Modelling of the agricultural sector: ammonia emissions and the nitrogen cycle

The agricultural sector is responsible for most of the ammonia emitted into the atmosphere, arising particularly from livestock wastes and when urea is used as a fertilizer. These ammonia emissions contribute a growing proportion of nitrogen deposition across Europe as emissions of nitrogen dioxide are controlled, and hence are receiving increased emphasis to reduce impacts of acidification and eutrophication (excess nitrogen) on sensitive ecosystems. Eutrophication threatens plant species able to thrive with low nitrogen availability, and is responsible for such changes as replacement of heathland by coarse grass. Ammonia also reacts with acidic species in the atmosphere contributing to fine particulate matter and possible health effects.

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During development of the Gothenburg protocol under the UN ECE Convention on Long-Range Transboundary Air Pollution, the IAU at Imperial College undertook the MARACCAS project on the potential for emission reduction with different agricultural practices across Europe: since at that time experience in this area was limited to relatively few countries such as the Netherlands. This has been followed by more detailed work on control of NH3 emissions from livestock farming in the UK, including the NARSES project, led by ADAS. This covers control of emissions generated from animal housing, storage of wastes, and spreading on the land, and can now be used in the UKIAM model in investigating cost-effective strategies to achieve compliance with EC and international legislation while also improving environmental protection in the UK. Since ammonia emissions can lead to substantial local deposition near the source, the IAU is also collaborating with CEH Edinburgh in considering how local measures can be effective in protecting ecosystem areas of special value such as the NATURA 2000 sites.

There is now international recognition of the need to address the whole nitrogen cycle which is being boosted by the increasing use of fertilizers worldwide, including the generation of N2O as a potent greenhouse gas, and water related problems of nitrate leaching as well as ammonia emissions. Agriculture is also a major source of another greenhouse gas, methane, CH4. Thus an integrated approach to nitrogen and the agricultural sector is required, since measures to help one problem can affect another. Future projections for agricultural activities and land-use, affected by CAP reform and other influences on farming, are also important in considering compliance with potential emission ceilings in 2020 and beyond.