The Role of Isoprene in Secondary Organic Aerosol Formation 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? 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)

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

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.

Isoprene Contributes to SOA Formation 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

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

? 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

Reaction Procedure 1. Combine isoprene in aqueous buffer with metal/dust and/or first generation products (Methyl Vinyl Ketone/Methacrolein) 2. Place stir bar inside the vial 3. Expose vials to light source on a stir plate 4. Analyze reaction products using Gas Chromatography-Mass Spectrometry (GC-MS)

What would the results mean? 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

GC-MS Sample Preparation 1. Mix EtOAc with our sample 2. Vortex samples to mix 3. Centrifuge for 10 minutes 4. Pipet 100 μL EtOAc layer into GC-MS vials 5. Run through the GC-MS instrument

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

Previous Isoprene Research at Oak Crest Undergraduate Researchers: Howard Yan and Natalie De Vries Howard & Natalie Energy Source UV Lamp Time 3 hours Rationale Concentrated light source likely to cause reaction

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

New Experiments To Simulate Atmospheric Conditions Howard & Natalie Our Group Energy Source UV Lamp Sunlight Time 3 hours 6-7 hours Rationale Concentrated light source likely to cause reaction Simulate atmospheric conditions

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

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

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

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

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

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

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

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

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 ??

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.) ??

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