Test of numerical methods for the integration of kinetic equations in tropospheric chemistry

The numerical solution of ordinary differential equations systems (ODEs) describing the atmospheric chemistry requires a large computational effort because of their stiff nature: in a three-dimensional photochemical model the solution of the ODEs requires at least 70% of the total CPU time. Several numerical integration techniques have been developed in order to provide accurate and computationally efficient solutions to ODEs. In this work we present a comparison between two classical methods, the Hybrid Solver and the Quasi Steady State Approximation method, and the Chemical Solver for Ordinary Differential Equations. The chemical mechanism used is SAPRC90, which is the chemical scheme of the CALGRID model. The accuracy is evaluated comparing the results of every method with the solution obtained with the Livermore Solver for Ordinary Differential Equations (LSODE). This comparison has been made varying the parameters of the error tolerances, and taking into account the trade-off between solution accuracy and computational efficiency. (C) 1999 Elsevier Science B.V.