Recent developments in odour modelling and assessment in Styria and Salzburg, Austria

It can safely be stated that odour assessment is among the least harmonized issues within the EU. Even on a national level, local authorities sometimes use different approaches. In Austria, most regulations concerning odour are determined on a national level. However, neither common modelling techniques nor assessment methods are defined in the corresponding laws. In an effort to harmonize odour assessment in Austria, two provinces – Styria and Salzburg – issued a new guideline setting thresholds for odour-hour frequencies in dependence on the annoyance potential. The limit values were derived from examinations of complaint rates by neighbours of various odorous sources (pig and broiler sheds, compost facilities) and existing dose-response relationships published in literature. Indeed, odour frequency and odour type were sufficient to predict complaint frequencies with high accuracy in a logistic regression model. Recently, the corresponding modelling technique for odour hours has been improved, too. By definition, an odour hour requires 6 minutes of odour recognition by a qualified panel. Dispersion models typically provide hourly-mean concentration values. Therefore, further methods are necessary to obtain the 90th percentile of the odour concentration distribution for odour-hour assessment. For regulatory purposes often a constant value is used (e.g. 4.0 in Germany, or 2.3 in Lombardy, Italy). It can be demonstrated that such a simple approach is not valid in most applications, while the newly developed concentration-variance method, which has been implemented in the Lagrangian dispersion model GRAL, is better suited for odour-hour estimations. A comparison of observed odour-hour frequencies based on EN16841-1 and modelled frequencies using GRAL showed good agreement close and farther away from the odour source. Furthermore, odour emission factors from animal husbandry have been investigated by olfactometric measurements (EN13725) and finally be updated, because the emission factors listed in the comprehensive German guideline VDI3894-1 seem to be much too low, at least for pigs and chicken.