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(15-36) DRIFTS Studies of Heterogeneous Reactions of Atmospheric Reservoir Gases on Ice and Acid Hydrate Surfaces. Zellner, Reinhard*,1, 1 Institute for Physical and Theoretical Chemistry, University of Essen, Essen, Germany ABSTRACT- Under cold conditions the atmosphere contains a number of different particles, liquid and solid, with different chemical composition. They present a surface or solvent for reactions which may not be possible between the same species in the gas phase. Heterogeneous processes of gas phase species on aerosol surfaces represent a mechanism for the removal of gaseous species and a means for their chemical transformations i. e. the conversion of nitrogen oxides in the gas phase (i.e. denitrification, formation of HONO). The adsorption on these surfaces will change their physical and chemical characteristics and the reactivity towards further reactions with gas phase species. We present Diffuse Reflectance Infrared Spectroscopy (DRIFTS) as a useful method to obtain both, qualitative and quantitative information about surface processes. Our experimental investigations were focussed on the reactions of gas phase species (NO, NO2, N2O5, HNO3, HCl) on pure ice surfaces and on amorphous and crystalline hydrates of HCl, HNO3 and H2SO4. These surfaces may be considered to be representative water-ice stratospheric clouds (type II PSC) or cirrus clouds as well as type I PSC. The reactions were studied in a continuous slow flow apparatus which combines the DRIFTS experimental set-up as well as the analysis of the gas-phase using FTIR spectroscopy. The solid surfaces were generated on the temperature-controlled object-slider which contains a reference material with a high reflectance. The gas phase species, diluted in a carrier gas, pass the thin frozen surface and the transformation of the solid surface and of the gas phase is analyzed in-situ. We will present the results of the mechanism and reactivity of heterogeneous processes. The reaction order concerning the gas phase species, the reaction products and the sequence of the reactivity of the reaction of gas-phase species on different solid surfaces will be reported. Key words: DRIFTS, PSC |
