Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/23/2004
Publication Date: 1/5/2005
Citation: Baak, B.H., Todd, R.W., Cole, N.A., Koziel, J.A. 2005. Ammonia and hydrogen sulfide flux and dry deposition velocity estimates using vertical gradient method at a commercial beef cattle feedlot. In: State of the Science Animal Manure and Waste Management, January 4-7, 2005, San Antonio, Texas. 2005 CDROM. Interpretive Summary: The isolation chamber and micrometeorological vertical gradient flux are two very different methods used to estimate gaseous emissions from animal feeding operations. This study compared ammonia and hydrogen sulfide emissions estimated by the two methods and then related emissions to environmental conditions at a commercial beef cattle feedyard. Ammonia emissions in summer were more than 10 times those in winter. Ammonia emissions estimated using the isolation chamber were less than half those estimated using the gradient flux method in summer, but the two methods were within 12% of each other in winter. Hydrogen sulfide emissions were much greater in the summer; on average, hydrogen sulfide was deposited, not emitted, from the feedyard in winter. Temperature and evaporation of water from pen surfaces were important factors determining emissions. Deposition velocity, an indication of how effectively gases are transported, was greatest during warm daytime conditions, and least during nighttime.
Technical Abstract: Approaches used to measure and estimate trace gas emissions from surface sources include isolation chamber and wind tunnel techniques, micrometeorological vertical gradient and eddy correlation methods and Gaussian dispersion and backward Lagrangian models. Objectives of this study were to compare NH3-N and H2S-S fluxes from a commercial feedyard in the Texas Panhandle using a vertical gradient flux method with previous measurements at the same location using the isolation chamber method; and investigate the relationship of NH3-N and H2S-S fluxes and dry deposition velocities with meteorological variables and atmospheric stability classes. NH3'N and H2S-S fluxes and dry deposition velocities using a gradient flux method were conducted from January 22nd to 24th 2003 and June 16th to July 6th 2004. NH3 and H2S concentrations were measured continuously at 3-m and 6-m heights using chemiluminescence, and profiles of wind speed and ambient temperature were measured at multiple heights on a 10-m tower. Mean ammonia flux estimated using the gradient flux method was approximately 3,671 (+/-2,624) Ug NH3-N/m2/min during Summer 2004 and 317 (+/-209) Ug NH3-N/m2/min during Winter 2003. Hydrogen sulfide flux was 21.71 +/-20.71) Ug H2S-S/m2/min during Summer 2004 and '0.99 (+/-2.91) Ug H2S-S/m2/min during Winter 2003. Ammonia and H2S-S flux had general diurnal patterns with the highest fluxes in daytime and lowest fluxes in nighttime that correlated to manure temperature changes and active evaporation. The highest average deposition velocities also occurred during daytime with unstable atmospheric conditions and the lowest during nighttime with very stable conditions.