The Role of Isoprene in Secondary Organic Aerosol Formation

Alfonso CastellanosEvan Jones

Jenny WeiPaul Fang

Summer Research Connection SeminarOak Crest Institute of Science8/12/2011

Isoprene

Aerosols are EverywhereWhat 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

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

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

?

Isoprene

Secondary Organic Aerosols

?

Isoprene

Secondary Organic Aerosols

Methyl Vinyl Ketone

Methacrolein

Reaction Procedure

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

???

Time (t)A

bund

ance

1

21. Gas Chromatography

separates compounds2. Mass Spectrometry

fragments compounds

2 2

m/z

Abu

ndan

ce

m/z

Abu

ndan

ce

m/z

Abu

ndan

ce

How GC-MS Can Be Used to Identify Compounds

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

Howard Yan, Natalie De Vries

+

+

Isoprene

Isoprene

Methacrolein

MVK

+Dust

+ Dust

Methacrolein dimer

???

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

Isoprene + TiO2 + MVKIsoprene + TiO2

+

Isoprene pH 6 MVK

+/- ??

Retention time = 7.4 min

Isoprene pH 6 + MVK + dustIsoprene pH 5 + MVK + dust

+

Isoprene pH 5 or 6

+

MVK MVK dimer

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

Reaction A Isoprene

+MVK

+Dust or TiO2

Reaction B Isoprene

+MVK

+Dust or TiO2

Reaction C Isoprene

+MVK

No light No metal catalyst

Controlling Light Intensity For Each Reaction

First Round of Experiments Control Experiments

Isoprene + MVK (no light)*Isoprene + MVK + dust (no light)Isoprene + MVK + dust (light)Isoprene + MVK (light)

Isoprene pH 6

+/-

MVK

+

*Sample not exposed to heat or light

MVK dimer

Isoprene + MVK + TiO2 (light)Isoprene + MVK +TiO2 (no light)Isoprene + MVK (light)Isoprene + MVK (no light)*

+

Isoprene pH 4

+/-

MVK

*Sample not exposed to heat or light

??

MVK + TiO2

MVK +TiO2 + Isoprene

Isoprene Control Reaction

+

IsopreneMVK

+/- ??

• 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

Conclusions

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.)

??

AcknowledgementsMentor: Marc Baum

Oak Crest Institute of ScienceHoward YanNatalie De VriesSean Kennedy John Moss

Summer Research ConnectionSherry TsaiJames Maloney

Family

SponsorsNational Science FoundationHoward Hughes Medical Institute Siemens Foundation