Author
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Lefcourt, Alan |
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Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/1/2002 Publication Date: 10/1/2002 Citation: LEFCOURT, A.M. POTENTIAL PROBLEMS FOR MEASURING AMMONIA EMISSIONS FROM FARM STRUCTURES. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 45(5):1585-1591. 2002. Interpretive Summary: Ammonia originating from animal manures on farms can adversely affect the heath of animals and workers, and has been linked to detrimental effects on the environment. It is important to be able to accurately measure ammonia emissions from farm buildings in order to be able to establish fair and equitable regulations and to allow for effective evaluation of methods for reducing ammonia losses from farm structures. Most techniques for measurin emissions rely on sub-sampling, that is, sampling ammonia at a single point and then multiplying that measured value by an estimated total air flow through the structure to determine the ammonia emission rate. This study examined the influence of sub-sampling under a variety of conditions on estimated ammonia emission rates. Tests were made using a large environmental chamber with a fixed air flow rate. Ammonia was released into the chamber from one of two positions. The resulting ammonia concentrations swere measured either in a single exhaust duct or using a sampling port in the exhaust plenum where exhaust gasses were well mixed. For measurements made in the exhaust duct, measured ammonia emission rates were double actual values when the release position and the sampling duct were aligned in terms of chamber air flow, and were half when the positions were not aligned. Placing a wooden barrier between aligned release and measurements positions had little affect on measured emissions. Using an oscillating fan to disperse the ammonia reduced measured ammonia emissions to three-quarters of actual values. When measurements were made in the plenum, measured and actual ammonia emission rates were essentially identical. We suggest that the easiest method for making accurate measurements is to collect and mix all the exhaust from a building prior to sub-sampling. Technical Abstract: The ability to accurately measure ammonia emissions from farm buildings is an important issue both in terms of establishing emissions regulations and for effective evaluation of mitigation techniques. Most techniques for measuring emissions rely on sub-sampling. This study examines the influence of sub-sampling under a variety of conditions on estimated ammonia recoveries. Tests were made using a large environmental chamber with controlled releases of ammonia from a gas cylinder from one of two positions within the chamber. Ammonia concentrations were measured in continuous air samples from either a single exhaust duct or a sampling port in the exhaust plenum where exhaust gasses were well mixed. The chamber temperature was maintained at 22.2 degrees C with an flow of 10.5 air exchanges per h. For measurements made in the exhaust duct, ammonia recoveries were 217% when the release position and the sampling duct were aligned in terms of chamber air flow, and were 52% when the positions were not aligned. Placing a wooden barrier between aligned release and measurements positions only reduced ammonia recoveries to 173%. In contrast, using an oscillating fan to disperse the ammonia release reduced ammonia recoveries to 78%. When measurements were made in the plenum, recoveries were essentially 100%, and placement of a continuously-wetted barrier between the release position and the exhaust ducts did not influence recoveries. Results from this study indicate that accurate measurement of total ammonia emission rates from farm structures requires consideration of all air flow pathways, and suggest that the easiest method for making accurate measurements is to collect and mix all the exhaust from a building prior to sub-sampling. |
