A methodology for the measurement of distributed agricultural sources of ammonia outdoors-Part 2: field validation and farm measurements

Recurved passive ammonia flux (PAF) samplers based on absorption by oxalic acid were evaluated in two contrasting field environments. First, a flux frame 12 m high and 55.2 m long was used to support a vertical array of up to 156 flux samplers downwind of a controlled point or line source of ammonia (NH3). The upwind distance of the NH3 source was chosen so that the whole NH3 plume was captured by the flux frame. These measurements were used to calibrate the flux frame's collection efficiency (CE). The plume dispersion was modelled with ADMS. Second, individual columns of seven flux samplers at heights between 0.3 and 10.4 m were used to measure the NH3 emissions from a free-range sow paddock. The controlled release measurements gave measured overall CEs of over 80% and strong agreement between the measured and modelled flux densities (R2>0.9). The farm measurements showed that this method is insufficiently sensitive for use in a climate for which the wind direction and other critical meteorological parameters may vary widely throughout the several days required for a measurement.