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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