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Published August 15, 1996 | Published
Journal Article Open

Stratospheric observations of CH_3D and HDO from ATMOS infrared solar spectra: Enrichments of deuterium in methane and implications for HD


Stratospheric mixing ratios of CH_3D from 100 mb to 17 mb (≈ 15 to 28 km) and HDO from 100 mb to 10 mb (≈ 15 to 32 km) have been inferred from high resolution solar occultation infrared spectra from the Atmospheric Trace MOlecule Spectroscopy (ATMOS) Fourier-transform interferometer. The spectra, taken on board the Space Shuttle during the Spacelab 3 and ATLAS-1, -2, and -3 missions, extend in latitude from 70°S to 65°N. We find CH_3D entering the stratosphere at an average mixing ratio of (9.9±0.8) × 10^(−10) with a D/H ratio in methane (7.1±7.4)% less than that in Standard Mean Ocean Water (SMOW) (1σ combined precision and systematic error). In the mid to lower stratosphere, the average lifetime of CH_3D is found to be (1.19±0.02) times that of CH_4, resulting in an increasing D/H ratio in methane as air "ages" and the methane mixing ratio decreases. We find an average of (1.0±0.1) molecules of stratospheric HDO are produced for each CH_3D destroyed (1σ combined precision and systematic error), indicating that the rate of HDO production is approximately equal to the rate of CH_3D destruction. Assuming negligible amounts of deuterium in species other than HDO, CH_3D and HD, this limits the possible change in the stratospheric HD mixing ratio below about 10 mb to be ±0.1 molecules HD created per molecule CH_3D destroyed.

Additional Information

© 1996 by the American Geophysical Union. Received November 3, 1995; revised April 3, 1996; accepted April 12, 1996. Paper number 96GL01402. We thank L. R. Brown, T. L. Brown, J. C. Foster, C. B. Farmer, G. D. Lynch, O. F. Raper, and G. C. Toon for their assistance. Research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.

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