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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


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