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Environmental fate & pathways

Phototransformation in air

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Description of key information

Rate constant for OH-mediated photolysis at 25 deg. C is 1.24+/-0.09.  From  peer reviewed journal (KC=1) Orkin, V.L., Huie, R.E., Kurylo, M.J. (1996) Atmospheric lifetimes of HFC-143a and HFC-245fa: flash photolysis resonance fluorescence measurements of the OH reaction rate constants.  J. Phys. Chem.  100, 8907-8912.

Key value for chemical safety assessment

Half-life in air:
9 600 d

Additional information

An overall OH rate constant was calculated to be 9.7x 10-15cm3/molecule-sec, with a half-life of 1108 days (3.04 years). This calculation assumes a 12-hr day and an OH radical concentration of 1.5 x 106OH/cm3(USEPA, 2008a).

Photodegradation occurs primarily with hydroxyl radicals, resulting in a half-life of approximately 9,600 days (Orkin et al., 1996; Hayman and Derwant, 1997 and Naik et al., 2000). A photochemical trajectory model has calculated a photochemical ozone creation potential (POCP) of 0.0 for HFC-143a, thus HFC-143a should make a negligible contribution to photochemical ozone production (Hayman and Derwent, 1997).

 

A two-dimensional chemical-radiative-transport model of the global atmosphere determined the atmospheric lifetime of 1,1,1,-trifluoroethane to be 47.2 years, compared with 53.5 years as previously reported by Grainer et al., 1999.  The difference in values appears to result from the slow, but not trivial loss in the stratosphere. The direct global warming potential (GWP) of HFC-143a at 20-, 100- and 500 year time horizons was calculated to be 5,695, 4,352, and 1,537, respectively (relative to a value of 1 for CO2).  The model took into account evaluated atmospheric lifetimes and radiative forcings. The percent difference in GWP for HFC-143a for the 100-year time horizon in this study (4,352) was 19% less than that reported (5,400) by the Grainer et al. (1999) (Naik et al., 2000, U.S. EPA, 2009).  In the 4th IPCC assessment report, the GWP over a 100 year time horizon was assessed at 4470 with an atmospheric lifetime of 52 years (4th IPCC assessment report, table 2.14 chapter 2, 2007)

Grainer, C. et al. 1999. Climate effects of ozone and halocarbon changes in Scientific Assessment of Ozone Depletion: 1998, Ch. 10, Rep. 44, pp.383 -416, Global Ozone Res. and Monit. Proj. World Meteorol. Org., Geneva, Switzerland.

Hayman, GD and Derwent, RC, 1997. Atmospheric chemical reacitivity and ozone-forming potentials of potential CFC replacements. Environ. Sci. Technol. 31, 327 -336.

Naik, V., Jain, AK, Patten, KO, and Wuebbles, DJ. 2000. Consistent sets of atmospheric lifetimes and radiative forcings on climate for CFC replacements: HCFCs and HFCs. J. Geophysical Res. 105, (D5), 6903 -6914.

Orkin, VL, Huie, RE, Kurylo, MJ. 1996. Atmospheric lifetimes of HFC-143a and HFC-245fa: Flash photolysis resonance fluoresence measurements of the OH reaction rate constants. J. Phy. Chem., 100, 8907 -8912.

U.S.EPA 2008a. Estimation Programs Interface Suite for Microsoft Windows v. 4.00. United States Environmental Protection Agency, Washington, D.C., USA.

U.S.EPA 2009. Federal Register Vol 74, No. 68, Friday April 10, 2009 p. 16629.