Ground-Based mm-Wave Heterodyne Spectroscopy of Stratospheric Chlorine Oxide

Abstract

Chlorine oxide, formed in the catalytic cycle is an important monitor of the conversion of ozone to O2 by free chlorine in the stratosphere. Current models predict mixing ratios for CℓO peaking at a value < 1:109 near 35 km altitude (1), and model profiles give an integrated column density towards the zenith of < 2.5 × 1014 cm-2, making radiometric detection of emission lines extremely difficult through the intervening atmosphere. Heretofore, experimental detection has relied on balloon-born in-situ measurements (2) or on attempts at remote mm-wave (3) or IR detection (4) from high-flying aircraft or balloon platforms. We have developed and successfully used a ground-based mm-wave spectrometer employing some novel features to detect the J = 11/2 → 9/2 rotational transition of CℓO in emission at 204.352 GHz. Our observations were conducted near Amherst, Mass, (elevation ~ 300 m) above sea level) during the period mid-January to mid-April 1980.