Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa71a..09b&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SA71A-09
Physics
0305 Aerosols And Particles (0345, 4801), 0322 Constituent Sources And Sinks, 0340 Middle Atmosphere: Composition And Chemistry
Scientific paper
Inconsistencies have been noted between model predictions and observations of mesospheric composition in narrow regions of the mesosphere. Several arctic rocket campaigns between 1978 and 1993 have observed oxygen atom "bite-outs," narrow layers just below 85 km depleted in atomic oxygen, correlated with NLC observations1. Separate observations from the HALOE instrument on UARS indicated the presence of a band of enhanced water vapor centered near 70 km at mid-latitudes that has not yet been adequately explained by current HOx models2. Because the upper mesosphere and lower thermosphere (MLT) contains a variety of surfaces such as ice particles and ablated meteoric dust, heterogeneous reactions might influence these observed phenomena. Reactions currently being considered are the recombination of oxygen atoms to form molecular oxygen and the reaction of molecular hydrogen with atomic oxygen to form water. To investigate these possible surface-mediated reactions, Knudsen cell experiments have been performed to quantify the oxygen atom recombination coefficient on mineral oxide powders representative of meteoritic composition. Oxygen atoms, produced by means of a microwave frequency discharge, and reagent gases are admitted to a low-pressure, well-mixed reactor in which the loss of the reactant species to a sample surface competes with escape through an exit aperture. Steady state reactant and product concentrations are measured by laser-induced fluorescence and mass spectrometry. By varying the area of the exit orifice in the presence or absence of the surface or reagent gases being investigated, atomic oxygen loss coefficients (γ) can be derived and then related to specific heterogeneous chemical reactions. Preliminary values will be reported for surface-mediated oxygen loss coefficients on several dust surrogates at room temperature and at pressures characteristic of the mesopause region. 1 Gumbel, J., Murtagh, D. P. Espy, P. J., Witt, G., and Schmidlin, F. J., J. Geophys. Res., 103, 23,399-23,413 (1998). 2 Summers, M. E, and Siskind, D. E., Geophys. Res. Lett., 26, 1937-1840 (1999). This work is supported by the Aeronomy and Atmospheric Chemistry Programs of the National Science Foundation, the Ionospheric, Thermospheric and Mesospheric Physics Program of the National Aeronautics and Space Administration, and the Postdoctoral Program in Environmental Chemistry of the Henry and Camille Dreyfus Foundation.
Boulter James E.
Marschall Jochen
Spangler E. L.
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