Download - 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
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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
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[Xie et al., 2013, ACP]
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Updated isoprene oxidation scheme for isoprene + OH
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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?
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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
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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
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NO/NO2 Crossover TimeLower NOXHigh NOX
Xie predicts earlier NO-NO2 crossover for all isoprene runs
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• 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
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Ozone Peak
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Xie predicts higher ozone for all isoprene runs
Lower NOXHigh NOX
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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
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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
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Reaction Rate of VOCs + OH
High NOX
ISOP: 1.26 ppm, NOX: 0.35 ppm (ISOP/NOX: 3.73)
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Integrated Reaction Rate of VOCs + OH Lower NOXHigh NOX
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OH conc.
HO2 from Aldehydes
Lower NOXHigh NOX
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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
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NO2 Recycling Rate
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Xie predicts 64% more PANs than SAPRC07
Which accounts for 85% of the total increase in recycled NO2
Lower NOX
Summary
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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
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Acknowledgment
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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.
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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
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Sensitivity Runs
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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
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Radical Cycle
OH
NO
Lower NOXHigh NOX
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Radical Cycle Overview
High NOx ————> Lower NOX
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Radical Cycles
NewRadical
NewRadical
TerminationLoss of Radicals
PropagationProducts
TerminationLoss of Radicals
PropagationProducts
New NO
New NO
Oxidation, Photolysis & Reaction
Nitrogen productsLoss of NO and NO2
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)
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Radical Cycles - High NOX Case
NewRadical
NewRadical
TerminationLoss of Radicals
PropagationProducts
TerminationLoss of Radicals
PropagationProducts
New NO
New NO
Oxidation, Photolysis & Reaction
Nitrogen productsLoss of NO and NO2
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)
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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