# MEMORANDUM

To: Deborah Ottinger, EPA
From: Mark Flugge, ICF

Donald Wuebbles, University of Illinois
Date: March 1, 2013
Re: Analysis of p roposed GWPs for Table A

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(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 Wueb bles on proposed Global Warming Potentials (GWPs) submit ted by Dupont for 10 compounds that currently do no t 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 inf ormation 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 EP A

 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 facili ty 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 EP A The GWPs for 10 compounds have been proposed by DuP ont, as shown in Table 1 Error! Reference source not found.

. Table 1: Proposed alternate GWPs submitted by DuPon t 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) 2 043-55-2 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 suppor ting evidence for the listed proposed 100-year integration GWPs. Dr. Donald Wuebbles analyzed thos e materials, and his evaluation is provided below. 

### General Findings: Atmospheric Lifetimes The first six compounds contain iodine, which almos t always means they will most likely be destroyed v ia photolysis due to the weakness of the iodine bond ( the iodine compound should also react with OH but n ot as easily as the compound looked at in the Young et al . [2008] paper they cite). The Supporting Documenta tion uses the same loss rate and estimated lifetime of 1 2.8 days in each case (based on laboratory studies by Young et al. (2008), which suggest a lifetime of a few da ys in summer and a few weeks in winter based on the iodine compound they studied, which is none of the six her e). Our previous 3-D model results for iodine speci es (assuming mid-latitude emissions) ranged from 5 day s for CF 3 I to 13.6 days for CH 3 I. So the selected value is reasonable, but may be slightly high or low dependi ng on the specific compound. I did go over the Youn g et al. (2008) paper, but I didn’t find any further insight s 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 reacti on with OH and O 3 . 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 esti mated to be the same, 7.6 days for each compound. The aut hors assumed an average OH concentration 1 × 10 6 molecules per cm 3 and [an average] O 3 [concentration] of 35 ppb. However, our 3-D modeli ng studies indicate that for short-lived gases (with largely mid-latitu de emissions) that a more appropriate OH value woul d be 5– 7 × 10 5 molecules per cm 3 (based on a study of other short-lived compounds). Therefore the atmospheric lifetimes of the compounds are likely underestimate d 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 saf e, I suggest using a lifetime twice as long as thei r estimate for these three compounds. Possibly a major concern though is the potentially long lifetime of the reaction products (e.g., C 5 F 12 I may go to C 5 F 12 OH, which could have a long lifetime except through hydrolysis, so it would depend whether the molecul e 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 wou ld tend to give a 4–6 day lifetime, but it depends on the molecule being at an altitude where it can be raine d out (the Andersen et al. [2005, 2012] papers just assume that either rainout or reactions will get rid of th e products). The tenth compound, C 6 H 5 F 9 O, has a measured room temperature rate constant wi th OH measured by Ellis et al. (2003). The resulting lifetime is 20 days using the same assumed average OH as they did for the ot her compounds. This lifetime is long enough that the hi gher end average OH of 7 × 10 5 molecules per cm 3 from the 3-D model would be more appropriate. There is no re action rate with ozone. This suggests a longer life time by about a factor of 1.4. 

### General Findings: Radiative Forcing and GWPs For the six compounds containing iodine and also th e 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 spect ra at room temperature for the other three compound s have been measured directly. To determine the Radiative Forcing (RF) and the res ulting GWPs for ALL compounds, the authors use the Pinnock et al. (1995) approach. To determines the r adiative forcing, the Pinnock et al. [1995] approac h estimates the RF using Keith Shine’s narrowband rad iative transfer model (we have a similar model exce pt that ours can be applied to full 3-D atmospheric constit uent distributions instead of just the vertical dis tribution used in their study). More importantly, their appro ach derives the radiative forcings and GWPs assumin g a constant mixing ratio of the compound in the tropos phere and assumes none of the compound reaches the stratosphere. The big problem is the assumption of constant mixing ratio in the troposphere. Our analy ses 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 tend ing 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 inac curate the estimated GWPs are that they received for the 1 0 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 underestimat ed. However the RF and GWP derivations for these compounds likely overestimate the resulting GWPs. S ince the correction to the GWP for lifetime basical ly scales with the lifetime for short-lived gases (bas ed on our new paper we are about to submit to Scien ce), the GWPs for the seventh, eighth and ninth compounds wo uld double and the GWP for the tenth compoundAnalysis of proposed GWPs for Table A-1 Page 4 of 4

would increase by 40 percent. However, the assumpti on used to calculate the RF is likely to be an over estimate by more than these corrections. Therefore, ultimate ly, use the GWPs they provided as being adequate. 

## Next Steps
ICF recommends a conference call with the memorandu m authors and EPA to further discuss these finding at EPA’s convenience. 

## References Andersen, M.P.S., O.J. Nielsen, A. Toft, T. Nakayam a, Y. Matsumi, R.L.Waterland, R.C. Buck, M.D. Hurle y, and T.J. Wallington. 2005. Atmospheric chemistry of C x F 2x+1 CH=CH 2 (x = 1, 2, 4, 6, 8): Kinetics of gas-phase reactio ns with Cl atoms, OH radicals, and O 3 . **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 ch emistry of C x F 2x+1 CH=CH 2 (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. At mospheric 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. Wallingt on, and T.J. Smyth. 1995. Radiative forcing of clim ate 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 Fluorot elomer Iodide ( **n** -C 4 F 9 CH 2 CH 2 I): Kinetics and Products of Photolysis and Reactio n 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. Olse n. In preparation. Climate advantages of proposed s hortlived compounds as replacements for longer-lived HC FCs and HFCs.