STRATOSPHERIC OBSERVATIONS OF CH3D AND HDO FROM ATMOS INFRARED SOLAR SPECTRA - ENRICHMENTS OF DEUTERIUM IN METHANE AND IMPLICATIONS FOR HD

Stratospheric mixing ratios of CH3D from 100 mb to 17 mb (approximate to 15 to 28 km) and HDO from 100 mb to 10 mb (approximate to 15 to 32 km) have been inferred from high resolution solar occultation infrared spectra from the Atmospheric Trace MOlecule Spectroscopy (ATMOS) Four ier-transform interferometer. The spectra, taken on board the Space Sh uttle during the Spacelab 3 and ATLAS-1, -2, and -3 missions, extend i n latitude from 70 degrees S to 65 degrees N. We find CH3D entering th e stratosphere at an average mixing ratio of (9.9 +/- 0.8) x 10(-10) w ith a D/H ratio in methane (7.1 +/- 7.4)% less than that in Standard M ean Ocean Water (SMOW) (1 sigma combined precision and systematic erro r). In the mid to lower stratosphere, the average lifetime of CH3D is found to be (1.19 +/- 0.02) times that of CH4, resulting in an increas ing 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 stratosphe ric HDO are produced for each CH3D destroyed (1 sigma combined precisi on and systematic error), indicating that the rate of HDO production i s approximately equal to the rate of CH3D destruction. Assuming neglig ible amounts of deuterium in species other than HDO, CH3D 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 CH3D dest royed.