Secondary Organic Aerosol Secondary Organic Aerosol Formation from Gas and Formation from Gas and Particle Phase Reactions Particle Phase Reactions of Aromatic Hydrocarbons of Aromatic Hydrocarbons Di Hu Di Hu PhD Committee Meeting PhD Committee Meeting March 24, 2004 March 24, 2004
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Secondary Organic Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons Di Hu PhD Committee Meeting March 24, 2004.
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Secondary Organic Aerosol Secondary Organic Aerosol Formation from Gas and Formation from Gas and
Particle Phase Reactions of Particle Phase Reactions of Aromatic HydrocarbonsAromatic Hydrocarbons
Di HuDi HuPhD Committee MeetingPhD Committee Meeting
March 24, 2004March 24, 2004
Outline Outline
Why aromaticsWhy aromatics
SOA formation potential from SOA formation potential from aromaticsaromatics
Overall goal of my researchOverall goal of my research
In the US, transportation sources In the US, transportation sources contribute contribute ~67%~67% to the total aromatic to the total aromatic emissions which range from emissions which range from 1.9 x 101.9 x 1066 to to 2.4 x 102.4 x 1066 tons/year. tons/year.
Why aromatics?Why aromatics?Total US VOC Reactivity Budget
Composition, Chemistry, and Climate of the Atmosphere; New Composition, Chemistry, and Climate of the Atmosphere; New York, 1995York, 1995
Average Composition in 1ppmC Urban Air
Alkenes12%
Alkanes53%
Unspeciated
6%
Aldehydes2%
Aromatics27%
Jenkin et al. show that in their Jenkin et al. show that in their model calculations up to model calculations up to 40%40% of of photochemically produced photochemically produced ozoneozone can be attributed to emissions of can be attributed to emissions of aromatics in urban areas. aromatics in urban areas. (Atmos. Environ. 1996)(Atmos. Environ. 1996)
SOA Formation Potential of SOA Formation Potential of AromaticsAromatics
CH3
O
O
OH
CH3
O
OH
O
CHO CHO
OH
CHO
OH
O2N
CH3
O
O
OH
O
CH3
O
O
O
CH3
O
O
O
H
OO
H3C
H
O O
CH3
O
H
O
O
H
CH3
O
O
H
H
O
O
H
H
O
O
O
H
CH3
O
O
H
H
O
O
O
CH3
CH3
O
H
O
H
O
O
HO
O
H3C
OH
OHO
CH3
O
O
HO
H
O
O
OH
H
O
O
OCH3
O
OH
OOH
CH3
O
O
O
CH3
O
OH
OO
OH
OO
OH
CH3OH O
O
H
O
OH
CH3
O
OHO
H
O
H
OHO
CH3
O
H
OH
CH3 H
O
OH
O
H H
O
OH
O
H
CH3
O
O
H
OOH CH3
O
H
O
OH
OOO
OH
CH3H O
O
Aromatic aldehydes
Ring-retaining carbonyls
Ring-opening carbonyls
Ring-opening oxo-carboxylic acids
Ring-opeining hydoxy-carbonyls
SOA Formation Potential of SOA Formation Potential of AromaticsAromatics
Recent research has provided strong Recent research has provided strong evidence for polymerization evidence for polymerization reactionsreactions on aromatic aerosols. on aromatic aerosols.
This results in a much lower volatility This results in a much lower volatility SOA material and SOA material and higher aerosol higher aerosol yieldsyields than partitioning can predict. than partitioning can predict.
Evidences for Polymer Evidences for Polymer Formation in SOA from the Formation in SOA from the
Photo-oxidation of Photo-oxidation of Aromatics/NOx SystemAromatics/NOx System
FTIR Spectra of Toluene and FTIR Spectra of Toluene and Glyoxal AerosolsGlyoxal Aerosols
Slide from Dr. Myoseon Jang Slide from Dr. Myoseon Jang
-0.004
0.000
0.004
0.008
0.012
0.016
0.020
0.024
0.028
0.032
0.036
0.040
8001200160020002400280032003600
wavelength (cm-1)
ab
so
rban
ce (
gly
oxal)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
ab
so
rban
ce (
tolu
en
e)
Glyoxal/Acid-Catalyst
OH & COOH
15
59
, N
O217
25
, C
=O
16
45
, O
NO
2
13
40
, N
O2
12
82
, O
NO
2 s
t
C-O
-C s
tretc
h
Toluene/NOx
(NH
4)2
SO
4, 1
10
0
Toluene/NOx/Acid-Catalyst
Kalberer et al. recently have identified Kalberer et al. recently have identified polymers as the main constituents of polymers as the main constituents of SOA formed from the photo-oxidation SOA formed from the photo-oxidation of 1,3,5-trimethylbezene, which of 1,3,5-trimethylbezene, which account for about account for about 50%50% of the aerosol of the aerosol mass after 30 hours of aging. mass after 30 hours of aging. ((Science, 2004Science, 2004))
LDI-TOFMS Spectrum of SOA from LDI-TOFMS Spectrum of SOA from Photo-oxidation of 1,3,5-Photo-oxidation of 1,3,5-
TrimethylbezeneTrimethylbezene
Time Evolution of Polymer in Time Evolution of Polymer in SOA Measured by LDI-MSSOA Measured by LDI-MS
Overall Goal of This ProjectOverall Goal of This Project
Integrate particle phase Integrate particle phase heterogeneous processes with gas heterogeneous processes with gas phase reaction as a unified, multi-phase reaction as a unified, multi-phase, chemical reaction phase, chemical reaction mechanism, which will ultimately mechanism, which will ultimately permit the prediction of amounts of permit the prediction of amounts of SOA that result from aromatics SOA that result from aromatics reacting in the atmosphere.reacting in the atmosphere.
Overall ApproachOverall Approach
Kinetic mechanism developmentKinetic mechanism development
Simulation of chamber experimentsSimulation of chamber experiments
Gas Phase ReactionsGas Phase Reactions
Toluene react with OHToluene react with OH
OCH3
OHO
.
Recent research from Mario Molina’s Recent research from Mario Molina’s group has shown that the pathway to group has shown that the pathway to form epoxide radicals are neglectable.form epoxide radicals are neglectable.
Existing MechanismsExisting Mechanisms
Carbon BondCarbon Bond
Carter’s MechanismCarter’s Mechanism
Master Chemical MechanismMaster Chemical Mechanism
Do these reactions well represent what Do these reactions well represent what really happens in the particle phase?really happens in the particle phase?
The Outdoor Chamber Reactor The Outdoor Chamber Reactor SystemSystem
Hanging TeflonHanging Teflon
Dual 270mDual 270m33 chamber chamber fine particle t fine particle t 1/21/2 >17 h >17 h
Product AnalysisProduct Analysis
Toluene/propylene/NOx/sunlight Toluene/propylene/NOx/sunlight chamber experiments were carried chamber experiments were carried out with neutral seed and acidic out with neutral seed and acidic seed. seed.
Analytical MethodsAnalytical Methods
DerivatizationDerivatization methods to identify methods to identify the the precursors of polymersprecursors of polymers..
LC-ESIMS/MSLC-ESIMS/MS to identify to identify structure of structure of polymers. polymers.
PFBHA PFBHA O-(2,3,4,5,6-O-(2,3,4,5,6-pentafluorobenzyl) -hydroxylamine for pentafluorobenzyl) -hydroxylamine for
carbonyl groupscarbonyl groups
FF
F
F F
CH2 O NH2
H2O
PFBHA
R1
C
O
R2
CH2
F F
F
FF
ONC
R1
R2
acetone or ketone
PFBBrPFBBr, Pentafluorobenzyl bromide , Pentafluorobenzyl bromide derivatization for carboxylic and aromatic-OHderivatization for carboxylic and aromatic-OH
CH2 C
O
OH
H3C CH3
C
O
H O
FF
F
F F
CH2Br
C CH2
O
HO C O CH2
F F
F
FF
OH3C CH3
HBr
PFBBr
C CH2
O
O C O CH2
F F
F
FF
OCH3 CH3
CH2
FF
F
F F
2 HBr
The three slides are from Prof. Rich KamensThe three slides are from Prof. Rich Kamens
BSTFA BSTFA for hydroxyl, and/or carboxylic for hydroxyl, and/or carboxylic groupsgroups
Too ambitious to measure the rate Too ambitious to measure the rate coefficient of each single particle phase coefficient of each single particle phase reaction.reaction.
Cross reaction of the multi-functional Cross reaction of the multi-functional aldehydesaldehydes
Many products are not commercially Many products are not commercially available.available.
Do chamber experiment with different toluene and Do chamber experiment with different toluene and NOx concentrations at different RH and NOx concentrations at different RH and temperature.temperature.
Measure particle mass, acidity and HNO3 in particle Measure particle mass, acidity and HNO3 in particle phase.phase.
Explore relationships that influence rates of Explore relationships that influence rates of particle formationparticle formation– particle HNO3particle HNO3– RH and temperatureRH and temperature
Overall ApproachOverall Approach
Kinetic mechanism developmentKinetic mechanism development