Ammonia Emission Estimates

There have been a number of improvements to the ammonia (NH₃) emission estimates since the 1998 inventory. An in-depth study into the non-agricultural sector has enabled a number of sources to be better characterised, allowing emissions estimates to be included in more detail. Emissions from the agricultural sector are taken directly from the agricultural NH₃ inventory compiled for MAFF (now a part of DEFRA) each year by a consortium of organisations. There is on-going work to improve the NH₃ emission estimates from both agricultural and non-agricultural sources.

1 See Appendix 4 for definition of UN/ECE Categories

Ammonia emissions are dominated by agricultural sources with emissions from livestock and their wastes comprising 71% of the total emission. These emissions derive mainly from the decomposition of urea in animal wastes and uric acid in poultry wastes. Emissions depend on animal species, age, weight, diet, housing systems, waste management and storage techniques. Hence emissions are affected by a large number of factors which make the interpretation of experimental data difficult and emission estimates uncertain (DOE, 1994). The other agricultural sources included are emissions from fertiliser use, crops and decomposition of agricultural vegetation. These are particularly uncertain owing to the complexity of the processes involved.

Sutton et al (2000a, 2000b) give estimates of a number of non-agricultural emission estimates, some of which have been incorporated here. The non agricultural sources comprise a number of diverse sources and equal 20% of the total. However, emission estimates for these sources are very uncertain due to a lack of data. Emissions of ammonia from road transport although relatively small are increasing as a result of the increasing number of three way catalysts in the vehicle fleet. Detailed consideration has been given to the current emissions and potential future emissions from non-agricultural sources in Handley et al (2001).