The Government and devolved administrations have recently published a consultation document entitled 'The Air Quality Strategy for England, Scotland, Wales and Northern Ireland'. The air quality modelling work undertaken for this report indicated that policies currently in place or to take effect before 2005 will lead to the NO₂ annual average objective of 40 m gm^-3 being achieved at all background locations, except inner London, and at most roadside locations by 2005. However, the national modelling identified a number of major urban road links where concentrations at the roadside may exceed the objective.

A pilot study has already been undertaken to estimate the number of households likely to be exposed to exceedances of the NO₂ objective. This considered 102 road links, including a case study of the North Circular Road in London, and involved visits to each road and the use of a postcode to determine numbers of residential addresses. The site visits found that 23 road links have houses within 10m of the kerb, with a total estimate of more than 1,200 houses. Using the postcode data, a total of over 2,600 houses were found to exist along these road links, but the data sets were not detailed enough to determine how many of these are within 10 m of the kerb. The current study aims to consider the location of the houses in more detail through the use of more detailed digital map data.

The Geographical Information System (GIS) method developed in this study used a variety of digital map data: OS Landline, OS Oscar, OS Address Point and aerial photographs, linked together within a GIS. A total of 102 links were analysed, finding an estimated number of households in the range of 1,783 to 2,365. The range of estimates is attributed to various sources of uncertainty mainly related to limitations of the OS data and the interpretation of the Address Point database. However, this result is considered to be more accurate than that provided by the pilot survey, because of the much greater level of detail available concerning the nature of the buildings along the individual road links.

The links considered were those with the highest predicted NO₂ concentrations. However, those with lower traffic flows, and hence lower predicted concentrations, are more likely to be residential roads, and therefore may represent higher risks in terms of exposure.

Contents Page         Chapter 1