An implicit-explicit approach for atmospheric transport-chemistry problems Original Research Article

We investigate numerical algorithms for use in air pollution models. The emphasis is on the time integration aspects in connection with advection, vertical turbulent diffusion and stiff chemistry. The time integration scheme considered is a second-order implicit-explicit BDF scheme which handles advection explicitly and vertical turbulent diffusion and chemistry implicitly. The investigation is divided into three parts. In the first part we propose a Gauss-Seidel technique for the implicit solution of the chemistry and vertical turbulent diffusion. In the 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 the implicit-explicit scheme to a 3D test model and discuss vectorization and parallelization aspects.