HR: 1340h
AN: A33B-1188    [Abstracts]
TI: O₂⁺ as Reagent ion in the PTR-MS Instrument: Detection of Gas-phase Ammonia
AU: Wisthaler, A
EM: armin.wisthaler@uibk.ac.at
AF: Institute of Ion and Applied Physics, University of Innsbruck, Technikerstrasse 25, Innsbruck, 6020, Austria
AU: Norman, M
EM: michael.norman@slb.nu
AF: Institute of Ion and Applied Physics, University of Innsbruck, Technikerstrasse 25, Innsbruck, 6020, Austria
AU: Norman, M
EM: michael.norman@slb.nu
AF: now at: Environment and Health Administration, Stockholm City, Box 8136, Stockholm, 10420, Sweden
AU: * Hansel, A
EM: armin.hansel@uibk.ac.at
AF: Institute of Ion and Applied Physics, University of Innsbruck, Technikerstrasse 25, Innsbruck, 6020, Austria
AB: Oxygen was used as a source gas in a conventional Innsbruck PTR-MS instrument to produce O₂⁺ ions as chemical ionization (CI) reagents instead of H₃O⁺ ions. The use of O₂⁺ ions as CI reagents allows for fast, highly sensitive and specific measurements of gas-phase ammonia (NH₃) via the electron transfer reaction O₂⁺ + NH₃ -> NH₃⁺ + O₂. The instrument was tested to be linear in the 2 to 2000 ppbv range. Instrument sensitivity was observed to be humidity-independent and amounted to ~40 cps/ppbv. The instrumental background was determined by sampling NH₃-free air from a heated platinum/palladium catalyst. A humidity-dependent increase of the instrumental background from 70 pptv at dry conditions to 470 pptv at humid conditions was observed. The corresponding 2σ-detection limits at 1 s signal integration time were 90 pptv for dry conditions and 230 pptv for humid conditions, respectively. The observed background may be intrinsically formed in the ion source but it may also be the result of incomplete NH₃ oxidation in the catalyst used for zeroing. The reported background levels and detection limits are thus to be considered as upper limits. The 1/e response time of the instrument was in the range of 3 to 5 s. The PTR-MS instrument was successfully deployed in the field to monitor changes in gas-phase NH₃ concentrations in the few seconds to tens of seconds time range. Laboratory and field intercomparison measurements between the PTR-MS instrument and a commercial NH3 analyzer (AiRRmonia) were in good agreement. The use of O₂⁺ ions as CI reagents will significantly improve the analytical capabilities of the Innsbruck PTR-MS instrument.
DE: 0394 Instruments and techniques
DE: 0452 Instruments and techniques
DE: 0469 Nitrogen cycling
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting