A micrometeorological technique for detecting small differences in methane emissions from two groups of cattle

Potential approaches for reducing enteric methane (CH 4 ) emissions from cattle will require verification of their efficacy at the paddock scale. We designed a micrometeorological approach to compare emissions from two groups of grazing cattle. The approach consists of measuring line-averaged CH 4 mole fractions upwind and downwind of each group and using a backward-Lagrangian stochastic model to compute CH 4 emission rates from the observed mole fractions, in combination with turbulence statistics measured by a sonic anemometer. With careful screening for suitable wind conditions, a difference of 10% in group emission rates could be detected. This result was corroborated by simultaneous measurements of daily CH 4 emissions from each animal with the sulfur hexafluoride (SF 6 ) tracer-ratio technique.