Odour emission scenarios for fattening pigs as input for dispersion models: A step from an annual mean value to time series

For the assessment of odour annoyance by dispersion models, the odour emission rate of the source has to be known. In general, an annual mean value is used, although the live mass of the animals increases dramatically during the fattening period and odour emission from the building is known to depend strongly on indoor air temperature and ventilation rate. This annual mean value of the odour emission rate was compared with various emission scenarios for a continuous flow production system with a constant live mass of 75 kg and an all-in/all-out system. For the last one an inverse transfer sampling method was used to avoid an interaction between the growth of the animals and the annual variation of the outdoor temperature. The variation of the emission factor was taken into account twofold, first by a schematized diurnal emission pattern for the various seasons and second by a steady state simulation model that employs a sensible heat balance to calculate indoor temperature and ventilation rate which both influence the odour release. The results indicate an underestimation of the odour emission rate of a livestock building during summer compared with winter when using an annual mean value. For the all-in/all-out system, this effect is superposed by an overestimation at the beginning of the fattening period and an underestimation at the end. Using the emission model which takes into account a time series of the odour emission rate, a more realistic description of the odour emission characteristics can be achieved compared with an annual mean value.