Executive Summary
The Government has recently published a consultation document on the Review of the NAQS which sets out proposals for amending the NAQS following a review carried out during 1998. The national modelling of roadside NO2 concentrations, carried out as part of this review, indicated that policies currently in place or to take effect before 2005 will lead to the annual average objective 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 of 21 ppb annual mean in 2005.
This report describes the methodology used and the results of a pilot study to further analyse some of the road links where concentrations at the roadside may exceed the objective in 2005. The study provides a semi-quantitative estimate of the population likely to be exposed to roadside NO2 concentrations greater than 21 ppb annual mean in 2005, as a result of housing adjacent to major roads (within 10 m of the edge of the road) in UK cities outside London. Fieldwork has been undertaken in 14 cities, including a case study area in London.
Previous work indicated that 761 road links in the UK were predicted to exceed the NO2 objective for 2005. In this pilot study 103 road links have been surveyed, involving collecting information on the presence of houses within 10 m of the kerb and approximate numbers of these. 23 road links have been found to have houses within this distance of the kerb, with a total estimate of more than 1,200 houses. Further analysis has been undertaken on these 23 road links, using detailed postcode data. A total of over 2,600 houses were found to exist along these road links using this method, but the datasets are not detailed enough to determine how many of these are within 10 m of the kerb.
A comparison of local and national traffic flow data for Manchester, Salford and Birmingham has also been undertaken. This has shown that the datasets of actual flow measurements in Manchester and Salford correspond reasonably well with the national data, whereas modelled traffic flows on road links in Birmingham show considerable differences from the national dataset. A comparison has also been made between predicted roadside NO2 concentrations for 2005 using the local traffic flow data and that using the original national figures. 71% of the links analysed in this way have been estimated to have concentrations based on the local trafic flow data within a 10% range of the national modelled NO2 concentration.
It is recommended that further work is carried out to provide a more complete analysis of potential population exposure to roadside concentrations of NO2 or other air pollutants. Additional detailed GIS data should soon be available from the Ordnance Survey, to provide more accurate locations of houses along road links. The detailed ground truth survey data obtained during the current study could provide an excellent comparison with detailed GIS or aerial photography analysis. It is recommended that additional work be carried out to compare these methods of analysis with the results of this study so that a robust and systematic technique can be developed for use on subsequent reviews of the NAQS.
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Report and site prepared by the National Environmental Technology Centre, part of AEA Technology, on behalf of the UK Department of the Environment, Transport and the Regions