Detection of organic compound signatures in infra-red, limb emission spectra observed by the MIPAS-B2 balloon instrument

摘要

Organic compounds play a central role in troposphere chemistry andincreasingly are a viable target for remote sensing observations. Inthis paper, infra-red spectral features of three organic compoundsare investigated in thermal emission spectra recorded on a flighton 8 May 1998 near Aire sur l'Adour by aballoon-borne instrument, MIPAS-B2, operating at high spectralresolution. It is demonstrated, for the first time, that PAN andacetone can be detected in infra-red remote sensing spectra of theupper troposphere; detection results are presented at tangentaltitudes of 10.4 km and 7.5 km (not acetone). In addition, the resultsprovide the first observation of spectral features of formic acid inthermal emission, as opposed to solar occultation, and confirm thatconcentrations of this gas are measurable in the mid-latitude uppertroposphere, given accurate spectroscopic data. For PAN, two bandsare observed centred at 794 cm−1 and 1163 cm−1. For acetone andformic acid, one band has been detected for each so far with bandcentres at 1218 cm−1 and 1105 cm−1 respectively. Mixing ratiosinferred at 10.4 km tangent altitude are 180 pptv and 530 pptv forPAN and acetone respectively, and 200 pptv for formic acid withHITRAN 2000 spectroscopy. Accuracies are on the order of 15 to40%. The detection technique applied here is verified by examiningweak but known signatures of CFC-12 and HCFC-22 in the same spectralregions as those of the organic compounds, with results confirmingthe quality of both the instrument and the radiative transfer model.The results suggest the possibility of global sensing of the organiccompounds studied here which would be a major step forward inverifying and interpreting global tropospheric model calculations.