Predicting odour impact using the Austrian odour dispersion model (AODM)

Using a dispersion model to calculate ambient odour concentrations, the sep aration distance between livestock buildings and residential areas is defin ed by the occur impact criteria using a combination of a pre-selected odour threshold and an exceeding probability. The dynamic Austrian Odour Dispers ion Model (AODM), a Gaussian model, is used to calculate the direction-depe ndent separation distances for several combinations of these two values, wh ich represent the protection level of various land use categories. The calc ulated direction-dependent separation distances are a function of the preva iling wind velocity and atmospheric stability conditions. At a site in the Austrian North-alpine foreland, the direction-dependent separation distance (calculated on the basis of a two year time series of meteorological data) for pure residential areas (3% exceeding probability over the year for an odour threshold of 1 OU/m(3)) lies between 99 m (for northerly winds with a probability of less than 3%) and 362 m (for westerly winds with a probabil ity of 34%). For west and east the main wind directions, odour sensation ca n be expected more often for higher wind velocities and a neutral or stable atmosphere around sunset. Northerly and southerly winds show the typical d iurnal variation of a local valley wind system with predominantly northerly daytime up-valley and southerly night-time down-valley winds.