Prakash V. Bhave, Ph.D.

Physical Scientist

PM Model Performance Workshop

February 10, 2004

Postprocessing Model Output for Comparison to Ambient Data

HorizontalTransport

Cloud Processing

Chemical Reactions

Photo-chemistry

DepositionGas-Phase Emissions

Aerosol Emissions

Condensation&

Evaporation

VerticalMixing

Air Quality Model

Gridded Values of:

Aerosol ConcentrationParticle Size DistributionChemical Composition

Model Output

Emissions Model

Meteorology Model

Input

AmbientSampling

Point Values of:

PM2.5 Mass ConcPM2.5 Chemical Comp.

ObservationsLaboratoryAnalysis

Mo

del

Evalu

ation

Traditional PM Model EvaluationsAir Quality Model

AmbientSampling

Laboratory Analysis

Input

Model Tuning Model Postprocessing

Modification of model inputs or atmospheric chemical & physical formulae to improve agreement between model results and observations.

e.g., multiply NH3 emissions by 2 and rerun the model

e.g., raise or lower the minimum eddy diffusivity and rerun the model

e.g., modify a rate constant and/or reaction probability and rerun the model

Modification of model outputs to simulate ambient sampling conditions, sampling artifacts, and analytical biases.

Notes:• Inputs are unchanged• Atmospheric processing is

unchanged• No need to rerun the air

quality model

Emissions Model

Meteorology Model

Input

HorizontalTransport

Cloud Processing

Chemical Reactions

Photo-chemistry

DepositionGas-Phase Emissions

Aerosol Emissions

Condensation&

Evaporation

VerticalMixing

Air Quality Model

AmbientSampling

Point Values of:

PM2.5 Mass ConcPM2.5 Chemical Comp.

ObservationsLaboratory

Analysis

Enhancing PM Model Evaluations

- Adjust for site T,RH - Inlet Collection - Substrate Artifacts - Lab Analyses

Postprocessing

PM2.5 Mass ConcPM2.5 Chemical Comp.

Output for Eval.

Mo

del

Evalu

ation

H2O

NO3

SVOC

Nonvolatile Material

• Models predict both gas and particle-phase concentrations

• Gas/particle partitioning of semi-volatile species is a function of T, RH

• What if the met model provides a gridded temperature field that is warmer than at the site?i.e., Tmodel > Tambient

Ambient Equilibration

Model Results at Nashville - July 2, 1999 1100EST

0

1

2

3

4

5

6

-5 -2 0 +2 +5

Temperature Bias in Met Model [K]

PM

2.5

[mg

/ m

3 ]

Sec Organics

Nitrate

Ammonium

Nonvolatile

Ambient Equilibration

PM2.5 Inlet Simulation

0

1

2

3

4

5

6

0.1 1.0 10.0

Particle Diameter [mm]

Ae

ros

ol C

on

ce

ntr

ati

on

[mg

/m3 ]

Model Output

PM2.5 = 16.7 mg/m3

PM2.5 Inlet Simulation

0

1

2

3

4

5

6

0.1 1.0 10.0

Particle Diameter [mm]

Ae

ros

ol C

on

ce

ntr

ati

on

[mg

/m3 ]

Model Output

Aerodynamic

PM2.5 = 15.5 mg/m3

PM2.5 Inlet SimulationEPA PM2.5 Well Impactor Ninety-Six (WINS)

Peters, Vanderpool, and Wiener, AS&T 34:389-397, 2001, Eq.1

0%

20%

40%

60%

80%

100%

0.1 1.0 10.0

Aerodynamic Diameter [mm]

Penetration %

PM2.5 Inlet Simulation

0

1

2

3

4

5

6

0.1 1.0 10.0

Particle Diameter [mm]

Ae

ros

ol C

on

ce

ntr

ati

on

[mg

/m3 ]

Model Output

Aerodynamic

FRM Inlet

PM2.5 = 14.9 mg/m3

Other Postprocessing Steps• Substrate Artifacts

Adsorption/desorption from substrate during sampling Have been characterized experimentally Can be estimated with moderate difficulty

• Chemical Analyses Lab conditions = 20-23 ºC, 30-40% RH Exceeds CRH of NH4HSO4, NH4NO3, NaHSO4, Aerosol water content can be estimated

• Organic Mass/Carbon Ratio Measurements reported as Organic Carbon Models assume some ratio (e.g., POA = 1.2 in NEI,

SOAb = 1.475 in CMAQ, SOAa = 1.67 in CMAQ)

AcknowledgementsPete Finkelstein, ORD

John Irwin, OAQPS

Brian Timin, OAQPS

Rob Gilliam, ORD

Brian Eder, ORD

Ken Schere, ORD

S.T. Rao, ORD

Disclaimer Notice:• This work has been funded wholly by the United States Environmental Protection

Agency. It has been subjected to Agency review and approved for presentation.

Atmospheric Processes Modeling

HorizontalTransport

Cloud Processin

g

Chemical Reactions

Photo-chemistry

DepositionGas-Phase Emissions

Aerosol Emissions

Condensation&

Evaporation

VerticalMixing