5.08 METHODS FOR INCORPORATING THE INFLUENCE OF URBAN METEOROLOGY IN AIR POLLUTION ASSESSMENTS

The COST 715 programme is a European activity which supports scientific exchange and networks, on meteorology applied to urban air pollution problems. For urban pollution assessments one needs the input of heat, energy, or pollution near the ground, averaged over an area. The properties of the urban surface vary enormously over very short distances making this difficult regardless of computing power. This paper is concerned with ways of averaging dispersion to account for urban processes. COST 715 has considered most of the available methods. All methods require measurements for testing, but as these need to be made above roof level, where data is not routinely available, except during detailed measurement campaigns. There is an ongoing debate as to where to site meteorological instruments in urban areas. COST 715 has concluded that regulators in many European countries are applying methods to urban dispersion problems which may be suspect, because of the way urban meteorological data is handled. An inventory of European urban meteorological sites has been prepared and COST 715 has made recommendations on the sitting of urban meteorological instruments so that pollution calculations are more reliable. Table 1 illustrates some of the methods proposed in practical urban dispersion calculations. No single solution to the averaging problem has emerged. Although more complex computer models are seen as the way of tackling this complex issue, it is worth cautioning that they often make assumptions that may not be realistic. These are, for example, assuming a low blending height in the atmosphere, above which horizontally averaged variables satisfy similarity theory, and that the flow is in equilibrium, in layers below the blending height