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We conducted field experiments to evaluate how factors such as sweep air flowrate, time since urine deposition, and flux chamber footprint area affect ammonia fluxes from open-lot feedyard and dairy surfaces as measured using three different flux chamber designs. The chambers included a 26.5-cm diameter chamber (North Carolina State University design), a 49-cm diameter chamber (EPA-type design), and a 1.2 m x 2.4 m rectangular chamber (West Texas A&M University design). Clean sweep air collected upwind of the feedyard (<50 ppb NH3-N) was supplied to the chambers using a large compressed air tank, and ammonia concentrations were measured using a Thermo Environmental Instruments 17C chemiluminescence NH3 analyzer. Ammonia fluxes increased up to 10-fold between sweep airflow rates of 0.1 and 1.0 volumetric changes per minute. Ammonia fluxes from urine spots were highly dependent on the time since the urine was excreted. In one instance, the flux decreased at 57 ug/m2/min for every minute elapsed during the first two hours after excretion. Maximum fluxes and variability among individual flux measurements decreased with increasing flux chamber footprint area. A better knowledge of how these factors affect calculated emission rates will be beneficial to future development of emission factors for open-lot feedyards and dairies.