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Photoxidation products of alpha-pinene: Role of terpenes in cloud nucleation

Photoxidation products of alpha-pinene: Role of terpenes in cloud nucleation. PASI Workshop Caltech, Pasadena Jan 16,2004. Why does it rain in the rainforest?.

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Photoxidation products of alpha-pinene: Role of terpenes in cloud nucleation

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  1. Photoxidation products of alpha-pinene: Role of terpenes in cloud nucleation PASI Workshop Caltech, Pasadena Jan 16,2004

  2. Why does it rain in the rainforest?

  3. The importance of this project is to generate thermodynamical data (i.e: equilibrium constant and enthropy change) to understand the role of monoterpenes in cloud nucleation over conifer forests.

  4. Outline • Background info. • Results • Conclusions • Acknowledgements

  5. Background info. • Terrestrial vegetation releases terpenes to the atmosphere • Monoterpenes are highly reactive and undergo free-radical addition with O3 • Photo-oxidations of terpenes and isoprene yield products, which partially remain in the gas phase • Some less volatile photo-oxidation products partition between the gas phase and particulate phases, accumulate in the condense phase and, thus contribute to the ambient particulate mass.

  6. More background info……. • Alpha and beta pinene are typical biogenic terpenes produced over conifer forests. • Their photoxidation products are thought to play an important role in nucleation of water. http://czech.ifas.ufl.edu/content/Hydrology/warm.html

  7. Pinonic Acid • Pinonic acid is formed by photoxidation of alpha-pinene in presence of ozone • DATA Formula: C10H16O3 Molecular Weight: 184.23 ∆Gº=Gº pinonic- (Gº a-pinene+Gº ozone) Keq= e-∆Gº/RT

  8. Pinic Acid • Pinic acid is formed by photoxidation of alpha-pinene in presence of ozone • DATA Formula: C9H14O4 C10H16 + 5/3O3 C9H14O4 + HCHO ∆Gº=Gº pinic- (Gº a-pinene+5/3Gº ozone)

  9. Chemical Equilibrium Constants Kp(T)

  10. Data treatment Geometry Optimization utilizing Force Fields UFF Geometry Optimization utilizing DFT Becke 3:P86 Basis set: 6-311G** Frequency calculations utilizing HF Basis set: 6-31G*

  11. Method validation 1 NIST

  12. Results Equilibrium constant for trans- and cis-pinonic acid and cis-pinic acid

  13. Results ∆S for trans- and cis-pinonic acid and cis-pinic acid

  14. Conclusions • Pinic acid is more abundant than any pinonic acid isomer due to its higher equilibrium constant, as reported by Jenkin (2000) • Cis-pinonic acid is more abundant than trans-pinonic acid because its equilibrium constant is higher. This data coincides with a study made by O’Dowd (2002) • The enthropy change of the photoxidation of alpha-pinene to yield pinic and pinonic acid is negative due to the reduction of number of free molecules (i.e: ozone). The process enthropy for the formation of the cis- product is higher due to steric hinderance. It’s lower for pinic acid because of the stoichiometry of the reaction.

  15. Future studies • Calculate the thermodynamical data for trans-pinic acid. • Calculate the thermodynamical data for other subproducts of the photoxidation of alpha-pinene and beta-pinene. • Study the role of the major subproducts in cloud nucleation.

  16. References • O'Dowd, C.D., Aalto, P., Hameri, K., Kulmala, M. and Hoffmann, T.  2002.  Atmospheric particles from organic vapours.  Nature416: 497-498 • Jenkin, M.E., Shallcross, D.E. and Harvey, J.N. 2000. Development and application of a possible mechanism for the generation of cis-pinonic acid from the ozonolysis of alpha and beta-pinene. Atmospheric Environment 34: 2837-2848

  17. Acknowledgements • We would like to thank: • Dr. Mario Blanco from Caltech • Dr. Sergio Aragon from UCSF • NSF

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