Setting acceptable odour criteria using steady-state and annual hourly weather data

In air dispersion models, the predicted distance at which odour dilutes to a certain concentration (e.g., the chosen acceptable concentration) varies if steady-state or annual hourly weather data are used. As a result, different acceptable odour concentration criteria are required for these two types of weather conditions. The objective of this study was to determine the equivalent odour criteria in terms of concentration and frequency that result in the same setback distance for both weather conditions. Odour dispersion from a typical pig farm in Saskatchewan, Canada, was simulated using the CALPUFF model using both steady-state and annual hourly weather data. Results showed that, in order to obtain long setback distances (3, 4 or 5 km), the odour occurrence frequencies should be larger under steady-state stable atmospheric conditions than under annual hourly variable weather conditions. Alternatively, for the same odour occurrence frequency, the concentration should be set higher under steady-state atmospheric conditions than under annual hourly weather conditions. To obtain short setback distances (≤2 km), the odour occurrence frequencies for the same concentration level were different for the two weather conditions and depended on the concentration level selected.