Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Photoprocessing of Pyruvic Acid in the Earth’s atmosphere

Kathryn L. Plath, Kaito Takahashi, Rex T. Skodje, and Veronica Vaida

Pyruvic acid is a ketoacid produced in the atmosphere from biogenically emitted organic compounds through photochemical oxidation. It has been observed in the gas-phase, in collected aerosols, and in rainwater. Furthermore, it has been measured in continental and marine atmospheres. Pyruvic acid, as well as other ketoacids, is known to be a good nucleating agent for aerosols and clouds.We propose a new mechanism for the photoprocessing of pyruvic acid. Using visible light to promote the molecule into a vibrational overtone of the OH stretch, the molecule possesses enough energy to surmount the barrier for a unimolecular reaction. This reaction is facilitated by the hydrogen bond present in the stable conformer of the molecule. The process involves excitation by red photons of the OH stretching vibrational manifold of the ground electronic state at energies sufficiently high to exceed the transition state for reaction. The early time dynamics for photodecarboxylation of pyruvic acid has been studied spectroscopically by analysis of frequencies, intensities, and bandwidths of the OH stretching vibrational overtone transitions. As evidence of this reaction we have data showing early time dynamics using cavity ring-down spectroscopy to illustrate the lifetimes of these overtones. Additionally, we have photochemical data of increased carbon dioxide produced upon photolysis with low energy photons.