Abstract
The environmental impact of odour is determined by direction dependent separation distances to avoid odour annoyance. In general, the separation distances are calculated by dispersion models using time resolved meteorological data sets of wind velocity, wind direction and the stability of the atmosphere. The calculated ambient odour concentrations are evaluated by odour impact criteria defined by an odour threshold concentration and a related exceedance probability. A relevant model prerequisite is the emission flow rate of an odour source, in most cases assumed as a constant value over time. In reality it is well known that this is not a realistic assumption. In the present study, the sensitivity of the separation distances to increased variations in the emission rates – from a constant value up to a coefficient of variation of 20% - is investigated. This is here undertaken for the national odour impact criterion of Ireland with an odour concentration threshold of 3 ou/m³ of the hourly mean value and an exceedance probability of 2% (98-percentile). The sensitivity study shows that the assumption of a constant odour emission rate will underestimate the separation distances, especially in the main wind directions. The higher the variability of the emission rate, the larger the separation distances. This means that, in the future, time resolved odour emission rates will constitute a necessary prerequisite to calculate reliable separation distances.
