Simultaneous stratospheric measurements of H2O, HDO, and CH4 from balloon‐borne and aircraft infrared solar absorption spectra and tunable diode laser laboratory spectra of HDO

Abstract

High‐resolution infrared solar absorption spectra recorded from a balloon‐borne platform at 33‐km altitude and an aircraft at 12‐km altitude have been analyzed to derive simultaneous stratospheric concentrations of H2O, HDO, and CH4. The data were obtained near 33°N with the University of Denver interferometer during a balloon flight in October 1979 and with the NCAR interferometer aboard a Sabreliner aircraft in September 1982. The analysis of the balloon spectra indicates the H2O mixing ratio increased from 3.5 to 4.8 ppmv and the CH4 mixing ratio decreased from 1.15 to 0.70 ppmv between 18 to 38 km. Tunable diode laser laboratory spectra were recorded and analyzed to derive absolute intensities and air‐broadened half widths of selected lines of the v2 band of HDO. With these parameters, which are reported here, an HDO profile that increases from 0.61 ppbv near 18 km to 0.88 ppbv near 29 km is inferred from the balloon spectra, corresponding to a D/H ratio, normalized to the reference value of 158 atomic parts per million of Standard Mean Ocean Water (SMOW), of 0.55 to 0.67. The average D/H value of 0.40 above 12 km, derived from the aircraft spectra, provides additional spectroscopic evidence for a large depletion in the D content of water vapor in the lower stratosphere. The simultaneous vertical profiles for the three gases retrieved from the balloon spectra are consistent, within the estimated precision of the data (±10%), with methane oxidation as the sole source of stratospheric H2O in addition to H2O transported upward through the tropopause. However, there is an indication of a small increase in the total hydrogen in H2O and CH4 with altitude, and we believe more precise simultaneous measurements are required.