9321582 Tolbert Chemical reactions on type I polar stratospheric clouds (PSCs) are currently believed to be a key step in polar ozone destruction. Although type I PSCs are thought to be composed of nitric acid/water vapor (HNO3/H2O) mixtures, their exact chemical composition and phase are still uncertain. This research project will use infrared, visible, and ultraviolet spectroscopy to determine the chemical composition of type I PSCs. First, the optical constants for NHO3/H2O mixtures will be measured over a wide wavelength range for use in comparisons with field observations of type I PSCs. Laboratory studies of model type I PSC film growth will also be performed. These studies will use in situ FTIR spectroscopy as a probe of the chemical composition and phase of the condensed material during PSC nucleation and growth. In addition to using spectroscopy to identify PSCs, new spectroscopic experiments will study surface reactions on type I PSCs. The reaction of chlorine nitrate (CIONO2) with hydrochloric acid (HCl) on type I PSCs is currently believed to be the single most important heterogenous reaction promoting ozone loss. Previous work has shown that this reaction depends strongly on the relative humidity is increased. Large angle reflectance FTIR spectroscopy will be used to probe the surface reaction of CLONO2 with HCI on model type I PSC films. Surface spectroscopic probes of the condensed phase during should yield insight into the complex mechanism of this important heterogenous reaction. In addition to chemical reactions on PSCs, there is now heightened interest in heterogenous chemistry on the global stratospheric sulfate aerosol (SSA) layer. Chemical reactions on background and volcanic SSAs may be responsible for the down ward trend in ozone observed in the last decade. This project will investigate the chemical and physical properties of SSAs, composed primarily of sulfuric acid and water vapors (H2SO4) and(H2O). Spectroscopi c experiments will also be performed to characterize low temperature liquid and frozen sulfuric acid films representative of SSAs fro use in comparisons with field observations of SSAs. In addition, the chemical reactivity of SSAs will be studied. A combination of gas phase and condensed phase detection of reactants and products will be used to obtain a more complete picture of the condensed phase reactions. Initial studies will focus on the uptake and reactivity of HOx reservoir species in sulfuric acid as a function of composition and phase of the acid.
