A COMPARISON OF NUMERICAL TECHNIQUES FOR SOLUTION OF ATMOSPHERIC KINETIC-EQUATIONS

Numerical modeling of atmospheric chemistry is a computationally inten sive problem. The equations describing the interaction among various m odeled chemical species are coupled, nonlinear ordinary differential e quations. Spatial dependencies in comprehensive three-dimensional air quality models require the solution of this system at thousands of spa tial points. Even with increasing computer power, there is a need for efficient and accurate numerical solvers with expanded capabilities, s ince the next generation of air quality simulation models needs to add ress the increasingly complex chemistry issues emerging in new model a pplications. Variants of the commonly used quasi steady-state approxim ation and the hybrid methods currently used in several modeling system s are examined against a reference mechanism describing chemical inter actions related to tropospheric oxidant and acid formation. Additional modifications to the methods are incorporated to yield more robust in tegration techniques. The chemistry solution methodology used in the r egional acid deposition model is also incorporated in this comparison as a base methodology for representing the reference chemical mechanis m. The methods are tested against the Gear integration scheme for a va riety of test cases including traditional box-model calculations and d etailed three-dimensional simulations, and their relative accuracies a nd efficiencies are investigated. Performance and implementation issue s related to chemical integration schemes are examined in the context of the demands and needs of the chemistry component of future comprehe nsive atmospheric chemistry/transport simulation models. (C) 1998 Else vier Science Ltd. All rights reserved.