ACE-FTS observations of acetonitrile in the lower stratosphere

This work reports the first infrared satellite remote-sensing measurements of acetonitrile (CH3CN) in the Earth's atmosphere using solar occultation measurements made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) between 2004 and 2011. The retrieval scheme uses new quantitative laboratory spectroscopic measurements of acetonitrile (Harrison and Bernath, 2012). Although individual ACE-FTS profile measurements are dominated by measurement noise, median profiles in 10° latitude bins show a steady decline in volume mixing ratio from ~150 ppt at 11.5 km to <40 ppt at 25.5–29.5 km. These new measurements agree well with the scant available air- and balloon-borne data in the lower stratosphere. An acetonitrile stratospheric lifetime of 73 ± 20 yr has been determined.