Particle model simulation of pollutants dispersion from a line source in complex terrain

Pollutant transport and dispersion in complex orography are usually difficult to model accurately, due to the problem of properly reproducing wind and turbulence fields and interactions between pollutants and orography. In these situations the well-known Gaussian approach is limited. For studies of line sources (i.e. highways), models are available which are adequate for flat terrain and steady-state conditions (i.e. US-EPA recommended CALINE-3 and HIWAY-2). In complex terrain, however, no well-tested models are available. A possible approach to the problem is the use of a wind field model with a Lagrangian dispersion model well suited to consider both orography-induced inhomogeneities and line sources. We present the application of SPRAY particle model to reproduce pollutants dispersion from a highway at the bottom of a deep alpine valley, where pollutants are well confined and stagnation may occur. Model results for NOx are compared to those of the EPA recommended model HIWAY-2 and to measured concentrations.