HR: 0830h
AN: A21E-1030    [PDF]
TI: Measurements of Oxygen Atom Uptake Coefficients on Powdered Mineral Oxide Surrogates for Meteoritic Dust
AU: * Boulter, J E
EM: james.boulter@sri.com
AF: SRI International, Molecular Physics Laboratory 333 Ravenswood Avenue, Menlo Park, CA 94025 United States
AU: Marschall, J
EM: jochen.marschall@sri.com
AF: SRI International, Molecular Physics Laboratory 333 Ravenswood Avenue, Menlo Park, CA 94025 United States
AB: The atomic oxygen density increases by greater than two orders of magnitude between 70 km and 100 km, making it the dominant reactive species in the mesosphere and lower thermosphere. At the same altitude, mineral dust particles resulting from the condensation of ablated meteoric material provide sites for surface-mediated reactions. Heterogeneous oxygen atom recombination may influence the total odd oxygen budget and compete with other proposed heterogeneous oxygen atom reactions. Knudsen cell experiments are performed to quantify the oxygen atom uptake coefficient ($\gamma$) on two meteoritic dust surrogates, Fe$_{2}$O$_{3}$ and Mg$_{2}$SiO$_{4}$. Oxygen atoms are admitted to a low-pressure reactor (where the gas mean free path is larger than characteristic cell dimensions) in which the loss of reactants to a sample surface competes with escape through an exit orifice. Steady state oxygen atom concentrations are measured by multiphoton laser-induced fluorescence and mass spectrometry. Uptake coefficients are measured by utilizing exit orifices of varying size in either the presence or absence of a temperature-controlled powder sample. Measurements must be corrected for the total participating area of the powder, which may differ from the geometric area by orders of magnitude. Highly porous powders typically used in Knudsen cell experiments possess morphologies and pore structures that are very difficult to characterize. However, the incorporation of experimentally determined parameters such as the specific surface area and effective diffusion coefficient can lead to improved surface area corrections. Experimentally determined uptake coefficients will be presented, along with modeling results supporting the experimental approach.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0340 Middle atmosphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting