Using a dispersion model to calculate ambient odour concentrations, the separation distance between
livestock buildings and residential areas is defined by the odour impact criteria incorporating the probability of exceeding a pre-selected odour threshold in odour units (OU) per cubic metre. The dynamic Austrian odour dispersion model (AODM), a Gaussian model, is used to calculate the direction-dependent separation distances for several combinations of these two values, which represent the protection level of various land use categories. The calculated direction-dependent separation distances are a function of the prevailing wind velocity and atmospheric stability conditions. At a site in the Austrian North-alpine foreland, the directiondependent separation distance for a 1000-head pig unit (calculated on the basis of a 2-year time series of meteorological data) for pure residential areas (3% probability of threshold exceedance over the year for an odour threshold of 1OUm
3) lies between 99 m(for northerly winds with a probability of less than 3% per year) and 362 m(for westerly winds with a probability of 34%). For themain wind directions, West and East, odour sensation can be expected more often for higher wind velocities and a neutral or stable atmosphere
around sunset. North and South winds show the typical diurnal variation of a local valley wind system with predominantly northerly daytime up-valley and southerly nighttime down-valley winds. Odour sensation is therefore most likely around noon for North winds and during nighttime for South winds.