A COMPARISON OF DIFFERENT RANKING SCHEMES FOR ASSESSING THE EFFECT OFLARGE POINT SOURCES OF POLLUTION IN THE UK

The availability of national maps of critical loads for soils, vegetat ion and freshwaters helps enable the assessment of the effects of larg e point sources of pollution in the UK. The deposition ''footprint'' o f most major sources has been modelled and combined in a GIS with a na tional critical loads database. As part of an integrated pollution con trol strategy (IPC) it may be helpful to rank point sources in order o f their effects on the environment A comparison of the discriminating power and effectiveness of several ranking schemes has been carried ou t A variety of ranking schemes were investigated, such as; total area where sulphur deposition exceeds the critical load or average mass dep osited on areas where the critical load is exceeded. Their relative me rits were compared for several ''current'' and future scenarios, such as, actual 1993 emissions or predicted emissions for 2001. Rankings fo r the unit emissions provided a measure of the pollution potential of each source and were a complex function of the location of sensitive a reas and meteorological conditions. Rankings under other scenarios ten ded to be dominated by the relative magnitude of the emissions. Compar ison between the ranking schemes was made using non-parametric statist ics. The comparisons reveal complex interactions between different sch emes. The approach is providing practical solutions to a pollution con trol strategy based on maximising environmental benefits.