,637

2,800‐years

1,1,1,2,2,3,4,5,5,5‐decafluoro‐3‐methoxy‐4‐

trifluoromethyl‐pentane (HFE‐7300)

310

3.8‐years†

408

5.0‐years

3‐ethoxy‐1,1,1,2,3,4,4,5,5,6,6,6‐dodecafluoro‐2‐

trifluoromethyl‐hexane (HFE‐7500)

100

2.2‐years

136

3.0‐years

* The GWPs in the second column are generally rounded to two (or three) significant figures to reflect the precision of estimated

radiative efficiencies and atmospheric lifetimes. However, the GWPs in the third column are not rounded because rounding to two or

three significant figures would in some cases obscure the (often relatively small) impact of increased lifetimes.

** GWPs were scaled for an assumed increase in atmospheric lifetime by the memorandum authors. GWPs in this third column are not

rounded to a specific number of significant figures in order to show the (often small) relative increase in GWP value for the increased

lifetime.

† A lifeƟme of 4.12 years and a resultant GWP of 340 was calculated by the memorandum authors based on the updated estimation

approach detailed in the methodology document provided by 3M (Mader, 2012) and described below.

General Findings: Supporting Materials

On March 6, EPA received copies of supporting materials from 3M, namely Ko and Chang, 1992, and Guschin et

al., 1998.

Regarding the report from Ko and Chang (1992), it confirms the use of a 1‐D atmospheric model, and as

mentioned above, use of such a model is considered out‐of‐date by today’s standards. In addition, the report

acknowledges that the estimates presented are subject to a variety of uncertainties in addition to the model

calculated radiative forcing including the reaction rate measurements, the assumed atmospheric

concentration of OH (and O(1

D)), and the possible existence of other removal processes for the compounds

considered.

Regarding the report from Guschin et al. (1998), relative rate reactions were used to estimate the rate of

reaction of HFE‐7300 with OH using either methane (CH4) or methyl chloride (CH3Cl) as the reference

compound; and the experiments were performed at room temperature and approximately 200 Torr pressure

(i.e., no temperature dependence for the rate constant was assessed). In addition, Guschin et al. (1998)

measured ultraviolet absorption cross‐sections and determine that photolysis is not a significant destruction

mechanism for the compounds. As mentioned above, determining atmospheric lifetime using relative rates is

considered reasonable. However, it should be noted that the reliability of the determined atmospheric lifetime

depends on both the reliability of the rate constant for the reference compound (i.e., the rate constants for

the CH4 + OH reaction) and the reliability of the lifetime for the reference compound (i.e., the atmospheric

lifetime for CH4). The accepted values for these quantities have changed from those used by Guschin et al.

(1998): kCH4 + OH = 6.3 × 10−15 cm3 molecule−1 s

−1 (DeMore et al., 1997), and τOH = 8.9 years (Prinn et al., 1995).

For example, in the methodology document provided by 3M (Mader, 2012), the atmospheric lifetime for CH4

used in later estimates by 3M has been revised from 8.9 based on Prinn et al. (1995) to 9.6 years based on IPCC

(2001, p.248), which remains the currently accepted value. The lifetime of 3.8 years for HFE‐7300 should likely

be revised upwards to 4.1 years accordingly, which would result in a GWP value of 340.
Analysis of Submitted GWPs for Table A‐1    Page 6 of 6

Conclusions

It is important to note that the GWPs presented are often lower limits, because they are based on lifetimes

that are lower limits. For all of the long‐lived compounds (with lifetimes >>100 years), the errors in the GWPs

are likely to be small and largely result from the fact that they are based on lifetimes at lower limits, although

uncertainty in the radiative efficiency estimates also contribute to uncertainty in the GWP presented.

However, any errors in the GWPs for the shorter‐lived compounds (e.g., HFE‐7300, HFE‐7500) could be quite

significant.

References

3M Company. 3M Response to EPA Questions on Chemical Identities. March 6, 2013.

3M Company. Global Warming Potential Submissions for FC‐77, PIPM, PMM, PTAA, PTBA, PTPA, HFE‐7300, and

HFE‐7500. January 28, 2013.

3M Company. Revised Global Warming Potential Submissions for PMM, PTPA, PTAA. February 14, 2013.

3M Company. Revised Global Warming Potential Submissions for PIPM, PMM, PTAA, PTBA, PTPA, HFE‐7300,

and HFE‐7500. March 8, 2013.

DeMore, W. B., et al. 1997. JPL Publication No. 97‐4, NASA Jet Propulsion Laboratory, Pasadena, CA.

Goto, M., Inque, Y., Kawasaski, M., Guschin, A.G., Molina, L.T., Molina, M.J., Wallington, T.J., and Hurley, M.D.,

Environ. Sci. Technol., 36, 2395–2402, 2002.

Guschin, A.G., Molina, L.T., and Molina, M.J., Atmospheric Chemistry of Some Fluoroethers (L‐13791, L‐14374,

L‐14786, L‐14787, L‐15092, L‐15093, L‐15094 and L‐15095), Massachusetts Institute of Technology, report

prepared for 3M Company, May 1998, Cambridge, MA.

IPCC, 2001: Climate change 2001: Impacts, Adaptation and Vulnerability, Contribution of Working Group II to

the Third Assessment Report of the Intergovernmental Panel on Climate Change, J. J. McCarthy, O. F. Canziani,

N. A. Leary, D. J. Dokken and K. S. White (eds). Cambridge University Press, Cambridge, UK, 1032pp.

IPCC, 2007: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to

the Fourth Assessment. Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani,

J.P. Palutikof, P.J. van der Linden, and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 976pp.

Ivy, D.J., M. Rigby, M. Baasandorj, J.B. Burkholder, and R.G.Prinn. “Global emission estimates and radiative

impact of C4F10, C5F12, C6F14, C7F16 and C8F18.” Atmospheric Chemistry and Physics, 12: 7635‐7645, 2012.

Available online at: http://www.atmos‐chem‐phys.net/12/7635/2012/acp‐12‐7635‐2012.pdf

Ko, M.K.W. and D.T. Chang, Estimates of the Global Warming Potential of Proposed Chemical Compounds.

1992, Atmospheric and Environmental Research, Inc., Cambridge, MA

Mader, B.T. 2012. Methodology to Determine the Global Warming Potential Values (GWP) of 3M Chemicals.

E12‐0510, 3M Environmental Laboratory. August 2.

Pinnock, S., M.D. Hurley, K.P. Shine, T.J. Wallington, and T.J. Smyth. 1995. Radiative forcing of climate by

hydrochlorofluorocarbons and hydrofluorocarbons. J. Geophys. Res. 100(D11):23,227–23,238,

DOI: 10.1029/95JD02323

Prinn, R.G., et al. 1995. Science, 269, 187.

Sihra, K., M. D. Hurley, K. P. Shine, and T. J. Wallington. 2001. Updated radiative forcing estimates of 65

halocarbons and nonmethane hydrocarbons, J. Geophys. Res., 106, 20,493–20,505.

Tang, Yi, Atmospheric Fate of Various Fluorocarbons. Master’s Thesis, Massachusetts Institute of Technology,

Cambridge, MA.