Bepaling van bron-receptor relaties voor verzurende componenten

Abstract

In the framework of the Dutch Priority Program on acidification, the DAS model (Dutch Acidification System model) has been developed. This model describes the entire causal chain from emissions of acidifying components to their effects on ecosystems on a regional scale. In the atmospheric module of DAS the transport and deposition of acidifying species is described by means of so-called source-receptor relations. Assuming that the physical and chemical processes in the atmosphere may be approximated as first order, linear processes, the relation between an emission quantity in a source area and the resulting deposition flux in a receptor area can be described with a single transfer coefficient. In the Netherlands 20 receptor areas are defined. The number of source areas in the Netherlands and foreign countries is 39. The source-receptor relations are based on the results of the atmospheric transport model TREND. For the components NOx and SO2 different sets of transfer matrices are calculated for three emission height classes. This improves the calculation of the contribution to the deposition of sources at relatively short distances. As ammonia emissions take place at the surface or at low heights, no discrimination in emission heights is made for this component. By using the transfer matrices the calculation of atmospheric deposition is reduced to a simple matrix multiplication. In this way the computer time consuming applications of the TREND model can be avoided. However, during the procedure of calculating the transfer matrices, a number of assumptions and choices had to be made which limit the application of the matrices. In principle the assumption of a linear relation between emission and deposition is violated for all three acidifying components. Interactions between the compounds play a (sometimes important) role in atmospheric processes. As model parameters are validated for the present situation, deviations from a linear behaviour will become larger with increasing deviations from the present emission conditions. Next to limitations inherent to the method, there are some practical limitations. Only an average deposition value for a receptor area can be obtained. There is no information on the spatial variations in deposition within a receptor area. Detailed calculations with TREND show that the variation may be large. The meteorological conditions and the removal parameters are pre defined for the TREND calculations. Changes in these parameters require a re-calculation of the matrices. Nevertheless, it may be assumed that the error introduced by the assumptions of a linear emissiondeposition relation is acceptable in view of the uncertainties in the other modules of the DAS-model.<br>