Particulate Matter dispersion modeling in Alpine valleys

This presentation demonstrates that for the prediction of particulate matter dispersion using emission inventories in Alpine valleys, the results obtained from an applied dispersion model using annually averaged dispersion matrices compare reasonably well to the results from the CALPUFF dispersion model with hourly resolution run by CALMET flow fields, if the applied dispersion model is based on accurate data concerning the wind fields and mixing heights, and care is taken to the modeling of the different stability regimes and dispersion coefficients. The comparison to measurements shows a clear improvement of the model predictions with respect to the earlier model version without special treatment of Alpine meteorological conditions. PM10 (particulate matter with an aerodynamic diameter of less than 10 µm) is a matter of increasing concern. Comprehensive emission inventories and a dispersion model have been developed to predict the Swiss annual PM10 concentrations [Heldstab, de Haan, Filliger, and Künzle (1999): PM10 map and population exposure for Switzerland. Presented at 6th Int. Conf. on Harmonisation within atmospheric dispersion modelling. To be published in Int. J. Environment Pollution]. The second version of the Swiss PM10 model [de Haan, Heldstab, Filliger and Künzle (2000): Comprehensive PM10 emission inventories and dispersion modeling for Switzerland. To be presented at Int. Conf. Transport and Air Pollution, June 5-8, 2000, Avignon] aims at improving the modeling prediction capability in the Swiss Alps. The dispersion model uses annually averaged dispersion matrixes (spatial resolution of 200m x 200m up to 4 km away from the source, 1 km2 resolution up to a spatial extension of 200 km), which are applied to each cell of the different emission inventories. Emissions having distinct source characteristics are grouped into different inventories, i.e. urban and outer-urban emissions, and different source heights. The dispersion matrices are derived from a simple dispersion model and reflect the annually averaged ground concentration impact of a point source with specific source characteristics. The local wind conditions in alpine valleys are often determined either by the topographic forcing of the mesoscale circulation, or by thermally driven valley breezes. As a result, the circulation exhibits a complex pattern, which is neither homogeneous nor stationary, thus preventing the use of classical Gaussian approaches for modeling pollutant dispersion and the resulting ground level concentrations. In this presentation, three dispersion models (the german TA-Luft; Gryning, Holtslag, Irwin and Sivertsen (1987): Applied dispersion modelling based on meteorological scaling parameters. Atmospheric Env., 21, 79-89; Hanna and Paine 1999: Hybrid Plume Dispersion Model (HPDM) development and evaluation. J. Appl. Meteorol., 28, 206-224) are validated together with different schemes to group the hourly meteorological data for four alpine sites into stability class regimes. These dispersion models are then used to compute the annually averaged ground-level concentration impact of different source configurations, from which dispersion matrices are computed. For a single point source configuration, the result using the dispersion matrix is compared to a full CALMET/CALPUFF simulation. For extended particulate matter emission inventories in alpine valleys, the results using dispersion matrices are validated against measurements.