NITROGEN DEPOSITION AND STRATEGIES FOR THE CONTROL OF ACIDIFICATION AND EUTROPHICATION ACROSS GREAT-BRITAIN

It is now recognised that a multi-pollutant, multi-effect approach nee ds to be adopted to address the range of problems caused by atmospheri c pollution. In this paper we use a relatively simple trajectory model (HARM) to explore the coupled behaviour of sulphur dioxide (SO2), oxi des of nitrogen (NOx) and ammonia (NH3) and the possible effects of fu ture reductions in emissions of these pollutants on depositions of S a nd N across Great Britain. The performance of HARM with respect to con centrations and depositions of NOy and NHx is assessed by comparison w ith data from national monitoring networks. A range of emissions scena rios are modelled and the effects of these reductions on critical load s exceedance are explored using the critical loads function (CLF), whi ch allows both the acidification and eutrophication effects of S and N deposition to be explored simultaneously. Spatial variations in the r eductions of deposition of S and/or N required to meet critical loads are described. Reductions in emissions of the precursors of strong aci ds (SO2 and NOx) yield benefits in terms of ammonium deposition as a r esult of their coupled chemistry. The development of strategies to con trol nitrogen deposition will need to take this non-linearity in to ac count.