Intercomparison of Techniques to Measure NH3 Concentrations and Fluxes above a Fertilized Corn Field

M.R. Jones
National Risk Management Research Laboratory,
Washington, D.C. USA

A number of measurement techniques and methods were deployed to measure NH3 concentrations and fluxes. The experiment was conducted from April to August 2007 in a fertilized corn field near Lillington, North Carolina, where a consortium of government agencies and universities contributed six unique NH3 measurement techniques. An upgraded AMANDA system (Ammonia Measurement by ANnular Denuder sampling with on line Analyser), which measured NH3 concentrations via an improved conductivity cell, was configured in a 3-height gradient mode above the vegetation for determination of canopy-scale air-surface exchange. Two Nitrolux-200 (Pranalytica, Inc.) photoacoustic spectrometers were run in a 2–height NH3 flux gradient mode with automated switching between sampling heights. A 2-height manual denuder (URG) gradient system was run during two 2-week intensives to provide 3-hour integrated NH3 concentrations and fluxes. A second manual denuder (URG) system provided 12-hour integrated NH3 concentrations at a single measurement height for the duration of the experiment. Toward the end of the growing season, manual denuders (URG) were periodically deployed in a 5-height vertical profile to provide in- and above-canopy NH3 concentrations. Finally, weekly passive (ALPHA) NH3 samples were also collected for the duration of the experiment.

These techniques provided a broad range of the available methods for measuring NH3 concentrations and fluxes. The experiment demonstrated the benefits and weaknesses of the different methods and provided much needed NH3 flux and concentration data for fertilized cropping systems in the US.