CIMS is an acronym for the Chemical Ionization Mass Spectrometer.  Dave Tanner from Georgia Tech knows this instrument inside out.  Ambient air enters the system under a controlled flow, taking samples every 3 seconds.  The gases are reacted with Sulfur hexaflorine (SF6-) which form ionized products.  These ionized products enter the mass spectrometer and it will detect which compounds are present. The instrument can analyze for size and hence filter for selected compounds. One of the compounds that Dave is hopeful to find is Bromine Oxide, BrO-.

     Dave Tanner and a mass spectrometer

    Mass spectrometer
    Dave Tanner and his mass spectrometer

    If you have been reading these journals, you already know that the scientists calibrate their instruments frequently.  In this instrument the ambient air is scrubbed and then sampled.  This scrubbed value is subtracted from the ambient value to determine the concentration of the various compounds in the air. It is hard enough to detect the small quantities of Bromides (parts per trillion), so the instrument must be able to measure accurately. Dave Tanner and the photochemistry team are trying to understand oxidation of gases in the air and interaction with the snow.