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Title: AN APPROACH FOR MEASURING METHANE EMISSIONS FROM WHOLE FARMS

Author
item MCGINN, S - AG AND AGRI-FOOD CANADA
item FLESCH, T - UNIVERSITY OF ALBERTA
item Harper, Lowry
item BEAUCHEMIN, K - AG AND AGRI-FOOD CANADA

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2005
Publication Date: 1/3/2006
Citation: Mcginn, S.M., Flesch, T.K., Harper, L.A., Beauchemin, K.A. 2006. An approach for measuring methane emissions from whole farms. Journal of Environmental Quality. 35:14-20.

Interpretive Summary: Ruminant animals, like cattle and buffalo, have a fore-stomach which decomposes grasses to digestible components. In this enteric digestion process, methane is produced as a byproduct. Estimates of methane emissions from ruminants are typically measured by confining animals in sealed rooms to capture emitted gases, using hoods or masks over their heads to capture emitted gases, or by sampling air from the animal’s breath. These techniques are stressful to the animals and are not appropriate to evaluate large scale farm emissions with many animals and the variability between farms that may be caused by different farm management systems. This study describes the application of a technique by Agriculture and Agri-Food Canada in Lethbridge, the University of Alberta in Edmonton, and the USDA-ARS at the J.P. Campbell Sr. Natural Resource Conservation Center in Watkinsville, GA, to calculate farm methane emissions using a technique which does not interfere with the animals. This study was conducted at a commercial dairy farm in southern Alberta with a total of 473 cattle. Known quantities of tracer gases (sulfur hexafluoride and methane) were released from ten outlet locations (in the barn and open pens) using gas flow regulators. An inverse dispersion technique (called the backward Lagrangian stochastic dispersion model) was then used to infer farm emissions from gas concentrations measured downwind of the farm. Concentrations of tracer gases were measured by gas chromatograph analysis and open-path lasers. Wind information parameters were measured with a three dimensional sonic anemometer. Comparing the inferred emissions with the known release rate emissions showed that our calculations accounted for 86% of the released methane and 100% of the released sulfur hexafluoride. The studies also showed that the location of the concentration observations downwind of the farm was critically important to the success of this technique for calculating emissions. These results showed that this dispersion analysis technique will provide accurate whole-farm trace-gas emissions while allowing non-interference measurements. By obtaining better estimates of trace-gas emissions inventories, producers can evaluate management techniques to reduce emissions while increasing production efficiency and regulatory agencies can obtain more accurate and appropriate trace-gas emissions inventories.

Technical Abstract: Estimates of enteric methane (CH4) emissions from ruminants are typically measured by confining animal 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 (total of 321 cattle, including 152 lactating dairy cows). Sulphur hexafluoride (SF6) and CH4 were released from ten outlet locations (barn and open pens) using mass flow controllers. A Lagrangian Stochastic 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.