Guidance on the conversion of gaseous emission units to standardized emission factors and recommendations for data reporting

Emissions of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) from livestock production may be measured for different reasons and in consequence reported in a wide range of units. For the purpose of compiling national inventories of emissions of those gases, emissions from buildings and stores usually need to be expressed per animal or as a proportion of nitrogen (N) (NH3 and N2O) or volatile solids (VS) (CH4) excreted or stored. Much of the published data on gaseous emissions from livestock production is not reported in units that can be readily used for inventory compilation. This paper provides guidance for researchers wishing to convert a wide range of emission units into emission factors (EFs) and opens up opportunities for increased use of published data. We developed our methodology using reported emissions from housing and storage systems compiled from studies for the DATAMAN database so that we could convert reported emissions into agreed EFs referred to as 'required EFs' (RqEFs). Required EFs were either derived using data reported in the associated publication or estimated, using default data (e.g. annual N excretion by a particular type of livestock). The approach greatly increased the number of RqEFs. For example, the number of RqEFs of N2O-N from livestock buildings as a proportion of excreted N increased from 16 to 326, while the number of N2O RqEFs from manure stores as a proportion of stored N increased from 126 to 353. For two subsets of NH3-N emissions from livestock buildings and from slurry stores there were very good correlations between emissions estimated using the methodology we developed and reported emissions (R-2 = 0.97 and 0.97, respectively). We include a list of recommended information for inclusion in publications reporting emissions that will enable other workers to utilize this methodology.