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Secondary Organic Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons

Secondary Organic Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons. Di Hu PhD Committee Meeting March 24, 2004. Outline. Why aromatics SOA formation potential from aromatics Overall goal of my research. Sources of Aromatics. Anthropogenic Sources

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Secondary Organic Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons

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  1. Secondary Organic Aerosol Formation from Gas and Particle Phase Reactions of Aromatic Hydrocarbons Di Hu PhD Committee Meeting March 24, 2004

  2. Outline • Why aromatics • SOA formation potential from aromatics • Overall goal of my research

  3. Sources of Aromatics • Anthropogenic Sources Transportation Solvent use Fuel combustion • In the US, transportation sources contribute ~67% to the total aromatic emissions which range from 1.9 x 106 to 2.4 x 106 tons/year.

  4. Why aromatics? • Composition, Chemistry, and Climate of the Atmosphere; New York, 1995

  5. Toluene23.5% m,p-Xylene 12.6% 1,2,4-Trimetylbenzene 8.5% Benzene7.4% Composition, Chemistry, and Climate of the Atmosphere; New York, 1995 Why aromatics?

  6. Jenkin et al. show that in their model calculations up to 40% of photochemically produced ozone can be attributed to emissions of aromatics in urban areas. (Atmos. Environ. 1996)

  7. SOA Formation Potential of Aromatics Sunlight + OH highly oxygenated gas phase products NOx 2-hydroxy-3-oxobutanal Particle

  8. Jang & Kamens, ES&T 2001

  9. Kleindienst et al., 2004

  10. SOA Formation Potential of Aromatics • Recent research has provided strong evidence for polymerization reactions on aromatic aerosols. • This results in a much lower volatility SOA material and higher aerosol yields than partitioning can predict.

  11. Evidences for Polymer Formation in SOA from the Photo-oxidation of Aromatics/NOx System

  12. FTIR Spectra of Toluene and Glyoxal Aerosols Slide from Dr. Myoseon Jang

  13. Kalberer et al. recently have identified polymers as the main constituents of SOA formed from the photo-oxidation of 1,3,5-trimethylbezene, which account for about 50% of the aerosol mass after 30 hours of aging. (Science, 2004)

  14. LDI-TOFMS Spectrum of SOA from Photo-oxidation of 1,3,5-Trimethylbezene

  15. Time Evolution of Polymer in SOA Measured by LDI-MS 2.5hrs 3.5hrs 4.5hrs 6.5hrs methylglyoxal oligomers mixture of methylglyoxal, formaldehyde, 2,5-dimethylbenzaldehyde, and pyruvic acid

  16. Overall Goal of This Project • Integrate particle phase heterogeneous processes with gas phase reaction as a unified, multi-phase, chemical reaction mechanism, which will ultimately permit the prediction of amounts of SOA that result from aromatics reacting in the atmosphere.

  17. Overall Approach • Kinetic mechanism development • Outdoor chamber experiments • Simulation of chamber experiments

  18. Gas Phase Reactions

  19. Toluene react with OH Epoxy Radical Isomerization Bicyclic Radical Bicyclic Alkoxy Radical 1st generation products

  20. Recent research from Mario Molina’s group has shown that the pathway to form epoxide radicals are neglectable.

  21. Existing Mechanisms • Carbon Bond • Carter’s Mechanism • Master Chemical Mechanism

  22. Toluene react with OH Bicyclic Radical Bicyclic Alkoxy Radical 1st generation products

  23. 'C7H8' + OH ---->0.72*'CH3-C6H5(OH)-OO.' + 0.1*'C6H5CO-H' +0.18*'CRESOL’ +0.28*HO2+0.1*XO2 @ 1.18E-12* EXP(338.0/TK) 'CH3-C6H5(OH)-OO.' + NO ---->0.55*'H-CO-CH=CH-CO-H‘ +0.11*'CH3-CO-CH=CH-CO-H'+0.34*'H-CO-C(CH3)=CH-CO-H'+0.55*'CH3-CO-CO-H' + 0.45*'H-CO-CO-H'+ NO2 +HO @8.1E-12

  24. Reaction of 1st Generation Product

  25. 'CH3-CO-CH=CH-CO-H' + OH ----> 0.2*('CH3-CO-CH=CH-CO-O2.‘ +H2O) + 0.4*'OXOCYL_RAD' + 0.2*'CH3-CO-CH(OH)-CH(OO.)-CO-H' + 0.2*'CH3-CO-CH(OO.)-CH(OH)-CO-H' @ 5.58E-11 'OXOCYL_RAD' + NO -O2-> 'Maleic anhydrid' + 'CH3.' + NO2 @ 3.0*k_MEO2_NO 'CH3-CO-CH(OH)-CH(OO.)-CO-H' + NO ---->0.13*C5OHNO3 + 0.87*('CH3-CO-CH(OH)-CH(O.)-CO-H' + NO2)@ 0.71*k_MEO2_NO 'CH3-CO-CH(OH)-CH(O.)-CO-H' + O2 ----> 0.3*(C4OHALD + CO + H2O) + 0.5*('CH3-CO-CO-H'+ 'H-CO-CO-H'+ HO2) + 0.2*(C5OHALD+ HO2) @ k_DEC

  26. 2nd Generation Gas Phase Products

  27. 3rd Generation Gas Phase Products

  28. Simulation Results of Gas Phase Chemistry

  29. Particle Formation Processes • G/P Partitioning • Particle Phase Reactions

  30. G/P Partitioning • Kp =kon/koff = 7.501RTfom/(109Mwgp0L) • koff=kbT/h exp(-Ea/RT) • kbT/h = 6.211012 sec-1 at 298K • Relate Ea to log poL • kon=KPkoff kon koff Particle

  31. To Represent These Processes in the Mechanism

  32. C4OHALDgas + SEED ----> C4OHALDpart+ SEED @ kon C4OHALDgas + TSP ----> C4OHALDpart + TSP @ kon C4OHALDpart ----> C4OHALDgas @ koff

  33. Particle Phase Reactions

  34. Particle Phase Reactions big molecule

  35. Particle Phase Reactions Polymers

  36. GlyP + H2O ----> Gly2OHP @ kpart1 Gly2OHP + H2O ----> Gly4OHP @ kpart2Gly4OHP + GlyAcidP ----> pre-Poly1 @ kpart3Pre-Poly1 + C4OHALD ----> Poly1 @ kpart4 • Do these reactions well represent what really happens in the particle phase? • Particle phase reaction rate coefficients

  37. Outdoor Chamber Experiments

  38. The Outdoor Chamber Reactor System

  39. Hanging Teflon

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

  41. Product Analysis

  42. Toluene/propylene/NOx/sunlight chamber experiments were carried out with neutral seed and acidic seed.

  43. Analytical Methods • Derivatization methods to identify the precursors of polymers. • LC-ESIMS/MS to identify structure of polymers.

  44. PFBHA O-(2,3,4,5,6-pentafluorobenzyl) -hydroxylamine for carbonyl groups aldehyde or ketone

  45. P F B B r F F H C C H 3 3 O O H C H C O H C O F C H B r 2 2 F F F F H C C H O 3 3 O C H C O C H F H O C H B r 2 2 F F F F F F C H C H O O 3 3 C H C O C H F O C 2 H B r F C H 2 2 2 F F F F PFBBr, Pentafluorobenzyl bromide derivatization for carboxylic and aromatic-OH

  46. B S T F A c a r b o x y l i c a c i d C F o r a l c o h o l 3 C N R O H S i ( C H ) ( C H ) S i 3 3 O 3 3 ( C H ) S i O 3 3 R BSTFA for hydroxyl, and/or carboxylic groups The three slides are from Prof. Rich Kamens

  47. BF3-CH3OH + BSTFA Derivatization Method Citramalic acid GC-ITMS analysis - electron impact ionization (EI) - methane chemical ionization (CI-methane) - tandem mass spectrometry (MS/MS) Slide from Dr. Mohammed Jaoui

  48. Particle Phase Reaction Rate Coefficients • Too ambitious to measure the rate coefficient of each single particle phase reaction. • Cross reaction of the multi-functional aldehydes • Many products are not commercially available.

  49. Simple methyglyoxal experiments (daytime/NOx, nighttime) • Do chamber experiment with different toluene and NOx concentrations at different RH and temperature. • Measure particle mass, acidity and HNO3 in particle phase. • Explore relationships that influence rates of particle formation • particle HNO3 • RH and temperature

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