Transcript PowerPoint Presentation - Atmospheric Photochemistry

The Role of Isoprene in Secondary
Organic Aerosol Formation
Isoprene
Summer Research Connection Seminar
Oak Crest Institute of Science
8/12/2011
Alfonso Castellanos
Evan Jones
Jenny Wei
Paul Fang
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
Isoprene:
• VOC emitted by plants
• SOA precursor
Isoprene
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
What reactants or catalysts are
necessary for isoprene to form
SOAs or SOA intermediates?
?
Isoprene
Secondary
Organic
Aerosols
?
Secondary
Organic
Aerosols
Isoprene
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 ChromatographyMass Spectrometry (GC-MS)
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
2
Abundance
1. Gas Chromatography
separates compounds
2. Mass Spectrometry
fragments compounds
m/z
Time (t)
2
2
Abundance
1
Abundance
???
Abundance
How GC-MS Can Be Used to Identify Compounds
m/z
m/z
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
+
Isoprene
+ Dust
+
Isoprene
Methacrolein dimer
Methacrolein
+
MVK
Dust
???
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
Isoprene pH 6
MVK
+
??
+/Isoprene + TiO2 + MVK
Isoprene + TiO2
Retention time = 7.4 min
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
Reaction A
Isoprene
+
MVK
+
Dust or TiO2
Reaction B
Isoprene
+
MVK
+
Dust or TiO2
No metal catalyst
Reaction C
Isoprene
+
MVK
Controlling Light Intensity For Each
Reaction
First Round of Experiments
Control Experiments
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
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
MVK
+
Isoprene
??
+/-
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
MVK dimer
• In the MVK and TiO2 reactions, the following
compound formed with or without isoprene
??
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
Family
Oak Crest Institute of Science
Howard Yan
Natalie De Vries
Sean Kennedy
John Moss
Sponsors
National Science Foundation
Howard Hughes Medical Institute
Siemens Foundation
Summer Research Connection
Sherry Tsai
James Maloney