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Keutsch Group Meeting September 24 2008 Andy Huisman

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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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Photochemical modeling as a means of understanding field atmospheric measurements: preliminary data and observations.

Keutsch Group Meeting

September 24 2008

Andy Huisman

glyoxal background
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

model measurement disparity
Model / Measurement Disparity
  • Model under-predicts SOA growth
  • Growing deviation of model over time
photochemical modeling
Photochemical Modeling

http://irina.eas.gatech.edu/lectures/lec29fig3.jpg

simplified kinetics
Simplified Kinetics
  • Photochemistry is first or second order
  • Coupled reactions: suppose
translating ideas to formulae
Translating ideas to formulae

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

complications
Complications: =

783 Terms

760 Compounds

master chemical mechanism
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 ;

master chemical mechanism1
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
tools of the trade
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)
compiling the mcm into matlab
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>

compiling the mcm into matlab1
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=

compiling the mcm into matlab2
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=

computational tricks
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
additions to mcm
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
additions to mcm1
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
additions to mcm2
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?
computation steps
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
graphical representations
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

caltech chamber summary
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
caltech chamber data
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)

future directions
Future Directions
  • Add lateral transport and vertical mixing for BEARPEX data
  • Evaluate overlap integrals for Caltech photolysis
  • Fix midnight discontinuity
future directions1
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?
acknowledgements
Acknowledgements
  • Keutsch Research Group
  • Master Chemical Mechanism
  • BEARPEX / Caltech Collaborators
  • UW – Madison Chemistry Department
  • NDSEG / ARO