the emission; this is the entrance of the airborne pollutants into the open atmosphere. The local position of this entrance is the emission source, - the transmission, including all phenomena of transport, dispersion and dilution in the open atmosphere, - the immission; this is the entrance of the pollutant into an acceptor. As we are regarding odoriferous pollutants, the immisson is their entrance into a human nose. About air pollution from industrial emission sources, i.g. S02 from power plants, a wide knowledge is available, including sophisticated methods of emission measurement, atmospheric diffusion calculation and measurement of immission concentration in the ambient air. In most countries we have complete national legal regulations, concerning limitation of air contaminent emissions, calculation of stack height and at least evaluation and determination of maximum inmission values. Within this situation the question arises, whether these wellproved methods and devices are suitable for agricultural odour emissions from agricultural sources too. It is well known that all calculations and values, established in air pollution control, are based on large sets of data, obtained by a multitude of experiments and observations. The attempt to apply these established dispersion models to agricultural emission sources, leads to unreasonable results. A comparison in table 1 shows that the large scale values of industrial air pollutions, on which the established dispersion models are based, are too different from those in agriculture. In order to modify the existing dispersion models or to design other types of models, we need the corresponding sets of observations and of experimental data, adequate to the typical agricultural conditions. There are already a lot of investigations to measure odour at the source and in the ambient air. But we all know about the reliability of those measurements and about the difficulties to quantify these results adequate to a computer model calculating the relation between emission and immision depending on various influences and parameters. So we decided to supplement the odour measurements by tracer gas measurements easy to realise with high accuracy. The aim is to get the necessary sets of experimental data for the modification of existing dispersion models for agricultural conditions. 2. INSTRUMENTAL 2.1 EMISSION the published guideline VDI 3881 /2-4/ describes, how to measure odour emissions for application in dispersion models. Results obtained by this method have to be completed with physical data like flow rates etc. As olfactometric odour threshold determination is rather expensive, it is supplemented with tracer gas emissions, easy to quantify. In the mobile tracer gas emission source, fig. 2, up to 50 kg propane per hour are diluted with up to 1 000 m3 air per hour. This blend is blown into the open atmosphere. The dilution device, including the fan, can be seperated from the trailer and mounted at any place, e.g. on top of a roof to simulate the exaust of a pig house or in the middle of a field to simulate undisturbed air flow. 2.2 TRANSMISSION For safety reasons, propane concentration at the source is always below the lower ignition concentration of 2,1 %. As the specific gravity of this emitted propane-air-blend is very close to that of pure air (difference less than 0,2%) and as flow parameters can be chosen in a wide range, we assume