Inferential model estimates of ammonia dry deposition in the vicinity of a swine production facility

This project investigates NH 3 dry deposition around a commercial swine production facility in eastern North Carolina. Passive diffusion-tube samplers were used to measure weekly integrated NH 3 concentrations at 22 locations along horizontal gradients from the barn/lagoon emissions complex (source) out to a distance of 700 m. A two-layer canopy compensation point model was used to predict bi-directional NH 3 exchange within a 500 m circular buffer surrounding the source. The model takes into account differences in soil and vegetation emission potential, as well as canopy physical characteristics, among three primary surfaces surrounding the site: forest, crops spray fertilized with swine waste, and other fertilized crops. Between June 2003 and July 2005, mean observed NH 3 concentrations ranged from 169.0 μg NH 3 m −3 at a distance of 10 m from the source to 7.1 and 13.0 μg NH 3 m −3 at 612 and 698 m in the predominant upwind and downwind directions, respectively. Median predicted dry deposition rates ranged from 145 kg NH 3–N ha −1 yr −1 at 10 m from the source to 16 kg NH 3–N ha −1 yr −1 at 500 m, which is ≈3.5× wet deposition of NH 4 +–N. Assuming a steady-state emission factor of 7.0 kg NH 3 animal −1 yr −1 and a median population of 4900 animals, NH 3 dry deposition over the nearest 500 m from the barn/lagoon complex accounted for 10.4% (3567 kg NH 3) of annual emissions (34,300 kg NH 3). A model sensitivity analysis shows that predicted deposition rates are more sensitive to assumptions regarding cuticular uptake relative to soil and vegetation emission potentials.