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The Role of Isoprene in Secondary Organic Aerosol Formation

The Role of Isoprene in Secondary Organic Aerosol Formation. Isoprene. Alfonso Castellanos Evan Jones Jenny Wei Paul Fang. Summer Research Connection Seminar Oak Crest Institute of Science 8/12/2011. Aerosols are Everywhere. What are aerosols?

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The Role of Isoprene in Secondary Organic Aerosol Formation

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  1. The Role of Isoprene in Secondary Organic Aerosol Formation Isoprene Alfonso Castellanos Evan Jones Jenny Wei Paul Fang Summer Research Connection Seminar Oak Crest Institute of Science 8/12/2011

  2. Aerosols are Everywhere What are aerosols? • Small, particulate matter suspended in the atmosphere. Where do they come from? • Volcanic eruptions • Deserts • Biological activity • Saltwater bodies • Human activities (e.g. burning coal, oil, tropical forests)

  3. Why are Aerosols Important? Climate Change: • Scatter and absorb sunlight • Change the size of cloud particles • Components of acid rain Health Effects: • Harmful to cardiopulmonary health Chemical Effects: • Sites for chemical reactions

  4. Secondary Organic Aerosols (SOAs) Aerosols are produced from the atmospheric oxidation of volatile organic compounds (VOCs), which are emitted by plants, household products, and combustion of hydrocarbons.

  5. Isoprene Contributes to SOA Formation Isoprene: • VOC emitted by plants • SOA precursor Why study isoprene? • SOAs containing carbon skeletons similar to that of isoprene were found over forest regions • Contribution to SOA formation is of greater significance than previously assumed • Aside from methane, isoprene is the highest globally emitted VOC from biogenic sources • Mechanisms of isoprene photooxidation are not well understood Isoprene

  6. What reactants or catalysts are necessary for isoprene to form SOAs or SOA intermediates? ? Secondary Organic Aerosols Isoprene

  7. ? Secondary Organic Aerosols Isoprene Possible Reactants/Conditions to Test: • pH (4-7) • First generation isoprene oxidation products • Methyl Vinyl Ketone (MVK) • Methacrolein • Metal oxide • TiO2 • ZnO • Dust (sieved) Methacrolein Methyl Vinyl Ketone

  8. Reaction Procedure

  9. What results do we anticipate? • We anticipate a reaction will occur and we will detect new compounds in our reaction mixture that are not our starting materials What would the results mean? • If the new compounds we discover are SOAs, this will indicate that isoprene can, in fact, form SOAs through photocatalysis on dust or metal oxide surfaces

  10. GC-MS Sample Preparation

  11. How GC-MS Can Be Used to Identify Compounds ??? Abundance 1 2 2 2 Time (t) • Gas Chromatography separates compounds • Mass Spectrometry fragments compounds Abundance Abundance Abundance m/z m/z m/z

  12. Previous Isoprene Research at Oak Crest  Undergraduate Researchers:  Howard Yan and Natalie De Vries

  13. Results From Previous Research + + Dust Isoprene Methacrolein dimer Methacrolein + + Dust Isoprene MVK ??? Howard Yan, Natalie De Vries

  14. New Experiments To Simulate Atmospheric Conditions

  15. Isoprene pH 6 hν MVK ?? +/- TiO2 + Isoprene + TiO2 + MVK Isoprene + TiO2 Retention time = 7.4 min

  16. MVK dimer Isoprene pH 5 or 6 hν MVK dust + + Isoprene pH 6 + MVK + dust Isoprene pH 5 + MVK + dust Retention time = 8.0 min

  17. Preliminary Results Summary • Reactions with MVK and dust/TiO2 seem to form new products => Conduct control experiments: • are results repeatable? • does product formation require light? • does product formation require metal or dust? • As we started our second round of experiments, we discovered MVK dimer in our MVK solution

  18. Control Experiments No metal catalyst No light Reaction A Isoprene + MVK + Dust or TiO2 Reaction B Isoprene + MVK + Dust or TiO2 Reaction C Isoprene + MVK

  19. Controlling Light Intensity For Each Reaction First Round of Experiments Control Experiments

  20. Isoprene pH 6 MVK dimer MVK hν + dust +/- Isoprene + MVK (no light)* Isoprene + MVK + dust (no light) Isoprene + MVK + dust (light) Isoprene + MVK (light) *Sample not exposed to heat or light

  21. Isoprene pH 4 MVK hν + +/- TiO2 ?? Isoprene + MVK + TiO2 (light) Isoprene + MVK +TiO2 (no light) Isoprene + MVK (light) Isoprene + MVK (no light)* *Sample not exposed to heat or light

  22. MVK Isoprene hν TiO2 ?? Isoprene Control Reaction + +/- MVK + TiO2 MVK +TiO2 + Isoprene

  23. ?? Conclusions • In the MVK and dust reactions, light and dust seem to have an opposite effect on the degradation of MVK dimer • In the MVK and TiO2 reactions, the following compound formed with or without isoprene MVK dimer

  24. ?? Future Directions • Identify the product from the MVK and TiO2 reaction and investigate as candidate for SOA intermediate • Analyze the contents of the dust particles • Experiment with other variables • Different dust particles (volcanic, desert, etc.) • Longer periods of time (e.g. 2 days, 3 days, etc.)

  25. Acknowledgements Mentor: Marc Baum Oak Crest Institute of Science Howard Yan Natalie De Vries Sean Kennedy John Moss Summer Research Connection Sherry Tsai James Maloney Family Sponsors National Science Foundation Howard Hughes Medical Institute Siemens Foundation

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