mm-wave spectroscopy of stratospheric trace gases at the South Pole over an 11-month cycle: O3, N2O, HNO3, NO2, and ClO

The authors have employed a ground-based, cryogenically cooled, tunable heterodyne spectrometer operating near 275 GHz (1.1 mm) to make frequent quantitative measurements of various trace gases at the Amundsen-Scott South Pole Station over an 11 month period starting in February, 1993. The detector is a high frequency Schottky diode cooled to 20 K. The i.f. output is coupled to a 512 channel filter-bank spectrometer with a resolution of 1 MHz per channel. This bandwidth and resolution allows vertical profiles to be recovered from deconvolution of pressure-broadened line shapes over the range ~16 to 45-50 km, with accuracy depending on the mixing ratio of the species as a function of altitude. The authors present an overview of the data collected by this system for O₃, N₂O, NO₂, HNO₃, and ClO in the polar vortex. Vertical profiles of the chosen trace gases are affected variously by gas-phase chemistry, heterogeneous chemistry on particle surfaces, condensation, photochemistry, and transport. A unique record has been obtained from which the dynamical development of the Antarctic winter vortex, the extent and influence of downward transport in the mesosphere and stratosphere, the timing of polar stratospheric cloud formation, and the onset and duration of ozone destruction by chlorine photochemistry can all be obtained