Tracer dispersion above an urban area in valleys

摘要

The dispersion of a neutral tracer above a urban area in Grenoble (France) is studied in the meteorological conditions of two different days. This analysis is supported by an experiment of a steady three hour release of SF_6 on day 1 (30 Oct. 96) and a two hour release on day 2 (31 Oct. 96). The site is characterized by a complex terrain at the junction of three valleys. The mean wind measured at a sensor tower (60 m high) near the emission point was strong (7 m/s) and from northwest on day 1, and low (2 m/s) and from southeast on day 2. The concentrations measured from the experiments are compared with the results from a large addy simulation (LES) and with the results from dispersion models based on a gaussian approach.