Atmospheric ozone seems to be increasing in the troposphere (where it causes air pollution and is directly toxic to plants), but decreasing in the stratosphere (where it shields the Earth's surface from harmful solar ultraviolet radiation). We have long recognized the critical role played by ozone in the lower and middle atmosphere, but only recently have come to understand some aspects of the cycles that control its formation and destruction. This proposal deals with a series of experimental projects designed to determine critical kinetic and photochemical parameters involving ozone chemistry. The latter include the yield of electronically excited oxygen atoms following 0.3 photolysis above 300 nm (of importance in the troposphere) and below 250 nm (vital in the upper stratosphere). Reactivity of the highly labile atomic product with H.20 and HCI will also be examined, with a view toward elucidating the detailed mechanisms by which such reactions occur. Such studies will be vital in developing a comprehensive understanding of photochemical interferences in proposed detection schemes of atmospheric OH by laser.induced fluorescence. Also planned are refinement of off.diagonal LIF techniques for detection of OH and O.2, the latter including direct measurements of excited state predissociation lifetimes (on a picosecond time scale|) critical to the quantification of observed spectra. In addition, we shall continue our initial efforts in which the techniques of molecular simulation on a supercomputer are applied to the mechanistic examination of reactions not conveniently studied in the laboratory. Together, these laboratory and computer experiments will support the development of field techniques and mathematical models used to integrate our understanding of ozone's behavior in the increasingly perturbed atmosphere.
