Dispersion modeling of odour, gases, and respirable dust using AERMOD for poultry and dairy barns in the Canadian Prairies.

For determining setback distances considering multiple air pollutants, a comprehensive study was conducted to simulate the atmospheric dispersion of odour, ammonia (NH), hydrogen sulfide (HS), and respirable dust using an US EPA air dispersion model AERMOD for a commercial dairy, broiler, and cage-layer barn in the Canadian Prairies. The simulation was conducted using five years of meteorological data. Setback distances were determined with the input of varying monthly emission rates of all four air pollutants and odour impact criteria specifically developed for all three odour sources. Results showed the layer barn had the greatest odour impact area (maximum 3023 m for an annual average odour concentration of 0.01 OU m) followed by the broiler and dairy barns. Due to the prevailing south wind for all three barns, odour traveled farthest in the north. Using the suggested odour impact criteria by the Government of Saskatchewan defined for all odour sources, maximum setback distances were decreasing from 1941 to 641 m for the layer barn and from 980 to 320 m for the broiler barn along with the increasing of odour concentration (OC) thresholds (1-6 OU m), all in the north direction. While for the dairy barn, setback distances were determined only under an OC limit of 1 OU m; maximum 205 m in the north and minimum 171 m in the south. Using the newly developed odour impact criteria specifically for the three odour sources, maximum setback distance of 558 m in the north was determined for the layer barn under an odour threshold of 9 OU m. Additionally, the results suggest the use of odour impact criteria for determining setback distance rather than using gas/respirable threshold limits set in ambient air quality standards as the former always requires much greater setback distances than the latter.