Predicting odour impact using the Austrian odour dispersion model (AODM) G. Schauberger* and M. Piringer** *Institute of Medical Physics and Biostatistics, University of Veterinary Medicine Vienna, Veterinärplatz 1, A-1210 Vienna, Austria (E-mail: gunther.schauberger@vu-wien.ac.at) **Central Institute for Meteorology and Geodynamics, Hohe Warte 38, A 1190 Vienna, Austria (E-mail: martin.piringer@zamg.ac.at) Abstract 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 using a combination of a pre-selected odour threshold and an exceeding probability. 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 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 probability of 34%). For west and east the main wind directions, odour sensation can be expected more often for higher wind velocities and a neutral or stable atmosphere around sunset. Northerly and southerly winds show the typical diurnal variation of a local valley wind system with predominantly northerly daytime up-valley and southerly night-time down-valley winds. Keywords Dispersion model; livestock building; separation distance; odour impact criteria Introduction Odour is one of the major nuisances in the environment mainly caused by livestock units and industry (Schauberger et al., 2001). To overcome the odour nuisance as far as possible, a separation distance between the odour source and residential areas is used to reduce the odour annoyance to an acceptable level. Apart from empirical guide lines used to estimate the separation distance (for Central European guide lines see, e.g. Piringer and Schauberger, 1999), it can also be calculated by dispersion models. The following information has to be available: odour release (Martinec et al., 1998; Schauberger et al., 1999), a dispersion model (e.g. the regulatory Gaussian model used in Austria, see ÖNorm M 9440, 1992/96), the calculation of the instantaneous odour concentration (Schauberger et al., 2000b), and the validation of the instantaneous odour concentration taking into account the FIDO factors (frequency, intensity, duration and offensiveness) of odour sensation and the reasonableness. The Austrian Odour Dispersion Model, AODM, consists of an odour emission module based on a steady-state balance model including a simple odour release parameterisation (Schauberger et al., 1999 and 2000a). The Gaussian regulatory model ÖNorm M 9440 (1992/96) is used to calculate half-hourly mean values of odour concentrations depending on atmospheric stability class, wind direction, and wind velocity. The third feature of the AODM is the calculation of the instantaneous concentration. The model is discussed in detail by Schauberger et al. (2001). Odour concentrations calculated by dispersion models at a certain distance from the source have to be evaluated against the odour impact criteria. Watts and Sweeten (1995) Water Science and Technology Vol 44 No 9 pp 197–204 © IWA Publishing 2001 197