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Ammonia emissions from a beef feedlot: Comparison of inverse modeling techniques using long-path and point measurements of fenceline NH3
- Shonkwiler, Kira B., Ham, Jay M.
- Agricultural and forest meteorology 2018 v.258 pp. 29-42
- ammonia, ammonium nitrogen, beef, beef cattle, crude protein, dust, ecosystems, emissions, emissions factor, feedlots, models, national parks, nitrogen, Colorado, Texas
- Nitrogen (N) deposition in Rocky Mountain National Park, USA (RMNP) and adjacent alpine ecosystems has led to increased focus on ammonia (NH3) emissions from livestock operations in this region. A study was conducted at a commercial beef feedlot in Northern Colorado, USA to quantify NH3 fluxes, estimate emission factors (EFs), and evaluate measurement methodologies. Point and line-integrated fenceline NH3 measurements were taken over a 78-day study at a large feedlot east of RMNP focusing on transport towards the park. Ammonia fluxes were estimated using two inverse models, a backward Lagrangian stochastic approach (WindTrax) and a simpler inverse dispersion approach (FIDES) using input data from both NH3 datasets. Line-integrated NH3 concentrations were obtained from a long-path laser and single-point concentrations were collected with a cavity ring-down analyzer, both positioned on the downwind fenceline. Mean feedlot NH3 concentration (±1 standard deviation, σ) was 601±246μgm−3 (1013±421 ppbv), where peak values often exceeded several ppmv. Concentrations from the long-path sensor were slightly higher than the point sensor when winds were from the feedlot (p=0.0005), but 2.5 times less data were collected with the long-path instrument due to dust or laser-reflector alignment issues. Regardless of the model used, fluxes showed a diel pattern peaking in the afternoon with early morning minimums. Emissions varied more by inverse model than by sensor, with WindTrax emissions 25% higher than FIDES. Composite 24-h mean emissions (±1σ) from FIDES were 48±24μgm−2s−1 (EF=71±35ghd−1d−1), while WindTrax averaged 60±30μgm−2s−1 (EF=89±44ghd−1d−1) (p<<0.0001). Overall 24-h mean EF for the summer (across both models) was 80±39ghd−1d−1. When dietary N was considered (13.25% crude protein), based on 24-h composites FIDES estimated NH3-N released to the atmosphere to be 35.6% of fed-N, while WindTrax showed 44.6% fed-N. The overall mean across models was 40.0% fed-N.