| Summary: | For the first time CH_3CN has been measured in the Earth's atmosphere by means of infrared remote sensing. Vertical profiles of volume mixing ratio were retrieved from 12 solar occultation measurements by the balloon-borne JPL MkIV interferometer between 1993 and 2004. Profile retrieval is possible in an altitude range between 12 and 30 km with a precision of ∼20 ppt in the Arctic and ∼30 ppt at mid-latitudes. The retrieved CH_3CN profiles show mixing ratios of 100–150 ppt a few kilometers above the tropopause that decrease to values below 40 ppt at altitudes between 22 and 30 km. The CH_3CN mixing ratios show a reasonably compact correlation with the stratospheric tracers CH_3Cl and CH_4. The CH_3CN altitude profiles and tracer correlations are well reproduced by a 2-dimensional model, suggesting that CH_3CN is long-lived in the lower stratosphere and that previously-proposed ion-molecule reactions do not play a major role as loss processes of CH_3CN. © 2005 American Geophysical Union. Received 2 August 2005; revised 6 September 2005; accepted 20 September 2005; article first published online 6 December 2005. We would like to thank the various launch crews for conducting the balloon flights, and to D. Petterson and J. Landeros of JPL for their excellent support prior and during the measurement campaigns. We also wish to thank S. Sharpe and C. Rinsland for providing their CH_3CN absorption cross sections prior to publication, and A. Goldman and I. Kleiner for valuable discussions about the CH_3CN partition function. Thanks also to J. Margolis, L. Brown, and again C. Rinsland for laboratory spectra from Kitt Peak. Work at AER was supported by the NASA Atmospheric Chemistry Modeling and Analysis Program. Work at the Jet Propulsion Laboratory, California Institute of Technology, was performed under a contract with the National Aeronautics and Space Administration. Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries ...
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