The advantageous utilization of triangular prismatic grid for flow simulation over irregular geometries is widely recognized. Such grid is here utilized to diagnose the atmospheric conditions and pollutant dispersion over complex inhomogeneous surfaces. One case with an extremely complex surface is resolved with regular prismatic grid. A second case, including parts of flat and mountainous areas, is resolved with completely unstructured grid. The atmospheric calculations rely on field data. The detailed surface description achieved through the triangular mesh allows facing lack of observations at significant sites, while it permits the selective use of the measurements for the determination of the local atmospheric conditions. The simulations are compared against observed pollutant concentrations. A quite satisfactory agreement is obtained, indicating that diagnostic models using improved surface resolution can provide reasonable results over complex terrain. This is considered very important since the use of diagnostic models is strongly suggested in emergency response cases. ¿ 1999 American Geophysical Union