MEMORANDUM

To: Erin Birgfeld

Cc: Bella Maranion

From: Sarah Percy, Mark Wagner

Date: September 10, 2003

Re: Re-evaluation of a C-6 Oxyfluorocarbon (trade name Novec 1230) and References Deliverable under EPA Contract Number 68-D-00-266, Work Assignment 2-05 Task 03

Based on analysis developed by ICF’s subcontractor, Dr. Don Wuebbles, please find a revised discussion of the atmospheric lifetime and Global Warming Potential (GWP) for C-6 oxyfluorocarbon. This memorandum presents a review of the literature that supported the GWP and ALT evaluation conducted in January of 2003. Additionally, a revised assessment of the GWP based on the mass of C-6 oxyfluorcarbon and CO 2 is provided. Please contact Mark Wagner at (202) 862-1155 if you have any questions.

Summary

Based on an analysis of the C-6 oxyfluorocarbon, derived using the IPCC recommended approach for such assessments, it was determined that the chemical has an atmospheric lifetime of up to two weeks and a GWP of between 0.6 and 1.8.

Discussion of Results

The previous examination of the C-6 oxyfluorocarbon, trade name Novec 1230 (CF 3 CF 2 C=OCFCF 3 CF 3 ), was conducted in October 2002 without the review of any literature that could directly aid in the determination of the atmospheric lifetime or radiative forcing on climate associated with this compound. Using the IPCC approach, it was concluded that absorption of solar radiation for photodissociation of the oxyfluorocarbon would likely be in the 250-350 nm region, implying a lifetime of days up to as much as a year, with the lifetime most likely much shorter than a year. Based on this, the concluded 100-year integration GWP for the C-6 oxyfluorocarbon would range from a value of 6, based on the reaction products producing six carbon dioxide molecules, up to 100, accounting for a lifetime as long as one year.

In January 2003, three additional papers on C-6 oxyfluorocarbon photolysis were reviewed. The first of these, and the most credible, Taniguchi et al. (2003), published in
the Journal of Physical Chemistry A, deals with the reaction of the C-6 oxyfluorocarbon in the atmosphere and associated reaction products. This paper concludes that photolysis is the significant reaction. Taniguchi et al . found that the photolysis quantum yield for the C-6 oxyfluorocarbon is significantly less than unity. The paper concludes that the atmospheric lifetime due to photolysis will be 1-2 weeks, and suggests the need forfurther study. However, the authors also suggest that one of the products, CF 3 COF, would be water soluble and subject to rainout. This means as many as two of the carbons could get washed out and not become carbon dioxide in the atmosphere. The other four carbons would likely result in atmospheric carbon dioxide. In addition, whatever C-6 oxyfluorocarbon, and therefore CF 3 COF, is transported into the free troposphere outside of cloud regions may also result in atmospheric carbon dioxide. The net result is that 4+ carbons in the C-6 oxyfluorocarbon would eventually result in carbon dioxide in the atmosphere.

The second paper, Guschin et al . (1999), makes a rough estimate of the atmospheric lifetime of the C-6 oxyfluorocarbon by comparing its ultraviolet and visible absorption spectra to acetaldehyde, and suggests that this comparison implies an atmospheric lifetime for the C-6 oxyfluorocarbon of 5 days. However, this is only a crude estimate and does not take into account the quantum yields measured in the much later work by Taniguchi et al . This implied 5-day lifetime was then used in a paper entitled, Global Warming Potentials of 3M Novec 1230 Fire Protection Fluid , author unknown, to estimate a100-year integrated GWP of 1.0. Additionally, this paper assigns a radiative forcing of 0.50 Wm -2 ppbv -1

.
The evaluation of the radiative forcing is based on the approach used by Pinnock et al

. (1995). However, Pinnock et al . assumes a constant mixing ratio for the substance in both the troposphere and stratosphere, which would most certainly not be the case for the C-6 oxyfluorocarbon. This assumption is not valid for C-6 oxyfluorocarbon and the radiative forcing would likely be smaller. This implies a much smaller GWP except that the assumed lifetime is too small based on the analysis of Taniguchi et al

.
In conclusion, the new information found in the literature suggests that the original GWP estimate should be revised. The direct GWP for a 100-year integration, calculated using the IPCC approach (originally developed by Dr. Don Wuebbles), would likely have a value of 1 or less. This is based on the atmospheric lifetime of up to two weeks (instead of 5 days), but with the radiative forcing likely much less than 0.50 Wm -2 ppbv -1 , because of the expected rapid fall off in mixing ratio of the C-6 oxyfluorocarbon with altitude. In addition, however, one must consider and add in the GWPs of any reaction products that are sufficiently long-lived. As stated above, 4+ CO 2 molecules will be produced and enter into the atmosphere as a result of the photodissociation of the C-6 oxyfluorocarbon. By definition, the GWP of each of these is 1. Therefore, depending on the exact value of the direct GWP of the C-6 oxyfluorocarbon and the amount of CF 3 COF actually rained out, the total GWP for the C-6 oxyfluorocarbon and its products will be greater than 4 to as high as 7. In accordance with its definition, the GWP has been further revised and
evaluated to account for mass 1 . Multiplying the direct and indirect GWP’s by the ratio of
CO 2 mass to C-6 oxyfluorocarbon mass results in a 100 year GWP for C-6 oxyfluorcarbon between 0.6 and 1.8. The total GWP is comprised of a direct value of less than 1 but greater than zero plus an indirect GWP of 0.56 to 0.84, based on 4 to 6
carbons available for conversion to CO 2

.

1 The definition of GWP can be found at <http://yosemite.epa.gov/oar/globalwarming.nsf/content/EmissionsNationalGlobalWarmingPotentials.htm>Finally, although it has not yet been adopted by IPCC, the direct GWP for short-lived gases like this C-6 oxyfluorocarbon would depend on where and when the emissions occurred. Thus, the direct GWPs, just like ODPs for short-lived gases (e.g., see Wuebbles, et al., 2001), would depend on what region or at which latitude the emissions occurred. This, however, should have a very minimal effect for the C-6 oxyfluorocarbon, in question.

References

Guschin, A. G.; Molina, L.T.; and Molina, M.J. (1999). Atmospheric Chemistry of L15381, L-15566 and L-14703 and Integrated Band Strengths of L-14374, L-14375, L14752, L-13453 and L-14703. Report prepared for 3M Specialty Chemicals Division Laboratory, St. Paul, Minnesota.

Pinnock, S.; Hurley, M.D.; Shine, K.P.; Wallington, T.J.; Smyth, T.J. (1995). Radiative forcing by hydrochlorofluorocarbons and hydrofluorocarbons. J. Geophys. Res., 100

, 23227-23238.

Taniguchi, N.; Wallington, T.J.; Hurley, M.D.; Guschin, A.G.; Molina, L.T. (2003). Atmospheric Chemistry of C2F5C(O)CF(CF3)2: Photolysis and Reaction with Cl Atoms, OH Radicals, and Ozone. J. Phys. Chem. A ., 107(15); 2674-2679.

Wuebbles, D. J.; Patten, K.O.; Johnson, M.T.; and Kotamarthi, R. (2001). The new methodology for Ozone Depletion Potentials of short-lived compounds: n-propyl bromide as an example. J. Geophys. Res. , 106, 14551-14571.