MEMORANDUM 

To: Deborah Ottinger, EPA

From: Mark Flugge, ICF

Donald Wuebbles, University of Illinois 

Date: March 1, 2013

Re: Analysis of proposed GWPs for Table A-1

(EPA Contract Number EP-W-07-068, Task Order 091: Support for Implementing and Refining 

Mandatory GHG Reporting Requirements for Suppliers of Industrial GHGs and Emitters of 

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

Introduction 

Per technical direction received on August 23, this memorandum presents an analysis by Dr. Donald Wuebbles 

on proposed Global Warming Potentials (GWPs) submitted by Dupont for 10 compounds that currently do not 

appear in Table A-1: the compendium of GWPs for the Greenhouse Gas Mandatory Reporting Rule (GHGRP). 

The purpose of the analysis is to: 

1. Review the proposed 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 10 Compounds as Proposed to EPA 

 General Findings: Atmospheric Lifetimes 

 General Findings: Radiative Forcing and GWPs 

 Conclusions 

 Next Steps 

 References 

Please contact Marian Van Pelt at (202) 862-1129 (Marian.VanPelt@icfi.com) or Mark Flugge at (202) 862-1231 

(Mark.Flugge@icfi.com) with any questions or comments. 

Background 

On August 21, 2012, the DuPont Chamber Works facility submitted documentation of alternate Global 

Warming Potentials (GWPs) for several compounds not currently included in Table A-1 of the Greenhouse Gas 

Mandatory Reporting Rule (GHGRP). 

EPA is considering including these GWPs in Table A-1. 
Analysis of proposed GWPs for Table A-1 Page 2 of 4 

Analysis of GWPs for 10 Compounds as Proposed to EPA 

The GWPs for 10 compounds have been proposed by DuPont, as shown in Table 1Error! Reference source not 

found.. 

Table 1: Proposed alternate GWPs submitted by DuPont for 10 compounds that currently do not appear in 

Table A-1: the compendium of GWPs for the GHGRP 

Compound CAS # Proposed Alternative 

GWP

perfluorethyl iodide (2-I) 354-64-3 3 

perfluorbutyl iodide (PFBI, 42-I) 423-39-2 3 

perfluorhexyl iodide (6-I) 355-43-1 2 

perfluoroctyl iodide (8-I) 507-63-1 2 

1,1,1,2,2-pentafluoro-4-iodo butane (22-I) 40723-80-6 2 

1,1,1,2,2,3,3,4,4-nonafluoro-6-iodo hexane (42-I) 2043-55-2 2 

perfluorobutyl ethane (42-U) 19430-93-4 2 

perfluorohexyl ethane (62-U) 25291-17-2 1 

perfluorooctyl ethane (82-U) 21652-58-4 1 

1H,1H, 2H,2H-perfluorohexan-1-ol (42-AL) 2043-47-2 5 

For each of these compounds, DuPont presents supporting evidence for the listed proposed 100-year 

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

General Findings: Atmospheric Lifetimes 

The first six compounds contain iodine, which almost always means they will most likely be destroyed via 

photolysis due to the weakness of the iodine bond (the iodine compound should also react with OH but not as 

easily as the compound looked at in the Young et al. [2008] paper they cite). The Supporting Documentation 

uses the same loss rate and estimated lifetime of 12.8 days in each case (based on laboratory studies by Young 

et al. (2008), which suggest a lifetime of a few days in summer and a few weeks in winter based on the iodine 

compound they studied, which is none of the six here). Our previous 3-D model results for iodine species 

(assuming mid-latitude emissions) ranged from 5 days for CF3I to 13.6 days for CH3I. So the selected value is 

reasonable, but may be slightly high or low depending on the specific compound. I did go over the Young et al. 

(2008) paper, but I didn’t find any further insights to addressing the lifetime issue. 
Analysis of proposed GWPs for Table A-1 Page 3 of 4 

The next three compounds all have measured reaction rates from Anderson et al. (2005, 2012) for reaction 

with OH and O3. Only room temperature reaction rates are provided, but this may be ok as these compounds 

likely do not have a strong temperature dependence. However the resulting atmospheric lifetime is estimated 

to be the same, 7.6 days for each compound. The authors assumed an average OH concentration 1 × 106

molecules per cm3 and [an average] O3 [concentration] of 35 ppb. However, our 3-D modeling studies indicate 

that for short-lived gases (with largely mid-latitude emissions) that a more appropriate OH value would be 5–

7 × 105 molecules per cm3 (based on a study of other short-lived compounds). Therefore the atmospheric 

lifetimes of the compounds are likely underestimated by as much as a factor of 2. However, the simple 

assumption for ozone would tend to give a lifetime [that is] too long (since most emissions occur over land in 

areas where ozone is likely higher). To play it safe, I suggest using a lifetime twice as long as their estimate for 

these three compounds. 

Possibly a major concern though is the potentially long lifetime of the reaction products (e.g., C5F12I may go to 

C5F12OH, which could have a long lifetime except through hydrolysis, so it would depend whether the molecule 

was in a location where it might be rained out). I suggest to EPA that further analyses are needed of the 

reaction products for all 10 compounds. Rainout would tend to give a 4–6 day lifetime, but it depends on the 

molecule being at an altitude where it can be rained out (the Andersen et al. [2005, 2012] papers just assume 

that either rainout or reactions will get rid of the products). 

The tenth compound, C6H5F9O, has a measured room temperature rate constant with OH measured by Ellis et 

al. (2003). The resulting lifetime is 20 days using the same assumed average OH as they did for the other 

compounds. This lifetime is long enough that the higher end average OH of 7 × 105 molecules per cm3 from the 

3-D model would be more appropriate. There is no reaction rate with ozone. This suggests a longer lifetime by 

about a factor of 1.4. 

General Findings: Radiative Forcing and GWPs 

For the six compounds containing iodine and also the tenth compound, the authors use ab initio calculations 

to determine the infrared absorption. This approach is fine as analyses in recent years have shown ab initio

techniques to be quite accurate. The infrared spectra at room temperature for the other three compounds 

have been measured directly. 

To determine the Radiative Forcing (RF) and the resulting GWPs for ALL compounds, the authors use the 

Pinnock et al. (1995) approach. To determines the radiative forcing, the Pinnock et al. [1995] approach 

estimates the RF using Keith Shine’s narrowband radiative transfer model (we have a similar model except that 

ours can be applied to full 3-D atmospheric constituent distributions instead of just the vertical distribution 

used in their study). More importantly, their approach derives the radiative forcings and GWPs assuming a 

constant mixing ratio of the compound in the troposphere and assumes none of the compound reaches the 

stratosphere. The big problem is the assumption of constant mixing ratio in the troposphere. Our analyses 

suggest that this approach can result in errors of 49 to 233 percent for the compounds we analyzed in a recent 

study, with the Pinnock et al. [1995] approach tending to overestimate the GWP value (see Wang et al., in 

preparation). 

Conclusions 

Without doing full 3-D modeling studies on each of the 10 compounds, I can’t tell EPA exactly how inaccurate 

the estimated GWPs are that they received for the 10 compounds. The GWPs for the first six compounds 

containing iodine are likely overestimated, perhaps by as much as a factor of 2 to 4. The atmospheric lifetimes 

for the last four compounds are likely underestimated. However the RF and GWP derivations for these 

compounds likely overestimate the resulting GWPs. Since the correction to the GWP for lifetime basically 

scales with the lifetime for short-lived gases (based on our new paper we are about to submit to Science), the 

GWPs for the seventh, eighth and ninth compounds would double and the GWP for the tenth compound 
Analysis of proposed GWPs for Table A-1 Page 4 of 4 

would increase by 40 percent. However, the assumption used to calculate the RF is likely to be an overestimate 

by more than these corrections. Therefore, ultimately, use the GWPs they provided as being adequate. 

Next Steps 

ICF recommends a conference call with the memorandum authors and EPA to further discuss these finding at 

EPA’s convenience. 

References 

Andersen, M.P.S., O.J. Nielsen, A. Toft, T. Nakayama, Y. Matsumi, R.L.Waterland, R.C. Buck, M.D. Hurley, and 

T.J. Wallington. 2005. Atmospheric chemistry of CxF2x+1CH=CH2 (x = 1, 2, 4, 6, 8): Kinetics of gas-phase reactions 

with Cl atoms, OH radicals, and O3. J. Photochem. Photobiol. A: Chemistry 176(1–3):124–128. 

Andersen, M.P.S., R.L. Waterland, S.P. Sander, O.J. Nielsen, and T.J. Wallington. 2012. Atmospheric chemistry 

of CxF2x+1CH=CH2 (x = 1, 2, 4, 6 and 8): Radiative efficiencies and global warming potentials. J. Photochem. 

Photobiol. A: Chemistry 233:50–52. 

Ellis, D.A., J.W. Martin, and S.A. Mabury. 2003. Atmospheric Lifetime of Fluorotelomer Alcohols. Environ. Sci. 

Technol. 37(17):3816–3820, DOI: 10.1021/es034136j 

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 

Young, C.J., M.D. Hurley, T.J. Wallington, and S.A. Mabury. 2008. Atmospheric Chemistry of 4:2 Fluorotelomer 

Iodide (n-C4F9CH2CH2I): Kinetics and Products of Photolysis and Reaction with OH Radicals and Cl Atoms. J Phys 

Chem A 112(51):13,542-13,548 

Wang, D., D.J. Wuebbles, K.O. Patten, and S.C. Olsen. In preparation. Climate advantages of proposed shortlived compounds as replacements for longer-lived HCFCs and HFCs.