Stratospheric CH3CN from the UARS microwave limb sounder

CH3CN in the stratosphere has been measured by the Microwave Limb Sounder ( MLS) on the Upper Atmosphere Research Satellite (UARS), providing the first global CH3CN dataset. The MLS observations are in broad agreement with pas t high and midlatitude observations of CH3CN, although concentrations are a little larger than previously observed. In the tropics, where CH3CN has no t up to now been measured, a persistent 'peak' in the profiles is seen arou nd 22hPa, which may be evidence of a tropical stratospheric CH3CN source. C omparisons are made with the NCAR SOCRATES model, including runs having an artificial tropical stratospheric CH3CN source.