AN IMPLICIT EXPLICIT APPROACH FOR ATMOSPHERIC TRANSPORT-CHEMISTRY PROBLEMS

We investigate numerical algorithms for use in air pollution models. T he emphasis is on the time integration aspects in connection with adve ction, vertical turbulent diffusion and stiff chemistry. The time inte gration scheme considered is a second-order implicit-explicit BDF sche me which handles advection explicitly and vertical turbulent diffusion and chemistry implicitly. The investigation is divided into three par ts. In the first part we propose a Gauss-Seidel technique for the impl icit solution of the chemistry and vertical turbulent diffusion. In th e second part we discuss stability properties of the implicit-explicit BDF scheme, assuming the third-order upwind biased finite difference discretization of the advection operator. In the third part we apply t he implicit-explicit scheme to a 3D test model and discuss vectorizati on and parallelization aspects.