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This chapter explains special terms which are used throughout the RAINS-DEP documentation. More general terms are explained in Terms and codes used in RAINS-EMCO.
The definitions in this part are alphabetically ordered.
In RAINS, estimates of future deposition of air pollutants are based on transfer matrices for long range transport. The DEP modul can be used to calculate sulfur and nitrogen deposition resulting from the emissions of each country. These contributions can then be summed up to obtain, together with the 'background', the total deposition at any grid location. These calculations are based on (linear) source-receptor matrices derived from a Lagrangian model of long-range transport of air pollutants in Europe, developed by EMEP (Co-operative programme for monitoring and evaluation of the long range transmission of air pollutants in Europe, EMEP/MSC-W Reports (Barret et al.1994-96).
The EMEP model describes the chemical processes within the air parcels by ordinary first-order differential equations, integrated over time along the trajectories as they follow atmospheric motion. During transport, the equations take into account emissions from the underlying grid of a 150*150 km resolution, chemical processes in the air, and wet and dry deposition to the ground surface. Model calculations are based on six-hourely input data of the actual meteorological conditions for the specific years.
In order to capture the inter-annual meteological variability, model runs have been performed for eleven years (1985-1995, Barrett et al., 1996). Budgets of sources have been averaged over these eleven years and re-scaled to provide the spatial distribution of one unit of emissions. The resulting atmospheric transfer matrices are then used as input in the RAINS Model.
The use of such 'country to grid' transfer matrices implicitly assumes that the spatial relative distribution of emissions within a country will not dramatically change in future. Analysis undertaken at IIASA indicates that the error in computed deposition introduced by this simplification lies within the general range of model uncertainties when considering long-range transport (Alcamo, 1987).
A critical load (CL) is defined as a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified elements of the environments do not occur according to the present knowledge. Significant harmful effects of acid deposition are assumed to occur when critical values of chemical compounds in forest soils and freshwaters are exceeded.
In DEP, critical loads are compared with estimates of deposition to determine where ecosystems may be at risk under various emission scenarios.
The critical loads assessment is based on complex dynamic models describing processes in key ecosystems, e.g., soils, surface waters, and vegetation systems. These models include the computation of the depletion of the acid buffer capacity of ecosystems under the influence of precipitation, evaporation, water flows, and budgets of chemical ecosystem constituents (Hettelingh et al., 1991).
The critical load calculation involves a two-step approach. The first step applies a qualitative relative sensitivity approach to distinguish ecosystems' sensitivity to acidification. The method of relative sensitivity developed at the Stockholm Environment Institute (Kuylenstierna and Chadwick, 1989) is used. This method is qualitative in the sense that weights are assigned to four indicators for ecosystem sensitivity, i.e., bedrock lithology, soil type, land use, and annual rainfall. In the second step computations are performed to assign critical loads to all areas distinguished on the map of relative sensitivities. The approach used is based on the Steady State Mass Balance Method (SSMB). This SSMB method assumes steady state equilibrium between the soil solid phase and the soil solution. The SSMB computes the maximum acid input to the system that will not cause an excess of the critical alkalinity value. The latter value is computed from average thresholds for chemical values, i.e., pH, aluminum and the aluminum-calcium ratio.
Alcamo J., (1987): Uncertainty of Forcast Sulfur Deposittion Due to Uncertain Spatial Distribiution of SO2 Emissions. Preprints of the 16th NATO/CCMS International Technical Meeting on Air Pollution Modelling and its Application, Lindau, FRG.
Amann M., Bertok I., Cofala J., Gyrfas F., Heyes C., Klimont Z., Schöpp W., (1996) Cost-effective Control of Acidifiaction and Ground-Level Ozone, International Institute for Applied Systems Analysis, Laxenburg, Austria.
Barrett K., Seland Ø., (eds.) (1994-96) EMEP/MSC-W Reports Oslo, Sweden.
Hettelingh, J.-P., Downing, R.J., de Smet, P.A.M. (eds.) (1991) Mapping Critical Loads for Europe. Coordination Center for Effects, Technical Report No. 1, RIVM Report No. 259101001, Bilthoven, The Netherlands.
Hettelingh J.P., Downing R.J., de Smet P. (eds.) (1993) Calculation and Mapping of Critical Loads for Europe. Coordination Center for Effects, Coordination Center for Effects, RIVM Report No. 259101003, Bilthoven, The Netherlands
Hettelingh, J.-P., Downing, R.J., de Smet, P.A.M. (eds.) (1995) Calculation and Mapping of Critical Loads in Europe. Coordination Center for Effects, RIVM Report No. 259101004, Bilthoven, The Netherlands.
Kuylenstierna, J.C.I. and Chadwick, M.J. (1989) The relative sensitivity of ecosystems in Europe to the indirect effects of acidic depositions. In: J. Kämäri, D.F. Brakke, A. Jenkins, S.A. Norton and R.F. Wright, eds. Regional Acidification Models, Springer Verlag, Berlin.
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