Minor Constituent Concentrations Measured from a High Altitude Aircraft using High Resolution Far-Infrared Fourier Transform Spectroscopy

Far-infrared emission spectroscopy has been demonstrated to be a valuable method for remote sensing of trace species in the stratosphere, with the ability to simultaneously detect a number of key chemical species. SAFIRE-A is a new far-infrared Fourier Transform (FT) spectrometer which has been specifically designed to operate on board of a high altitude aircraft in the lower stratosphere and upper troposphere regions where relatively few remote sensing measurements have been made. Using new technology, the sensitivity of the FT spectrometer method has been substantially improved for the long wavelength region. Results are reported for measurements of O3, HNO3 and N2O at 17 and 19 km using a detection window near 23 cm-1. Geographical and altitude variability of the volume mixing ratio of these constituents and their relative correlation are discussed. Ozone measurements agree well with in situ measurements, except in regions of strong stirring and mixing associated with deformation of the northern vortex edge. Whilst SAFIRE measurements of trace gases do not capture all of the local variability seen by rapid in-situ techniques, they can indicate horizontal variability close to, but not intercepted by, the aircraft's flight path. A possible detection of ClO at the low background levels expected outside the polar vortex is also reported.