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The Isotopic Composition of Carbon Dioxide in the Middle Atmosphere. Mao-Chang Liang 1 , Geoffrey A. Blake 1 , Brenton R. Lewis 2 , and Yuk L. Yung 1 1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA
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Mao-Chang Liang1, Geoffrey A. Blake1, Brenton R. Lewis2, and Yuk L. Yung1
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA
2Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australia
Of the many trace molecules that can be used to examine atmospheric transport processes and chemistry (e.g., CH4, N2O, SF6, and the CFCs), carbon dioxide is unique in the middle atmosphere, because of its high abundance (~370 ppmv in the stratosphere, dropping to ~100 ppmv at the homopause). The mass independent isotopic fractionation (MIF) of oxygen first discovered in ozone is thought to be partially transferred to carbon dioxide via the reaction O(1D) + CO2 in the middle atmosphere. Indeed, while the reactions of trace molecules with O(1D) usually lead to their destruction, the O(1D) + CO2 reaction regenerates carbon dioxide. This ‘recycled’ CO2 is unique in its potential to trace the chemical (reactions involving O(1D) in either a direct or indirect way) and dynamical processes in the middle atmosphere. When transported to the troposphere, it will produce measurable effects in biogeochemical cycles involving CO2.
Thiemens et al. 1995
Lämmerzahl et al. 2002
xt = (0.80, 0.75, 0.70)
xm = (0, 0.05%, 0.1%)
Three-box model illustration:
a) 17O(CO2) = xt17O(CO2)t + xs17O(CO2)s +
xm17O(CO2)m - 17O(CO2)t
18O(CO2) = xt18O(CO2)t + xs18O(CO2)s +
xm18O(CO2)m - 18O(CO2)t
b) xm << xs < xt and xt + xs + xm = 1
c) different degree of air mixing from
troposphere, stratosphere, and mesosphere is
Yung et al. JGR, 1997; Thiemens et al. Science, 1995;
Lämmerzahl et al. GRL, 2002; Liang et al. JGR, 2005 (accepted)
Contact: see http://www.gps.caltech.edu/~mcl