The Austrian Odour Dispersion Model AODM is used to calculate the separation distance between livestock buildings and ambient residential areas for different odour impact criteria. These are defined as a combination of pre-selected odour threshold and an exceeding probability representing the protection level of various land use categories in different countries.

The AODM consists of three modules: (1) odour release on the basis of a simulation model for the indoor climate of livestock buildings, (2) a regulatory dispersion model (Gauss) to calculate hourly or half-hourly ambient odour concentrations and (3) a fluctuation module, calculating the instantaneous odour concentration, depending on wind velocity and stability of the atmosphere. The calculated separation distances for a pig fattening unit of 1000 heads are compared with those estimated from empirical guide lines used in some countries (Austria, Germany, Switzerland, The Netherlands, USA), and resulting discrepancies are discussed.

The AODM odour concentrations are calculated by means of a statistics of stability classes representative for the Austrian flatlands north of the Alps. A two-year time series of meteorological data collected at the Austrian city Wels is used. Stability classes are determined as a function of half-hourly mean wind velocity and a combination of sun elevation angle and cloud cover. For selected odour impact criteria, the occurrence of odour sensation is analysed for diurnal and annual variability and for the dependance on wind velocity, wind speed, and stability of the atmosphere. Whereas there is a good co-incidence between the calculated diurnal variation of the occurrence of odour sensation and the observed time of complaints, the agreement is less good for the annual variation. Possible explanations will be presented and discussed.