Measurements of gaseous emissions from naturally ventilated livestock barns.

摘要

Agriculture contributes over 80% of national NH3 emission and ~55% is attributed to animal livestock operations. Livestock barns are one of the major emission sources due to their large footprint. Therefore, a pressing need exists to develop effective emissions mitigation techniques. However, lack of reliable emission measuring techniques, especially for naturally ventilated (NV) livestock barns, impedes development of effective strategies for mitigating emissions. Furthermore, multiple inlets and outlets associated with NV animal housing and unstable ambient meteorology presents a huge challenge in the determination of ventilation rate.;Due to high investment in use of the direct method, indirect methods are preferably used for determining ventilation rates in NV animal buildings. In this thesis, two widely used indirect methods (CO2-balance and H2O-balance method) were evaluated against a direct method. The results revealed that CO2-balance method overestimated barn air exchange rates (AER), while H2O-balance method underestimated the AER. Integration time and wind velocity, on the other hand, had significant effects on both indirect methods. The two indirect methods also were not reliable during milking time or at low indoor-outdoor differences in temperatures, absolute humidity, and CO2 concentrations.;In view of complexity of current direct methods, two simple direct methods were developed and determined to be suitable for AER measurement with marginal relative errors. The two methods were based on measurements of wind speed at a local weather tower or at only one location adjacent to the center of the barn. The third simple approach, via CO2-balance method, evaluated two gas-sampling regimes: indoor-outdoor and perimeter samplings. The results showed no significant differences between the two sampling regimes. The indoor-outdoor sampling regime was thus recommended because of its cost-effectiveness.;The last research component was the search for robust but simple and reliable devices for determining NH3 concentrations in NV dairy barns. Towards this effort, two passive samplers, Ogawa passive sampler (Ogawa) and passive flux sampler (PFS), were evaluated against a photoacoustic infrared spectroscope (INNOVA). Results indicated that the two passive samplers are reliable alternatives to the sophisticated and expensive INNOVA for up to three-days continuous monitoring of NH3 concentrations in NV dairy barns.