9711923 Hoffmann Carbonyl sulfide (COS) is the primary reduced-sulfur source of sulfuric acid in the stratosphere, and is the most abundant sulfur compound in the atmosphere. The production of sulfuric acid aerosol from carbonyl sulfide involves the photodissociation of COS and oxidation by oxygen to yield sulfur dioxide, which, in turn, is oxidized by hydroxyl radicals to sulfuric acid. Sulfuric acid condensation leads to the formation of aerosols. The stratospheric sulfate aerosol layer influences the earth's radiation budget. It is proposed that certain reaction pathways that link the global sulfur and nitrogen cycles (via the oxidation of COS and reduction of nitric acid) may play an important role in the heterogeneous chemistry of the upper troposphere and lower stratosphere, and may affect the ratios of NOy to NOx in the upper troposphere. In this project, the bulk-phase kinetics, mechanisms, and thermodynamics of selected reactions and processes involving COS in concentrated sulfuric acid solutions will be investigated over a broad range of temperature and solute conditions. Reactions of COS with water (acid-catalyzed hydrolysis), protonated hydrogen peroxide, nitronium ion, sulfate radical anion, and nitrate radical will be studied. Secondary research objectives include: the determination of the speciation of binary sulfuric acid/water systems and ternary sulfuric/nitric acid/water systems as a function of temperature, composition, and thermal history, the determination of the acidic strength of the perhydroxonium ion and protonated COS, and the determination of the effective Henry's Law constants for hydrogen peroxide and carbonyl sulfide. Experimental techniques to be employed include multi-wavelength rapid-scan stopped-flow spectrophotometry, long path-length laser absorption spectroscopy in a liquid-phase cryogenically-controlled White cell configuration, Raman spectroscopy, time-resolved Raman spectroscopy, and attenuated total reflectance FTIR.
