Sensitivities of Four Air Dispersion Models to Climatic Parameters for Swine Odor Dispersion

Abstract

Using air dispersion models to predict downwind livestock odor concentrations in order to establish science-based setback distances has the potential to become a common practice for regulatory agencies. In this study, four air dispersion models, ISCST3, AUSPLUME, INPUFF2, and CALPUFF, were used to simulate odor dispersion from a swine farm. The sensitivity analyses were conducted to develop an understanding of how model climatic parameters affect downwind odor concentrations and travel distances. Under steady-state weather conditions, the results indicated that the odor dispersion was mainly affected by atmospheric stability, wind speed, wind direction, and air temperature. Odor transport was favored by stable atmospheric conditions, low wind speed, and high ambient temperature. The four models' predictions for odor concentrations varied greatly within 1 km from the source; beyond that, ISCST3 and CALPUFF gave similar results (within 17%), while AUSPLUME's and INPUFF2's predictions were much lower than those of ISCST3 by up to 45.3%. However, when hourly averaged annual meteorological data were used, CALPUFF predicted the highest odor concentrations (up to 71.4% higher than those of ISCST3), and AUSPLUME's predictions were also higher than those of ISCST3, which were very different from the results obtained under steady-state weather conditions. INPUFF2's predictions were the lowest (up to 40.5% lower than those of ISCST3). When determining setback distances, it is recommended that if steady-state weather data are used, the odor concentration criterion allowed should be higher than the criterion allowed when using hourly annual or monthly weather data for the same neighboring land use.