Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 18, 2000
Publication Date: N/A
Technical Abstract: Flux-gradient techniques use tracer concentrations gradients to infer fluxes from a surface. In this study we compared tracer emission rates computed from a flux-gradient (FG) approach with estimates from an integrated horizontal flux (IHF) method and a dispersion-model based (backward Lagrangian stochastic, BLS) flux estimation technique. A pre-emergent herbicide (active ingredient metolachlor) was applied to a bare soil field. Average tracer concentrations, windspeed, and stability parameters were measured in the center of the field. Emission rates were calculated using FG, IHF, and BLS techniques. During the course of seven days, 20 comparison measurement periods were selected. We assumed the IHF method as "truth" in the experiment. We found that the FG formula underestimated tracer fluxes by 30 to 40%. This suggests the turbulent Schmidt number (Sc) for tracers is approximately 0.6, and not unity as is often assumed in FG calculations. The BLS-based estimates were in better agreement with the IHF technique.