Identifying the contribution of different urban highway air pollution sources

This paper describes the methodology and results, and draws conclusions from a large-scale source apportionment study undertaken in a large urban conurbation in the northwest of England. Annual average oxides of nitrogen (NOx) emission and ambient air pollution contributions have been estimated for road traffic sources. Ground level air pollution concentrations were estimated over a 1552-km(2) area with a resolution of up to 20 m, using emissions estimates and the second generation ADMS-Urban Gaussian dispersion model. Road traffic emissions were split into car and motorcycles; heavy and light goods vehicles; and buses to represent domestic users; commercial users and bus companies. Car related emissions were split further in to journey lengths under 3 km; journeys between 3 and 8 km; and journeys over 8 km to represent journeys which could be either walked or cycled; journeys for which a bus can easily be used and other journeys. These source sections were chosen so that the relevant authorities could target key groups in terms of reducing air pollution. The results confirm that the areas most likely to exceed air quality objectives are typically close to main arterial routes and close to urban centres and that the major culprits of road traffic related air pollution are goods vehicles and car journeys over 8 km. The paper also discusses the implications of the results and suggests how these can be used in the assessment of actions to reduce air pollution concentrations.