Applicability of the inverse dispersion method to measure emissions from animal housings

Abstract

Abstract. Emissions from agricultural sources substantially contribute to global warming. The inverse dispersion method has been successfully used for emission measurement from various agricultural sources. The method has also been validated in multiple studies with artificial gas releases mostly on open fields. Release experiments from buildings have been very rare and were partly affected by additional nearby sources of the same gas. What is also lacking are specific release studies for naturally ventilated animal housings. In this study, a known and predefined amount of methane was released from an artificial source inside a barn that mimics a naturally ventilated dairy housing. For concentration measurements, open-path devices (OP) with a path length of 110 m were placed in downwind direction of the barn at a distance of 50 m, 100 m, 150 m, and 200 m and additionally, a 3D ultrasonic anemometer (UA) was placed in the middle of the OP paths at 50 m, 100 m and 150 m. Upwind of the barn, an additional OP and an UA were installed. The median recovery rates of the experiment depending on the used OP and UA combination ranged between 0.56–0.71. It is concluded that for the present study case, the effect of the building and a tree in the main wind axis led to a systematic underestimation of the inverse dispersion method derived emission rate probably due to deviations of the wind field and turbulent dispersion from the ideal assumptions.