Estimates of In-Canopy Ammonia Sources and Sinks Using Measured Profiles and Turbulence Closure Models

Jesse O. Bash
U.S. EPA National Exposure Research Laboratory,
Research Triangle Park, NC USA

Estimates of in-canopy sources and sinks of ammonia in a fertilized corn, Zea Mays, field were inferred using measured in-canopy concentration profiles and analytical half order and K-e turbulence closure models. Ammonia concentrations were measured at four heights in the canopy and one height above the canopy using manually collected denuders in addition to three collocated above canopy continuous Ammonia Measurement by ANnular Denuder with online Analysis (AMANDA) concentration. Vertical profiles of wind speed, heat, and momentum fluxes were made from inside the canopy to a height of 10 meters using 3-D sonic anemometers. Ancillary vertical profiles of temperature were measured using copper/constantan thermocouples for model evaluation. K-e modeled ammonia and sensible heat fluxes agreed well with above canopy micrometeorological fluxes. The soil was found to be a consistent emission source, while the vegetation canopy was typically a net ammonia sink with the lower portion of the canopy being a constant sink. The upper portion of the canopy was dynamic, exhibiting periods of local deposition and evasion. The use of Eulerian based in-canopy models allowed for a physically descriptive partitioning of atmospheric-soil and atmospheric-vegetation exchange of measured scalars.