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

Comparison with Observations

Equilibrium Kinetic APC

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.

Acknowledgements

NOAA # DW13921548 and NSF Career Award # Atm-0348819

Jerome Fast, William Gustafson Jr., PNNL, Richland, WA

Georg Grell and Steven Peckham, NOAA, ESRL, Boulder, CO

All members from Air Quality Forecasting Lab, NCSU, Raleigh, NC