|Todd, Richard - Rick|
Submitted to: Agriculture Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2007
Publication Date: 5/14/2007
Citation: Flesch, T.K., Wilson, J.D., Harper, L.A., Todd, R.W., Cole, N.A. 2007. Determining ammonia emissions from a cattle feedlot with an inverse dispersion technique. Agriculture and Forest Meteorology. 144:139-155. Interpretive Summary: Ammonia is a nitrogen compound released to the atmosphere from concentrated animal feeding operations. Excess ammonia-nitrogen can overfertilize and degrade sensitive ecosystems. Ammonia is a precursor to minute atmospheric particles that can affect health and degrade air quality. Accurate estimation of ammonia emissions from cattle feedlots requires measurements of ammonia concentration and some kind of atmospheric dispersion model that incorporates the physical mechanism of how ammonia is removed and swept away from the feedlot into the atmosphere. This research tested such a model, called a backward Lagrangian stochastic (BLS) dispersion model, in the complicated case of a cattle feedlot. Measuring ammonia concentration and wind variables inside the feedlot yielded better data and ammonia emission estimates than measurements taken outside of and downwind from the feedlot. Data collected during twelve days in summer 2004 and ten days in summer 2005 showed that, on average, each animal in the feedlot released 150 grams (0.33 lb) of ammonia every day to the atmosphere. This ammonia-nitrogen loss was 63% (2004) or 65% (2005) of the nitrogen that was fed to the cattle, and was consistent with results of other studies. Application of the BLS dispersion model will improve the ability to monitor and quantify ammonia emissions from cattle feeding operations.
Technical Abstract: An inverse-dispersion technique is used to calculate ammonia (NH3) gas emissions from a cattle feedlot. The technique relies on a simple backward Lagrangian stochastic (bLS) dispersion model to relate atmospheric NH3 concentration to the emission rate Qbls. Because the wind and the source configuration are complicated, the optimal implementation of the technique is unclear. Two categorically different measurement locations (for concentration and winds) are considered: within the feedlot and downwind. The in-feedlot location proved superior, giving a nearly continuous Qbls timeseries. We found average emissions of 0.15 kg NH3/animal/day in both 2004 and 2005, representing a loss of 63% (2004) or 65% (2005) of the dietary nitrogen in the animal feed. Downwind measurement locations were less useful for several reasons: a narrow range of useable wind directions; ambiguity in the choice of wind statistics to use in the calculations; low NH3 concentrations; and downwind deposition of NH3. When addressing a large source (like a feedlot) that modifies the ambient wind flow, we recommend in-source measurements for use in inverse dispersion applications.