Concentrations of carbonyl sulfide and hydrogen cyanide in the free upper troposphere and lower stratosphere deduced from ATMOS/Spacelab 3 infrared solar occultation spectra

Volume mixing ratio profiles of carbonyl sulfide (OCS) and hydrogen cyanide (HCN) have been deduced from the analysis of 0.01 cm −1 resolution infrared solar absorption spectra obtained with the ATMOS (Atmospheric Trace Molecule Spectroscopy) Fourier transform spectrometer, operating in the occultation mode on board Spacelab 3 on April 30 to May 1, 1985. The profiles of OCS have been retrieved from spectroscopic fittings of absorption lines observed between 2038 and 2061 cm −1 and identified as ν 3 band transitions of OCS; they extend from 12 to 27 km altitude for sunset occultations near 28°N and from 18 to 26 km for two sunrises occurring at 46.8° and 49.0°S. The 28°N results agree satisfactorily with model calculations and with column density determinations by airplane above 12 km altitude. The investigation for HCN was based on the analysis of transitions belonging to both the ν 3 fundamental and the 2ν 2 bands of HCN, centered at 3311.48 and 1426.53 cm −1 , respectively; the HCN profiles extend from 12 to 32 km for the 28°N latitude sunsets and from 13 to 30 km for sunrise events near 48°S. For both latitudes the mean results indicate a decrease of about 15±5% from the bottom to the top of their altitude span. The northern hemisphere retrievals reported here represent the first volume mixing ratio profiles covering the upper troposphere and the lower stratosphere simultaneously. The sunrise data provide first profiling of both species at southern mid‐latitudes.