A consistent method for modelling PM10 and PM2.5 concentrations across the United Kingdom in 2004 for air quality assessment

A modelling method has been developed to map PM10 and PM2.5 concentrations across the UK at background and roadside locations. Separate models have been calibrated using gravimetric measurements and Tapered Element Oscillating Microbalance instruments (TEOM) using source apportionments appropriate to the size fractions and sampling methods. Maps have been prepared for a base year of 2004 and predictions have been calculated for 2010 and 2020 on the basis of current policies. Comparisons of the modelling results with air quality regulations suggest that exceedences of the EU Daughter Directive stage 1 24-h limit value for PM10 at the roadside in 2004 will be largely eliminated by 2020. The concentration cap of 25 μg m−3 for PM2.5 proposed within the CAFÉ Directive is expected to be met at all locations. Projections for 2010 and 2020 suggest that the proposed exposure reduction (ER) target is likely to be considerably more stringent and require additional measures beyond current policies. Thus the model results suggest that the balance between the stringency of the concentration cap and the ER target in the proposed directive is appropriate. Measures to achieve greater reductions should therefore have the maximum public health benefit and air quality policy is not driven by the need to reduce concentrations at isolated ‘hotspots’.