Investigation of the vertical distribution of ammonia, methane, and carbon dioxide in a naturally ventilated dairy barn Evaluation of gaseous pollutants concentrations

The determination of emissions and ventilation rates from naturally ventilated barns (NVB) is widely acknowledged as challenging due to its structure, especially the large vents at the sides that allow environmental interference inside and around the barn. When measuring emission fluxes directly at these large vents, a high number of sensors for velocity and gas concentrations is needed. In order to achieve the highest possible accuracy with the least us-age of sensors, it is requisite to study the spatial distribution of the gases and find an optimal gas sampling position. We studied the influence of the sampling height on the gas concentrations which were measured at the outlet of an NVB, taking the wind direction and wind speed into account. A high-frequency Fourier-transform-infrared spectrometer was employed to measure gas concentrations (CO2, CH4, and NH3) at six different heights from the ground and an ultrasonic anemometer to estimate wind flow characteristics. Gas concentrations were measured every 3 minutes at each height over a period of two months. We found that the mean gas concentrations were significantly different at each height under most wind flow conditions. However, under straight crossflow conditions, there were no significant differences in CO2 and CH4 concentrations at the middle (1.5 m, 1.8 m) and bottom (0.6 m) heights. The gas concentrations, especially NH3, were highest at the top height (2.7 m), almost under all wind flow conditions. The outcomes of the presented study will be useful for the design of optimized gas sampling setups for the direct measurement of emissions from large naturally ventilated barns. © 2022, VDI Verlag GMBH. All rights reserved.