Effects of diurnal emission patterns and sampling frequency on precision of measurement methods for daily ammonia emissions from animal houses

Ammonia concentrations and airflow rates are the main parameters needed to determine ammonia emissions from animal houses. It is possible to classify their measurement methods into two main groups according to the sampling frequency: semi-continuous and daily average measurements. In the first method, ammonia concentrations and airflow rates are monitored during a certain period and instant emission rates are calculated. When using daily average methods, 24-h average ammonia concentrations and airflow rates are used to determine the average daily emission rate. As less information is used in the second method, an error may be expected. The aim of this work was to determine the nature and magnitude of this error. Three databases containing data from semi-continuous ammonia emissions measurements from different animal houses (pigs, poultry and rabbits) in three European countries (Denmark, The Netherlands and Spain) were used to characterise this error. An average systematic deviation between methods of 1.5% was found. The magnitude of this bias was directly related to the daily variation of ammonia concentration and airflow rate. The magnitude of this bias, and also the random component of the error, were modelled. The developed model adequately described variation in bias in the studied dataset (R2 = 0.85) and can be used as a tool to decide which type of measurement methods can be used.