9414843 Anderson Several key areas of atmospheric chemistry suffer from a lack of data on reaction rate coefficients and reaction mechanisms, especially in the conditions (pressure, temperature, and composition) of the Earth's atmosphere. These areas include (1) many of the reactions that limit the rate at which natural and anthropogenic free radicals in the stratosphere destroy ozone, (2) vital reactions that couple the chemical cycles of oxygen, nitrogen, and hydrogen throughout the troposphere and stratosphere, and (3) the mechanisms by which dimethylsulfide is oxidized in the remote atmosphere to form sulfate aerosols. In addition, many aspects of a comprehensive theory explaining the relative reactivity of molecules with free radicals are still not well developed. One objective of this research is to allow investigators to test simultaneous observations of many of the species central to atmospheric chemistry in order to determine whether laboratory chemistry agrees with atmospheric observations. Tests of this sort are currently hindered more by incomplete kinetic data than any other cause,particularly at the pressures (10 - 200 torr) and temperatures (185- 250 Kelvin) found in the upper troposphere and lower stratosphere. The investigators will employ a technique known as high pressure flow kinetics to probe numerous key reactions over the full range of tropospheric and lower stratospheric temperatures, pressures, and compositions. This technique, simultaneously avoids complicating wall reactions and extends the range of flow tube kinetics to atmospheric pressure. By avoiding wall reactions, experiments can be performed at temperatures far lower than previously obtainable. A second objective is enhanced knowledge of the oxidation pathways of dimethyl sulfide (DMS). DMS, a naturally occurring sulfur compound emitted from the ocean surface into the marine atmosphere, is the most important naturally occurring sulfur species in the atmosphere. It is believed to be the source of most of the aerosol particles in the marine atmosphere; these particles, in turn, serve as condensation nuclei for marine clouds. It has been postulated that the availability of these condensation nuclei affects the albedo of clouds, and thus that changes in DMS production caused by global climate change could in turn lead to further climate forcing, either ameliorating or worsening the initial effect. The sulfate aerosols also directly scatter a small portion of the incoming solar radiation away from the Earth's surface. The investigators will focus on three key points in a proposed DMS oxidation sequence in a effort to reconcile atmospheric observations with laboratory measurements. A key aspect of the work will be the observation of both reactant and product species in the reactions being studied. Fluorescence and absorption measurement of free radicals will be combined with high resolution Fourier transform infrared spectroscopy, which will allow simultaneous measurement of many species. The addition of a mass spectrometer will allow the detection of otherwise undetectable species at low concentrations, particularly in the DMS system.
