Three-dimensional characterization of the ammonia plume from a beef cattle feedlot

In Canada approximately 45% of ammonia (NH3) emissions are attributed to dairy and beef cattle industries. The present study focused on NH3 emissions from a beef feedlot with a one-time capacity of 17,220 head. The aim was to improve the Canadian NH3 emission inventories and air quality forecasting capabilities. A Cessna 207, equipped with a fast-response NH3/NOy detector and a quadrupole aerosol mass spectrometer, was flown in a grid pattern covering an area of 8 × 8 km centered on a feedlot (800 × 800 m) at altitudes ranging from 30 to 300 m above ground. Stationary ground measurements of NH3 concentration and turbulence parameters were made downwind of the feedlot. Three flights were conducted under varying meteorological conditions, ranging from very calm to windy with near-neutral stratification. NH3 mixing ratios up to 100 ppbv were recorded on the calm day, up to 300 m above ground. An average feedlot NH3 emission rate of 76 ± 4 μg m−2 s−1 (equivalent to 10.2 g head−1 h−1) was estimated. Characteristics of the measured NH3 plume were compared to those predicted by a Lagrangian dispersion model. The spatially integrated pattern of NH3 concentrations predicted and measured agreed but the measured was often more complex than the predicted spatial distribution. The study suggests that the export of NH3 through advection accounted for about 90% of the emissions from the feedlot, chemical transformation was insignificant, and dry deposition accounted for the remaining 10%.