Radioactive ~(85)Kr and CO_2 Balance for Ventilation Rate Measurements and Gaseous Emissions Quantification through Naturally Ventilated Barns

摘要

Animal housing is a major source of gaseous emissions, such as ammonia (NH_3), methane (CH_4), nitrous oxide (N_2O), and carbon dioxide (CO_2). Ammonia is an atmospheric pollutant and responsible for eutrophication and soil acidification, while CO_2,CH4, and N_2O are greenhouse gases (GHG) that contribute to global warming. The quantification of gaseous emissions from livestock buildings with natural ventilation systems is a particularly difficult task and is associated with uncertainties that are largely unknown. One key issue is to measure the ventilation rate and then to quantify the gaseous emissions. Therefore, in this study, the ventilation rate was determined by three different methods simultaneously. Field experiments were carried out to study the ventilation rate in a naturally ventilated dairy barn located in northern Germany during the summer seasons from 2006 to 2010. The air exchange rates (AER) as well as the ventilation rates were determined by the decay of the radioactive tracer krypton-85, the carbon dioxide (CO_2) balance, which was used as the reference method in this study, and the combined effects of wind pressure and temperature difference forces (WT method). Subsequently, the results were compared with each other by carrying out Pearson correlation analysis and developing a regression model. During each field experiment, continuous measurements of gas concentrations (NH_3, CO_2, CH_4, and N_20) inside and outside the building and ~(85)Kr tracer gas experiments were carriedout. Meanwhile, the temperature was measured and recorded inside and outside the barn. Furthermore, the wind velocity was measured. Although the WT method showed minor over estimation by about 1.11 (p < 0.05) times the reference method, it is not reliable because it showed no linear correlation (0.05; p = 0.88) with the reference method. This was due to large fluctuations in the wind velocity (direction and speed), which negatively affected the WT method, which is basically dependent on wind velocity.In contrast, the ~(85)Kr tracer gas technique showed a good linear correlation (0.82; p < 0.05) with the reference method, which accentuates that the ~(85)Kr tracer gas technique is a promising method. However, this technique overestimated the air exchange rate by about 2.05 (p < 0.05) times the reference method. Therefore, the ~(85)Kr tracer gas technique should be further developed to produce values consistent with those estimated by the reference method. The emissions factors, subject to the reference method, were 32, 157.7, 13736, and 7.9 kg year~(-1) AU~(-1) for NH3, CH4, CO2, and N_2O, respectively.