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Secondary Organic Aerosol Formation: Ozonolysis of Terpenes

Secondary Organic Aerosol Formation: Ozonolysis of Terpenes. George Marston , Yan Ma and Rachel Porter Department of Chemistry .

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Secondary Organic Aerosol Formation: Ozonolysis of Terpenes

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  1. Secondary Organic Aerosol Formation: Ozonolysis of Terpenes George Marston, Yan Ma and Rachel Porter Department of Chemistry

  2. "The American Petroleum Institute filed suit against the EPA [and] charged that the agency was suppressing a scientific study for fear it might be misinterpreted. The suppressed study reveals that 80 percent of air pollution comes not from chimneys and auto exhaust pipes, but from plants and trees." ‘79 "A tree is a tree. How many more do you have to look at?" '66 "Trees cause more pollution than automobiles do.” ‘88 Ronald Reagan

  3. Background • The ozonolysis of alkenes is important for atmospheric chemistry: • Oxidation of VOCs • Generation of radicals • Generation of oxygenated products Secondary Organic Aerosol (SOA)

  4. SOA Formation • Acid products from the ozonolysis of terpenes are components of SOA and may lead to particle formation • Health implications • SOA can have direct and indirect effects on climate change

  5. Alkene Ozonolysis Criegee Intermediate

  6. OH Formation

  7. Terpenes -pinene -pinene 3-carene terpinolene

  8. -Pinene Ozonolysis Products

  9. First step k1 (1  )k1

  10. Aims • To develop mechanisms for acid formation in terpene ozonolysis • To model results to provide input of rate constants and branching ratios for the Master Chemical mechanism • To determine which channel (CI) gives rise to which product • To determine branching ratios for decomposition of primary ozonides • To compare product yields from different terpenes

  11. Methodology Enone Enal

  12. Experimental • Static reaction chamber coupled to gas chromatography / mass spectrometry / flame ionisation detection • Acid products trapped on filters and derivatised to methyl esters (BF3/Methanol) • Enal and enone synthesised from ozonolysis of a suitable terpene

  13. -Pinene Results

  14. Enal Results

  15. Enone Results • Only Pinonic Acid and Norpinonic Acid are observed

  16. Enone Results

  17. Branching Ratio

  18. Pinonic Acid Formation

  19. -Pinene Summary

  20. 3-Carene Yields

  21. 3-Carene, Enone and Enal 3-carene Enal Enone

  22. 3-Carene and Enone

  23. 3-Caronic Acid Mechanism

  24. 3-Carene Summary

  25. -pinene

  26. Mechanism +RO2 -pinene -H2CO +O2 -pinene

  27. Pinalic-4-acid 92 % 8 % + Pinalic-3-acid Pinalic-4-acid

  28. Terpinolene 93 % 7 % + Terpinolalic Acid (a) Terpinolalic Acid (b)

  29. Hydroperoxide Formation 80 % 20 %

  30. Hydroperoxide Formation ? favoured over  ? Formation of hydroperoxide directly from quenching of nascent Criegee Intermediates?

  31. Summary • Ring opening in -pinene and terpinolene • Intramolecular reactions • Hydroperoxide formation • Improvements in mechanisms • Uncertainties: • Some quantitative data, but more needed

  32. Acknowledgements • Natural Environment Research Council • University of Reading • Dr Yan Ma • Dr David Johnson • Rachel Porter • Dr Andy Russell • Dr David Chappell • Tim Wilcox • Thomas Luciani

  33. Mechanisms

  34. Mechanisms

  35. Mechanisms

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