Stratospheric HCl from infrared spectra

HCl has been observed in the stratosphere from balloon borne spectroscopic measurements of a portion of the fundamental band in the 3 microns wavelength region. The observation of absorption lines using the sun as a source at solar zenith angles larger than 90° indicates an HCl volume mixing ratio equal to (3.8 ± 1.5) × 10 −10 at 20 km increasing with altitude at least up to 30 km where the value is (1.4 ± 0.6) × 10 −9 . The total zenith amount above 21 km is found to be (10± 3.5) × 10 −14 cm −2 in agreement with previous observations performed up to this altitude. A maximum number density equal to (7.2 ± 3) × 10 8 cm −3 is observed at 24 ± 2 km altitude.