MULTISCALE MODELING OF POLLUTANT TRANSPORT AND CHEMISTRY

A multiscale transport scheme is used in solving the coupled nonlinear system of atmospheric continuity equation. This upwind finite element scheme employs a local nonlinear filter to eliminate negative concentrations. Two different nesting techniques are considered to assess their potential of being used in photochemical models. The test problem is the advection of chemically reacting puffs in a rotational velocity field. The mechanism is a very simple description of atmospheric chemistry. The results are compared to the case where no advection takes place. The multiscale scheme performs well in matching the transport with nonlinear chemistry when constraint elements are used for nesting. The other technique, i.e., nesting with transition elements, that performed equally well in advection tests proved to be inappropriate for following the chemical kinetics. This result has a very important implication: transport schemes that will be used in air quality models should be tested with the chemistry. The efficiency of the transport algorithm is also discussed. Some comments are made about the general trends in pollutant transition from urban to regional scales.