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Secondary Aerosol Formation from Atmospheric Gas and Particle Phase Reactions of Toluene

Secondary Aerosol Formation from Atmospheric Gas and Particle Phase Reactions of Toluene. Di Hu and Richard Kamens. Funded by the USEPA STAR program: July 30, 2003 to July 29, 2006 Dr. Darrell Winner project monitor. Department of Environmental Science and Engineering, UNC, Chapel Hill.

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Secondary Aerosol Formation from Atmospheric Gas and Particle Phase Reactions of Toluene

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  1. Secondary Aerosol Formation from Atmospheric Gas and Particle Phase Reactions of Toluene Di Hu and Richard Kamens Funded by the USEPA STAR program: July 30, 2003 to July 29, 2006 Dr. Darrell Winner project monitor Department of Environmental Science and Engineering, UNC, Chapel Hill

  2. A simple “efficient” multi-phase chemical mechanism for predicting secondary organic aerosol formation from toluene atmospheric reactions

  3. Volatile aromatic compounds comprise up to 45% of the atmospheric volatile hydrocarbon mixture, in urban US and European locations

  4. 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 are in the range of 2x 106 tons/year.

  5. Laboratory studies show that gas phase reactions ofaromaticsform a host of oxygenates   secondary organic aerosol material (SOA) • hydroxy unsaturated dicarbonyls • OH keto-carboxylic acids • Nitrated hydroxy carbonyls

  6. %yieldbenzaldehyde 8 creosols 18glyoxal 12methylglyoxal 12benzoquinone 6nitro-toluenes 2 Major products (Calvert et al., 2002)

  7. Edney and Keindienst et al, 2001

  8. Historically “lumped” aromatickinetic models have focused on Ozone formation: look at the CB4 mechanism (Gery 1989, Jeffries 2002)

  9. { TOLUENE CHEMISTRY… CB4 } OH + TOL = 0.08 XO2 + 0.36 CRES + 0.44 HO2 + 0.56TO2 TO2 + NO = 0.90*NO2 + 0.90*HO2 + 0.90*OPEN TO2 = CRES + HO2 OH + CRES = 0.4 CRO + 0.60 XO2 + 0.60 HO2 + 0.30 OPEN OPEN = C2O3 + HO2 + CO, OPEN + O3 = 0.03*RCHO + 0.62 C2O3 + 0.70 HCHO+ 0.03 XO2 + 0.69 CO + 0.08 OH + 0.76 HO2 + 0.2MGLY

  10. New aromatic SOA mechanisms: Craig Stroud, Paul Makar et al. (ES&T 2004) used the master mechanism (~300 gas phase reactions) to simulate Toluene and high NOx conc SOA organic nitrates dominate the particle phase Griffin et al. and Pun et al. (JGR 2002) modern aromatic mechanism; do not include particle phase reactions; have used it to simulate SOA trends on an airshed scale

  11. A simple reaction scheme for Toluene

  12. O=CH CH 3 CH OH 3 + H O 2 O + HO 2 benzaldehyde o-cresol CH 3 .CH 2 CH 3 OH OH OH H . H toluene CH CH CH 3 3 3 OH . OH NO . O 2 O +O H H 2 H H O NO oxygen bridge C7 diene-dial rearrangement OH H +O . O 2 H + HO 2 H ring cleavage O + radical H CH H OH 3 H butenedial pentenedial methylglyoxal, glyoxal O H NO NO 2 +O 2 * . + O2

  13. Reaction of 1st Generation pentene dicarbonyls

  14. TOPEN

  15. Maleic anhydride C5OHALD RALDNO3

  16. ROHACID C4KETALD Tracers

  17. New Mechanism has: 50 gas phase reactions 24 gas to particle phase “reactions” 16 particle phase reactions + CB4 (2002) chemistry

  18. After an initial nucleation, we are assuming that gas particle partitioning of products dominates the formation of new particle mass.

  19. 10 min 6 min 3 min bkg Post nucleation (SMPS data)

  20. Methyl glyoxal Gas phase reactions CH3-C-C=O CH3-C-C=O particle Gas and particle phases were then linked via G/P partitioning iCgas + surf  iCpart

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

  22. Glyoxal in the gas and particle phase H CH H H 3 methylglyoxal glyoxal Vapor pressures ~ 10 torr

  23. Glyoxal in the gas and particle phase (PFBHA)

  24. GLYgas + STSP  GLYpart500 x kon

  25. Kalberer et al. (Science, 2004) show that oligomerization occurs at a rapid rate in aerosol from 1,3,5 TriMe benzene + NOx + lightMGLY and GLY and other carbonyls may participate in this particle phase reaction Particle phase reactions

  26. Particle Phase Reactions GLY ----> GLYP @ 500*kon_glyT

  27. heat DMA1 DMA2 Smog chamber Volatile Tandem DMA system

  28. Plot volume fraction remaining vs. reaction time in the chamber 60% 50% Vol. remaining 40% 100oC 30% 1 2 3 4 5 6 hours Based on the tandem DMA experiments, which are interpreted to show oligomer formation over time, we calculated rates of formation

  29. Simulations solid lines: data dashed lines: model

  30. O3 NO NO2 0.15 ppm Toluene +0.42ppm Propylene in sunlight

  31. 1ppm Toluene + 0.33 ppm NOx O3 NO NO2

  32. Model simulation of TSP Data model

  33. TSP and SMPS particle mass SMPS Filter data

  34. NO O3 NO2 0.6ppm Toluene + 0.4 ppm NOx

  35. Fit to Toluene data model data

  36. Model simulation of TSP Data model

  37. Components of the particle phase (very, very tentative) %

  38. Experiments over a varity of temperature, light humidity conditions and lower concentrations Particle phase reactions types and rates of oligomer formation “Post Nucleation” rates Quantum yields and photolyis rates of product carbonyls Expansion of the mechanism to other aromatics What is next?

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