1. 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, NC Mark Z. Jacobson Stanford University, Stanford, CA

2. Outline BACKGROUND AND OBJECTIVES PRELIMINARY RESULTS Stand alone condensation solvers Gas/particle mass transfer approaches 3-D test using WRF/Chem-MADRID SUMMARY

3. Major Aerosol Dynamics Processes Mass Transfer to/from the Surface of Particles Nucleation Condensable Species Volatile Species Thermodynamic Equilibrium at the Particle Surface Condensational GrowthShrinkage by VolatilizationCoagulation Size-resolved PM Chemical Composition Bulk Gas Phase

4. Gas/Particle Mass Transfer Approaches in AQMs ApproachesDescription 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

5. 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)

6. Objectives Identify a reliable yet efficient condensation scheme Improve gas/particle mass transfer treatment Apply improved modules for 3-D AQ simulation and forecast

7. Test of Condensation Schemes System with condensation of H 2 SO 4 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)

8. Sensitivity of APC scheme to Size Resolution Case from Seigneur et al. (1986) and Zhang et al., 1999

9. ICs for Test of Gas/Particle Mass Transfer Approaches Cases CharacteristicsMonthTemp (K) RH (%) TNa+TNH4/ TSO4 TNO3/ TSO4 Hong Kong High Na +, high coarse NO 3 - May303.45 773.10.5 Tampa Bay High Na +, high coarse NO 3 - Aug.300.4582.92.20.2 Fresno Low Na +, low coarse NO 3 - Dec.283.1 82.88.44.7

10. Test of Gas/Particle Mass Transfer Approaches Hong Kong on May 7, 1998 H + (aq) + Cl - (aq)  HCl (g) H + (aq) + NO 3 - (aq)  HNO 3(g) NH 4 + (aq) + OH - (aq)  NH 3(aq) +H 2 O (aq) NH 3(aq)  NH 3(g) 2Na + (aq) +SO 4 2- (aq)  Na 2 SO 4(s)

11. 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

12. CPU time of MADRID Approach Bulk Equilibrium KineticHybrid APCWalcek Equi./ APC CPU time, s2.084.18107.133.86 Time step, s60300.5varied

13. 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

14. Comparison with Observations EquilibriumKinetic APC

15. Nitrate Predictions: Equilibrium vs. Kinetic Approaches Equilibrium Kinetic APC Fine modeCoarse mode HNO 3(g) + NaCl (s)  NaNO 3(s) + HCl (g) HNO 3(g) + Cl - (aq)  NO 3 - (aq) + HCl (g)

16. Predicted Size-Resolved Composition at Galveston Equilibrium Kinetic APC

17. 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.

18. 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