Development and Validation of the Multilayer Model MUSE - The Impact of the Chemical Reaction Mechanism on Air Quality Predictions

As a new constituent of the European Zooming Model (EZM) system, the multilayer model MUSE is designed to serve as an efficient tool for simulating transport and transformation of air pollutants in the urban scale and thereby in supporting local scale air quality management in the most cost effective way.Comparison of simulation results achieved with MUSE with corresponding results of the validated three-dimensional photochemical dispersion model MARS reveals that the model MUSE is capable of reproducing the spatial and diurnal variation of the major photochemical air pollutants.In order to investigate the effect of the chemical reaction mechanism on air quality predictions, three different reaction mechanisms ranging from the compact mechanism KOREM to the comprehensive mechanisms EMEP and RACM are compared. The latter mechanism is a revised version of the RADM2 mechanism, the improvement mainly focussing on the description of the RO₂ chemistry and biogenic emissions.The intercomparison reveals that despite of similar predicted ozone concentrations, the chemical mechanisms are still performing differently in many aspects. Thus, the choice of a suitable chemical reaction mechanism is mainly depending on the accuracy of the emission inventory as well as on the available computer memory and CPU time.