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

- 1 4

- 3 )

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 tetrafluoroethylene

. Tetrafluoroethylene 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 tetrafluoroethylene have been measured in an environmental chamber; the atmospheric lifetime of tetr afluoroethylene has been estimated as 1.9 days; the infrared spectrum of tetrafluoroethylene has been accurately measured and the GWP of tetrafluoroethylene has been estimated as 0.021 relative to CO 2 with a 100

- year integration time horizon. DuPont is re questing a provisional GWP of 0.021 be assigned for tetrafluoroethylene

. Evidence Supporting Request :

F

- GHG Identity : Tetrafluoroethylene Chemical Formula : C 2 F 4 CAS Number: 116

- 14

- 3

Estimated GWP: 0. 021 relative to CO 2 with a 100

- year integration time horizon

Data and analysis: Acerboni et al. have measured kinetic rate constants for the vapor phase reaction of tetrafluoroethylene with OH, NO 3 and O 3
. [3] A chemical transport model was applied to calculate the atmosph eric distributions and lifetime of
t etrafluoroethylene ; the global and yearly averaged lifetime was calculated as 1.9 days. Quantitative infrared cross

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

- 2600 cm - 1 , and r adiative forcing calculations were per formed assuming either constant vertical concentration profiles or the distribution derived from the chemistry transport model. A GWP of 0.021 relative to CO 2 with a 100

- year integration time horizon was established

.The methods used in determining this GWP value 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 publication in the peer

- reviewed literature , DuPont requests that a provisional GWP of 0.021 be assigned for tetrafluoroethylene

.

1. "Mandatory Reporting of Greenhouse Gases: Additional Sources of Fluorinated GHGs; Final Rule" , Fe deral Register 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 perfluoroalk enes. Atmospheric Environment, 2001. 35 (24): p. 4113

- 4123.