HR: 0830h
AN: A21E-1028    [PDF]
TI: Miniature chemical ionization mass spectrometer for light aircraft measurements of tropospheric ammonia
AU: Silver, J A
AF: Southwest Sciences, Inc., 1570 Pacheco Street, Suite E-11, Santa Fe, NM 87505 United States
AU: Bomse, D S
AF: Southwest Sciences, Inc., 1570 Pacheco Street, Suite E-11, Santa Fe, NM 87505 United States
AU: Massick, S M
AF: Southwest Sciences, Inc., 1570 Pacheco Street, Suite E-11, Santa Fe, NM 87505 United States
AU: * Zondlo, M A
EM: mzondlo@swsciences.com
AF: Southwest Sciences, Inc., 1570 Pacheco Street, Suite E-11, Santa Fe, NM 87505 United States
AB: Tropospheric ammonia plays important roles in the nucleation, growth, composition, and chemistry of aerosol particles. Unfortunately, high frequency and sensitive measurements of gas phase ammonia are lacking in most airborne-based field campaigns. Chemical ionization mass spectrometers (CIMS) have shown great promise for ammonia measurements, but CIMS instruments typically consume large amounts of power, are highly labor intensive, and are very heavy for most airborne platforms. These characteristics of CIMS instruments severely limit their potential deployment on smaller and lighter aircraft, despite the strong desire for ammonia measurements in atmospheric chemistry field campaigns. To this end, a CIMS ammonia instrument for light aircraft is being developed using a double-focusing, miniature mass spectrometer. The size of the mass spectrometer, comparable to a small apple, allows for higher operating pressures (0.1 mTorr) and lower pumping requirements. Power usage, including pumps and electronics, is estimated to be around 300 W, and the overall instrument including pumps, electronics, and permeation cells is expected to be about the size of a small monitor. The ion source uses americium-241 to generate protonated water ions which proton transfer to form ammonium ions. The ion source is made with commercially available ion optics to minimize machining costs. Mass spectra over its working range (~ 5-120 amu) are well represented by Gaussian shaped peaks. By examining the peak widths as a function of mass location, the resolution of the instrument was determined experimentally to be around 110 (m/delta m). The sensitivity, selectivity, power requirements, size, and performance characteristics of the miniature mass spectrometer will be described along with the possibilities for CIMS measurements on light aircraft.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0322 Constituent sources and sinks
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting