1. Evaluation of Two Numerical Algorithms in Simulating Particle Condensational Growth and Gas/Particle Mass Transfer Yang Zhang and Christian Seigneur Atmospheric & Environmental Research, Inc.

2. Aerosol Processes Organic PM Inorganic PM Nucleation Condensation/ Volatilization Coagulation Non-equilibrium Mass Transfer Thermodynamic Equilibrium Aerosol Dynamics Particle Chemical Composition Particle Size Distribution

3. Condensation Algorithm Particle diameter Initial conditions Moving boundaries (exact solution) Moving center (mass changes within the section) Stationary sections (mass moves from section to section) x x x

4. The Spline Interpolation l Use of the full moving approach at a small time step, then use of the cubic spline interpolation in mapping the new size distribution to the original size distribution at a larger time step l Combination of the full moving and the fixed size section approaches

5. The Bott Algorithm l The governing equation for condensation/evaporation l Conservative, positive-definite, computationally fast

6. Condensation: Volume Size Distribution

8. Mass Transfer Approaches l Kinetic approach »explicit mass transfer treatment »individual particles and bulk gas phase may not be in equilibrium l Equilibrium approach »equilibrium between all particles and bulk gas phase »uniform chemical composition for all particles l Hybrid approach »equilibrium between whole particulate phase and bulk gas phase »condensational growth law to distribute condensable species among particles

9. PM Composition for Case 3 (HNO 3 = 5 ppb, NH 3 = 5 ppb)

10. PM Composition for Case 2 (HNO 3 = 15 ppb, NH 3 = 15 ppb, and NaCl = 3  g m -3 )

11. Summary l For simulation of condensational growth, the Bott algorithm causes some upstream numerical diffusion, the spline interpolation algorithm leads to a larger numerical diffusion over a larger size range. l For simulation of gas/particle mass transfer, the two algorithms predict similar particle size distribution for cases without NaCl and significantly different results for cases with NaCl.

12. Acknowledgements Coordinating Research Council, Inc. Electric Power Research Institute