A dual tracer ratio method for comparative emission measurements in an experimental dairy housing

Abstract

Agriculture, and in particular dairy farming, is an important source of ammonia (NH 3 ) and non-carbon dioxide greenhouse gas (GHG) emissions. This calls for the development and quantification of effective mitigation strategies. Our study presents the implementation of a dual tracer ratio method in a novel experimental dairy housing with two identical, but spatially separated housing areas. Modular design and flexible floor elements allow the assessment of structural, process engineering and organisational abatement measures at practical scale. Thereby, the emission reduction potential of specific abatement measures can be quantified in relation to a reference system. Emissions in the naturally ventilated housing are determined by continuous dosing of two artificial tracers (sulphur hexafluoride SF 6 , trifluoromethylsulphur pentafluoride SF 5 CF 3 ) and their real-time detection in the ppt range with an optimized GC-ECD method. The two tracers are dosed into different experimental sections, which enables the independent assessment of both housing areas. Mass flow emissions of NH 3 and GHGs are quantified by areal dosing of tracer gases and multipoint sampling as well as real-time analysis of both tracer and target gases. Validation experiments demonstrate that the technique is suitable for both areal and point emission sources and achieves an uncertainty of less than 10 % for the mass emissions of NH 3 , methane (CH 4 ) and carbon dioxide (CO 2 ), which is superior to other currently available methods. Comparative emission measurements in this experimental dairy housing will provide reliable, currently unavailable information on emissions for Swiss dairy farming and demonstrate 3 the reduction potential of mitigation measures for NH 3 , GHGs and potentially other pollutants.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

“…The latter is difficult to achieve in ruminants as forced exhaust air systems are not common. Some research institutes have built identical animal compartments where a comprehensive assessment of gaseous N emissions across the individual compartments is possible (Pollet et al, 1998;Mathot et al, 2012;Mohn et al, 2018). As the number of test compartments is limited to few, this type of equipment is more suitable to generate information about developments with time and to confirm whether effects from balance experiments can be recovered in entire herds.…”

Methane Emissions and Milk Fatty Acid Profiles in Dairy Cows Fed Linseed, Measured at the Group Level in a Naturally Ventilated Housing and Individually in Respiration Chambers

“…All the cows were given permanent access to water. The cows were milked at 05: 30 At the group level, emissions were measured as described in detail by Mohn et al [20]. Briefly, the housing system provided two spatially separated experimental sections with three rows of cubicles with straw.…”

“…The position of the housing axis was orthogonal to prevailing wind directions, minimizing cross-contamination between the experimental sections. The dual tracer ratio method [20,21] was applied to quantify emissions for each experimental section independently and detect potential cross-contamination. It involved constant dosing of the tracer gases SF 6 and trifluoromethyl sulfur pentafluoride (SF 5 CF 3 ), one per section, at floor level using mass flow controllers (Contrec AG, Switzerland) to regulate the total flow and critical steel orifices to achieve homogenous spatial distribution.…”

“…Concentrations of the tracer gases and target gases (CH 4 and CO 2 ) were analyzed in real time by gas chromatography with electron capture detection (GC-ECD, model 7890A, Agilent Technologies AG, Switzerland) and by cavity ring-down spectrometry (CRDS, CH 4 , CO 2 , model G2301, Picarro Inc., USA). More details on the implemented analytical technique and its performance with respect to suitability for point/areal sources, sensitivity, and uncertainty have been described in Mohn et al [20]. The applied measurement sequence provided emission data with a temporal resolution of 10 min per section.…”

Reduced emissions of warm mix asphalt during construction

“…An additional sampling was conducted at the lee side of the construction site in order to determine the total emissions of the pavement activities. Dilution of pollutants for the lee side measurements was considered using a tracer gas technique with constant tracer gas dosing (SF 6 or SF 5 CF 3 ) at the main emission sources (both paver and one roller compacter) (Mohn et. al., 2018).…”