Evaluation of the SAFE_AIR code against air pollution field and laboratoryexperiments

The SAFE-AIR model simulates the transport and diffusion of airborne pollut ants using Gaussian plume segments and/or puffs. The model is able to deal with both non-stationary and inhomogeneous conditions. SAFE AIR is an evolu tion of the AVACTA II model "recommended" by the US Environmental Protectio n Agency. With respect to AVACTA II, SAFE-AIR contains a number of improvem ents among which: the complete change of the wind held generation, differen t algorithms calculating the wind field spatial average providing the advec tion velocities of pollutant elements, and a more realistic description of deposition patterns. The model evaluation of some aspects of SAFE-AIR was p erformed using field data (from the KNRC Katrex experiments, flat terrain, convectively unstable and neutral conditions) and laboratory data (from the EPA wind tunnel Rushil experiments, two-dimensional schematic hill, neutra l conditions). This paper contains a comprehensive description of the resul ts of these model evaluations. These exercises allowed us to draw some conc lusions coherent with what one could expect from a similar model. Among the m: (1) the model performance is better when the wind tunnel experiments are simulated than when an open-air experiment is performed; (2) the simulatio n results are in better agreement with measurements performed in an almost neutral atmosphere than with those performed in unstable conditions. (3) th e model has still some problems in simulating emissions near the ground, wh ile the results relative to elevated emissions are more satisfactory; (4) t he choice of the cr-function is the most critical among the options conside red in our numerical experiments. We believe these conclusions both rather general and useful as far as the calibration and operational use of SAFE-AI R are concerned. (C) 2000 Elsevier Science Ltd. All rights reserved.