Abstract: To simulate the urban dispersion of denser-than-air gases, an urban denser-than-air dispersion model known as SLAB_URBAN model was developed. The model is based on the shallow layer theory. A new urban boundary and dispersion coefficients parameterization representing the urban wind and turbulence features is applied to the model. Tests were performed during the field campaign Urban 2000 which was held in October 2000 in Salt Lake City. The tracer data sets are adopted to demonstrate the SLAB_URBAN model performance.The focus of the comparisons is on the maximum concentration, on a given monitoring arc, normalized by the emission rate. At Urban 2000, for all samples and release times, the predictions of the SLAB_URBAN model are shown to agree with observations. Furthermore, SLAB_URBAN model is evaluated by comparison with other urban dispersion models. The SLAB_URBAN model predictions are shown to perform well in all urban dispersion models.