Comparing emissions from a cattle pen as measured by two micrometeorological techniques

Accurate measurement of ammonia (NH₃) emissions from livestock pens is challenging. Two micrometeorological techniques, the integrated horizontal flux (IHF) and the backward Lagrangian stochastic (bLS) dispersion techniques were used to measure NH₃ emissions from an isolated cattle pen (20 × 20 m) in Victoria, Australia. The bLS technique is simple and insensitive to the presence of animals, but typically gives discontinuous measurements due to the need for target wind directions and wind conditions above accepted thresholds. In contrast, the IHF technique as implemented here gives near-continuous measurements with no restriction on wind directions. However, IHF needs more complex field measurements, and there are ambiguities when applied to an animal pen due to the presence of animals. Over the 29 days of our experiment, we collected 124 coincidental bLS and IHF emission measurements from the pen (30-min each). We found no statistical difference in the bLS and IHF calculations when the IHF turbulent flux correction factor (TF_cor) was set to 15%. Our results confirm that the IHF and bLS techniques, using independent sensors and having very different equipment layouts, gives nearly equivalent results. This suggests the choice of the two methods in future experiments can focus on their different strengths and weaknesses.