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Ammonia (NH3) and hydrogen sulfide (H2S) are emitted from beef cattle feedlots with NH3 being greater by nearly three orders of magnitude. Nearly 30% of the U.S. beef cattle are fed in the High Plains of Texas. Earlier research indicates that abatement technologies may be needed to significantly reduce NH3 emissions. To date, little is known about the appropriate measurement methods to evaluate the effectiveness of NH3 emission controls. In this research, we determined the (a) variability of NH3 and H2S fluxes within a single pen and (b) the relationships between NH3 and H2S fluxes and manure characteristics as a part of a larger field study to determine the effectiveness of the urease inhibitor NBPT. A dynamic, flow-through chamber system was used to estimate NH3 flux from experimental beef cattle pen with a 15.6 m2/head stocking density. The total of 27 measurements were completed within one day using a flux chamber interfaced with an on-site, mobile-instrument shelter. Manure samples from each location were analyzed for moisture content, total kjeldahl nitrogen (TKN), NH4-N, NO3-N, and C:N to characterize their relations with NH3-N and H2S-S flux. The NH3-N flux varied by nearly 30 fold between 512 to 14,993 g/m2-min. The H2S-S flux varied from 0.52 to 8.07 g/m2-min. In addition, flux from fresh urine and feces were also measured for nearly one day. The cumulative NH3-N emissions from fresh feces were 2.5 to 13.7% of NH3-N from urine. The apparent variation of flux within a typical pen has important implications on the selection of appropriate measurement methods for statistically significant evaluation of emission controls.