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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 9, SEPTEMBER 1998

PROFESSIONAL PUBLICATIONS...
ATMOSPHERIC CHEMISTRY AND DYNAMICS

Item #d98sep9

“Mass-Independent Oxygen Isotope Fractionation in Atmospheric CO as a Result of the Reaction CO + OH,” T. Röckmann et al.,Science 281, 544-546 (July 24, 1998).

Atmospheric CO exhibits isotope-fractionation effects that are not related to the mass of the substituted isotope. Excess ¹⁷O was detected in atmospheric CO at high northern latitudes during the summer. This excess ¹⁷O ranged up to 7.5^o/_oo. The excess results from the reaction CO + OH ® CO₂ + H, which is the most common reaction of CO in the atmosphere. The surviving CO exhibits the excess, meaning that the reaction with OH demonstrates a preference for CO with ¹⁸O over that with ¹⁷O, raising fundamental questions about the kinetic processes involved. No theoretical explanation is known to explain this selective process. A similar effect also occurs in the formation of ozone, where the reaction ¹⁶O + ¹⁸O¹⁸O occurs 50% more readily than the reaction ¹⁸O + ¹⁶O¹⁶O. The anomaly does make the concentration of C¹⁷O a good marker for the age of CO in the atmosphere.

Item #d98sep10

“Seasonal Cycles and QBO Variations in Stratospheric CH₄ and H2O Observed in UARS HALOE Data,” W. J. Randel et al., J. Atmos. Sci. 55 (2), 163-185 (1998).

Stratospheric methane and water vapor were measured from 1991 to 1997 during the Halogen Occultation Experiment that employed the Upper Atmosphere Research Satellite. The data reveal latitudinal gradients in atmospheric mixing in the subtropics and across the polar vortices. They indicate a strong descent inside the polar vortices during winter and spring. And they show a strong seasonal upwelling in the tropical upper atmosphere associated with the semiannual oscillation. All of these findings are in agreement with the processes of the mean meridional circulation as understood from stratospheric meteorological analyses. Most of the variance in interannual variations is related to the equatorial quasibiennial oscillation, which also affects the latitudinal position of the tropical “reservoir” in the middle atmosphere.