An atmospheric pollution model, the Harwell Trajectory Model, is used to explore the effects of a range of possible future emissions scenarios on levels of sulphur deposition and critical loads exceedence across the UK. The structure of the HTM and the basis of the critical loads concept are described. Model output is illustrated for emissions scenarios which reflect the possible effects of the 30% reduction in SO₂ emissions demanded by the Helsinki Protocol and the UK's current commitments 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 little environmental benefit for the UK as a whole. A 60% reduction leads 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.