1 Introduction

This report describes the receptor modelling methods that have been used to predict PM₁₀ concentrations across the country as part of the review of the UK National Air Quality Strategy (NAQS). The NAQS gives the following objective for PM₁₀ to be achieved by the end of 2005:

• 24-hour running mean of 50 mgm-3, measured as the 99th percentile.
  

The European Union 'Daughter Directive' gives the following limit values for PM₁₀:

• Stage 1, to be achieved by 1 January 2005: annual mean limit value of 40 mgm-3 and 24-hour limit value of 50mgm-3, not to be exceeded more than 35 times a year (approximately equivalent to a 90th percentile of 50mgm-3).
  
• Stage 2, to be achieved by 1 January 2010: annual mean limit value of 20 mgm-3 and 24-hour limit value of 50mgm-3, not to be exceeded more than 7 times a year (approximately equivalent to a 98th percentile of 50mgm-3).
  

The Stage 2 limit values are indicative and will be reviewed in the light of information on health and environmental effects, technical feasibility and experience in the application of Stage 1 limit values in Member States.

The source apportionment of airborne particulate matter in the United Kingdom has recently been comprehensively reviewed by the Airborne Particle Expert Group in their first report (APEG, 1998). A new receptor modelling technique has been developed which has given new quantitative insights into the sources of PM₁₀ in the UK. The receptor modelling technique was extended to provide forecasts of concentrations for comparison with the NAQS objective and EU 'Daughter Directive' limit values for PM₁₀. Projections of PM₁₀ concentrations for 2005 were calculated by multiplying the individual contributions to daily particle concentrations by emissions reduction factors derived from model studies. The forecasts of changes in emissions presented within the APEG report were for a 'business as usual' scenario, defined as the likely impact of current national and international policies on current emissions.

This report describes the further development of these receptor modelling and forecasting methods that has been carried out by air quality experts at AEA Technology NETCEN on behalf of the Department of the Environment Transport and the Regions.

Section 2 provides a brief summary of the receptor modelling technique and projection results presented in the APEG report. Projections for a 'business as usual' scenario were calculated for eight city centre monitoring site locations based on both 1995 and 1996 measurement data. Similar projections based on 1995 and 1996 data for additional monitoring site locations are presented in section 3. Section 4 provides a detailed analysis of the PM₁₀ concentrations that are likely to result from a range of alternative emission reduction scenarios. These projections show the relative lack of sensitivity of the forecast concentrations to extreme changes in emissions.

The receptor modelling methods have also been applied to 1997 monitoring data and section 5 provides a comprehensive review of projections based on this data and a comparison with the projections based on 1995 and 1996 data. Methods for projecting concentrations at roadside and industrial sites are presented in section 6 and section 7. Some alternative emission reduction scenarios have been examined for sites that are likely to exceed the EU Stage 1 24-hour limit value in 2004 for the business as usual scenario. These are listed in section 8.

The majority of the national modelling of future PM₁₀ concentrations carried out by AEA Technology NETCEN has been done on an individual monitoring site basis. This enables the receptor modelling and projections to be firmly based on actual observations of current PM₁₀ concentrations. Maps of both current and projected PM₁₀ concentrations are however required for the quantification of health impacts similar to those presented by COMEAP (1998). While maps of annual mean PM₁₀ concentrations have been presented by Stedman (1998), this report provides the first maps of annual means and numbers of exceedance days for comparison with PM10 objectives and limit values. The daily PM₁₀ mapping methods that have been developed are presented in section 9. The use of these mapping methods does, however, increase the uncertainty of the projections compared with those for individual sites.