### R equest to Use an Alternate GWP for Hexafluoropropylene (CAS Number: 116

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Summary:

EPA recently promulgated a mandatory reporting regulation for Fluorinated Greenhouse Gases ( F

- GHG). The regulation requires f acilities to monitor and report CO 2 - equi valent F

- GHG process vent emissions, if those emissions exceed a threshold of 10,000 metric tons CO 2 - equivalent per year. [1] Estimated CO 2 - equivalent emissions are obt ained by multiplying the F

- GHG mass emissions by the Global Warming Potential for the individual fluorinated gases that comprise the flow. EPA has provided a t able of 100

- year time horizon GWP values for about 70 individual F

- GHG

, and specifies that these values are to be used for the purpose of computing CO 2 - equivalent emissions

. [2] A default GWP value of 2,000 is to be used for any F

- GHG not listed in Table A

- 1. T he regulation allows a facility to request a lower provisional GWP when clear scientific evidence exists to support such a lower value.

Table A

– 1 does not list a GWP for hexafluoropropylene. Hexafluoropropylene is a s hort

lived fluorinated alkene. T he default GWP value of 2,000 is inappropriate for such gases and a substantial body of evidence in the peer

- reviewed scientific literature has established that the GWP s of fluorinated alkenes are modest . Kinetic rate constants for the atmospheric degradation of hexafluoropropylene have been measured in an environmental chamber; the atmospheric lifetime of hexa fluoropropylene has been estimated as 6 days; the infrared spectrum of hexafluoropropylene has been accurately measured and the GWP of hexafluoropropylene has been estimated as 0.25 relative to CO 2 with a 100

- year integration time horizon. DuPont is reque sting a provisional GWP of 0.25 be assigned for hexafluoropropylene.

Evidence Supporting Request :

F

- GHG Identity : Hexafluoropropylene Chemical Formula : C 3 F 6 CAS Number: 116

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Estimated GWP: 0.25 relative to CO 2 with a 100

- year integration time hori zon

Data and analysis: Acerboni et al. have measured kinetic rate constants for the vapor phase reaction of hexafluoropropylene with OH, NO 3 and O 3
. [3] A chemical transport model was applied to calculate the atmosph eric distributions and lifet ime of hexafluoropropylene ; the global and yearly averaged lifetime was calculated as 6 days. Quantitative infrared cross

- sections of hexafluoropropylene were obtained at 298 K in the region 100

- 2600 cm - 1 , and r adiative forcing calculations were performed assuming either constant vertical concentration profiles or the distribution derived from the chemistry transport model. A GWP of 0.25 relative to CO 2 with a 100

- year integration time horizon was established

.The methods used in determining this GWP val ue are essentially identical to those used for the values obtained for the gases listed in Table A

- 1: (1) the kinetic rate constants for reaction with critical atmospheric oxidants were measured and an atmospheric lifetime was determined; (2) the infrared absorption spectrum of the substance was measured ; and (3) the atmospheric lifetime and infrared absorption spectrum were incorporated into a radiative transfer model to estimate the contribution of the substance to greenhouse forcing.

Based on this pub lication in the peer

- reviewed literature , DuPont requests that a provisional GWP of 0.25 be assigned for hexafluoropropylene.

1. "Mandatory Reporting of Greenhouse Gases: Additional Sources of Fluorinated GHGs; Final Rule" , Federal Reg ister 75:230 (December 1, 2010) p.74774. 2. "Table A

- 1 to Subpart A of Part 98

— Global Warming Potentials" : Table A

- 1 in 40 CFR part 98, subpart A. 3. Acerboni, G., et al., Atmospheric degradation and global warming potentials of three perfluoroalkenes. Atm ospheric Environment, 2001. 35 (24): p. 4113

- 4123.