A mass-flow model of ammonia emissions from UK livestock production

This paper describes a mass-flow approach to estimating ammonia (NH3) emissions from livestock production at the national scale. NH3 is emitted from a pool of ammoniacal-N (TAN) in livestock excreta. This pool is not added to during manure management, but is depleted by losses as gaseous emissions and leachate and by immobilization in litter. At each stage of manure management, a proportion of TAN will be lost, mainly as NH3, and the rest passed on to the next stage. This approach enables rapid and easy estimation of the consequences of abatement at one stage of manure management (upstream) on NH3 losses at later stages of manure management (downstream). Such a model facilitates scenario analysis of abatement options and cost-curve production. Model output is most sensitive to variation in estimates of the length of the housing period for cattle. Thus, the collation of accurate data on factors such as the length of the housing period and other ‘activity’ data, are as important in compiling accurate inventories of national emissions as improving the accuracy of emission factors. Priorities for research should be to accurately quantify the relationship between NH3 emissions from livestock buildings and the proportion of the day those buildings are occupied, and to characterize and quantify the transformations of N that take place during storage of litter-based manures.