Numerical solution of the atmospheric diffusion equation for chemically reacting flows

A comprehensive study of numerical techniques for solving the atmospheric diffusion equation is reported. Operator splitting methods are examined in which the three-dimensional problem is converted into a sequence of one-dimensional problems. A Galerkin, linear finite element scheme with a nonlinear filter is found to be computationally superior to the other methods tested for the advection-diffusion components. The chemical reaction dynamics component, treated within the splitting scheme, is generally highly stiff. A second-order predictor, iterated corrector technique, in combination with an asymptotic treatment of the stiff components, is found to be computationally superior for the chemical kinetics. The validity of the pseudo steady state approximation for certain reactive species is also investigated.