In 1994 the UK became a signatory to the revised Sulphur Protocol to the UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP). This marked a major step forward for environmental protection in the UK with a proposed 80% reduction in national SO2 emissions by 2010. Although this was clearly a significant policy development, it has become increasingly apparent that the quality of air and damage to natural and anthropogenic receptors (buildings. freshwaters etc) is determined by other pollutants as well: in particular the oxides of nitrogen which play a major role in both acidic deposition and the formation of photochemical pollutants (especially ozone). In the light of this, a new UNECE Protocol on Acidification, Eutrophication and Low level Ozone is currently being negotiated. At the international level, the development of this Protocol, together with a similar exercise within the EU, will provide the major policy context for work over the next two, years.
The EMEP model provides the direct modelling input to policy development at the European level, supplying the source-receptor relationships used in the integrated assessment models. However, the UK has maintained and developed an independent modelling programme through Air and Environment Quality Division to provide improved predictions of concentrations and depositions pollutants to inform policy makers and the scientific community within the UK.
The model comparison carried out for the UK Review Group on Acid Rain 4th report has highlighted the importance of maintaining such a capability to compare with output from the EMEP model. In this inter-model comparison, the model proposed for use here, HARM, appeared to come closest to reproducing the distributions of depositions of most pollutants indicated by data from the monitoring networks. HARM output has been used extensively in the build up to the latest UNECE Protocol. The new Protocol is being developed in a multi-pollutant, multi-effect framework seeking to reduce emissions of sulphur dioxide, nitrogen oxides, volatile organic compounds and ammonia, which variously contribute to acidification, eutrophication and low level ozone. In the light of this, HARM and the ozone model, ELMO will be needed to help the UK explore the likely outcomes of a range of potential negotiating strategies. In addition, they will be needed to inform the work of the new Jointly Established Body advising Ministers on transboundary pollution matters (NEGTAP). Finally, the models need to be further developed to maximise their robustness and accuracy.