Agricultural and Forest Meteorology 105 (2000) 325–326
Foreword
The EXAMINE North Berwick experiment
Fluxes of ammonia and interacting chemical species between
oilseed rape and the atmosphere
The environmental impacts of atmospheric ammo-nia and the need to reduce emissions are increasingly being recognized as problems that must be addressed internationally. The atmospheric lifetime of ammonia allows substantial transboundary fluxes with impacts occurring remote from the source country. It is in this regard that both the United Nations Economic Com-mission for Europe (UNECE) and the European Union have recently established national limits for ammonia emission for the first time. Under the auspices of the UNECE, the Parties to the Convention on Long-Range Transboundary Air Pollution agreed the Gothenburg Protocol in December 1999, while the Member States of the EU have this year reached political agreement on the National Emissions Ceilings Directive (NECD). Both these instruments seek to control the linked prob-lems of acidification, eutrophication and photochem-ical oxidants, taking an integrated approach involv-ing the control of SO2, NOx, VOCs and NH3
emis-sions. The integration of these issues is ambitious, but is necessary because of the intimate linkages be-tween these pollutants. For example, further control of SO2 and NOx may be insufficient to avoid
acid-ification and eutrophication; in both cases, the inte-grated picture requires NH3 to be included in the
analysis.
In the early 1980s, the first international air pol-lution controls were based on flat-rate targets to sta-bilize or reduce emissions. The limitation of this ap-proach was that it neither quantified the relationship of the controls to the environmental benefit expected, nor
gave the possibility for cost–benefit optimization. Im-provements have allowed these elements to be linked through modelling of emissions, atmospheric trans-port, deposition and impacts, in combination with an assessment of costs. Both the Gothenburg Protocol and the NECD have been developed on this basis, using the critical loads approach to minimize the area where deposition exceeds ecosystem sensitivity thresholds. Providing a reliable assessment necessarily depends on a sound scientific understanding of the behaviour of each pollutant. As NH3is included in international
pollution control for the first time, it therefore be-comes increasingly important to be able to quantify its sources, transport and sinks. While much work has been done to quantify emissions from sources such as animal wastes and fertilizers, one of the main uncer-tainties regarding atmospheric ammonia is to quan-tify its biosphere–atmosphere exchange. This infor-mation is necessary to identify whether different veg-etation types are sources or sinks, as well as to esti-mate the impact of ammonia on natural ecosystems and forests. The fact that ecosystems may at one time emit ammonia and at another time absorb it is a par-ticular complexity. Ammonia is a trace gas with both intimate biological and chemical interactions. Hence, it is equally necessary to quantify the plant physi-ological controls on ammonia uptake and to under-stand the controls on ammonium aerosol formation/ destruction.
These multiple linkages point to the need for inter-national efforts to measure ammonia fluxes and
326 Foreword / Agricultural and Forest Meteorology 105 (2000) 325–326
velop models that can contribute to the policy analy-sis. The EXAMINE project, funded by the European Commission, the UK Department of the Environment, Transport and the Regions, and other national organi-zations, has taken just such an approach in the North Berwick experiment reported in this special issue. By bringing together expertise crossing the bounds of me-teorology, chemistry, agronomy and biology, a more integrated picture of the controls on ammonia fluxes has emerged. As with all scientific endeavour, the anal-ysis identifies many new questions and complexities. These are important, since they often hold the key to understanding the limits and optimization of emissions control. At the same time, however, the work recog-nizes the need to develop practical models that can be applied more widely. It is approaches such as these that will be necessary to underpin the next generation of international air pollution controls and the relevant policy measures.
M.L. Williams∗
Chairman
EMEP Steering Body UNECE Convention on Long Range Transboundary Air Pollution Department of Environment Transport and the Regions Ashdown House 123 Victoria Street London, SWID 6DE, UK.
A. Ghazi Head
Global Change and Biodiversity Unit Research Directorate General European Commission 200 Rue de la Loi B-1049, Brussels, Belgium.
