CERC — Environmental Software and Services

Clean Air Zones

NOx concentration source apportionment image Changes in NOx emissions image

The UK government has published the principles for setting up new Clean Air Zones (CAZ) in England. A CAZ can limit entry by more polluting vehicles, for instance by road charging or traffic management. Local authorities who propose a CAZ need to consider how its introduction will impact on vehicle emissions and pollutant concentrations, in order to have confidence that their objectives will be achieved.

CERCís consultancy team has been assisting UK local authorities with their Air Quality Management responsibilities since 1995. We have extensive experience in the assessment of air quality measures on challenging timescales.

We use our ADMS-Urban and EMIT software, originally developed specifically for local authorities, to assist with their responsibilities under the UK Air Quality Strategy. We apply a range of techniques for the robust assessment of CAZs, such as:

  • Source apportionment of emissions and concentrations, for instance to determine the relative contributions from diesel cars below Euro 6 standard. Map 1, from a recent assessment, shows the proportion of total NOx concentration due to particular vehicle types at specific locations.
  • Assessment of the impact of measures, including changes in emissions and concentrations due to changes in road traffic flows and fleet composition. Map 2 shows the changes in emissions predicted from the implementation of a mitigation measure.


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