Towards a Harmonized Odour Guideline for Some Austrian Provinces

Currently some provinces in Austria attempt to set up a harmonized regulation for assessing odour nuisance. The Austrian laws do not stipulate that any nuisance is to be prevented, but only “unacceptable” nuisance. “Unacceptable” is not a scientific or medical term but needs to be interpreted in a legal context. In the new guideline different odour impact criteria (OIC) are set up with regard to the hedonic tone of odours. For each category a maximally allowed frequency is defined. Frequencies are to be assessed on the total number of hours of a year, where the computed 90th percentile within one hour is above a certain threshold concentration (e.g. 1 odour unit [ou] per m³). Such is termed an odour hour. Dispersion modelling is the major methodology for odour assessments. Unlike in Germany, no specific model is prescribed, but model developers need to prove the capability of their model to accurately simulate the 90th percentile odour concentration of an hour. For instance, the Lagrangian particle model GRAL, which is frequently used in Austria, offers a new module to compute the 90th percentile based on the work of Oettl and Ferrero (2017a). The 90th percentile is thereby a function of the three dimensional odour-concentration field and the atmospheric turbulence, thus, the model is able to take into account the effects of overlapping odour plumes, too. It could be demonstrated that modelled odour-hour frequencies using this novel approach are in very good agreement with observed odour hours assessed by field inspections following the new European standard EN 16841-1. Field inspections, therefore, may also be used for odour assessment, whenever modelling is not possible (e.g. unknown source strengths). OICs are derived upon dose-response relationships, which were established by evaluating historical citizen’s complaints using the dispersion model GRAL. Relationships between the percentage of annoyed residents and modelled odour-hour frequencies were found to be quite different for odorants having a very high potential of offensiveness and such with a moderate potential. Discontinuous odour sources are assessed by using OICs based on the 0.5th percentile evaluated for concentrations larger than 1 ou m-3. The corresponding concentration thresholds for the four distinguished hedonic tones were derived by matching the affected non-attainment areas resulting from the regulations for continuous sources with those resulting from the 0.5th percentile regulation.