CMAQ-Urban compliance modelling system: summary report
Published 9 October 2026
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This report provides a high-level summary of the CMAQ-Urban modelling system that was used to provide supplementary assessment for the 2025 air quality compliance assessment under the Air Quality Standards Regulations (2010).
A full technical report with the details of the modelling approach will be published in due course.
Modelling system components
The CMAQ-Urban modelling system is an integrated modelling framework that combines:
- CMAQ (the Community Multi-scale Air Quality model) – this provides regional-scale atmospheric chemistry and transport modelling, driven by meteorological data from the Weather Research and Forecasting (WRF) model
- ADMS (Atmospheric Dispersion Modelling System) – this is used for roadside (the ADMS-Roads model) and industrial dispersion modelling (the ADMS model)
Together, these components provide comprehensive air quality predictions across the UK.
This integrated approach enables the model to represent both the large-scale atmospheric chemistry and the more localised impacts of road traffic and industrial emissions at scales relevant to the assessment of compliance under the Air Quality Standards Regulations (2010).
The model outputs are evaluated against measurement data and the outputs required for compliance reporting produced.
CMAQ
CMAQ is a state-of-the-science regional chemical transport model.
It provides regional background pollutant concentrations, representing the large-scale transport, chemistry and deposition of pollutants across the UK and surrounding domain.
CMAQ is driven by meteorological data generated by the WRF model. This provides the atmospheric conditions required to simulate pollutant transport and dispersion at the regional scale.
Emissions inputs are processed through a dedicated system before being supplied to CMAQ. Dedicated chemistry schemes are used to represent chemical and aerosol processes.
By tracking sources through the modelling system, CMAQ calculates how each source contributes to air pollutant concentrations throughout the UK.
This source apportionment is split into 21 different categories and accounts for both initial sources and secondary sources created by atmospheric chemistry.
ADMS
The ADMS-Roads model provides high-resolution roadside dispersion modelling.
It accounts for the characteristics of road traffic emissions and their dispersion in the near-road environment, including the influence of street geometry such as road width and surrounding building height.
ADMS-Roads results are integrated with the CMAQ regional background to provide total concentration estimates at locations relevant to compliance assessment near roads.
The ADMS industrial point source model captures the localised impacts of emissions from industrial facilities. Industrial point source parameters including stack (chimney) height, exit velocity, temperature and emission rates are used to model pollutant rise and dispersion, with results integrated with the CMAQ-Urban model.
Model inputs
Inputs to the CMAQ-Urban model include:
- regional air quality contributions from the Northern Hemisphere
- emissions from Europe from the European Monitoring and Evaluation Programme (EMEP) inventory
- emissions from the UK from the National Atmospheric Emissions Inventory (NAEI)
- emissions from biogenic sources (living natural sources such as trees) from the Model of Emissions of Gases and Aerosols from Nature (MEGAN)
- land use and terrain data
- meteorological measurements
Some emissions are calibrated following model validation against measurements to improve agreement with observations.
Data quality
The new model has been assessed as fit for purpose using appropriate statistical tools.
Further assessment was carried out for nitrogen dioxide and particulate matter, which showed the model met the best practice guidelines of the Forum for Air Quality Modelling (FAIRMODE) using a core set of statistical measures and the modelling quality objective (MQO).
Further details on the assessment of the model performance will be included in the full technical report.