Development and Application of a State-of-the-Science Plume-in-Grid Model CMAQ-APT
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Development and Application of aState-of-the-Science Plume-in-Grid Model
CMAQ-APT
Prakash Karamchandani, Christian Seigneur, Krish Vijayaraghavan and Shiang-Yuh Wu,
AER, San Ramon, CA
Alan Hansen and Naresh KumarEPRI, Palo Alto, CA
CMAQ Workshop, October 2002
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Plume-in-Grid Modeling
• 3-D air quality models create an artificial dilution of stack emissions– lower concentrations of plume material– unrealistic concentrations upwind of stack– incorrect chemical reaction rates– incorrect representation of transport
• Subgrid-scale representation of plumes can remove some or all of these major limitations
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Previous PiG Models
• Previous Plume-in-Grid (PiG) models include PARIS, URM, UAM-V, CAMx and CMAQ
• All these PiG representations had limitations due to a simplified treatment of plume dispersion (empirical or first-order diffusion), simplified chemical mechanism in some cases and no effect of turbulence on plume chemistry
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CMAQ-APT
• Development of a new PiG model that uses the state-of-the-science for the host model (CMAQ) and the plume model (SCICHEM)
• SCICHEM includes advanced treatments for plume dispersion (second-order diffusion) and chemistry (multistage mechanism, effect of turbulence)
• CMAQ with Advanced Plume Treatment (APT)
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Plume Dispersion
• SCICHEM uses the SCIPUFF framework to simulate plume dispersion
• A myriad of puffs is released from the source to represent the plume
• Puffs are split when they become too large so that the effect of wind shear and turbulence on plume dispersion are properly characterized
• Puffs that overlap are merged
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Plume Chemistry
• Plume chemistry is simulated with a chemical kinetic mechanism that evolves through three stages as the plume becomes dispersed into the background air (Karamchandani et al., 2000)
• Effect of turbulence on plume chemistry can be simulated
• Crosswind plume resolution can be improved by using more puffs
• SCICHEM has been evaluated with plume data from SOS 95 and SOS 99
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Evolution of Plume Chemistry
Early Plume Dispersion
NO/NO2/O3 chemistry
1
2Mid-range Plume Dispersion
Reduced VOC/NOx/O3 chemistry — acid formation from OH and NO3/N2O5 chemistry
Long-range Plume Dispersion
3
Full VOC/NOx/O3 chemistry — acid and O3 formation
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SCICHEM/CMAQ Interface
Domain, grid informationGeophysical dataMeteorological dataDeposition velocities
Models-3CMAQ
SCICHEM
Emissions,IC/BC
Outputconcentrationsand deposition
Outputpuff
information
Pointsource
emissions
Dumppuffs
chemicalconcentrations
chemicalconcentrations
I/OAPI
I/OAPI
I/OAPI
I/OAPI
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Plume Dumping Criteria
• Chemical criterion: the plume has become chemically mature as determined by reaching the third stage of plume chemistry and a given threshold for the plume concentration ratio of O3 / (O3 + NO2)
• Physical criterion: the plume width must exceed the host model grid size
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CMAQ-APT Application
• Eastern United States with two nested grid domains (12 and 4 km resolution)
• Episode of 11 to 15 July 1995• MM5 simulation of Seaman and Michelson (2000)
• Thirty largest NOx point sources simulated with APT
• Simulation with CMAQ and CMAQ-APT• CMAQ-APT is about 1.6 times slower than CMAQ for
this simulation
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CMAQ Surface O3 Concentrations13 July 1995, 3 p.m.
12 kmdomain
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Effect of APT PiG Treatment onSurface O3 Concentrations
13 July 1995, 3 p.m.
CM
AQ
-AP
T -
C
MA
Q
12 kmdomain
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Effect of Point Source NOx Emissionson Surface O3 Concentrations
without PiG Treatment
CM
AQ
-
Bac
kgr
oun
d
12 kmdomain
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Effect of Point Source NOx Emissionson Surface O3 Concentrations
with APT PiG Treatment
CM
AQ
-AP
T -
B
ack
grou
nd
12 kmdomain
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CMAQ Surface HNO3 Concentrations13 July 1995, 3 p.m.
12 kmdomain
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Effect of APT PiG Treatment onSurface HNO3 Concentrations
13 July 1995, 3 p.m.
CM
AQ
-AP
T -
C
MA
Q
12 kmdomain
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Effect of Point Source NOx Emissionson Surface HNO3 Concentrations
without PiG Treatment
CM
AQ
-
Bac
kgr
oun
d
12 kmdomain
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Effect of Point Source NOx Emissionson Surface HNO3 Concentrations
with APT PiG Treatment
CM
AQ
-AP
T -
B
ack
grou
nd
12 kmdomain
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Conclusions
• CMAQ-APT provides an improved representation of the impact of large point sources
• For isolated point sources, CMAQ-APT predicts less impact on O3 formation (up to 80 ppb less) and less impact on HNO3 formation (up to 24 ppb less)
• CMAQ-APT has been subjected to a comprehensive beta-testing by three organizations
• It will be applied to the California San Joaquin Valley for several CCOS episodes