MODELING FUTURE ACID DEPOSITION - A CRITICAL LOADS APPROACH

An atmospheric pollution model, the Harwell Trajectory Model, is used to explore the effects of a range of possible future emissions scenari os on levels of sulphur deposition and critical loads exceedence acros s the UK. The structure of the HTM and the basis of the critical loads concept are described. Model output is illustrated for emissions scen arios which reflect the possible effects of the 30% reduction in SO2 e missions demanded by the Helsinki Protocol and the UK's current commit ments under the LCPD to a 60% reduction by 2003. Emissions reductions are achieved both by blanket reductions and by targeting reductions on particular large sources. An emissions reduction of 30% would have li ttle environmental benefit for the UK as a whole. A 60% reduction lead s to a much clearer change in the pattern of critical loads exceedence ; targeted emissions reductions appear to be more effective still and point the way for future policy.