Measurements of ammonia emissions from spreading of manure using gradient FTIR techniques

Emissions of biogenic trace gases from soils and plants often show strong spatial and temporal variation. Thus, there is a need for the development of area-integrating measurement techniques with good time resolution. The present paper describes area-integrated measurements of ammonia emissions after spreading of pig slurry on a wheat field, based on flux–gradient measurements using Fourier transform infrared (FTIR) spectroscopy. Two methods are described; the aerodynamic method where the flux is derived from measured micrometeorological parameters, and a tracer method where the flux is derived from simultaneous measurements of a tracer gas released over the area under study. Although not ideal in the actual measurement situation, this latter method has a potential for use on more local sources with less restrictions on micrometeorological conditions, and is thus included for validation. A code for modelling of the “footprint” of gradient measurements is also described, and is used to compare the results from the above-mentioned methods.