Analysis of model calculations of odour sensation episodes in the vicinity of livestock buildings

Odour is one of the major pollution sources from livestock husbandry, especially in the swine industry causing a great need for odour related research. Environmental agencies are confronted by complaints of people living in the vicinity of animal production farms. Reports about these complaints show similar time patterns, concentrated during the warm season and during the day in the morning hours in and in the afternoon and evening hours.

In this paper we compare the time pattern of the complaints with the time pattern of odour sensation which were calculated by dispersion models. With the aid of the Austrian odour dispersion model (AODM), a Gaussian model which was adapted for the prediction of odour sensation, the separation distance is calculated for a threshold of 1 odour unit (OU) per cubic metre which is exceeded in 3% of the year. 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 for a 1000 head pig unit (calculated on the basis of a two-year time series of meteorological data) 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 the main 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 night-time down-valley winds. Odour sensation is therefore most likely around noon for North wind and during night time for South wind.

The results of this study lead to the following open questions: (1) Is a constant odour emission over the year a realistic approach? (2) Is a threshold and an exceedance probability an appropriate method to assess the annoying level? (3) Should we weight odour sensation by time of the day and time of the year? (4) Is odour perception sensitivity of humans depending on temperature and humidity?