Stratospheric profiles of heavy water vapor isotopes and CH3D from analysis of the ATMOS Spacelab 3 infrared solar spectra

Abstract

Stratospheric volume mixing ratio profiles of H218O, H217O, HDO, and CH3D near latitudes of 30°N and 47°S have been retrieved from ∼0.01‐cm−1 resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission (April 29 to May 6, 1985). Improved heavy isotope water vapor and CH3D spectroscopic parameters determined from ∼0.005‐ to 0.01‐cm−1 resolution room temperature laboratory spectra have been used in the retrievals. The profiles of the three water vapor isotopes show an increase in the volume mixing ratio with altitude over the range of measurements (20 to 54 km for H218O, 20 to 46 km for H217O, and 20 to 34 km for HDO). Deuterium‐to‐hydrogen and heavy‐to‐normal oxygen isotope ratio profiles have been calculated by dividing the retrieved isotopic profiles by the previously reported profiles of H216O and CH4 obtained from the same spectral data and then referencing these results to the isotopic composition of standard mean ocean water (SMOW). At 20 km the 18O/16O ratio in H2O is slightly (∼8%) depleted relative to SMOW; this ratio increases with altitude and is slightly positive above ∼36 km. No evidence has been found for the large 18O enhancements reported previously. The 17O/16O water vapor results are similar to those for 18O/16O. The ATMOS measurements show depletions of ∼63% in the D/H content of water vapor near 20 km and an increase in this ratio with altitude up to 34 km. The D/H ratio in stratospheric methane is close to the isotopic ratio in SMOW over the 18 to 28 km altitude range. No differences between the water vapor or methane isotopic compositions at 30°N and 47°S were detected. The results are compared with previously reported measurements and calculations.