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EVALUATION AND IMPROVEMENT OF GAS/PARTICLE MASS TRANSFER
TREATMENTS FOR 3-D AEROSOL SIMULATION AND
FORECAST
Xiaoming Hu and Yang Zhang North Carolina State University,
Raleigh, NCMark Z. Jacobson
Stanford University, Stanford, CA
Outline
BACKGROUND AND OBJECTIVES PRELIMINARY RESULTS
Stand alone condensation solvers Gas/particle mass transfer
approaches 3-D test using WRF/Chem-MADRID
SUMMARY
Major Aerosol Dynamics Processes
Mass Transfer to/from the Surface of ParticlesNucleation
CondensableSpecies
Volatile Species
Thermodynamic Equilibrium at the Particle Surface
Condensational Growth Shrinkage by Volatilization
CoagulationSize-resolved PM Chemical
Composition
Bulk Gas Phase
Gas/Particle Mass Transfer Approaches in
AQMs
Approaches Description
Solvers for condensation/evaporation equation
Kinetic Simulates gas/particle mass transfer for each size section explicitly
Yes, for all bins
Equilibrium
Assumes an instantaneous chemical equilibrium between the gas and the particulate phases
No
Hybrid Combines both kinetic and equilibrium approaches
Yes, for coarse bins only
Solvers for Condensation Equation
Eulerian approaches (e.g., Bott; Walcek)
Lagrangian approaches (e.g., Trajectory-Grid)
Hybrid (e.g., Analytical Predictor of Condensation (APC) scheme)
Objectives
Identify a reliable yet efficient condensation scheme
Improve gas/particle mass transfer treatment
Apply improved modules for 3-D AQ simulation and forecast
Test of Condensation Schemes
System with condensation of H2SO4 only
Test conditions
Hazy
Condensation rate
9.9 µg cm-3 per 12-h
“Exact” solution
APC, 500 bins
Case from Seigneur et al. (1986) and Zhang et al., (1999)
0
5
10
15
20
25
30
35
0.001 0.01 0.1 1 10
d (µm)
dV
/d lo
g d
(µ
m3 c
m-3
)
Initial
Exact
Bott
APC
Walcek
TG ( 2 pulses)
Sensitivity of APC scheme to Size Resolution
Case from Seigneur et al. (1986) and Zhang et al., 1999
0
5
10
15
20
25
30
35
0.001 0.01 0.1 1 10
d (µm)
dV
/d lo
g d
(µ
m3 c
m-3
)
Initial
Exact
APC_12 bins
APC_30 bins
ICs for Test of Gas/Particle Mass Transfer Approaches
Cases Characteristics Month Temp (K)
RH (%)
TNa+TNH4/TSO4
TNO3/TSO4
Hong Kong
High Na+, high coarse NO3
-
May 303.45 77 3.1 0.5
Tampa Bay
High Na+, high coarse NO3
-
Aug. 300.45 82.9 2.2 0.2
Fresno Low Na+, low coarse NO3
-
Dec. 283.1 82.8 8.4 4.7
Test of Gas/Particle Mass Transfer Approaches Hong Kong on May 7, 1998
H+(aq) + Cl-(aq) HCl(g)
H+(aq) + NO3
-(aq) HNO3(g)
NH4+
(aq) + OH-(aq) NH3(aq)
+H2O(aq)
NH3(aq) NH3(g)
2Na+(aq)+SO4
2-(aq) Na2SO4(s)
Comparison with Observed PM Size Distribution
Hong Kong on May 7-8, 1998
•Similar obs. PM size distribution on May 7-8•Similar meteorology but higher emissions on May 8•Kinetic approach with emissions gives the best fit
Box model simulations
CPU time of MADRID
Approach
BulkEquilibrium
Kinetic Hybrid
APC WalcekEqui./APC
CPU time, s 2.08 4.18 107.13 3.86
Time step, s 60 30 0.5 varied
Application of WRF/Chem-MADRID with TexAQS2000
Episode & Resolution Period: Aug. 28 – Sept. 2, 2000 Domain: 88 x 88 grid cells Horizontal resolution: 12 km Vertical resolution: 57 layers
Meteorology Yonsei Univ. PBL scheme NOAH land-surface scheme Goddard short wave radiation Rapid and accurate rad. tran.
model (RRTM) long wave rad.
Initial & Boundary Conditions North Amer. Reg. Reanalysis
Emissions Gas: TCEQ inventory PM: NEI v3
Chemistry Gas: CBM-Z Aerosol:
• MADRID (Equilibrium vs. Kinetic)
Gulf of Mexico
Nitrate Predictions: Equilibrium vs. Kinetic
Approaches
Equilibrium
Kinetic APC
Fine mode Coarse mode
HNO3(g) + NaCl(s) NaNO3(s) + HCl(g)
HNO3(g) + Cl-(aq) NO3
-(aq) + HCl(g)
Predicted Size-Resolved Composition at Galveston
Kinetic approach prediction at GALC on Aug. 29
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 2 3 4 5 6 7 8
Sections
µg
m-3
Cl
NO3
NH4
SO4
Na
Equilibrium
Kinetic APC
Bulk equilibrium approach prediction at GALC on Aug. 29
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 2 3 4 5 6 7 8
Sections
µg
m-3
Cl
NO3
NH4
SO4
Na
Summary
Bulk equilibrium approach failed to reproduce the observed size-resolved composition under conditions with high concentration of reactive species in the coarse particles.
Kinetic/hybrid approaches with APC are competitive for 3-D application in terms of both accuracy and computational efficiency.
WRF/Chem-MADRID with kinetic mass transfer approach predicts more coarse mode nitrate than the equilibrium approach for the TexAQS2000 episode.
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