REDUCING THE CONTRIBUTION OF AMMONIA TO NITROGEN DEPOSITION ACROSS EUROPE H.M.ApSIMON, S.COULING, D.COWELL and R.F.WARREN Imperial College Centre for Environmental Technology, London SW7 2PE, U.K. Abstract. European emissions of reduced nitrogen, arising principally from agriculture, are comparable with those of oxidised nitrogen from mobile and stationary combustion sources. It is therefore important to include ammonia emissions in working towards a new protocol on nitrogen under the programme of the UN Economic Commission for Europe on the control of transboundary air pollution. However the nature of the sources and the subsequent atmospheric transport and chemistry are very different from other acidifying pollutants. This paper describes work in hand under the MARACCAS project to compare agricultural activities in different European countries and to assess the applicability and efficacy of potential abatement measures. The aim is to derive abatement costs for each country relating successive emission reductions to the costs of achieving them, to be used by the UN ECE Task Force on Integrated Assessment Modelling (TFIAM) - in particular with our Abatement Strategies Assessment Model, ASAM. The paper will also address the large uncertainties involved in integrated assessment modelling with respect to ammonia, and suggest how these may be allowed for in deriving cost-effective abatement strategies. Key words: emissions, nitrogen, ammonia, agriculture, integrated assessment modelling, abatement strategies 1. Introduction In developing the second protocol for sulphur, the Oslo protocol, maps of critical loads across Europe were used as an indication of sustainable levels of deposition of sulphur. Integrated assessment models including the RAINS model of IIASA (Alcamo et al., 1987), the CA SM model of the Stockholm Environment Institute (SEI,1991), and our own model ASAM (Abatement Strategies Assessment Model- ApSimon et a1.,1994) were used to indicate cost-effective strategies for reducing the exceedance of these critical loads. Under the Task Force on Integrated Assessment Modelling (TFIAM) of the UN Economic Commission for Europe (UN ECE) a similar procedure is now being applied to nitrogen deposition in the context of development of a new protocol for NOx. This is far more complicated because NOx is a contributor to problems of tropospheric ozone and eutrophication as well as acidification, and for the latter two effects nitrogen deposition from ammonia is also important. Accordingly all three integrated assessment models are being adapted to treat a combination of sulphur and nitrogen species in relation to acidification and eutrophication. Thus the ASAM model now includes SO2, NOx from stationary combustion, and from the transport sector, and ammonia, with the potential to add VOCs in relation to ozone formation in due course. In order to include ammonia in these models it is necessary to have information on the emissions from each country, the transport through the atmosphere from the source areas to deposition across Europe, the sensitivity of the ecosystems affected by this deposition, and on the measures which can be taken to abate the emissions and hence reduce the effects. To derive cost-effective strategies it is also necessary to know not only the abatement techniques, but also their costs. In addition the variability in agricultural systems and climates in different countries greatly affects both the emissions, and the extent to which they can be controlled. This paper therefore begins by discussing the contribution of ammonia to transboundary air pollution as compared with NOx. A brief outline of ASAM is then given as an example of an integrated assessment model, and the way in which emission reduction scenarios for Europe may be derived for a combination of pollutants and effects to suggest the levels of abatement needed in each country. The paper concludes with the Water, Air and Soil Pollution 85: 1891-1896, 1995. 9 1995 Kluwer Academic Publishers. Printed in the Netherlands.