02Reducing roadside NOX emissions in cities is a priority in the UK

The most immediate action required on poor air quality is tackling NO2 concentrations around roads2, as it is the only statutory limit that the UK currently fails to meet.3Unsurprisingly, the main cause of this is vehicles, with road transport responsible for 80 per cent of NO2 roadside concentrations and diesel vehicles being the worst offenders, contributing 35 per cent of NO2 roadside concentrations.4

This problem is particularly prevalent in UK cities, as shown in Figure 1. Urban areas are home to 88 per cent of roads which are predicted to have concentrations of NO2 above legal limits.

Box 1: The geography of air pollution

Much focus of environmental policy in recent years has been on reducing carbon dioxide emissions. Because carbon emissions contribute to the heating of the globe as a whole, the policy response has mainly been at the national and international levels.

Nitrogen oxide emissions are local – their impacts are felt where the emissions occur. This means that a local policy response is more appropriate in tackling this pollutant.



  • 2 When addressing NO2 concentrations caused by transport, it is essential to consider emissions of oxides of nitrogen (NOx). NOx comprises of primary NO2 and Nitric Oxide (NO), which is harmless but easily converts to NO2 in the air.
  • 3 National air quality objectives and European Directive limits for nitrogen dioxide cam into force on 1st January 2010
  • 4 DEFRA and DfT, UK plan for tackling roadside nitrogen dioxide concentrations (2017), London: The Stationery Office