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Yunseok Im and Myoseon Jang October 25, 2011

Partitioning-Heterogeneous Reaction Consortium SOA model to Predict Aromatic SOA Formation in the Presence of NO x and SO 2. Yunseok Im and Myoseon Jang October 25, 2011 Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida. . Introduction

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Yunseok Im and Myoseon Jang October 25, 2011

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  1. Partitioning-Heterogeneous Reaction Consortium SOA model to Predict Aromatic SOA Formation in the Presence of NOx and SO2 YunseokIm and Myoseon Jang October 25, 2011 Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida.

  2. Introduction Secondary Organic Aerosol (SOA) SOA is formed by accommodation of organic compounds which are created from either atmospheric oxidation reactions associated with photochemical NOxcycles in the gas phase or particle phase heterogeneous reactions SO2 ---> H2SO4 Heterogeneous reactions Preexisting Acidic Inorganics Kp NH3 • SOA is major component of atmospheric carbon • (20~90% of Total organic Carbon)

  3. Aromatic hydrocarbons • Aromatics are major anthropogenic VOCs in urban area. • Source: Motor vehicles, Solvent use, Biomass burning • (20% of VOC emission from gasoline, Schauer et al, ES&T, 2002) • Concentration ranges of toluene in urban air : 2-39 ppb (Finlayson-Pitts and Pitts, 2000) Xylene Toluene

  4. Motivation Current SOA models (partitioning model) Under-predict the field observed SOA mass There are something more than partitioning process. Aerosol phase chemistry (Heterogeneous RXN) Oligomerization / Acid-catalyzed-heterogeneous RXN Effect of SO2 on SOA formation (Aromatics) (SO2 oxidation)

  5. PHRCSOA model (Partitioning-Heterogeneous Reaction Consortium SOA model)

  6. PHRCSOA Model Structure PHRCSOA (Partitioning-Heterogeneous Reaction Consortium SOA )model Model structure RH + Ox ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20 Gas Gas phase reaction products • MCM • MORPHO ij: Stoichiometric coefficient for product groups Aerosol Lumping of products OMP Partitioning SOA mass OMH Heterogeneous reaction SOA mass OMAC Acid-catalysis OMolg Oligomerization OMT Total Aerosol Mass OMT = OMP + OMH

  7. Example of Toluene oxidation of MCM • 776 reactions • 147toluene oxygenated products http://mcm.leeds.ac.uk/MCM/browse.htt?species=TOLUENE

  8. Lumping based on vapor pressure and reactivity Heterogeneous Reactivity (Fast, Medium, Slow, Partitioning only) i= 1 (10-6 mmHg) i= 2 (10-5mmHg) i= 3 (10-4mmHg) i= 4 (10-3mmHg) i= 5 (10-2mmHg) • Fivedifferent vapor pressuregroups i = 1, j = H-f i = 1, j = H-m i = 1, j = PO i = 1, j = H-s Cao and Jang, ES&T, 2009

  9. Toluene + Ox ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20 Slow Reactivity High Reactivity Less Volatile 147 PRODUCTS 20 LUMPING GROUPS Very Volatile

  10. The Effect of NOx on SOA formation NOx = 30 ppb NOx = 150 ppb Reactivity Reactivity Vapor pressure (mmHg) Vapor pressure (mmHg)

  11. The Effect of NOx on SOA formation • Gas kinetic model (MCM) simulation at various NOx (10-350ppb) α4,s α4,M α4,P

  12. PHRCSOA Model Structure Model structure RH + Ox ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20 Gas phase reaction products ij: Stoichiometric coefficient for product groups Lumping of products OMp Partitioning SOA mass OMH Heterogeneous reaction SOA mass OMAC Acid-catalysis OMolg Oligomerization OMT Total Aerosol Mass OMT = OMP + OMH

  13. SOA Model Concept GAS PHASE Non Gas kinetic model (MCM) SO2 oxidation H2SO4 ORGANIC PHASE 20 product lumping groups INORGANIC PHASE CP (OMP) Cgas KP Partitioning Cin Solubility Acid-Catalyzed Heterogeneous Oligomerization OMH • Phase separation (organic vs. Inorganic) • Inorganic phase – Acid-catalyzed RXN • Organic phase – Oligomerization (Non-volatile)

  14. Model Equations Schell et al., JGR, 2001 Modification of the mass balance equation used in CMAQ Where, = = Acid-catalysis Oligomerization Excess acidity Inorganic thermodynamics Basicity of organics lumping parameter

  15. Chamber experiments 52 + 52 = 104 m3 UF Atmospheric Photochemical Outdoor Reactor (UF-APHOR) dual chambers Toluene, P-Xylene (200ppb) NOx (30 ppb) SO2 (80 ppb) With/ without

  16. Toluene Gas phase simulation vs. Exp. Without SO2 Toluene O3 Temp: 16 – 42 oC RH : 10 – 33 % NOx With SO2 • Reasonably prediction • Toluene decay • O3 formation • NOxchemistry • Artificial OH radical • :2.0E+8 molecules cm-3s-1 • Bloss et al : 4.0E+8 • Cao et al: 4.0E+8 Toluene O3 SO2 NOx

  17. Toluene SOA simulation vs. Exp. Without SO2 Exp. OMT • Yield increase • : 20~40% OMP OMH Exp. With SO2 OMT OMP OMH

  18. Without SO2 P-xylene Gas phase simulation vs. Exp. P-Xylene O3 Temp: 14 – 41 oC RH : 9 – 35 % NOx With SO2 • O3 under-prediction • Artificial OH radical • :1.7E+8 molecules cm-3s-1 O3 P-Xylene SO2 NOx

  19. P-Xylene SOA simulation vs. Exp. Without SO2 Exp. • Yield increase • : 20~40% OMT OMP OMH Exp. With SO2 OMT OMP OMH

  20. Conclusion The model reasonably predicts the Experiments for Aromatics Gas kinetics : MCM SOA formation : PHRCSOA model. In the presence of SO2, 30 % yield increase for SOA from Toluene and P-xylene. Uncertainty of Model Accuracy of gas product prediction of MCM Solubility calculation of organic compounds on inorganic phase (inorganic phase was assumed as water)

  21. Future Work - Model evaluation for other individual SOA precursors. and the Mixtures of VOCs. - Application to the regional Air quality Model, CMAQ SOA module (partitioning and Heterogeneous OM)

  22. Thank you

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