1. Department of Environmental Science and Engineering UNC, Chapel Hill
Secondary Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons
Richard Kamens and Di Hu
Funded by the USEPA STAR program July 30, 2003 to July 29, 2006
Department of Environmental Science and Engineering
UNC, Chapel Hill

2. The overall goal of this project is to represent new chemistry as a unified, multi-phase, chemical reaction mechanism that will explain the observed chemical phenomena and amounts of secondary organic aerosol that result from aromatics reacting in an urban atmosphere.

3. Current Approaches do not incorporate newly discovered particle phase heterogeneous reactions that lead to significant SOA formation A “next generation” chemical mechanistic approach is needed that captures the essence of the fundamental chemistry that leads to secondary aerosol formation

4. Volatile aromatic compounds comprise a significant part of the urban hydrocarbon mixture in the atmosphere, up to 45% in urban US and European locations
If an alcohol happened to be present hemiacetal and acetal formation could also take place after acid catalysis.
Note that the ultimate result in this case is conversion of the aldehyde carbonyl to hydroxy and alkoxy groups.
In addition to hydration and polymerization, if alcohols are present hemiacetal and acetal formation may take place on the protonated carbonyls.
If we take at look at the aldehyde SOA from the bag experiments in the IR region we are able to see evidence of these types of transformations.

5. Toluene, m- & p-xylenes, benzene and 1,2,4-trimethyl benzene, o-xylene and ethylbenzene make up 60-75% of this load. In the US, transportation sources contributed ~67% to the total aromatic emissions which range from 2.4 x 106 to 1.9 x 106 tons/year.

6. Laboratory studies show that gas phase reactions of aromatics and biogenics form a host of oxygenates   secondary organic aerosol material (SOA)
hydroxy unsaturated dicarbonyls
di and tri carboxylic acids
Nitrated hydroxy carbonyls

7. Is there Atmospheric Evidence for SOA formation??

8. Turpin and co-workers
In the LA area estimated on smoggy days {from OC /EC ratios}, that as much as % of the aerosol organic carbon comes from secondary aerosol formation (1984 and 1987 samples)
On average, organic carbon can make up between 10-40% of the total fine TSP in the US

10. Spyros Pandis also recently looked at OC/EC ratios (Pittsburgh area)
He estimates that SOA formation can account for 35-50% of the organic carbon

11. OC/EC Ratio and Photochemical Activity
Pittsburgh, 2001

12. In the context of this work, how much of this SOA comes from aromatic emissions in to an airshed?

13. kinetic mechanism development outdoor chamber experiments Tolune,
Overall Approach
kinetic mechanism development
outdoor chamber experiments
Tolune,
m-xylene
1,3 5 trimethyl benzenes
Simulation of chamber experiments

14. kinetic mechanism development
Overall Approach
kinetic mechanism development
Illustrate this with a simple reaction scheme of toluene

19. Now let me go back and explain in detail each of the reaction steps in the previous three slides.
No, shoot me if I start…..
If an alcohol happened to be present hemiacetal and acetal formation could also take place after acid catalysis.
Note that the ultimate result in this case is conversion of the aldehyde carbonyl to hydroxy and alkoxy groups.
In addition to hydration and polymerization, if alcohols are present hemiacetal and acetal formation may take place on the protonated carbonyls.
If we take at look at the aldehyde SOA from the bag experiments in the IR region we are able to see evidence of these types of transformations.

20. * toluene O2 . . OH oxygen bridge rearrangement butenedial
O=CH CH 3 OH
+ HO 2
+ H O
o-cresol
benzaldehyde CH 3 OH 2 . NO +O H * O2 +
toluene CH 3 H OH O . NO 2 +O
rearrangement
oxygen bridge OH H O . +O 2 CH 3 +
methylglyoxal
butenedial
+ HO
ring cleavage
radical

22. Pent-dione + OH 0.5 pent-rad +0.5 pent-oo
pent-oo  XO GLY+ 0.5 MGLY
+ 0.5 CO HO OHoxybutal
+0.25 but-tricarb
pent-rad  Maleic XO2 + HO2 + HCHO

23. Aromatic Aldehydes
Ring Aldehydes
Ring opening carbonyls
Oxo acids
OH-carbonyls

24. Edney and Keindienst et al, 2001

25. Historically, from a Modeling perspective Equilibrium Organic Gas-particle partitioning has provided a context for addressing SOA Formation
If an alcohol happened to be present hemiacetal and acetal formation could also take place after acid catalysis.
Note that the ultimate result in this case is conversion of the aldehyde carbonyl to hydroxy and alkoxy groups.
In addition to hydration and polymerization, if alcohols are present hemiacetal and acetal formation may take place on the protonated carbonyls.
If we take at look at the aldehyde SOA from the bag experiments in the IR region we are able to see evidence of these types of transformations.

26. Gas and particle phases can be linked via G/P partitioning
Methyl glyoxal
Gas phase reactions
CH3-C-C=O
1Cgas + surf  1Cpart
CH3-C-C=O
particle

27. Kp = kon/koff kon koff [ igas] + [part] [ ipart] kon koff particle
CH3-C-C=O O
[ igas] + [part] [ ipart]
Kp = kon/koff
kon
koff

29. Particle Phase reactions
Polymerization reactions

30. Particle Phase Reactions
+ ozone + acid seeds  aerosols
a-pinene

31. ESI-QTOF mass spectrum of SOA from reaction of a-pinene with ozone + acid seed aerosol.

32. Particle phase pinonaldehyde dimers from acid a-pinene +O3
M Na+ (ESI-QTOF Tolocka et al, 2003)

33. Particle Phase Reactions

34. GlyP + H2O ----> Gly2OHP Gly2OHP + H2O ----> Gly4OHP Gly4OHP + GlyAcidP ----> pre-Poly1 Pre-Poly1 + C4OHALD ----> Poly1

35. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
polymers
particle

36. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
particle
polymers

37. Particle Phase reactions
Gas phase reactions
C=O O
cis-pinonaldhyde
C=O O
polymers

38. The Outdoor Chamber Reactor System

40. Hanging Teflon
It took all of us to put up each panel of the Teflon walls.

41. Dual 270m3 chamber fine particle t 1/2 >17 h

42. Rates of polymerization. methylglyoxal +NOx chamber. experiments
Rates of polymerization methylglyoxal +NOx chamber experiments these rates may be related to HNO3 gas phase and associated particle HNO3

44. Quantum yields. dicarbonyls. multifunctional carbonyls. Liu et al
Quantum yields dicarbonyls multifunctional carbonyls Liu et al. 1999–adsorption cross sections

45. Pinonaldehyde quantum yields in natural sunlight
kphototyis = S ( al fl Il )
By adding pinonaldehyde to the chamber in clear sunlight in the presence of an OH scavenger and measuring its rate of decay
fl can be fit to the decay data assuming a shape with wave length similar to other aldehydes

46. Pinonaldehyde quantum yields in sunlight
Normalized to one
pinonaldehyde
CH3CH2CH2=O
CH2=O O
pinonaldehyde
CH3CH2=O

47. An Exploratory Chemical Model
Toluene + propylene + NOx + Sunlight  gas phase prod. + SOA

48. hexadiene-dicarb. butene-dicarbonyl. pentene-dicarbonyl. benzaldehyde
hexadiene-dicarb butene-dicarbonyl pentene-dicarbonyl benzaldehyde cresol maleic anhydride 43 AROMATIC reactions Carbon 4

51. carbonyl-PAN C4-carbonyl-acid butane-tricarbonyl OH-oxobutanal polymer1

52. A second generation Model

53. A second generation Model

57. Analysis

58. PFBHA O-(2,3,4,5,6-pentafluorobenzyl) -hydroxylamine for carbonyl groups

59. PFBBr, Pentafluorobenzyl bromide derivatization for carboxylic and aromatic-OH2 O 3 F B r P

60. BSTFA for hydroxyl, and/or carboxylic groups( 3 )

61. BF3-CH3OH + BSTFA Derivatization Method
Citramalic acid
GC-ITMS analysis
- electron impact ionization (EI)
- methane chemical ionization (CI-methane)
- tandem mass spectrometry (MS/MS)

62. What are some challenges?
Photolysis reactions of the 2nd and 3rd products
Quantum yields of product carbonylsParticle phase reactions
Wall reactions of the products
Integration of particle phase reactions
GC-Ion-trap analysis
ES-LCMS-MS

63. Aerosol sampling???
Presently methods to simultaneously measure gas and particle SVOCs have artifacts?
We need an new generation of analytical techniques…