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N IHTAUGT EE NO CF E(INNTSEERR FT ONRA A
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P IAVRE RT SMI TEYNOTF O
ISTRY
UNIVERSITY OF COPENHAGEN
Atmospheric chemistry of CF3CH2OCH3
Freja From Østerstrøm1, Ole John Nielsen1, Mads P. Sulbæk Andersen2
1
Copenhagen Center for Atmospheric Research, Department of Chemistry, University of Copenhagen, Universitetsparken 5,
DK-2100 Copenhagen Ø, Denmark
2 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 183-901, Pasadena, CA 91109, USA
1. Introduction
m
The chlorofluorocarbons (CFCs) have long been
recognized to be a major participant in chlorine
initiated photochemical reactions depleting the
stratospheric ozone layer. [1,2] Furthermore these
compounds are green house gases (GHGs) and
contribute to the global warming. Because of this,
there has been a substantial effort to find
environmentally acceptable alternatives.
The first generation CFC alternatives contained
hydrogen atoms (HCFCs), while the second generation
alternatives do not contain chlorine atoms (HFCs).
Third generation CFC alternatives are the so-called
hydrofluoroolefins (HFOs) and hydrofluoroethers
(HFEs).
Infrared spectrum of CF3CH2OCH3.
This study concerns the atmospheric chemistry
HFEs. Like the CFCs and other replacement
compounds, the HFEs are used in applications such as
electronics cleaning, fire extinguishing, lubricant
deposition, heat transfer and refrigeration. To be able
to use the HFEs, the environmental chemistry must be
known. Thus, in this study we want to determine the
reactivities of Cl atoms and OH radicals towards
CF3CH2OCH as well as the atmospheric degradation
products, the atmospheric lifetime, the IR spectrum
and the global warming potential for the title
compound, CF3CH2OCH, as a representative for the
HFE class of compounds.
This study was conducted using the smog chamber
at Ford Motor Company.
2. Experimental: Relative rate (OH/Cl + CF3CH2OCH3) and product study
All experiments were performed in a 140 litre Pyrex reactor connected to a Mattson Sirus 100 FTIR spectrometer. [3,4] Twenty two black light lamps surrounded the
reactor (GE F40BLB) and were used to photochemically initiate the experiments. Cl atoms were produced by photolysis of Cl2, and OH radicals by photolysis of CH3ONO in
the presence of NO in air. All experiments were performed at 296 ± 1 K.
Hydrogen atom abstraction can occur at the CH2and CH3-groups, respectively.
For reaction with Cl atoms there is (21±1) % and
(79±3) % at the CH2- and CH3-groups,
respectively.
For reaction with OH radicals there is (42±3)%
and (57±5) % at the CH2- and CH3-groups,
respectively.
CH3ONO + hv → CH3O + NO
CH3O + O2 → HO2 + HCHO
HO2 + NO → OH + NO2
Cl2 + hv → 2 Cl
The laboratory at Ford Motor Company.
3. Atmospheric lifetime
With the measured rate constant for the reaction of CF3CH2OCH3 with OH radicals, kOH = (4.66 ± 0.45) ∙ 10-13 cm3 molecules-1 s-1, and the global weighted average
concentration of OH radicals estimated to [OH] = 1∙106 molecules cm-3 [5] we can calculate the global atmospheric lifetime of CF3CH2OCH3 to 25 days. The local
concentrations of OH can vary a lot, so the local lifetime of CF3CH2OCH3 might be different from the one given here.
4. GWP
5. Data for fluorinated ethers and reference compounds
The integrated absorption cross section (600-1600 cm-1) is (1.55 ± 0.08) ∙ 10-16 cm
molecule-1. The radiative efficiency of CF3CH2OCH3 is then 0.21 W m-2 ppb-1 and the
AGWPs for CO2 are estimated by the World Meteorological Organization (WMO) to
0.197, 0.676 and 2.223 W m-2 ppm-1 [6] for the 20, 100 and 500 year horizons
respectively. The following formula is used to calculate GWP:
GWPx



τx
0
τx
0
Fx (t) e
t τx
dt
FCO 2 (t) R(t)dt
Compound
kCl
kOH
GWP100
CF3CH2OCH3
(2.28 ± 0.35)∙ 10-11 (4.66 ± 0.45)∙ 10-13
8
CF3CH2OCH3
(1.8 ± 0.9)∙ 10-11
(5.7 ± 0.8)∙ 10-13 Not calculated
C2F5CH2OCH3 (2.52 ± 0.37)∙ 10-11 (5.78 ± 1.02)∙ 10-13
6
C2F5CH2OCH3
(4.0 ± 0.8)∙ 10-11 (6.42 ± 0.33)∙ 10-13
5
n- C4F9CH2OCH3 (9.7 ± 1.4)∙ 10-14
≈1.2∙ 10-14
432
CFC-11, CFCl3
4750
Reference
This work
Oyaro et al. [8]
Thomsen et al. [9]
Oyaro et al. [10]
Wallington et al. [11]
WMO 2010 [7]
All rate constants given in the table are in units of cm3molecule-1s-1.
We use the above calculated atmospheric lifetime of 25 days to calculate the GWP.
The GWP of CF3CH2OCH3 is determined to be 29, 8 and 2 for the 20, 100 and 500
year time horizons, respectively. The determined value of GWP for CF3CH2OCH3 is a
factor of thousand smaller than the GWP value for CFC-11 for the 20 year time
horizon. [7] The climate effect of CF3CH2OCH3 is insignificant.
6. Conclusion
The fluorinated ether studied in the present work will not contribute significantly to
the radiative forcing of climate change.
7. References
1: M. J. Molina and F. S. Rowland, Nature, 1974, 249, 810
2: J. D. Farman, B. G. Gardiner and J. D. Shanklin, Nature, 1985, 315, 207 3: T. J. Wallington and S. M. Japar, J. Atmos. Chem., 1989, 9, 399
4: J. Sehested, T.
Ellermann, O. J. Nielsen, T. J. Wallington and M. D. Hurley, Int. J. Chem. Kinet., 1993, 25, 701
5: R. G. Prinn, J. Huang, R. F. Weiss, D. M. Cunnold, P. J. Fraser, P. G. Simmonds, A. McCulloch, P. Salameh, S. O’Doherty, R. H. J.
Wang, L. Porter and B. R. Miller, Science, 2001, 292, 1882-8 6: World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2006, Global Ozone, Research and Monitoring Project – Report 50,
Geneva, Switzerland, 2007
7: WMO, Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project-Report No. 52, 516 pp., Geneva, Switzerland, 2011
8: N. Oyaro, S. R. Sellevåg
and C. J. Nielsen, J. Phys. Chem. A, 2005, 109, 337-346, 9: D. L. Thomsen, V. F. Andersen, O. J. Nielsen and T. J. Wallington, Phys. Chem. Chem. Phys., 2011, 13, 2758-2764 10: N. Oyaro, S. R. Sellevåg and C. J. Nielsen, Environ.
Sci. Technol., 2004, 38, 5567-5576
11: T. J. Wallington, W. F. Schneider, J. Sehested, M. Bilde, J. Platz, O. J. Nielsen, L. K. Christensen, M. J. Molina, L. T. Molina and P. W. Wooldridge, J. Phys. Chem. A, 1997, 101, 8264-8274
Acknowledgements: We acknowledge financial support from the Danish Natural Science Research Council, the Villum Kann Rasmussen Foundation and EUROCHAMP2. This work was performed partly at the Jet Propulsion Laboratory, California Institute of Technology, under a contract
with the National Aeronautics and Space Administration. M.P.S.A. is supported by an appointment to the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities through a contract with NASA.