Improving odour assessment by using better dispersion models: some examples.

A critical aspect of odour assessments is modelling to define exposure characteristics in affected communities, and to examine the effects of odour control options. In many cases, odour dispersion is Influenced by complex or non steady-state meteorology that cannot be represented by the commonly used dispersion models, such as ISC3 and AUSPLUME. These models are based on a steady-state Gaussian plume assumption, which is often inaccurate. Recent developments in modelling of local meteorology and plume dispersion have enabled far more realistic predictions of odour dispersion. Three-dimensional models have been successfully applied to improve the predictions of odour impact and to better define the parameters for odour control options. These models more accurately represent features such as drainage flows along valley floors and around hills, and strong wind shear that can develop in stable conditions. Such conditions are often critical for a proper assessment of odour impact. Second-by-second fluctuations in odour concentrations can now be simulated using the KSP model developed by Yamartino et al. This model avoids the use of arbritrary methods of determining peak-to-mean ratios. New models can also provide detailed microscale wind fields, suitable for odour modelling in urban areas where odour dispersion is affected by very complex flows.