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Keutsch Group Meeting September 24 2008 Andy Huisman

Photochemical modeling as a means of understanding field atmospheric measurements: preliminary data and observations. Keutsch Group Meeting September 24 2008 Andy Huisman. Glyoxal Background. Smallest α -dicarbonyl Biogenic & anthropogenic sources Tracer for and agent of SOA growth *

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Keutsch Group Meeting September 24 2008 Andy Huisman

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  1. Photochemical modeling as a means of understanding field atmospheric measurements: preliminary data and observations. Keutsch Group Meeting September 24 2008 Andy Huisman

  2. Glyoxal Background • Smallest α-dicarbonyl • Biogenic & anthropogenic sources • Tracer for and agent of SOA growth* • Included in local and global photochemistry models • Recent measurements: satellites, DOAS, DNPH • LIP (Keutsch Group) * Volkamer et al. GRL 2007 L19807

  3. Model / Measurement Disparity • Model under-predicts SOA growth • Growing deviation of model over time

  4. Photochemical Modeling http://irina.eas.gatech.edu/lectures/lec29fig3.jpg

  5. Simplified Kinetics • Photochemistry is first or second order • Coupled reactions: suppose

  6. Translating ideas to formulae Adapted from Fu, T.-M., et al.JGR,113, D15303, doi:10.1029/2007JD009505, 2008

  7. Complications: = 783 Terms 760 Compounds

  8. Master Chemical Mechanism • Nearly explicit database of 135 VOCs • Provides a list of reactions and rates: % 6.9D-11*0.67 : MBO + OH = MBOAO2 ; % 6.9D-11*0.33 : MBO + OH = MBOBO2 ; % 1.4D-15*0.65 : MBO + NO3 = NMBOAO2 ; % 1.4D-15*0.35 : MBO + NO3 = NMBOBO2 ; % 8.6D-18*0.7 : MBO + O3 = IBUTALOH + CH2OOB ; % 8.6D-18*0.3 : MBO + O3 = HCHO + MBOOOA ; % 2.54D-11*EXP(410/TEMP)*0.164 : OH + C5H8 = ISOPAO2 ; % 2.54D-11*EXP(410/TEMP)*0.491 : OH + C5H8 = ISOPBO2 ; % 2.54D-11*EXP(410/TEMP)*0.086 : OH + C5H8 = ISOPCO2 ; % 2.54D-11*EXP(410/TEMP)*0.259 : OH + C5H8 = ISOPDO2 ; % 3.03D-12*EXP(-446/TEMP) : NO3 + C5H8 = NISOPO2 ;

  9. Master Chemical Mechanism • Nearly explicit database of 135 VOCs • Provides a list of reactions and rates Goals: • Develop a way to harness the information • Adaptive to changing data sets • Minimize human error • Meaningful calculations • Organize and display very large datasets

  10. Tools of the Trade • TUV Model (NCAR) – photolysis rates • MCM (Leeds) – kinetics + reactions • HOx + NOx cycling – Seinfeld & Pandis • Raw data (BEARPEX & Caltech) • Initialize & drive concentrations • Check accuracy of un-driven molecules • Matlab - computation engine (ode23tb)

  11. Compiling the MCM into Matlab • Fully automated compiling process • Loading through pattern recognition • Creates a new record for each molecule • Appends the reaction to existing statement % 6.9D-11*0.67 : MBO + OH = MBOAO2 ; k = 6.9e-11*0.67r{1} = MBO r{2} = OH p{1} = MBOAO2 Find “MBO” MBO=-J<1>*<MBO> MBO=-J<1>*<MBO>-6.9e-11*0.67*<OH>*<MBO>

  12. Compiling the MCM into Matlab • Fully automated compiling process • Loading through pattern recognition • Creates a new record for each molecule • Appends the reaction to existing statement % 6.9D-11*0.67 : MBO + OH = MBOAO2 ; k = 6.9e-11*0.67r{1} = MBO r{2} = OH p{1} = MBOAO2 Find “OH” OH=-6.9e-11*0.67*<OH>*<MBO> OH=

  13. Compiling the MCM into Matlab • Fully automated compiling process • Loading through pattern recognition • Creates a new record for each molecule • Appends the reaction to existing statement % 6.9D-11*0.67 : MBO + OH = MBOAO2 ; k = 6.9e-11*0.67r{1} = MBO r{2} = OH p{1} = MBOAO2 Find “MBOAO2” MBOAO2=+6.9e-11*0.67*<OH>*<MBO> MBOAO2=

  14. Computational Tricks • Matlab optimized for matrix math • Generate 2nd order terms by A(i,j,k)xC(n)xC(m) • Size(A)=760x760x760 – too large for Matlab • Pseudo-first order approach: ±10% CPU time

  15. Additions to MCM • Deposition • Crosslisted FACSIMILE and SMILES names • MBO ↔ C=CC(C)(C)O • MBOAO2 ↔ OCC(O[O])C(C)(C)O • C5H8 ↔ C=CC(=C)C • Unambiguous determination of functional groups • Deposition rate based on literature rates if available • Boundary Layer (BEARPEX only) • Loss to aerosol

  16. Additions to MCM • Deposition • Boundary Layer (BEARPEX only) • Assume 100 m nighttime, 800 m daytime • Drive height with scaled photolysis of NO2 • kDEP= (vdep / BL) x [A] if BL is well mixed • Loss to aerosol

  17. Additions to MCM • Deposition • Boundary Layer (BEARPEX only) • Loss to aerosol • kAER • Estimate Surface Area • 1. Use measured aerosol number density & size • 2. Use measured aerosol mass & size • Effect of relative humidity?

  18. Computation Steps • Load and compile reactions (10 minutes) • Add deposition if necessary (2 minutes) • Load and condition field data (1 minute) • Initialize conc. from data (1 minute) • Equilibrate intermediate species (2 days) • Production run (5 days) • CPU Time ≈ Model Time

  19. Multi-Day Production Data

  20. Multi-Day Simulation

  21. Graphical Representations Rate x 1x105 (cm-3 s-1) / N (cm-3) C58O Decomposition HOCH2CHO + OH Photolysis and OH-oxidation } C58O figure courtesy MCM website

  22. Overnight Decays

  23. Overnight Decays

  24. Caltech Chamber Summary • MBO Photooxidation • Black lights ≈ 0.06 x the sun? • OH from HONO • High NOx • Low RH% • Ignore • Deposition to walls • Loss to aerosol phase

  25. Caltech Chamber Data - JHONO

  26. Caltech Chamber Data - NOx

  27. Caltech Chamber Data - GLYOX

  28. Caltech Chamber Data Percent Yield:MCMMBOAO2: 67%MBOAO: 65%HOCH2CHO: 65%GLYOX: <13% Prelim. ModelHOCH2CHO: >44%GLYOX: <2% (high NOx) ES&T PaperGLYOX: 22% (high NOx)

  29. Future Directions • Add lateral transport and vertical mixing for BEARPEX data • Evaluate overlap integrals for Caltech photolysis • Fix midnight discontinuity

  30. Future Directions • OH recycling at low NOx • Scale GL aerosol loss at low RH% • Reversibility of GL uptake? • Source apportionment • Which molecules dominate GL production? • Which sources drive GL-related photochemistry? • Is the “morning spike” photochemically generated?

  31. Acknowledgements • Keutsch Research Group • Master Chemical Mechanism • BEARPEX / Caltech Collaborators • UW – Madison Chemistry Department • NDSEG / ARO

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