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

1. 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 formationA “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

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 ofaromaticsandbiogenics 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 50 - 80% of the aerosolorganic 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 OC/EC O3 Pittsburgh, 2001

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

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

14. 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…..

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

22. Pent-dione + OH 0.5 pent-rad +0.5 pent-oo pent-oo XO2 + 0.5 GLY+ 0.5 MGLY + 0.5 CO + 0.5HO2 +0.25 OHoxybutal +0.25 but-tricarb pent-rad  Maleic + 1.5 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

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

27. CH3-C-C=O O kon koff particle kon koff • [ igas] + [part] [ipart] Kp = 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 acida-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 cis-pinonaldhyde Gas phase reactions C=O C=O O O polymers particle

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

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

38. The Outdoor Chamber Reactor System

40. Hanging Teflon

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

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

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

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

46. Normalized to one O pinonaldehyde O Pinonaldehyde quantum yields in sunlight CH3CH2CH2=O CH2=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 cresol maleic anhydride 43 AROMATIC reactions + Carbon 4