Assessment of SAPRC07 with Updated Isoprene Chemistry against Outdoor Chamber Experiments

Yuzhi Chen 13th CMAS13th CMAS

Assessment of SAPRC07 with Updated Isoprene Chemistry against Outdoor

Chamber Experiments

Yuzhi Chena, Roger Jerrya, Kenneth Sextona, Jason Surratta, William Vizuetea

aUniversity of North Carolina at Chapel Hill

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13th Annual CMAS Conference, Chapel Hill, NC27 Oct 2014

Introduction


Motivation - Updated SAPRC07 in CMAQ

Xie et al. (2013) updated SAPRC07 with more explicit isoprene chemistry with additional OH and NO3 oxidation pathways that produce SOA precursors.

Isoprene epoxydiols (IEPOX)

OH/HO2 from Hydrox-peroxy aldehydes (HPALD)

Isoprene nitrates more explicit

Yuzhi Chen

[Xie et al., 2013, ACP]

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Updated isoprene oxidation scheme for isoprene + OH

Yuzhi Chen 13th CMAS13th CMAS 4

CMAQ runs suggest improved model performance

Uncertainties Remain: isoprene nitrates yield from ISOPO2 + NO pathway & NOX recycling efficiency

[Xie et al., 2013, ACP]

Objective

Can Xie model ozone?

How radical budgets and nitrogen cycling altered?


Methodologies

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Modeling:

MORPHO (UNC)

PERMM (Python-based Environment for Reaction Mechanisms/Mathematics)

UNC dual gas-phase chamber, Pittsboro, NC, 1994

Experimental:

24 isoprene runs

Compounds measured: O3, NOX, Isoprene,CO, HCHO…

Result


Model Performance

Ozone Peak

NO-NO2 crossover time time

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NO/NO2 Crossover Time

Mech NMB(%) R2

SAPRC07 -5.4 0.022

Xie -16.0 0.032

Mech NMB(%) R2

SAPRC07 -24.1 0.77

Xie -32.3 0.68

Lower NOXHigh NOX


NO/NO2 Crossover TimeLower NOXHigh NOX

Xie predicts earlier NO-NO2 crossover for all isoprene runs


• Xie is better• But not significant

• Both over-predict• Xie is worse

Ozone Peak

Mech NMB (%) R2 P value

SAPRC07 4.92 0.85 9.51E-06

Xie 11.08 0.76 1.42E-16

Mech NMB(%) R2 P value

SAPRC07 -9.79 0.13 0.38

Xie 0.58 0.14 0.36

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Lower NOXHigh NOX


Ozone Peak

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Xie predicts higher ozone for all isoprene runs

Lower NOXHigh NOX


Model Performance Summary

For All Runs:

Xie predicts earlier crossover

Xie predicts higher ozone

For Lower NOX experiments

Xie pushes the performance towards the wrong direction

However, statistics doesn’t tell us the story!

Case Study


O3, NOX, isoprene concentration times series

ISOP: 0.26 ppm, NOX: 0.45 ppm, (ISOP/NOX: 0.58)

ISOP: 1.26 ppm, NOX: 0.35 ppm (ISOP/NOX: 3.73)

0.75 ppm

0.97 ppm

0.61 ppm0.53 ppm

0.52 ppm

0.57 ppm

Lower NOX

0.53 ppm

0.64 ppm

0.85 ppm

High NOX


Reaction Rate of VOCs + OH

High NOX

ISOP: 1.26 ppm, NOX: 0.35 ppm (ISOP/NOX: 3.73)


Integrated Reaction Rate of VOCs + OH Lower NOXHigh NOX


OH conc.

HO2 from Aldehydes

Lower NOXHigh NOX


High NOx

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Why Xie makes more Ozone? Sources of NO2

Lower NOx

• High NOX — 65% NO2 made through NO + O3 for SAPRC07; 47% made through recycling from NOZ for Xie

• Lower NOX — 77% more NO2 recycled from NOZ for Xie


NO2 Recycling Rate

Yuzhi Chen

Xie predicts 64% more PANs than SAPRC07

Which accounts for 85% of the total increase in recycled NO2

Lower NOX

Summary


Xie predicts earlier NO-NO2 crossover time and higher ozone peak than original SAPRC07;

The cause is increased VOC + OH reactions and thus elevated HOX (OH & HO2) production from aldehydes;

Under low NOX condition, Xie goes in the wrong direction (bias 4.92% to 11.08%);

Over-prediction of second ozone peak driven by increased NO2 recycling from organic nitrates, mostly PANs (85%).

Modeling gas-phase SOA precursors (Methacrolein)

Incorporating the CMAQ SOA module into MORPHO and test the Xie mechanism against aerosol chamber experiments

Conclusion

Future Work


Acknowledgment

Yuzhi Chen

Special Thanks

Dr. William Vizuete, Dr. Jason Surratt, Dr. Ken Sexton, Dr. Evan Couzo, MAQ/CHAQ group, Dr. Harvey Jeffries, Dr. Harshal Parikh

We thank Dr. Ying Xie and Deborah Luecken at EPA for providing the

CMAQ source code of the Xie mechanism and CSQY file. We are

also grateful to Blaine Heffron for technical assistance in modeling,

and our former colleague Dr. Haofei Zhang, who provided insight and

expertise that greatly assisted this research.


References

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• Xie et al., 2013, Atmos. Chem. Phys., 13(16):8439–8455. Available at: http://www.atmos-chem-phys.net/13/8439/2013/

• Hutzell et al., 2011, Atmos. Environment, 46: 417-429.

• Crounse et al., 2011, PCCP, 13:13607-13613.

• da Silva et al., 2010, Environ. Sci. & Tech. 44 (1) :250-6.

• Henderson et al., 2009, Poster at the 8th CMAS Conference, Chapel Hill, NC.

Thank you!

Questions?

Backup Slides


Sensitivity Runs

Yuzhi Chen

Case Description *Kisom,ISOPO2 ISOPN yields

Run BASE K 0.06

Run A lower Kisom,ISOPO2 0.5K 0.06

Run Blower ISOPN

yieldK 0

• Halving ISOPO2 isomerization rate has no impact on O3

• ISOPN yields zero-out reduces O3 peak by 5.5%

Lower NOX case: JN2697RED

* K = (4.07e+8*EXP(-7694/TK) cm3/s


Radical Cycle

OH

NO

Lower NOXHigh NOX


Radical Cycle Overview

High NOx ————> Lower NOX


Radical Cycles

NewRadical

NewRadical

TerminationLoss of Radicals

PropagationProducts


PropagationProducts

New NO

New NO

Oxidation, Photolysis & Reaction

Nitrogen productsLoss of NO and NO2



O3 Production

O3 Production

＋ H2O

Net O3

ProductionNet O3

Production

O3 Reaction Loss

O3 Reaction Loss

inorganic processesorganic processes

hv

hv

hvq Q

Ee

OH cycle = Q/q

NO cycle = E/e

NO —> NO2

(NOZ)


Radical Cycles - High NOX Case

NewRadical

NewRadical


PropagationProducts


PropagationProducts

New NO

New NO





O3 Production

O3 Production

＋ H2O

Net O3

ProductionNet O3

Production

O3 Reaction Loss

O3 Reaction Loss

inorganic processesorganic processes

hv

hv

hvq Q

Ee

OH cycle = Q/q

NO cycle = E/e

NO —> NO2

(NOZ)


Generic Atmospheric Ozone Chemistry

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VOC + OH RO2

HO2

RCHO

RO+ NO

OH + NO2

O3

hv

O3PO2

RONO2

HNO3O2

(ISOP + OH)

NO + O3 NO2hv

Documents

Assessment of SAPRC07 with Updated Isoprene Chemistry against Outdoor Chamber Experiments