Effects of wind directional fluctuations on gas diffusion over a model terrain

Wind tunnel experiments were carried out to study the effects of wind directional fluctuations on gas diffusion, under a neutral stability condition, over terrain models using the overlapping method. Ground-level concentrations were measured under 3 conditions with standard deviations of wind directional fluctuation, σA, of 5°, 10° and 20°. From these experimental results, an attempt was made to reduce the general rule of the relation between σA and the maximum ground-level concentration, Cmax over a terrain. The verification and limitation in the application of this rule are discussed. Furthermore, it is reported that large σA has a strong influence on the ground-level concentration patterns and so unexpected concentration patterns appear under some conditions.