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TECHNICAL REPORTS

An Approach for Measuring Methane Emissions from Whole Farms

^a Agriculture and Agri-Food Canada, P.O. Box 3000, Lethbridge, AB, Canada T1J 4B1
^b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E3
^c Agricultural Research Service, United States Department of Agriculture, Watkinsville, GA 30677

^* Corresponding author (mcginn{at}agr.gc.ca)

Estimates of enteric methane (CH₄) emissions from ruminants are typically measured by confining animals in large chambers, using head hoods or masks, or by a ratiometric technique involving sampling respired air of the animal. These techniques are not appropriate to evaluate large-scale farm emissions and the variability between farms that may be partly attributed to different farm management. This study describes the application of an inverse-dispersion technique to calculate farm emissions in a controlled tracer-release experiment. Our study was conducted at a commercial dairy farm in southern Alberta, Canada (total of 321 cattle, including 152 lactating dairy cows). Sulfur hexafluoride (SF₆) and CH₄ were released from 10 outlet locations (barn and open pens) using mass-flow controllers. A Lagrangian stochastic (LS) dispersion model was then used to infer farm emissions from downwind gas concentrations. Concentrations of SF₆ and CH₄ were measured by gas chromatography analysis and open path lasers, respectively. Wind statistics were measured with a three-dimensional sonic anemometer. Comparing the inferred emissions with the known release rate showed we recovered 86% of the released CH₄ and 100% of the released SF₆. The location of the concentration observations downwind of the farm was critically important to the success of this technique.

Abbreviations: (C/F)_sim, theoretical ratio of concentration to emission • (F_area/F_point), ratio emissions based on area to that based on point configure of source • GC, gas chromatograph • h, obstacle height • LS, Lagrangian stochastic • x_s, source separation distance

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