Numerical techniques to solve condensational and dissolutional growth equations when growth is coupled to reversible reactions

Noniterative, unconditionally stable numerical techniques for solving condensational and dissolutional growth equations are given. Growth solutions are compared to Gear-code solutions for three cases when growth is coupled to reversible equilibrium chemistry. In all cases, results from the new growth schemes matched Gear-code solutions nearly exactly when growth and equilibrium calculations were operator-split with a 1 s time interval. Results also matched well for a 15 s interval. With a 15 s interval, the growth-equilibrium schemes can be used in a three-dimensional model. Longer operator splitting intervals, in some cases, induced oscillations in concentrations caused by delays in feedback between equilibrium and growth calculations. Simulation results indicated that gases and aerosols were closer to equilibrium when the relative humidity was 90% than when it was 40%. (C) 1997 American Association for Aerosol Research.