First experiences with methods to measure ammonia emissions from naturally ventilated cattle buildings in the U.K.

A method has been developed to measure the emission rate of ammonia from naturally ventilated U.K. livestock buildings. The method is based on measurements of ammonia concentration and estimates of the ventilation rate of the building by continuous release of carbon monoxide tracer within the building. The tracer concentration is measured at nine positions in openings around the perimeter of the building, as well as around a ring sampling line. Two criteria were evaluated to decide whether, at any given time, a given opening in the building acted as an air inlet or as an air outlet. Carbon monoxide concentration difference across an opening was found to be a better criterion than the temperature difference across the opening. Ammonia concentrations were measured continuously at the sampling points using a chemiluminescence analyser. The method was applied to a straw-bedded beef unit and to a slurry-based dairy unit. Both buildings were of space-boarded construction. Ventilation rates estimated by the ring line sample were consistently higher than by the perimeter samples. During calm weather, the ventilation estimates by both samples were similar (10–20 air changes h-1). However, during windy conditions (>5 m s-1) the ventilation rate was overestimated by the ring line sample (average 100 air changes h-1) compared to the perimeter samples (average 50 air changes h-1). The difference was caused by incomplete mixing of the tracer within the building. The ventilation rate estimated from the perimeter samples was used for the calculation of the emission rate. Preliminary estimates of the ammonia emission factor were 6.0 kg NH3 (500 kg live-weight)-1 (190 d)-1 for the slurry-based dairy unit and 3.7 for the straw-bedded beef unit.