Miniature Chemical Ionization Mass Spectrometer for Measuring Tropospheric Ammonia

Southwest Sciences proposes continuing development of an instrument for use on a lightweight aircraft capable of measuring tropospheric concentrations of ammonia. Gas phase ammonia plays important roles in determining the formation and composition of aerosol particles. Understanding the chemical and physical properties of aerosol particles is critical towards understanding global climate change, regional air pollution, and acid deposition. The instrument uses a state-of-the-art, miniature mass spectrometer that operates at higher pressures than conventional mass spectrometers, resulting in lower pumping, lighter weight, and consuming less power. In addition, the instrument uses chemical ionization mass spectrometry to obtain high selectivity, high sensitivity, and a low limit of detection (20 pptv). Phase I results have demonstrated excellent ion transmission from the chemical ionization source to the mass spectrometer. Phase II efforts will focus on optimizing the electrostatic lenses, inlet design, extensive calibration and background testing, data acquisition and analysis, and field-testing of the instrument. The expected prototype at the end of Phase II will measure ammonia at a frequency of 0.1-1 Hz and be the size of a computer monitor.