Bildung und Reaktionen von Oxidantien in fluessiger Phase Abschlussbericht

Abstract

In the course of the project numerous kinetic, spectroscopic and photochemical parameters for formation processes and reactions of oxidants in aqueous solution have been determined in laboratory investigations. By means of a newly developed laser-photolysis/long-path-laser-absorption experiment kinetic parameters for reactions of the nitrate radical in aqueous solution have been determined. It was found that not only temperature, but also pH and ionic strength strongly influence the rate of degradation of common cloudwater constituents. This finding is of importance because tropospheric cloud droplets undergo multible condensation-evaporation cycles during their lifetime leading to strong variations with regards to acidity as well as to ionic strength. Absolute quantum yields for the formation of OH radicals in the photolysis of aqueous solutions of NO_3"-, NO_2"- and H_2O_2 were determined at 308 and 351 nm as a function of pH and temperature. OH quantum yields were determined by a radical scavenger technique using the fast reaction between OH and SCN"- leading to the formation of (SCN)_2"- which was analysed by time-resolved visible absorption measurements. In the course of this project partial photolytic lifetimes for nitrate, nitrite and hydrogen peroxide were determined based on the measured quantum yields, the absorption coefficients of the precursors and the actinic flux within cloud droplets. An excimer laser photolysis-broadband-diode array absorption experiment was developed and extensive tests and experiments were performed on the photochemical generation and spectroscopic characterization of OH in aqueous solution. The experimental apparatus developed is a new and versatile instrument for the time- and spectrally- resolved study of aqueous phase reactions of transient species. The apparatus was applied for detailed studies of the UV-Vis absorption spectra of SO_x"-(x = 3,4,5), Cl_2"- and CO_3"-. Furthermore, numerous kinetic parameters for reactions of the fore-mentioned radical anions were derived. (orig.)SIGLEAvailable from TIB Hannover: F95B792+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman