### Global Warming Potential FC-77

Summary: This document describes analysis conducted by 3M to determine a Global Warming Potential (GWP) for components contained in FC-77. The forma t of this report is consistent with submittals to EPA for the use of Provisional GWP’s. The Mandatory Reporting Rule requires facilities to monitor and report CO 2 -equivalent 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 obtained by multiplying t he F-GHG mass emissions by the Global Warming Potential (GWP) for the indiv idual fluorinated gases that comprise the flow. EPA has provided a table of 100-year time horizon GWP values for about 70 individual F-GHG, and specifies that these values a re to be used for the purpose of computing CO 2 -equivalent emissions. [2] Default GWP’s can be use d for any fluorinatedGHG not listed in Table A-1. The regulation allows a facility to request a lower provisional GWP when clear scientific evidence exists to suppor t such a lower value. For the purposes of EPA’s request 3M estimated the FC-77 GWP assuming a 1:1 mixture of C 8 F 18 and C 8 F 16 O. Therefore the GWP of FC-77 is calculated as the average of the GWP’s of these components. Table A–1 does not list a GWP fo r FC-77, C 8 F 18 or C 8 F 16 O. As described in greater detail in a subsequent section , the atmospheric lifetime of C 8 F 18 has been estimated as 3200 years [3], and the atmospheric li fetime of C 8 F 16 O has been estimated at 2300 years [4]. The radiative forcing of each comp onent of FC-77 has been estimated [4] and using these data the GWP of FC-77 has been esti mated as 8900 relative to CO 2 with a 100-year integration time horizon. Evidence Supporting Request: F-GHG Identity: FC-77 (1:1 Mixture of C8F18 and C8F 16O)

Chemical Formula: 1:1 Mixture of C 8 F 18 and C 8 F 16 O

Estimated GWP: 8900 relative to CO 2 with a 100-year integration time horizon Data and analysis: Radiative Forcing: Individual absorption cross-sect ions were obtained from the spectrum of each individual component of FC-77 (See Figures 1 a nd 2). The spectral data was divided into sections with bandwidth 10 cm-1. Average abso rption cross-sections for each band were calculated. The cross-sections were then weighted using factors reported in Pinnock et al[5]. The weighted cross-sections were summed over all ba nds to obtain the value for instantaneous radiative forcing for each individual component. A "cloudy-sky" adjustment factor of 1.07 was then applied as noted in results . The values for C 8 F 18 and C 8 F 16 O are 0.56 W/m2/ppbV and 0.63 W/m2/ppbV, respectively. Atmospheric lifetime: The atmospheric lifetime for C 8 F 18 was estimated using a structurally similar chemical perfluorohexane as the mode of atm ospheric degradation for both compounds is likely the same. In fact the average atmospheric lifetime for C 3 F 8 , c-C 4 F 6 , C 4 F 10 , C 5 F 12 , and C 6 F 14 is 3140 and the GWP of the individual compounds va ries by 20% from this average. For comparison, GWPs listed by the IPCC [3] have an uncertainty listedas 35%. The atmospheric lifetime for perfluorohexa ne is 3200 years [3]. The atmospheric

lifetime for C 8 F 16 O was determined experimentally and was determined to be >2300 years [4] here we assume the lifetime is 2300 years. Using these data in the equation referenced by the IPCC [3] to determine the GWP of a given substance, a GWP of 8200 is determined for C 8 F 18 relative to CO 2 with a 100-year integration time horizon, and a value of 9600 is determined for C 8 F 16 O. Sine FC-77 is a 1:1 mixture of the two components the GWP is taken as the average of the two values and is 8900.

1. "Mandatory Reporting of Greenhouse Gases: Additiona l Sources of Fluorinated GHGs; Final Rule" , Federal Register 75:230 (December 1, 2010) p.7477 4.

2. "Table A-1 to Subpart A of Part 98—Global Warming P otentials" : Table A-1 in 40 CFR part 98, subpart A. 3. IPCC, 2007: Climate Change 2007: Impacts, Adapta tion and Vulnerability. Contribution of Working Group II to the Fourth Assessment. Repor t of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Pal utikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge , UK, 976pp 4. Ko, M.K.W. and D.T. Chang, Estimates of the Global Warming Potential of Propos ed Chemical Compounds. 1992, Atmospheric and Environmental Research, Inc. : Cambridge, MA
5. Pinnock, S., et al., Radiative forcing of climate by hydrochlorofluoroca rbons and hydrofluorocarbons. Journal of Geophysical Research, 1995. 100 (D11): p. 23227-23238.

### Figure 1. FTIR Spectra of C 8 

### F 18 

### isomer mixture 0 .2 .4 .6 .8

3500 3000 2500 2000 1500 1000 500

Absorbance / Wavenumber (cm-1) Paged X-Zoom CURSOR

File # 5 : HZPFOCT 1/9/1995 2:33 PM Res=.5cm-1

Perfluoro octanes, 10 0 ppm-meters in 1 atm air; 25 C.

### Figure 2. FTIR Spectra of C 8 F 16 O