Diurnal variation in ammonia, carbon dioxide and water vapour emission from an uninsulated, deep litter building for growing/finishing pigs

Abstract In an uninsulated livestock building with natural ventilation, the air temperature and airflow show a large variation according to the daily variations in weather and season. The objective of this investigation was to determine the diurnal variation in the emission of NH3, CO2 and moisture from an uninsulated building with a deep litter system for growing/finishing pigs and to investigate the influence of air temperature and airflow rate on the NH3 emission. The investigations were carried out in an uninsulated experimental building with 125 growing/finishing pigs in deep litter pens. The building was 12 m wide and 20 m long (240 m2), naturally ventilated but also equipped with exhaust fans. The NH3 concentration, the CO2 concentration, the outside and inside air temperature, the outside and inside relative humidity and the animal activity were measured continuously during 6 days at a constant airflow rate of 146 m3 m−2 h−1. During six nights the effect of airflow rate on the NH3 emission was investigated by changing the airflow rate in steps from 26 to 165 m3 m−2 h−1. The measurements were carried out between day 16 and day 46 from the beginning of the growing period. The NH3 emission from an uninsulated, deep litter building for growing/finishing pigs showed a clear diurnal variation. During the 6 days with constant airflow rate the emission varied from 6 to 247% of the mean, with the minimum around 6.00 a.m. and the maximum around 5.00 p.m. The daily mean of NH3 emission increased from 0·23 to 0·65 gh− per pig (day 16–day 43). The diurnal variation of NH3 emission was correlated to the inside air temperature (correlation coefficient rs=0·86–0·91) and the animal activity (rs=0·69–0·83). The increase of NH3 emission with the air temperature followed an exponential pattern. The relative NH3 emission flux increased from 0·2 to 2·0 between the air temperatures −2 to 14°C inside the building. An increase in airflow rate through the building from 26 to 165 m3 m−2h−1 increased the relative NH3 emission flux from 0·4 to 1·4. The CO2 emission during the 6 days at constant airflow rate had a daily mean between 81 and 120 gh−1 per pig with a diurnal variation from 61 to 249% of the mean. The CO2 emission was correlated to the inside air temperature (rs=0·42–0·83) and animal activity (rs=0·67–0·85). The daily mean of water vapour emission increased during the same days between 146 and 408 gh−1 per pig and varied from 18 to 269% of the mean. The water vapour emission was correlated to the inside air temperature (rs=0·53–0·97), animal activity (rs=0·57–0·85) and the water absorption capacity of the inlet air (rs=0·27–0·94). The diurnal variations in NH3, CO2 and water vapour emission were correlated to each other.