Pollutant transport schemes integrated in a numerical weather prediction model: model description and verification results

Regional air pollution models are usually off-line coupled with numerical weather prediction models. The present study, however, focuses on on-line coupled modelling, for which the air pollution model is an integral part of the meteorological model. To this purpose, simulations of the first European Tracer Experiment (ETEX), which supplies the best suited verification data for dispersion modelling of a passive tracer, have been performed using versions of the Danish Meteorological Institute High Resolution Limited-Area Model (DMI-HIRLAM). Simulation results have been compared with observed values as well as with results from other models. The operational version of DMI-HIRLAM using well-known basic advection schemes has been tested, showing the need for improvements for air pollution purposes. The fourth-order Bott algorithm for advection has thus been implemented in the semi-Lagrangian version of DMI-HIRLAM. Due to its practically perfect mass conservation properties and its low computational cost, this method turns out to be efficient for simulations of transport of pollutants in the atmosphere. This represents a first effort towards a fully integrated air pollution model, e.g. for forecasting purposes.