National Odour Impact Criteria: Are the Modelled Separation Distances Between Sources and Receptors Comparable?

Abstract

To determine separation distances between odour sources and residential areas (in order to safeguard against nuisance and complaints), odour impact criteria (OIC) are adopted by the national regulatory authorities. There is a wide variety of OIC used for this purpose, which differ by the odour concentration threshold (between 0.12 ou m-3 and 10 ou m-3), the averaging period (hourly or instantaneous) and by thetolerated exceedance probability of the adopted threshold (between 0.1% and about 35% of the time). Using two national OIC for the protection of rural residential properties (Ireland with a threshold of 6 ou m-3 and a tolerated exceedance probability of 2%) and Germany (with a threshold of 0.25 ou m-3 and a tolerated exceedance probability of 20%), the direction-dependent separation distances were calculated, and compared against those of 166 different OIC. It is interesting to investigate whether the large range ofnational OIC results in large differences in the modelled separation distances. For this investigation, the normalised mean standard error (NMSR) was selected as a statistical measure. There are two groups of OIC used in various jurisdictions: the first one with a low odour concentration threshold and a high tolerated exceedance probability (e.g. Germany); and the second group with a high odour concentration threshold and a low tolerated exceedance probability (e.g. Ireland). The modelled direction-dependent separation distances (using OIC which are supposed to offer the same protection level) can vary significantly. The OIC of the second group, considering higher ambient odour concentrations, show a much lower sensitivity to site-specific meteorological data. Therefore, a higher tolerated exceedance probability seems more appropriate for the determination of OIC. Even if the similarity of separation distances by various OIC could be determined, the direction-dependent separation distances differ considerably for the same protection level for a certain receptor type, e.g. rural residential properties.