A COMPARISON OF ADVECTION ALGORITHMS COUPLED WITH CHEMISTRY

Three-dimensional air quality models face the problem of solving the a dvection or advection-dominated transport equation. The performance of six advection algorithms coupled with chemistry is assessed here. The six algorithms are the forward-EuIer Taylor-Galerkin (FETG) method, t he implicit Chapeau-function method, a streamline upwind Petrov-Galerk in (SUPG) method, Smolarkiewicz's method, a semi-Lagrangian (SemiLag6) method, and the accurate space-derivative (ASD) method coupled with p eriodicity recovery. These methods are coupled with a 10-step chemistr y involving 10 species simulating the essence of atmospheric photochem ical reactions. The flow held is a two-dimensional, nondivergent rotat ing velocity field. The domain has 33 x 33 grid cells. Two test cases defined by the initial conditions are considered: (1) non-zero backgro und concentrations for all species except four that have an additional conic profile; (2) same as (1) for a region that covers 11 x 11 grid cells with the conic profile at its center, while the concentrations o f all species outside the 11 x 11 concentration platform are set equal to zero, After one full rotation in 24 h, for test case (1), the ASD gives the most accurate results, followed by FETG and the chapeau-func tion method. The Smolarkiewicz method gives the least-accurate result. For test case (2), no method performs well for NO and OH. For most sp ecies, ASD and FETG still yield accurate results. To assure highly acc urate advection results for all concentration profiles, however, one m ay have to resort to a particle-trajectory method such as the particle -grid modelling approach.