Preliminary pollutant dispersion modelling with calmet and calpuff over complex terrain in the Bolzano Basin (IT)

The assessment of the impact on air quality of a new waste incinerator for the city of Bolzano (Central Italian Alps) required to improve the forecast of dispersion processes within the Bolzano basin, especially in critical weather conditions (e.g. wintertime ground-based inversions under calm conditions). This led to test the CALMET and CALPUFF modelling chain performance in such a complex terrain. CALMET was used for the diagnostic reconstruction of meteorological fields, the input data being provided by a variety of in-situ measurements: surface temperature and wind (speed and direction) from eight different weather stations, wind profiles from a SODAR, and temperature profiles from a thermal profiler. Simulations performed with a prognostic approach (WRF model) showed that the strong complexity of the area affects the development of ground-based thermal inversions, as well as alternating up- and down-valley winds in the valleys merging into the basin. The simulation of such a complex pattern of meteorological fields is a challenging goal for the diagnostic pre-processor CALMET. Indeed in such a complex domain it is very difficult for CALMET to spatialize appropriately meteorological variables, such as surface temperature and wind speed and direction, strongly affecting the transport of pollutants. Therefore efforts were made to understand the causes of these deficiencies. In particular the operations of CALMET pre-processor were examined, and effects of different meteorological input passed to CALPUFF were analysed, to ascertain their impact on dispersion patterns.