SOME POTENTIAL PROBLEMS FOR MEASURING AMMONIA EMISSIONS FROM FARM STRUCTURES

摘要

The ability to accurately measure ammonia emissions from farm buildings is an important issue both for establishing emissions regulations and for effective evaluation of mitigation techniques. Most techniques for measuring emissions rely on sub-sampling within a space. 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 gases were well mixed. The chamber temperature was maintained at 22.2ºC with an airflow of 10.5 air exchanges per hour. 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 airflow, and were 52% when the positions were not aligned. Placing a wooden barrier between aligned release and measurement 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. It is suggested that measurement of ammonia emissions be restricted to farm structures with well-defined airflows and a limited number of exhaust openings, and that the most accurate method for estimating ammonia emission rates would be to collect and mix all of the exhaust streams from a structure prior to continuously measuring ammonia concentration and airflow