Process-based models are being used to predict ammonia (NH 3) emissions from manure sources, but their accuracy has not been fully evaluated for cattle manure. Laboratory trials were conducted to measure the NH 3 volatile fraction (undissociated NH 3 fraction divided by Henry's law constant) and volatilization flux from buffered ammonium-water solution and dairy cattle manure. Effects of ionic strength, ammoniacal N concentration, temperature and pH of the media, and air velocity over the media were evaluated. As represented in existing models, media type, temperature, and pH were verified to influence the NH 3 volatile fraction and mass transfer. Model prediction underestimated the volatile NH 3 fraction by 5% in solution trials and 94% in manure trials. This underestimation was attributed to an increase in surface pH created through the emission of carbon dioxide (CO 2). Ammonia emission rate from both the ammonium solution and manure surfaces was affected by temperature and air velocity. A frequently used dairy manure volatilization model predicted NH 3 emission rates from manure surfaces more accurately than that from buffered solution with average errors of-16% and +81%, respectively. Temperature significantly affected the difference between predicted and measured rates, with the greatest error at temperatures over 25°C. The results imply that further model development is needed to improve the accuracy of predicting NH 3 emissions from dairy cattle manure with an emphasis on the measurement and prediction of manure surface pH as affected by CO 2 emission.
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I would like to thank my adviser, Harold Keener, for his support, his very helpful attention to details, and his high expectations from me. I would also thank my initial advisor, Dr. Reza Ehsani, for his support and the freedom of action he gave me in my work, before he resigned from OSU. I also thank my graduate committee members Dr. Mark Bennett and Dr. Deborah Stinner for their support. I thank the department of Food, Agricultural and Biological Engineering for funding me in my research, and giving me the technical and personal assistance I needed. I also thank the American Society of Agricultural and Biological Engineers for giving me the opportunity to present my work and interact with other professionals in my field; their welcoming attitude towards beginning professionals is very encouraging. I thank my mother for bearing my absence from home during my PhD studies. I also thank all my friends in the graduate student room 250 for their help and support, and my friends and roommates as well.
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