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

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

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

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)

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

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

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

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

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

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

CMAQ Surface O3 Concentrations13 July 1995, 3 p.m.

12 kmdomain

Effect of APT PiG Treatment onSurface O3 Concentrations

13 July 1995, 3 p.m.

CM

AQ

-AP

T -

C

MA

Q

12 kmdomain

Effect of Point Source NOx Emissionson Surface O3 Concentrations

without PiG Treatment

CM

AQ

-

Bac

kgr

oun

d

12 kmdomain

Effect of Point Source NOx Emissionson Surface O3 Concentrations

with APT PiG Treatment

CM

AQ

-AP

T -

B

ack

grou

nd

12 kmdomain

CMAQ Surface HNO3 Concentrations13 July 1995, 3 p.m.

12 kmdomain

Effect of APT PiG Treatment onSurface HNO3 Concentrations

13 July 1995, 3 p.m.

CM

AQ

-AP

T -

C

MA

Q

12 kmdomain

Effect of Point Source NOx Emissionson Surface HNO3 Concentrations

without PiG Treatment

CM

AQ

-

Bac

kgr

oun

d

12 kmdomain

Effect of Point Source NOx Emissionson Surface HNO3 Concentrations

with APT PiG Treatment

CM

AQ

-AP

T -

B

ack

grou

nd

12 kmdomain

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